Expression, purification, structural and functional analysis of SycB: a type three secretion chaperone from Yersinia enterocolitica.

In Yersinia enterocolitica biovar 1B, a genome encoded TTSS designated as Ysa-Ysp system is used for virulence. SycB is an annotated chaperone to this system. SycB is soluble in presence of translocator YspC. SycB and its truncated form (∆SycB((1-114))) exist as dimers. YspC forms a 1:1 complex with SycB. Homology model of SycB shows a flexible N-terminal may be required for solubility and dimerization; and concave core formed by antiparallel helices of TPRs. Far UV CD spectra confirm that SycB is predominantly alpha helical. Near UV CD spectra show that SycB has tertiary structure at pH 7.2 (native folded protein), which disappears at pH 5 (molten globule) and SycB releases YspC at pH 5. SycB has a cooperative melting behavior. At pH 7.2, SycB shows solvent accessible hydrophobic patches. Concave core in the model exhibits ANS binding within FRET distance of tyrosines in the TPR, allowing a range of interaction of SycB with its ligand.