Department of Molecular & Cell Biology

Home Faculty and Research Faculty by Name Bryan A. Krantz

Bryan A. Krantz

Assistant Professor of Biochemistry, Biophysics and Structural Biology*
*and of Chemistry

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Research Interests

One-half of all proteins produced in a cell must at some point traverse a cellular membrane. Usually a dedicated integral membrane protein complex—or translocase channel (TC)—provides the conduit through which the transiting proteins passage. The generality of this problem in biology has meant that many types of translocases have been identified. The present challenge rests on better defining the molecular mechanisms of TCs and to establish the broader physical laws that govern transport.

Often, TCs contain a central pore too narrow to allow a folded substrate protein to passage, requiring that the protein unfold. My research group is interested in understanding how the substrate proteins unfold and how the unfolded chain reptates (or travels like a snake) through the narrow TC. Does a TC directly destabilize or unfold its substrate proteins? What drives polypeptide transport? Are the underlying dynamics of the reptating chain best characterized by Brownian-ratchet mechanisms? To address these questions we are investigating translocase channels central to microbial pathogenesis.

Protein translocation is critical to many host-pathogen interactions. Bacteria utilize TCs to either secrete toxins and virulence factors or display adhesin molecules on their outermost membranes; and by means of these secreted molecules, the pathogen can successfully attach to, disrupt, and/or invade its host’s cells. Anthrax toxin, for example, has proved to be a promising model system to study protein translocation. The toxin is composed of a TC, called protective antigen (PA), which allows its two substrate proteins, lethal and edema factors (LF and EF), to translocate across a host cell’s endosomal membrane and enter the cytosol. Once in the cytosol these factors catalyze enzymatic reactions that disrupt the host cell.

Anthrax toxin is an excellent model system to characterize protein translocation in vitro. We incorporate a range of biophysical approaches: solution spectroscopy, single-channel electrophysiology, and X-ray crystallography. Recently, a novel structural feature was identified inside of the PA channel, called the Φ clamp; this structure is a lumen-facing, hydrophobic heptad of phenylalanine residues located near the center of the channel. We believe the Φ clamp is used in a chaperone-like capacity and effectively couples the protein unfolding and transport processes. Understanding the functional consequences of this structural motif will provide key insights into the function of other translocases and unfolding machines in the cell.

The Φ clamp. (A) A view of the PA heptamer prior to insertion into a membrane, where Phe-427 (red) is highlighted. (B) A cartoon of PA in the translocase-channel conformation. The membrane-spanning channel that extends through the bilayer is a β barrel tube that can only accommodate unfolded translocating substrates as wide as an α helix. Within the channel is the Φ clamp—a heptad ring of Phe-427 side chains. This site is lumen-facing, solvent-exposed, and required for protein translocation. The ring of hydrophobicity is unique in that the surrounding pore lining is composed of small hydrophilic residues.

Selected Publications

Krantz BA, Finkelstein A, Collier RJ. (2006) "Protein translocation through the anthrax toxin transmembrane pore is driven by a proton gradient." J. Mol. Biol. 355: 968.

Krantz BA, Melnyk RA, Zhang S, Juris SJ, Lacy DB, Wu Z, Finkelstein A, Collier RJ. (2005) "A phenylalanine clamp catalyzes protein translocation through the anthrax toxin pore." Science. 309: 777.

Wolfe JT, Krantz BA, Rainey GJA, Young JAT, Collier RJ. (2005) "Whole-cell voltage clamp measurements of anthrax protective antigen pores." J. Biol. Chem. 280: 39417.

Krantz BA, Trivedi AD, Cunningham K, Christensen KA, Collier RJ. (2004) "Anthrax toxin’s lethal and edema factors unfold under acidic pH conditions." J. Mol. Biol. 344: 739.

Christensen KA, Krantz BA, Melnyk RA, Collier RJ. (2004) "Interaction of the 20 kDa and 63 kDa fragments of anthrax protective antigen: kinetics and thermodynamics." Biochemistry 44: 1047.

Sosnick TR, Dothager RS, Krantz BA. (2004) "Differences in the folding transition state of ubiquitin indicated by Φ- and psi-analyses." Proc. Natl Acad. Sci. 101: 17377.

Wigelsworth DJ, Krantz BA, Christensen KA, Lacy DB, Juris SJ, Collier RJ. (2004) "Binding stoichiometry and kinetics of the interaction of a human anthrax toxin receptor, CMG2, with protective antigen." J. Biol. Chem. 279: 23349.

Krantz BA, Dothager R, Sosnick TR. (2004) "Discerning the structure and energy of multiple transition states in protein folding using psi-analysis." J. Mol. Biol. 337: 463.

Krantz BA, Srivastava AK, Nauli S, Baker D, Sauer RT, Sosnick TR. (2002) "Understanding protein hydrogen bond network formation with kinetic D/H amide isotope effects." Nature Struct. Biol. 9: 458.

Krantz BA, Sosnick TR. (2001) "Engineered metal binding sites map the heterogeneous folding landscape of a coiled coil." Nature Struct. Biol. 8: 1042.

Last Updated 2007-07-31