Professional Education


  • Bachelor of Arts, Drew University (2003)
  • PhD, University of Massachusetts Medical School, Biochemistry and Biophysics (2012)

Stanford Advisors


Lab Affiliations


Journal Articles


  • Structural insights into neuronal K+ channel-calmodulin complexes PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Mruk, K., Shandilya, S. M., Blaustein, R. O., Schiffer, C. A., Kobertz, W. R. 2012; 109 (34): 13579-13583

    Abstract

    Calmodulin (CaM) is a ubiquitous intracellular calcium sensor that directly binds to and modulates a wide variety of ion channels. Despite the large repository of high-resolution structures of CaM bound to peptide fragments derived from ion channels, there is no structural information about CaM bound to a fully folded ion channel at the plasma membrane. To determine the location of CaM docked to a functioning KCNQ K(+) channel, we developed an intracellular tethered blocker approach to measure distances between CaM residues and the ion-conducting pathway. Combining these distance restraints with structural bioinformatics, we generated an archetypal quaternary structural model of an ion channel-CaM complex in the open state. These models place CaM close to the cytoplasmic gate, where it is well positioned to modulate channel function.

    View details for DOI 10.1073/pnas.1207606109

    View details for Web of Science ID 000308085200033

    View details for PubMedID 22869708

  • Xenopus laevis oocytes infected with multi-drug-resistant bacteria: implications for electrical recordings JOURNAL OF GENERAL PHYSIOLOGY O'Connell, D., Mruk, K., Rocheleau, J. M., Kobertz, W. R. 2011; 138 (2): 271-277

    Abstract

    The Xenopus laevis oocyte has been the workhorse for the investigation of ion transport proteins. These large cells have spawned a multitude of novel techniques that are unfathomable in mammalian cells, yet the fickleness of the oocyte has driven many researchers to use other membrane protein expression systems. Here, we show that some colonies of Xenopus laevis are infected with three multi-drug-resistant bacteria: Pseudomonas fluorescens, Pseudomonas putida, and Stenotrophomonas maltophilia. Oocytes extracted from infected frogs quickly (3-4 d) develop multiple black foci on the animal pole, similar to microinjection scars, which render the extracted eggs useless for electrical recordings. Although multi-drug resistant, the bacteria were susceptible to amikacin and ciprofloxacin in growth assays. Supplementing the oocyte storage media with these two antibiotics prevented the appearance of the black foci and afforded oocytes suitable for whole-cell recordings. Given that P. fluorescens associated with X. laevis has become rapidly drug resistant, it is imperative that researchers store the extracted oocytes in the antibiotic cocktail and not treat the animals harboring the multi-drug-resistant bacteria.

    View details for DOI 10.1085/jgp.201110661

    View details for Web of Science ID 000293122500011

    View details for PubMedID 21788613

  • Discovery of a Novel Activator of KCNQ1-KCNE1 K+ Channel Complexes PLOS ONE Mruk, K., Kobertz, W. R. 2009; 4 (1)

    Abstract

    KCNQ1 voltage-gated K(+) channels (Kv7.1) associate with the family of five KCNE peptides to form complexes with diverse gating properties and pharmacological sensitivities. The varied gating properties of the different KCNQ1-KCNE complexes enables the same K(+) channel to function in both excitable and non excitable tissues. Small molecule activators would be valuable tools for dissecting the gating mechanisms of KCNQ1-KCNE complexes; however, there are very few known activators of KCNQ1 channels and most are ineffective on the physiologically relevant KCNQ1-KCNE complexes. Here we show that a simple boronic acid, phenylboronic acid (PBA), activates KCNQ1/KCNE1 complexes co-expressed in Xenopus oocytes at millimolar concentrations. PBA shifts the voltage sensitivity of KCNQ1 channel complexes to favor the open state at negative potentials. Analysis of different-sized charge carriers revealed that PBA also targets the permeation pathway of KCNQ1 channels. Activation by the boronic acid moiety has some specificity for the Kv7 family members (KCNQ1, KCNQ2/3, and KCNQ4) since PBA does not activate Shaker or hERG channels. Furthermore, the commercial availability of numerous PBA derivatives provides a large class of compounds to investigate the gating mechanisms of KCNQ1-KCNE complexes.

    View details for DOI 10.1371/journal.pone.0004236

    View details for Web of Science ID 000265482100008

    View details for PubMedID 19156197

  • Preligand assembly domain-mediated ligand-independent association between TRAIL receptor 4 (TR4) and TR2 regulates TRAIL-induced apoptosis PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Clancy, L., Mruk, K., Archer, K., Woelfel, M., Mongkolsapaya, J., Screaton, G., Lenardo, M. J., Chan, F. K. 2005; 102 (50): 18099-18104

    Abstract

    Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a cytokine with potential therapeutic value against cancers because of its selective cytotoxicity to many transformed, but not normal, cells. The "decoy receptors" TRAIL-R3 (TR3) and TRAIL-R4 (TR4) were believed to negatively regulate TRAIL-induced cytotoxicity by competing for ligand binding with TRAIL-R1 (TR1) and TRAIL-R2 (TR2). Here, we show that inhibition of TRAIL-induced apoptosis by TR4 critically depends on its association with TR2 via the NH(2)-terminal preligand assembly domain overlapping the first partial cysteine-rich domain of both receptors. By contrast, ligand binding by TR4 is dispensable for its apoptosis inhibitory function, thereby excluding the possibility that TR4 was a "decoy" to inhibit apoptosis by binding up TRAIL. In primary CD8(+) T cells, which express only TR2 and TR4 and are resistant to TRAIL-induced apoptosis, stimulation with phorbol myristate acetate abrogated the ligand-independent interaction between TR2 and TR4 and enhanced their sensitivity to TRAIL-induced apoptosis. Hence, whereas most TNF receptors normally form only homotrimeric complexes, the preligand assembly domains in TR2 and TR4 permit mixed complex formation as a means to regulate apoptosis induction. We propose that TR4 is a "regulatory" rather than "decoy" receptor that inhibits apoptosis signaling by TRAIL through this previously uncharacterized ligand-independent mechanism.

    View details for DOI 10.1073/pnas.0507329102

    View details for Web of Science ID 000234010500040

    View details for PubMedID 16319225