Structure of FliM Provides Insight into Assembly of the Switch Complex in the Bacterial Flagella Motor

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Proc Natl Acad Sci USA

DOI:https://doi.org/10.1073/pnas.0602811103· OSTI ID:914286

Park, S; Lowder, B; Bilwes, A; Blair, D; Crane, B

Bacteria switch the direction their flagella rotate to control movement. FliM, along with FliN and FliG, compose a complex in the motor that, upon binding phosphorylated CheY, reverses the sense of flagellar rotation. The 2.0- Angstroms resolution structure of the FliM middle domain (FliMM) from Thermotoga maritima reveals a pseudo-2-fold symmetric topology similar to the CheY phosphatases CheC and CheX. A variable structural element, which, in CheC, mediates binding to CheD ({alpha}2') and, in CheX, mediates dimerization ({beta}x), has a truncated structure unique to FliM ({alpha}2'). An exposed helix of FliMM ({alpha}1) does not contain the catalytic residues of CheC and CheX but does include positions conserved in FliM sequences. Cross-linking experiments with site-directed cysteine mutants show that FliM self-associates through residues on {alpha}1 and {alpha}2'. CheY activated by BeF3- binds to FliM with {approx}40-fold higher affinity than CheY (Kd = 0.04 {micro}M vs. 2 {micro}M). Mapping residue conservation, suppressor mutation sites, binding data, and deletion analysis onto the FliMM surface defines regions important for contacts with the stator-interacting protein FliG and for either counterclockwise or clockwise rotation. Association of 33-35 FliM subunits would generate a 44- to 45-nm-diameter disk, consistent with the known dimensions of the C-ring. The localization of counterclockwise- and clockwise-biasing mutations to distinct surfaces suggests that the binding of phosphorylated CheY cooperatively realigns FliM around the ring.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 914286
• Report Number(s): BNL--78854-2007-JA
• Journal Information: Proc Natl Acad Sci USA, Journal Name: Proc Natl Acad Sci USA Journal Issue: 32 Vol. 103; ISSN 0027-8424; ISSN PNASA6
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
AFFINITY
BACTERIA
CROSS-LINKING
CYSTEINE
DIMENSIONS
DIMERIZATION
MUTANTS
MUTATIONS
PHOSPHATASES
PROTEINS
RESIDUES
RESOLUTION
ROTATION
TOPOLOGY
national synchrotron light source