Structural highlights
Publication Abstract from PubMedABSTRACT: BACKGROUND: Type III secretion systems are used by Gram-negative bacteria as "macromolecular syringes"to inject effector proteins into eukaryotic cells. Two hydrophobic proteins called translocatorsform the necessary pore in the host cell membrane. Both translocators depend on binding to asingle chaperone in the bacterial cytoplasm to ensure their stability and efficient transportthrough the secretion needle. It was suggested that the conserved chaperones bind the moredivergent translocators via a hexapeptide motif that is found in both translocators andconserved between species. RESULTS: We crystallized a synthetic decapeptide from the Yersinia enterocolitica minor type IIIsecretion translocator YopD bound to its cognate chaperone SycD and determined thecomplex structure at 2.5 A resolution. The structure of peptide-bound SycD is almostidentical to that of apo SycD with an all helical fold consisting of three tetratricopeptiderepeats (TPRs) and an additional C-terminal helix. Peptide-bound SycD formed a kinkedhead-to-head dimer that had previously been observed for the apo form of SycD. Thehomodimer interface comprises both helices of the first tetratricopeptide repeat. The YopDpeptide bound in extended conformation into a mainly hydrophobic groove on the concaveside of SycD. TPRs 1 and 2 of SycD form three hydrophobic pockets that accommodated theconserved hydrophobic residues at position 1, 3 and 6 of the translocator hexapeptidesequence. Two tyrosines that are highly conserved among translocator chaperones contributeto the hydrophobic patches but also form hydrogen bonds to the peptide backbone. CONCLUSIONS: The interaction between SycD and YopD is very similar to the binding of the Pseudomonasminor translocator PopD to its chaperone PcrH and the Shigella major translocator IpaB to itschaperone IpgC. This confirms the prediction made by Kolbe and co-workers that ahexapeptide with hydrophobic residues at three positions is a conserved chaperone binding motif. Because the hydrophobic groove on the concave side of translocator chaperones isinvolved in binding of the major and the minor translocator, simultaneous binding of bothtranslocators to a single type III secretion class II chaperone appears unlikely. Crystal structure of the Yersinia enterocolitica type III secretion chaperone SycD in complex with a peptide of the minor translocator YopD.,Schreiner M, Niemann HH BMC Struct Biol. 2012 Jun 18;12(1):13. PMID:22708907[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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