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Recognition and targeting mechanisms by chaperones in flagella assembly and operation
Structural highlights
FunctionFLIT_SALTY Dual-function protein that regulates the transcription of class 2 flagellar operons and that also acts as an export chaperone for the filament-capping protein FliD. As a transcriptional regulator, acts as an anti-FlhDC factor; it directly binds FlhC, thus inhibiting the binding of the FlhC/FlhD complex to class 2 promoters, resulting in decreased expression of class 2 flagellar operons. As a chaperone, effects FliD transition to the membrane by preventing its premature polymerization, and by directing it to the export apparatus.[1] [2] [3] [4] Publication Abstract from PubMedThe flagellum is a complex bacterial nanomachine that requires the proper assembly of several different proteins for its function. Dedicated chaperones are central in preventing aggregation or undesired interactions of flagellar proteins, including their targeting to the export gate. FliT is a key flagellar chaperone that binds to several flagellar proteins in the cytoplasm, including its cognate filament-capping protein FliD. We have determined the solution structure of the FliT chaperone in the free state and in complex with FliD and the flagellar ATPase FliI. FliT adopts a four-helix bundle and uses a hydrophobic surface formed by the first three helices to recognize its substrate proteins. We show that the fourth helix constitutes the binding site for FlhA, a membrane protein at the export gate. In the absence of a substrate protein FliT adopts an autoinhibited structure wherein both the binding sites for substrates and FlhA are occluded. Substrate binding to FliT activates the complex for FlhA binding and thus targeting of the chaperone-substrate complex to the export gate. The activation and targeting mechanisms reported for FliT appear to be shared among the other flagellar chaperones. Recognition and targeting mechanisms by chaperones in flagellum assembly and operation.,Khanra N, Rossi P, Economou A, Kalodimos CG Proc Natl Acad Sci U S A. 2016 Aug 30;113(35):9798-803. doi:, 10.1073/pnas.1607845113. Epub 2016 Aug 15. PMID:27528687[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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