Active site structure of the Shigella flexneri effector OspI

Abstract Ubc13 is a critical ubiquitin-conjugating enzyme involved in the nuclear factor-κB (NF-κB) signalling pathway. The Shigella flexneri effector OspI targets the host Ubc13 and modifies this enzyme by deamidation of Gln100 into Glu100. This modification inhibits the tumour necrosis factor (TNF) receptor-associated factor 6 (TRAF6)-catalyzed ubiquitination and diacylglycerol-CBM (CARD–Bcl10– Malt1)-TRAF6-NF-κB signal activation. We have previously reported the wild-type OspI crystal structure, but the catalytic triad does not form the canonical active site. Here, the crystal structure of OspI with a C62S mutation was determined at a resolution of 2.2 ?. This C62S mutant structure provided the active site conformation with the catalytic site of OspI.