YspC: a unique translocator exhibits structural alteration in the complex form with chaperone SycB

YspC is an annotated translocator of Yersinia secretion apparatus-Yersinia secretion protein type three secretion system of Yersinia enterocolitica, it forms an 1:1 complex with its cognate chaperone SycB. Unlike other translocators, YspC is highly soluble inspite of having a transmembrane region. Size exclusion chromatography shows that YspC exists predominantly in a monomeric form. Multiple sequence alignment and ConSurf (a web based bioinformatic tool) analysis confirm its significant deviation from the closest class of minor translocators. YspC also possesses a tertiary structure signal seen from near UV CD, further confirming its unique nature amongst the groups of translocators. Far UV CD depicts that YspC is predominantly an α-helical protein; however, its secondary structure alters in the YspC-SycB complex. Thermal denaturation curve predicts a cooperative melting behaviour for YspC which is altered in the YspC-SycB complex. Furthermore, trypsinolysis data confirms a different digestion pattern for YspC in isolation, when compared to the complex form with SycB. From the Forsters resonance energy transfer analysis, it can be predicted that the two tetratricopeptide repeat regions of SycB are masked while it forms a complex with YspC and this is further confirmed by the interaction studies of YspC with two truncated forms of SycB. YspC interacted with ∆SycB₁₋₁₁₄ and ∆SycB₃₆₋₁₁₄ (possessing only the two TPR regions). However, the complexes formed between YspC and truncated forms of SycB have altered physiological states.