Structure of the type III secretion and substrate-binding domain of Yersinia YopH phosphatase

Pathogenic strains of Yersinia deploy a type III secretion system to inject the potent tyrosine phosphatase YopH into host cells, where it dephosphory lates focal adhesion-associated substrates. The amino-terminal, non-catalyt ic domain of YopH is bifunctional; it is essential for the secretion and bi nding of the specific chaperone SycH, but also targets the catalytic domain to substrates in the infected cell. We describe the 2.2 Angstrom resolutio n crystal structure of residues 1-129 of YopH from Yersinia pseudotuberculo sis. The amino-terminal alpha -helix (2-17), comprising the secretion signa l, and beta -strand (24-28) of one molecule exchange with another molecule to form a domain-swapped dimer. Nuclear magnetic resonance (NMR) and gel fi ltration experiments demonstrated that YopH(I -129) could exist as a monome r and/or a dimer in solution. The topology of the dimer and the dynamics of a monomeric form in solution observed by NMR imply that YopH has the prope nsity to unfold partially. The dimer is probably not important physiologica lly, but may mimic how SycH binds to the exposed non-polar surfaces of a pa rtially unfolded YopH. Phosphopeptide-induced perturbations in NMR chemical shifts define a substrate-binding surface on YopH(1-129) that includes res idues previously shown by mutagenesis to be essential for YopH function.