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Mutational analysis of the C‐terminal cytoplasmic domain of FlhB, a transmembrane component of the flagellar type III protein export apparatus in Salmonella
Author(s) -
Inoue Yumi,
Kinoshita Miki,
Namba Keiichi,
Minamino Tohru
Publication year - 2019
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1111/gtc.12684
Subject(s) - mutant , cytoplasm , biology , mutation , c terminus , transmembrane domain , flagellum , transmembrane protein , microbiology and biotechnology , conformational change , biophysics , protein structure , genetics , biochemistry , receptor , gene , amino acid
The flagellar protein export apparatus switches its substrate specificity when hook length has reached approximately 55 nm in Salmonella . The C‐terminal cytoplasmic domain of FlhB (FlhB C ) is involved in this switching process. FlhB C consists of FlhB CN and FlhB CC polypeptides. FlhB CC has a flexible C‐terminal tail (FlhB CCT ). FlhB CC is involved in substrate recognition, and conformational rearrangements of FlhB CN –FlhB CC boundary are postulated to be required for the export switching. However, it remains unknown how it occurs. To clarify this question, we carried out mutational analysis of highly conserved residues in FlhB C . The flhB(E230A) mutation reduced the FlhB function. The flhB(E11S) mutation restored the protein transport activity of the flhB(E230A) mutant to the wild‐type level, suggesting that the interaction of FlhB CN with the extreme N‐terminal region of FlhB is required for flagellar protein export. The flhB(R320A) mutation affected hydrophobic interaction networks in FlhB CC , thereby increasing insolubility of FlhB C . The R320A mutation also affected the export switching, thereby producing longer hooks with the filament attached. C‐terminal truncations of FlhB CCT induced a conformational change of FlhB CN –FlhB CC boundary, resulting in a loose hook length control. We propose that FlhB CCT may control conformational arrangements of FlhB CN –FlhB CC boundary through the hydrophobic interaction networks of FlhB CC .