Interaction of the type III secretion chaperone SycD with YscY

Abstract

Poster Sessions C478 functional and structural studies were performed, focusing on SmeDEF, the most relevant antibiotic-and triclosan-removing multidrug efflux pump of S. maltophilia. Expression of smeDEF is regulated by the repressor SmeT. Triclosan released SmeT from its operator and induces the expression of smeDEF, thus reducing the susceptibility of S. maltophilia to antibiotics in the presence of the biocide. The structure of SmeT bound to triclosan is described. Two molecules of triclosan were found to bind to one subunit of the SmeT homodimer. The binding of the biocide stabilizes the N terminal domain of both subunits in a conformation unable to bind DNA. This complex structure is the first structural evidence of the ability of triclosan to act as an effector via its binding to a transcriptional regulator (SmeT). Given that SmeT mediate the susceptibility of Stenotrophomonas maltophilia to antibiotics by repressing SmeDEF expression, the present results provide information that aids our understanding of the molecular basis of biocide-induced antibiotic resistance. Keywords: complex, ligand, antibacterial MS36.P25Interaction of the type III secretion chaperone SycD with YscY Madeleine Schreiner,, Hartmut Niemann, Department of Chemistry, Bielefeld University, Bielefeld (Germany). E-mail: madeleine. schreiner@uni-bielefeld.deThe type III secretion system (T3SS) is used by several Gramnegative pathogenic bacteria to inject cytotoxins, so called effector proteins, into the host cell to manipulate their host for their own benefit. The effector translocation occurs via a needle-like nanomachine, the injectisome, which spans the whole bacterial envelope. The effectors enter the cell through a pore within the host cell membrane formed by bacterial translocator proteins. Both the effectors and translocators need chaperones for their efficient translocation. T3S chaperones work without the need for ATP hydrolysis and are divided into three subclasses: class I chaperones interacting with effector proteins, class II chaperones interacting with translocator proteins and class III chaperones interacting with needle components. [1] SycD (specific yop chaperone D) is the class II chaperone of the translocators YopB (Yersinia outer protein B) and YopD from the enteropathogen Yersinia enterocolitica. Additionally, SycD plays an important role in diverse regulatory processes of the T3SS and interacts with several other T3S proteins like TyeA, YscM2 or YscY. Like all structurally characterised class II chaperones SycD comprises an overall α-helical fold consisting of three tetratricopeptide repeats (TPR) providing a concave hydrophobic groove for translocator binding. SycD is known to form homodimers in solution involving the residues A61 and L65 of the first TPR as binding platform and mutations within these dimerisation-mediating residues lead to a stable monomeric chaperone that is not able to rescue a sycD null mutant of Y. enterocolitica.[2] Thus the dimerisation is either essential for the chaperone function or the T...