Pasteurella multocida PfhB2 toxin displays a novel unconventional cysteine protease fold

Abstract

Pasteurella multocida causes respiratory tract infections in a broad range of animals, as well as opportunistic infections in humans. P. multocida secretes a multi‐domain toxin, called PfhB2, which contains a YopT‐like putative cysteine protease domain at its C‐terminus. PfhB2's YopT domain contains a well‐conserved Cys‐His‐Asp catalytic triad that defines YopT family members, and shares high sequence similarity with the prototype YopT from Yersinia sp. PfhB2 is implicated in virulence. Its FHA (filamentous hemagglutinin) and Fic (filamention induced by cAMP) domains have been shown to provide protective immunity in turkeys and to adenylylate Rho‐GTPases in vitro, respectively. In contrast, little is known about PfhB2's YopT‐like domain. Here, we show that PfhB2‐YopT does not display cysteine protease activity in a manner similar to Yersinia YopT or any other characterized YopT family members. We, therefore, opted to characterize PfhB2‐YopT structurally. Using a catalytically inactive C3733S mutant of PfhB2‐YopT that provides enhanced protein stability, we determined the crystal structure of PfhB2‐YopTC3733S solved by experimental phasing with Selenomethionine derivative crystals at 2.2Å resolution. Our structure shows that PfhB2‐YopT exists as four molecules arranged as an asymmetric unit consisting of two dimers. Importantly, the Cys from each molecule of the dimer coordinates with the His and Asp from the other molecule to complete the catalytic triad. Such an unconventional orientation of the catalytic triad has never been observed for any class of Cysteine proteases. Thus, our PfhB2‐YopT structure represents a novel cysteine protease fold, and provides critical insights for the function of Cys‐His‐Asp containing domains that are often associated with large, multi‐domain bacterial toxins.Support or Funding InformationThis work was supported by funding from 1) an Indiana CTSI (Clinical and Translational Sciences Institute) Project Development Team Award and 2) the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH) under Award Number R01GM100092.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.