Dr. Rutaganira uses choanoflagellates—the closest living single-celled relatives to animals—to study the origin of animal cell communication. Dr. Rutaganira applies chemical, genetic, and cell biological tools to probe choanoflagellate cell-cell communication, with implications for understanding not only animal cell signaling, but also the origin of multicellularity in animals.

Academic Appointments

Honors & Awards

  • Hanna Gray Faculty Fellow, Howard Hughes Medical Institute
  • Investigator, CZ Biohub

Current Research and Scholarly Interests

Although all organisms respond to external stimuli, the origins of multicellularity necessitated the evolution of specialized mechanisms to coordinate the actions of individual cells into a singular response. Cell-cell signaling is critical for the biology of animals and other multicellular organisms but key steps in the evolution of signaling are not understood.

Our research aims to address the origin and core mechanisms of animal cell signaling during the transition to multicellularity. In multicellular organisms, receptors facilitate intercellular communication and adaptor molecules link cell surface signaling with central regulators of intracellular growth and survival. Although animal, plant and fungi evolved through separate and independent transitions to multicellularity cell surface receptor genes expanded and diversified in each of these lineages, suggesting that the expansion and specialization of receptor-mediated signaling enabled complex multicellularity. Nonetheless, few studies have assessed the functional relevance of signaling receptors in evolutionarily-relevant model organisms.

To reconstruct how molecule sensing was integrated with core signaling pathways during the evolution of animals, and uncover core principles of animal cell signaling, we investigate how unicellular relatives of animals use cell surface receptors to detect extracellular signals. We use chemical genetic approaches by leveraging available genomics resources combined with targeted pharmacology, transgene expression, and genome editing. We use choanoflagellates, a phylogenetically-relevant and experimentally-tractable model system to study the evolution of receptor signaling in animals. Our goal is to uncover the ancestral functions of receptor signaling in animals and develop a framework to identify general principles of receptor signaling relevant to other multicellular organisms (e.g. plants, fungi).

2023-24 Courses

Stanford Advisees

  • Doctoral Dissertation Reader (AC)
    Cindy Sandoval Espinoza, Ali Wilkening
  • Doctoral Dissertation Advisor (AC)
    Maria Nguyen, Hannah Reeves, Jia Zheng Woo

All Publications

  • Juneteenth in STEMM and the barriers to equitable science. Cell Mays, A., Byars-Winston, A., Hinton, A., Marshall, A. G., Kirabo, A., August, A., Marlin, B. J., Riggs, B., Tolbert, B., Wanjalla, C., Womack, C., Evans, C. S., Barnes, C., Starbird, C., Williams, C., Reynolds, C., Taabazuing, C., Cameron, C. E., Murray, D. D., Applewhite, D., Morton, D. J., Lee, D., Williams, D. W., Lynch, D., Brady, D., Lynch, E., Rutaganira, F. U., Silva, G. M., Shuler, H., Saboor, I. A., Davis, J., Dzirasa, K., Hammonds-Odie, L., Reyes, L., Sweetwyne, M. T., McReynolds, M. R., Johnson, M. D., Smith, N. A., Pittman, N., Ajijola, O. A., Smith, Q., Robinson, R. A., Lewis, S. C., Murray, S. A., Black, S., Neal, S. E., Andrisse, S., Townsend, S., Damo, S. M., Griffith, T. N., Lambert, W. M., Clemons, W. M. 2023; 186 (12): 2510-2517


    We are 52 Black scientists. Here, we establish the context of Juneteenth in STEMM and discuss the barriers Black scientists face, the struggles they endure, and the lack of recognition they receive. We review racism's history in science and provide institutional-level solutions to reduce the burdens on Black scientists.

    View details for DOI 10.1016/j.cell.2023.05.016

    View details for PubMedID 37295396

  • Total Synthesis and Functional Evaluation of IORs, Sulfonolipid-based Inhibitors of Cell Differentiation in Salpingoeca rosetta. Angewandte Chemie (International ed. in English) Raguž, L., Peng, C. C., Rutaganira, F. U., Krüger, T., Stanišić, A., Jautzus, T., Kries, H., Kniemeyer, O., Brakhage, A. A., King, N., Beemelmanns, C. 2022; 61 (41): e202209105


    The choanoflagellate Salpingoeca rosetta is an important model system to study the evolution of multicellularity. In this study we developed a new, modular, and scalable synthesis of sulfonolipid IOR-1A (six steps, 27 % overall yield), which acts as bacterial inhibitor of rosette formation in S. rosetta. The synthesis features a decarboxylative cross-coupling reaction of a sulfonic acid-containing tartaric acid derivative with alkyl zinc reagents. Synthesis of 15 modified IOR-1A derivatives, including fluorescent and photoaffinity-based probes, allowed quantification of IOR-1A, localization studies within S. rosetta cells, and evaluation of structure-activity relations. In a proof of concept study, an inhibitory bifunctional probe was employed in proteomic profiling studies, which allowed to deduce binding partners in bacteria and S. rosetta. These results showcase the power of synthetic chemistry to decipher the biochemical basis of cell differentiation processes within S. rosetta.

    View details for DOI 10.1002/anie.202209105

    View details for PubMedID 35901418

    View details for PubMedCentralID PMC9825905

  • Identification and structure of an extracellular contractile injection system from the marine bacterium Algoriphagus machipongonensis. Nature microbiology Xu, J., Ericson, C. F., Lien, Y. W., Rutaganira, F. U., Eisenstein, F., Feldmüller, M., King, N., Pilhofer, M. 2022; 7 (3): 397-410


    Contractile injection systems (CISs) are phage tail-like nanomachines, mediating bacterial cell-cell interactions as either type VI secretion systems (T6SSs) or extracellular CISs (eCISs). Bioinformatic studies uncovered a phylogenetic group of hundreds of putative CIS gene clusters that are highly diverse and widespread; however, only four systems have been characterized. Here we studied a putative CIS gene cluster in the marine bacterium Algoriphagus machipongonensis. Using an integrative approach, we show that the system is compatible with an eCIS mode of action. Our cryo-electron microscopy structure revealed several features that differ from those seen in other CISs: a 'cap adaptor' located at the distal end, a 'plug' exposed to the tube lumen, and a 'cage' formed by massive extensions of the baseplate. These elements are conserved in other CISs, and our genetic tools identified that they are required for assembly, cargo loading and function. Furthermore, our atomic model highlights specific evolutionary hotspots and will serve as a framework for understanding and re-engineering CISs.

    View details for DOI 10.1038/s41564-022-01059-2

    View details for PubMedID 35165385

    View details for PubMedCentralID PMC8894135

  • Structural and Functional Analysis of Bacterial Sulfonosphingolipids and Rosette-Inducing Factor 2 (RIF-2) by Mass Spectrometry-Guided Isolation and Total Synthesis. Chemistry (Weinheim an der Bergstrasse, Germany) Leichnitz, D., Peng, C. C., Raguž, L., Rutaganira, F. U., Jautzus, T., Regestein, L., King, N., Beemelmanns, C. 2022; 28 (8): e202103883


    We have analyzed the abundance of bacterial sulfonosphingolipids, including rosette-inducing factors (RIFs), in seven bacterial prey strains by using high-resolution tandem mass spectrometry (HRMS2 ) and molecular networking (MN) within the Global Natural Product Social Molecular Networking (GNPS) web platform. Six sulfonosphingolipids resembling RIFs were isolated and their structures were elucidated based on comparative MS and NMR studies. Here, we also report the first total synthesis of two RIF-2 diastereomers and one congener in 15 and eight synthetic steps, respectively. For the total synthesis of RIF-2 congeners, we employed a decarboxylative cross-coupling reaction to synthesize the necessary branched α-hydroxy fatty acids, and the Garner-aldehyde approach to generate the capnine base carrying three stereogenic centers. Bioactivity studies in the choanoflagellate Salpingoeca rosetta revealed that the rosette inducing activity of RIFs is inhibited dose dependently by the co-occurring sulfonosphingolipid sulfobacins D and F and that activity of RIFs is specific for isolates obtained from Algoriphagus.

    View details for DOI 10.1002/chem.202103883

    View details for PubMedID 34863043

    View details for PubMedCentralID PMC9305409

  • Using virtual interviewing to create a more accessible hybrid academic job market. Cell Termini, C. M., Rutaganira, F. U., Palavicino-Maggio, C. B., Spriggs, C. C., Evans, C. S., McReynolds, M. R. 2021; 184 (26): 6217-6221


    Virtual interviewing has become ubiquitous with the academic job market. Here, we highlight the best practices for candidates and departments to consider when using virtual interviewing. We propose how virtual interviews can be leveraged and adapted for hybrid academic job searches combining virtual and in-person activities in a post-pandemic world.

    View details for DOI 10.1016/j.cell.2021.11.027

    View details for PubMedID 34942095

    View details for PubMedCentralID PMC9717443

  • Mentoring during Uncertain Times. Trends in biochemical sciences Termini, C. M., McReynolds, M. R., Rutaganira, F. U., Roby, R. S., Hinton, A. O., Carter, C. S., Huang, S. C., Vue, Z., Martinez, D., Shuler, H. D., Taylor, B. L. 2021; 46 (5): 345-348


    Scientific success is mainly supported by mentoring, which often occurs through face-to-face interactions. Changes to the research environment incurred by the Coronavirus 2019 (COVID-19) pandemic have necessitated mentorship adaptations. Here, we describe how mentors can broaden their mentorship to support trainee growth and provide reassurance about trainee development amid uncertain circumstances.

    View details for DOI 10.1016/j.tibs.2021.01.012

    View details for PubMedID 33622580

    View details for PubMedCentralID PMC9716657

  • Patching the Leaks: Revitalizing and Reimagining the STEM Pipeline. Cell Hinton, A. O., Termini, C. M., Spencer, E. C., Rutaganira, F. U., Chery, D., Roby, R., Vue, Z., Pack, A. D., Brady, L. J., Garza-Lopez, E., Marshall, A. G., Lewis, S. C., Shuler, H. D., Taylor, B. L., McReynolds, M. R., Palavicino-Maggio, C. B. 2020; 183 (3): 568-575


    We identify problematic areas throughout the Science, Technology, Engineering and Mathematics (STEM) pipeline that perpetuate racial disparities in academia. Distinct ways to curtail these disparities include early exposure and access to resources, supportive mentoring networks and comprehensive training programs specifically for racially minoritized students and trainees at each career stage. These actions will revitalize the STEM pipeline.

    View details for DOI 10.1016/j.cell.2020.09.029

    View details for PubMedID 33125882

  • PI4KIIIβ is a therapeutic target in chromosome 1q-amplified lung adenocarcinoma. Science translational medicine Tan, X. n., Banerjee, P. n., Pham, E. A., Rutaganira, F. U., Basu, K. n., Bota-Rabassedas, N. n., Guo, H. F., Grzeskowiak, C. L., Liu, X. n., Yu, J. n., Shi, L. n., Peng, D. H., Rodriguez, B. L., Zhang, J. n., Zheng, V. n., Duose, D. Y., Solis, L. M., Mino, B. n., Raso, M. G., Behrens, C. n., Wistuba, I. I., Scott, K. L., Smith, M. n., Nguyen, K. n., Lam, G. n., Choong, I. n., Mazumdar, A. n., Hill, J. L., Gibbons, D. L., Brown, P. H., Russell, W. K., Shokat, K. n., Creighton, C. J., Glenn, J. S., Kurie, J. M. 2020; 12 (527)


    Heightened secretion of protumorigenic effector proteins is a feature of malignant cells. Yet, the molecular underpinnings and therapeutic implications of this feature remain unclear. Here, we identify a chromosome 1q region that is frequently amplified in diverse cancer types and encodes multiple regulators of secretory vesicle biogenesis and trafficking, including the Golgi-dedicated enzyme phosphatidylinositol (PI)-4-kinase IIIβ (PI4KIIIβ). Molecular, biochemical, and cell biological studies show that PI4KIIIβ-derived PI-4-phosphate (PI4P) synthesis enhances secretion and accelerates lung adenocarcinoma progression by activating Golgi phosphoprotein 3 (GOLPH3)-dependent vesicular release from the Golgi. PI4KIIIβ-dependent secreted factors maintain 1q-amplified cancer cell survival and influence prometastatic processes in the tumor microenvironment. Disruption of this functional circuitry in 1q-amplified cancer cells with selective PI4KIIIβ antagonists induces apoptosis and suppresses tumor growth and metastasis. These results support a model in which chromosome 1q amplifications create a dependency on PI4KIIIβ-dependent secretion for cancer cell survival and tumor progression.

    View details for DOI 10.1126/scitranslmed.aax3772

    View details for PubMedID 31969487

  • Phosphoregulation of the oncogenic protein regulator of cytokinesis 1 (PRC1) by the atypical CDK16/CCNY complex. Experimental & molecular medicine Hernández-Ortega, S., Sánchez-Botet, A., Quandt, E., Masip, N., Gasa, L., Verde, G., Jiménez, J., Levin, R. S., Rutaganira, F. U., Burlingame, A. L., Wolfgeher, D., Ribeiro, M. P., Kron, S. J., Shokat, K. M., Clotet, J. 2019; 51 (4): 1-17


    CDK16 (also known as PCTAIRE1 or PCTK1) is an atypical member of the cyclin-dependent kinase (CDK) family that forms an active complex with cyclin Y (CCNY). Although both proteins have been recently implicated in cancer pathogenesis, it is still unclear how the CDK16/CCNY complex exerts its biological activity. To understand the CDK16/CCNY network, we used complementary proteomic approaches to identify potential substrates of this complex. We identified several candidates implicating the CDK16/CCNY complex in cytoskeletal dynamics, and we focused on the microtubule-associated protein regulator of cytokinesis (PRC1), an essential protein for cell division that organizes antiparallel microtubules and whose deregulation may drive genomic instability in cancer. Using analog-sensitive (AS) CDK16 generated by CRISPR-Cas9 mutagenesis in 293T cells, we found that specific inhibition of CDK16 induces PRC1 dephosphorylation at Thr481 and delocalization to the nucleus during interphase. The observation that CDK16 inhibition and PRC1 downregulation exhibit epistatic effects on cell viability confirms that these proteins can act through a single pathway. In conclusion, we identified PRC1 as the first substrate of the CDK16/CCNY complex and demonstrated that the proliferative function of CDK16 is mediated by PRC1 phosphorylation. As CDK16 is emerging as a critical node in cancer, our study reveals novel potential therapeutic targets.

    View details for DOI 10.1038/s12276-019-0242-2

    View details for PubMedID 30992425

    View details for PubMedCentralID PMC6467995

  • Inhibition of Calcium Dependent Protein Kinase 1 (CDPK1) by Pyrazolopyrimidine Analogs Decreases Establishment and Reoccurrence of Central Nervous System Disease by Toxoplasma gondii. Journal of medicinal chemistry Rutaganira, F. U., Barks, J., Dhason, M. S., Wang, Q., Lopez, M. S., Long, S., Radke, J. B., Jones, N. G., Maddirala, A. R., Janetka, J. W., El Bakkouri, M., Hui, R., Shokat, K. M., Sibley, L. D. 2017; 60 (24): 9976-9989


    Calcium dependent protein kinase 1 (CDPK1) is an essential enzyme in the opportunistic pathogen Toxoplasma gondii. CDPK1 controls multiple processes that are critical to the intracellular replicative cycle of T. gondii including secretion of adhesins, motility, invasion, and egress. Remarkably, CDPK1 contains a small glycine gatekeeper residue in the ATP binding pocket making it sensitive to ATP-competitive inhibitors with bulky substituents that complement this expanded binding pocket. Here we explored structure-activity relationships of a series of pyrazolopyrimidine inhibitors of CDPK1 with the goal of increasing selectivity over host enzymes, improving antiparasite potency, and improving metabolic stability. The resulting lead compound 24 exhibited excellent enzyme inhibition and selectivity for CDPK1 and potently inhibited parasite growth in vitro. Compound 24 was also effective at treating acute toxoplasmosis in the mouse, reducing dissemination to the central nervous system, and decreasing reactivation of chronic infection in severely immunocompromised mice. These findings provide proof of concept for the development of small molecule inhibitors of CDPK1 for treatment of CNS toxoplasmosis.

    View details for DOI 10.1021/acs.jmedchem.7b01192

    View details for PubMedID 28933846

    View details for PubMedCentralID PMC5746462

  • Long-term oral kinetin does not protect against α-synuclein-induced neurodegeneration in rodent models of Parkinson's disease. Neurochemistry international Orr, A. L., Rutaganira, F. U., de Roulet, D., Huang, E. J., Hertz, N. T., Shokat, K. M., Nakamura, K. 2017; 109: 106-116


    Mutations in the mitochondrial kinase PTEN-induced putative kinase 1 (PINK1) cause Parkinson's disease (PD), likely by disrupting PINK1's kinase activity. Although the mechanism(s) underlying how this loss of activity causes degeneration remains unclear, increasing PINK1 activity may therapeutically benefit some forms of PD. However, we must first learn whether restoring PINK1 function prevents degeneration in patients harboring PINK1 mutations, or whether boosting PINK1 function can offer protection in more common causes of PD. To test these hypotheses in preclinical rodent models of PD, we used kinetin triphosphate, a small-molecule that activates both wild-type and mutant forms of PINK1, which affects mitochondrial function and protects neural cells in culture. We chronically fed kinetin, the precursor of kinetin triphosphate, to PINK1-null rats in which PINK1 was reintroduced into their midbrain, and also to rodent models overexpressing α-synuclein. The highest tolerated dose of oral kinetin increased brain levels of kinetin for up to 6 months, without adversely affecting the survival of nigrostriatal dopamine neurons. However, there was no degeneration of midbrain dopamine neurons lacking PINK1, which precluded an assessment of neuroprotection and raised questions about the robustness of the PINK1 KO rat model of PD. In two rodent models of α-synuclein-induced toxicity, boosting PINK1 activity with oral kinetin provided no protective effects. Our results suggest that oral kinetin is unlikely to protect against α-synuclein toxicity, and thus fail to provide evidence that kinetin will protect in sporadic models of PD. Kinetin may protect in cases of PINK1 deficiency, but this possibility requires a more robust PINK1 KO model that can be validated by proof-of-principle genetic correction in adult animals.

    View details for DOI 10.1016/j.neuint.2017.04.006

    View details for PubMedID 28434973

    View details for PubMedCentralID PMC5641232

  • Endosomal Phosphatidylinositol 3-Kinase Is Essential for Canonical GPCR Signaling. Molecular pharmacology Uchida, Y., Rutaganira, F. U., Jullié, D., Shokat, K. M., von Zastrow, M. 2017; 91 (1): 65-73


    G protein-coupled receptors (GPCRs), the largest family of signaling receptors, are critically regulated by endosomal trafficking, suggesting that endosomes might provide new strategies for manipulating GPCR signaling. Here we test this hypothesis by focusing on class III phosphatidylinositol 3-kinase (Vps34), which is an essential regulator of endosomal trafficking. We verify that Vps34 is required for recycling of the β2-adrenoceptor (β2AR), a prototypical GPCR, and then investigate the effects of Vps34 inhibition on the canonical cAMP response elicited by β2AR activation. Vps34 inhibition impairs the ability of cells to recover this response after prolonged activation, which is in accord with the established role of recycling in GPCR resensitization. In addition, Vps34 inhibition also attenuates the short-term cAMP response, and its effect begins several minutes after initial agonist application. These results establish Vps34 as an essential determinant of both short-term and long-term canonical GPCR signaling, and support the potential utility of the endosomal system as a druggable target for signaling.

    View details for DOI 10.1124/mol.116.106252

    View details for PubMedID 27821547

    View details for PubMedCentralID PMC5198513

  • Multistep Compositional Remodeling of Supported Lipid Membranes by Interfacially Active Phosphatidylinositol Kinases ANALYTICAL CHEMISTRY Tabaei, S. R., Guo, F., Rutaganira, F. U., Vafaei, S., Choong, I., Shokat, K. M., Glenn, J. S., Cho, N. 2016; 88 (10): 5042-5045


    The multienzyme catalytic phosphorylation of phosphatidylinositol (PI) in a supported lipid membrane platform is demonstrated for the first time. One-step treatment with PI 4-kinase IIIβ (PI4Kβ) yielded PI 4-phosphate (PI4P), while a multistep enzymatic cascade of PI4Kβ followed by PIP 5-kinase produced PI-4,5-bisphosphate (PI(4,5)P2 or PIP2). By employing quartz crystal microbalance with dissipation monitoring, we were able to track membrane association of kinase enzymes for the first time as well as detect PI4P and PI(4,5)P2 generation based on subsequent antibody binding to the supported lipid bilayers. Pharmacologic inhibition of PI4Kβ by a small molecule inhibitor was also quantitatively assessed, yielding an EC50 value that agrees well with conventional biochemical readout. Taken together, the development of a PI-containing supported membrane platform coupled with surface-sensitive measurement techniques for kinase studies opens the door to exploring the rich biochemistry and pharmacological targeting of membrane-associated phosphoinositides.

    View details for DOI 10.1021/acs.analchem.6b01293

    View details for PubMedID 27118725

  • Design and Structural Characterization of Potent and Selective Inhibitors of Phosphatidylinositol 4 Kinase III beta JOURNAL OF MEDICINAL CHEMISTRY Rutaganira, F. U., Fowler, M. L., McPhail, J. A., Gelman, M. A., Nguyen, K., Xiong, A., Doman, G. L., Tayshanjian, B., Glenn, J. S., Shokat, K. M., Burke, J. E. 2016; 59 (5): 1830-1839


    Type III phosphatidylinositol 4-kinase (PI4KIIIβ) is an essential enzyme in mediating membrane trafficking and is implicated in a variety of pathogenic processes. It is a key host factor mediating replication of RNA viruses. The design of potent and specific inhibitors of this enzyme will be essential to define its cellular roles and may lead to novel antiviral therapeutics. We previously reported the PI4K inhibitor PIK93, and this compound has defined key functions of PI4KIIIβ. However, this compound showed high cross reactivity with class I and III PI3Ks. Using structure-based drug design, we have designed novel potent and selective (>1000-fold over class I and class III PI3Ks) PI4KIIIβ inhibitors. These compounds showed antiviral activity against hepatitis C virus. The co-crystal structure of PI4KIIIβ bound to one of the most potent compounds reveals the molecular basis of specificity. This work will be vital in the design of novel PI4KIIIβ inhibitors, which may play significant roles as antiviral therapeutics.

    View details for DOI 10.1021/acs.jmedchem.5b01311

    View details for Web of Science ID 000372043400012

  • Inhibition of Calcium-Dependent Protein Kinase 1 (CDPK1) In Vitro by Pyrazolopyrimidine Derivatives Does Not Correlate with Sensitivity of Cryptosporidium parvum Growth in Cell Culture. Antimicrobial agents and chemotherapy Kuhlenschmidt, T. B., Rutaganira, F. U., Long, S., Tang, K., Shokat, K. M., Kuhlenschmidt, M. S., Sibley, L. D. 2016; 60 (1): 570-9


    Cryptosporidiosis is a serious diarrheal disease in immunocompromised patients and malnourished children, and treatment is complicated by a lack of adequate drugs. Recent studies suggest that the natural occurrence of a small gatekeeper residue in serine threonine calcium-dependent protein kinase 1 (CDPK1) of Cryptosporidium parvum might be exploited to target this enzyme and block parasite growth. Here were explored the potency with which a series of pyrazolopyrimidine analogs, which are selective for small gatekeeper kinases, inhibit C. parvum CDPK1 and block C. parvum growth in tissue culture in vitro. Although these compounds potently inhibited kinase activity in vitro, most had no effect on parasite growth. Moreover, among those that were active against parasite growth, there was a very poor correlation with their 50% inhibitory concentrations against the enzyme. Active compounds also had no effect on cell invasion, unlike the situation in Toxoplasma gondii, where these compounds block CDPK1, prevent microneme secretion, and disrupt cell invasion. These findings suggest that CPDK1 is not essential for C. parvum host cell invasion or growth and therefore that it is not the optimal target for therapeutic intervention. Nonetheless, several inhibitors with low micromolar 50% effective concentrations were identified, and these may affect other essential targets in C. parvum that are worthy of further exploration.

    View details for DOI 10.1128/AAC.01915-15

    View details for PubMedID 26552986

    View details for PubMedCentralID PMC4704151

  • Small molecule inhibition of Csk alters affinity recognition by T cells. eLife Manz, B. N., Tan, Y. X., Courtney, A. H., Rutaganira, F., Palmer, E., Shokat, K. M., Weiss, A. 2015; 4


    The C-terminal Src kinase (Csk), the primary negative regulator of Src-family kinases (SFK), plays a crucial role in controlling basal and inducible receptor signaling. To investigate how Csk activity regulates T cell antigen receptor (TCR) signaling, we utilized a mouse expressing mutated Csk (Csk(AS)) whose catalytic activity is specifically and rapidly inhibited by a small molecule. Inhibition of Csk(AS) during TCR stimulation led to stronger and more prolonged TCR signaling and to increased proliferation. Inhibition of Csk(AS) enhanced activation by weak but strictly cognate agonists. Titration of Csk inhibition revealed that a very small increase in SFK activity was sufficient to potentiate T cell responses to weak agonists. Csk plays an important role, not only in basal signaling, but also in setting the TCR signaling threshold and affinity recognition.

    View details for DOI 10.7554/eLife.08088

    View details for PubMedID 26302204

    View details for PubMedCentralID PMC4568592

  • Substrate recognition by the multifunctional cytochrome P450 MycG in mycinamicin hydroxylation and epoxidation reactions. The Journal of biological chemistry Li, S., Tietz, D. R., Rutaganira, F. U., Kells, P. M., Anzai, Y., Kato, F., Pochapsky, T. C., Sherman, D. H., Podust, L. M. 2012; 287 (45): 37880-90


    The majority of characterized cytochrome P450 enzymes in actinomycete secondary metabolic pathways are strictly substrate-, regio-, and stereo-specific. Examples of multifunctional biosynthetic cytochromes P450 with broader substrate and regio-specificity are growing in number and are of particular interest for biosynthetic and chemoenzymatic applications. MycG is among the first P450 monooxygenases characterized that catalyzes both hydroxylation and epoxidation reactions in the final biosynthetic steps, leading to oxidative tailoring of the 16-membered ring macrolide antibiotic mycinamicin II in the actinomycete Micromonospora griseorubida. The ordering of steps to complete the biosynthetic process involves a complex substrate recognition pattern by the enzyme and interplay between three tailoring modifications as follows: glycosylation, methylation, and oxidation. To understand the catalytic properties of MycG, we structurally characterized the ligand-free enzyme and its complexes with three native metabolites. These include substrates mycinamicin IV and V and their biosynthetic precursor mycinamicin III, which carries the monomethoxy sugar javose instead of the dimethoxylated sugar mycinose. The two methoxy groups of mycinose serve as sensors that mediate initial recognition to discriminate between closely related substrates in the post-polyketide oxidative tailoring of mycinamicin metabolites. Because x-ray structures alone did not explain the mechanisms of macrolide hydroxylation and epoxidation, paramagnetic NMR relaxation measurements were conducted. Molecular modeling based on these data indicates that in solution substrate may penetrate the active site sufficiently to place the abstracted hydrogen atom of mycinamicin IV within 6 Å of the heme iron and ~4 Å of the oxygen of iron-ligated water.

    View details for DOI 10.1074/jbc.M112.410340

    View details for PubMedID 22952225

    View details for PubMedCentralID PMC3488060

  • Integrin α9β1 in airway smooth muscle suppresses exaggerated airway narrowing. The Journal of clinical investigation Chen, C., Kudo, M., Rutaganira, F., Takano, H., Lee, C., Atakilit, A., Robinett, K. S., Uede, T., Wolters, P. J., Shokat, K. M., Huang, X., Sheppard, D. 2012; 122 (8): 2916-27


    Exaggerated contraction of airway smooth muscle is the major cause of symptoms in asthma, but the mechanisms that prevent exaggerated contraction are incompletely understood. Here, we showed that integrin α9β1 on airway smooth muscle localizes the polyamine catabolizing enzyme spermidine/spermine N1-acetyltransferase (SSAT) in close proximity to the lipid kinase PIP5K1γ. As PIP5K1γ is the major source of PIP2 in airway smooth muscle and its activity is regulated by higher-order polyamines, this interaction inhibited IP3-dependent airway smooth muscle contraction. Mice lacking integrin α9β1 in smooth muscle had increased airway responsiveness in vivo, and loss or inhibition of integrin α9β1 increased in vitro airway narrowing and airway smooth muscle contraction in murine and human airways. Contraction was enhanced in control airways by the higher-order polyamine spermine or by cell-permeable PIP2, but these interventions had no effect on airways lacking integrin α9β1 or treated with integrin α9β1-blocking antibodies. Enhancement of SSAT activity or knockdown of PIP5K1γ inhibited airway contraction, but only in the presence of functional integrin α9β1. Therefore, integrin α9β1 appears to serve as a brake on airway smooth muscle contraction by recruiting SSAT, which facilitates local catabolism of polyamines and thereby inhibits PIP5K1γ. Targeting key components of this pathway could thus lead to new treatment strategies for asthma.

    View details for DOI 10.1172/JCI60387

    View details for PubMedID 22772469

    View details for PubMedCentralID PMC3448403

  • Constraints on the use of lifespan-shortening Wolbachia to control dengue fever. Journal of theoretical biology Schraiber, J. G., Kaczmarczyk, A. N., Kwok, R., Park, M., Silverstein, R., Rutaganira, F. U., Aggarwal, T., Schwemmer, M. A., Hom, C. L., Grosberg, R. K., Schreiber, S. J. 2012; 297: 26-32


    Dengue fever, a viral disease spread by the mosquito Aedes aegypti, affects 50-100 million people a year in many tropical countries. Because the virus must incubate within mosquito hosts for two weeks before being able to transmit the infection, shortening the lifespan of mosquitoes may curtail dengue transmission. We developed a continuous time reaction-diffusion model of the spatial spread of Wolbachia through a population of A. aegypti. This model incorporates the lifespan-shortening effects of Wolbachia on infected A. aegypti and the fitness advantage to infected females due to cytoplasmic incompatibility (CI). We found that local establishment of the Wolbachia infection can occur if the fitness advantage due to CI exceeds the fitness reduction due to lifespan-shortening effects, in accordance with earlier results concerning fecundity reduction. However, spatial spread is possible only if the fitness advantage due to CI is twice as great as the fitness reduction due to lifespan shortening effects. Moreover, lifespan-shortening and fecundity-reduction can have different effects on the speed of wave-retreat. Using data from the literature, we estimated all demographic parameters for infected and uninfected mosquitoes and computed the velocities of spread of infection. Our most optimistic estimates suggest that the spatial spread of lifespan-shortening Wolbachia may be so slow that efficient spatial spread would require a prohibitively large number of point releases. However, as these estimates of demographic parameters may not accurately reflect natural conditions, further research is necessary to corroborate these predictions.

    View details for DOI 10.1016/j.jtbi.2011.12.006

    View details for PubMedID 22192469