Crystal Structure of the Yersinia enterocolitica Type III Secretion Chaperone SycT

Abstract

Several Gram-negative pathogens deploy type III secretion systems (TTSSs) as molecular syringes to inject effector proteins into host cells. Prior to secretion, some of these effectors are accompanied by specific type III secretion chaperones. The Yersinia enterocolitica TTSS chaperone SycT escorts the effector YopT, a cysteine protease that inactivates the small GTPase RhoA of targeted host cells. We solved the crystal structure of SycT at 2.5 Å resolution. Despite limited sequence similarity among TTSS chaperones, the SycT structure revealed a global fold similar to that exhibited by other structurally solved TTSS chaperones. The dimerization domain of SycT, however, differed from that of all other known TTSS chaperone structures. Thus, the dimerization domain of TTSS chaperones does not likely serve as a general recognition pattern for downstream processing of effector/chaperone complexes. Yersinia Yop effectors are bound to their specific Syc chaperones close to the Yop N termini, distinct from their catalytic domains. Here, we showed that the catalytically inactive YopT C139S is reduced in its ability to bind SycT, suggesting an ancillary interaction between YopT and SycT. This interaction could maintain the protease inactive prior to secretion or could influence the secretion competence and folding of YopT.

Protein Export According to Schedule: Architecture, Assembly, and Regulation of Type III Secretion Systems from Plant- and Animal-Pathogenic Bacteria

“…Despite their moderate amino acid sequence similarities, several class I chaperones share a conserved mixed ␣/␤ fold and form dimeric structures, as revealed by crystal structure analyses (36,37,68,169,321,327,340,441,494,520,553,565). Conserved structural features were also described for the chaperone-binding domains (CBDs) of T3S substrates, which are often located within the N-terminal 50 to 100 amino acids and are wrapped around the chaperone dimer in an extended conformation (37,321,441,494,520,598).…”

The Type III Secretion Chaperone SycE Promotes a Localized Disorder-to-Order Transition in the Natively Unfolded Effector YopE

“…A large family of such chaperones exists, with individual chaperones functioning in the translocation of only a single or just a few corresponding effectors. Although chaperones have limited sequence identity (Յ 20%), their folds and modes of effector binding are well conserved (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Chaperone dimers provide rigid and globular surfaces, around which effectors wrap an ϳ25-100-residue chaperone-binding (Cb) region in strikingly extended conformation (4,6,9,12,13).…”

A Solvent-Exposed Patch in Chaperone-Bound YopE Is Required for Translocation by the Type III Secretion System

“…There are a large number of such effector-dedicated chaperones, as each individual chaperone protein binds just a single effector, or in some cases a few effectors. These chaperones are divergent in sequence (Յ20% identity) but have similar protein folds, dimeric oligomerization states, and effector-binding modes (4,5,10,28,30,31,35,42,43,46,47). In the binding mode, the Cb region of the effector winds around the surface of the dimeric chaperone in a highly extended fashion ( Fig.…”