Honors & Awards

  • Graduate Research Fellowship, National Science Foundation (2014-2017)

Education & Certifications

  • B.A., Reed College, Biochemistry & Molecular Biology (2011)

Lab Affiliations

All Publications

  • Chemical structure-guided design of dynapyrazoles, potent cell-permeable dynein inhibitors with a unique mode of action. eLife Steinman, J. B., Santarossa, C. C., Miller, R. M., Yu, L. S., Serpinskaya, A. S., Furukawa, H., Morimoto, S., Tanaka, Y., Nishitani, M., Asano, M., Zalyte, R., Ondrus, A. E., Johnson, A. G., Ye, F., Nachury, M. V., Fukase, Y., Aso, K., Foley, M. A., Gelfand, V. I., Chen, J. K., Carter, A. P., Kapoor, T. M. 2017; 6


    Cytoplasmic dyneins are motor proteins in the AAA+ superfamily that power transport of cellular cargos towards microtubule minus-ends. Recently, ciliobrevins were reported as selective cell-permeable inhibitors of cytoplasmic dyneins. As is often true for first-in-class inhibitors, the use of ciliobrevins has been limited by low potency. Moreover, suboptimal chemical properties, such as the potential to isomerize, have hindered efforts to improve ciliobrevins. Here, we characterized the structure of ciliobrevins and designed conformationally-constrained isosteres. We identified dynapyrazoles, inhibitors more potent than ciliobrevins in vitro, and find that while ciliobrevins inhibit both dynein's microtubule-stimulated and basal ATPase activity, dynapyrazoles block only microtubule-stimulated activity. Single-digit micromolar concentrations of dynapyrazoles block intraflagellar transport in the cilium and lysosome motility in the cytoplasm, processes that depend on cytoplasmic dyneins. Together, our studies suggest that chemical structure-based analyses can lead to inhibitors with distinct modes of inhibition and improved properties.

    View details for DOI 10.7554/eLife.25174

    View details for PubMedID 28524820

  • Dynamics of IRES-mediated translation PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Johnson, A. G., Grosely, R., Petrov, A. N., Puglisi, J. D. 2017; 372 (1716)


    Viral internal ribosome entry sites (IRESs) are unique RNA elements, which use stable and dynamic RNA structures to recruit ribosomes and drive protein synthesis. IRESs overcome the high complexity of the canonical eukaryotic translation initiation pathway, often functioning with a limited set of eukaryotic initiation factors. The simplest types of IRESs are typified by the cricket paralysis virus intergenic region (CrPV IGR) and hepatitis C virus (HCV) IRESs, both of which independently form high-affinity complexes with the small (40S) ribosomal subunit and bypass the molecular processes of cap-binding and scanning. Owing to their simplicity and ribosomal affinity, the CrPV and HCV IRES have been important models for structural and functional studies of the eukaryotic ribosome during initiation, serving as excellent targets for recent technological breakthroughs in cryogenic electron microscopy (cryo-EM) and single-molecule analysis. High-resolution structural models of ribosome : IRES complexes, coupled with dynamics studies, have clarified decades of biochemical research and provided an outline of the conformational and compositional trajectory of the ribosome during initiation. Here we review recent progress in the study of HCV- and CrPV-type IRESs, highlighting important structural and dynamics insights and the synergy between cryo-EM and single-molecule studies.This article is part of the themed issue 'Perspectives on the ribosome'.

    View details for DOI 10.1098/rstb.2016.0177

    View details for Web of Science ID 000393403600002

    View details for PubMedID 28138065

    View details for PubMedCentralID PMC5311923

  • Fluorescently-tagged human eIF3 for single-molecule spectroscopy. Nucleic acids research Johnson, A. G., Petrov, A. N., Fuchs, G., Majzoub, K., Grosely, R., Choi, J., Puglisi, J. D. 2017


    Human translation initiation relies on the combined activities of numerous ribosome-associated eukaryotic initiation factors (eIFs). The largest factor, eIF3, is an ∼800 kDa multiprotein complex that orchestrates a network of interactions with the small 40S ribosomal subunit, other eIFs, and mRNA, while participating in nearly every step of initiation. How these interactions take place during the time course of translation initiation remains unclear. Here, we describe a method for the expression and affinity purification of a fluorescently-tagged eIF3 from human cells. The tagged eIF3 dodecamer is structurally intact, functions in cell-based assays, and interacts with the HCV IRES mRNA and the 40S-IRES complex in vitro. By tracking the binding of single eIF3 molecules to the HCV IRES RNA with a zero-mode waveguides-based instrument, we show that eIF3 samples both wild-type IRES and an IRES that lacks the eIF3-binding region, and that the high-affinity eIF3-IRES interaction is largely determined by slow dissociation kinetics. The application of single-molecule methods to more complex systems involving eIF3 may unveil dynamics underlying mRNA selection and ribosome loading during human translation initiation.

    View details for DOI 10.1093/nar/gkx1050

    View details for PubMedID 29136179

  • Identification of Selective Inhibitors of the Plasmodium falciparum Hexose Transporter PfHT by Screening Focused Libraries of Anti-Malarial Compounds. PloS one Ortiz, D., Guiguemde, W. A., Johnson, A., Elya, C., Anderson, J., Clark, J., Connelly, M., Yang, L., Min, J., Sato, Y., Guy, R. K., Landfear, S. M. 2015; 10 (4): e0123598


    Development of resistance against current antimalarial drugs necessitates the search for novel drugs that interact with different targets and have distinct mechanisms of action. Malaria parasites depend upon high levels of glucose uptake followed by inefficient metabolic utilization via the glycolytic pathway, and the Plasmodium falciparum hexose transporter PfHT, which mediates uptake of glucose, has thus been recognized as a promising drug target. This transporter is highly divergent from mammalian hexose transporters, and it appears to be a permease that is essential for parasite viability in intra-erythrocytic, mosquito, and liver stages of the parasite life cycle. An assay was developed that is appropriate for high throughput screening against PfHT based upon heterologous expression of PfHT in Leishmania mexicana parasites that are null mutants for their endogenous hexose transporters. Screening of two focused libraries of antimalarial compounds identified two such compounds that are high potency selective inhibitors of PfHT compared to human GLUT1. Additionally, 7 other compounds were identified that are lower potency and lower specificity PfHT inhibitors but might nonetheless serve as starting points for identification of analogs with more selective properties. These results further support the potential of PfHT as a novel drug target.

    View details for DOI 10.1371/journal.pone.0123598

    View details for PubMedID 25894322

    View details for PubMedCentralID PMC4404333

  • Dyotropic Rearrangements of Fused Tricyclic beta-Lactones: Application to the Synthesis of (-)-Curcumanolide A and (-)-Curcumalactone JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Leverett, C. A., Purohit, V. C., Johnson, A. G., Davis, R. L., Tantillo, D. J., Romo, D. 2012; 134 (32): 13348-13356


    Dyotropic rearrangements of fused, tricyclic β-lactones are described that proceed via unprecedented stereospecific, 1,2-acyl migrations delivering bridged, spiro-γ-butyrolactones. A unique example of this dyotropic process involves a fused bis-lactone possessing both β- and δ-lactone moieties which enabled rapid access to the core structures of curcumanolide A and curcumalactone. Our current mechanistic understanding of the latter dyotropic process, based on computational studies, is also described. Other key transformations in the described divergent syntheses of (-)-curcumanolide A and (-)-curcumalactone from a common intermediate (11 and 12 steps from 2-methyl-1,3-cyclopentanedione, respectively), include a catalytic, asymmetric nucleophile (Lewis base)-catalyzed aldol-lactonization (NCAL) leading to a tricyclic β-lactone, a Baeyer-Villiger oxidation in the presence of a β-lactone, and highly facial-selective and stereocomplementary reductions of an intermediate spirocyclic enoate. The described dyotropic rearrangements significantly alter the topology of the starting tricyclic β-lactone, providing access to complex spirocyclic cyclopentyl-γ-lactones and bis-γ-lactones in a single synthetic operation.

    View details for DOI 10.1021/ja303414a

    View details for Web of Science ID 000307487200039

    View details for PubMedID 22853802