Conformational Analysis of Clostridium difficile Toxin B and Its Implications for Substrate Recognition

Rebecca Swett, G. Andrés Cisneros, Andrew L. Feig, Jörg Langowski
2012 PLoS ONE  
Clostridium difficile (C. difficile) is an opportunistic pathogen that can cause potentially lethal hospital-acquired infections. The cellular damage that it causes is the result of two large clostridial cytotoxins: TcdA and TcdB which act by glucosylating cytosolic G-proteins, mis-regulation of which induces apoptosis. TcdB is a large flexible protein that appears to undergo significant structural rearrangement upon accommodation of its substrates: UDP-glucose and a Rho-family GTPase. To
more » ... terize the conformational space of TcdB, we applied normal mode and hinge-region analysis, followed by longtimescale unbiased molecular dynamics. In order to examine the TcdB and RhoA interaction, macromolecular docking and simulation of the TcdB/RhoA complex was performed. Generalized Masked Delaunay analysis of the simulations determined the extent of significant motions. This combination of methods elucidated a wide range of motions within TcdB that are reiterated in both the low-cost normal mode analysis and the extensive MD simulation. Of particular interest are the coupled motions between a peripheral 4-helix bundle and a small loop in the active site that must rearrange to allow RhoA entry to the catalytic site. These extensive coupled motions are indicative of TcdB using a conformational capture mechanism for substrate accommodation.
doi:10.1371/journal.pone.0041518 pmid:22844485 pmcid:PMC3402401 fatcat:dari2n2ddfbafk6mdszm3zsmhu