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The role of intrinsically disordered C‐terminal region of FliK in substrate specificity switching of the bacterial flagellar type III export apparatus
Author(s) -
Kinoshita Miki,
Aizawa ShinIchi,
Inoue Yumi,
Namba Keiichi,
Minamino Tohru
Publication year - 2017
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13718
Subject(s) - biology , mutant , cytoplasm , microbiology and biotechnology , domain (mathematical analysis) , c terminus , biophysics , substrate (aquarium) , function (biology) , biochemistry , amino acid , mathematical analysis , ecology , mathematics , gene
Summary The bacterial flagellar export switching machinery consists of a ruler protein, FliK, and an export switch protein, FlhB and switches substrate specificity of the flagellar type III export apparatus upon completion of hook assembly. An interaction between the C‐terminal domain of FliK (FliK C ) and the C‐terminal cytoplasmic domain of FlhB (FlhB C ) is postulated to be responsible for this switch. FliK C has a compactly folded domain termed FliK T3S4 (residues 268–352) and an intrinsically disordered region composed of the last 53 residues, FliK CT (residues 353–405). Residues 301–350 of FliK T3S4 and the last five residues of FliK CT are critical for the switching function of FliK. FliK CT is postulated to regulate the interaction of FliK T3S4 with FlhB C , but it remains unknown how. Here we report the role of FliK CT in the export switching mechanism. Systematic deletion analyses of FliK CT revealed that residues of 351–370 are responsible for efficient switching of substrate specificity of the export apparatus. Suppressor mutant analyses showed that FliK CT coordinates FliK T3S4 action with the switching. Site‐directed photo‐cross‐linking experiments showed that Val‐302 and Ile‐304 in the hydrophobic core of FliK T3S4 bind to FlhB C . We propose that FliK CT may induce conformational rearrangements of FliK T3S4 to bind to FlhB C .