4/2/2023 0 Comments Mota copterThese form the T-ring in the periplasmic space, which is not found in E. alginolyticus requires the additional proteins MotX and MotY for rotation ( McCarter, 1994a,b). ![]() Asp24 of PomB is equivalent to Asp32 of MotB, but correlated conformational change of PomA has not been tested. ![]() Thus, a putative mechanism for the motor is that proton flux coordinates conformational changes in MotA via MotB Asp32, and these conformational changes lead to a cyclic interaction with FliG that generates torque. Different patterns of protein digestion indicate a conformational change in MotA between wild-type stators and stators containing the mutation MotB Asp32 to Asn32, which mimics the protonation of Asp32 ( Braun et al., 1999 Kojima and Blair, 2001). This is the only conserved charged residue in MotA or MotB that is absolutely essential for function, and it is postulated that each stator contains two ion channels, each containing one MotB Asp32 residue ( Braun and Blair, 2001). The stoichiometry of stator complexes deduced from targeted disulfide cross-linking studies and chromatography appears to be A 4B 2 ( Braun et al., 2004 Kojima and Blair, 2004b Sato and Homma, 2000) ( Figure 4.1), with the membrane-spanning helices of MotA subunits surrounding a suspected proton-binding site at residue Asp32 of MotB ( Sharp et al., 1995a,b). alginolyticus show a similar pattern ( Yakushi et al., 2006), but with differences in which conserved charged residues are most important for function ( Yorimitsu et al., 2002, 2003). PomA and FliG of the Na +-driven flagellar motor of V. No single mutation in these residues completely abolishes torque generation, and charge-reversing mutations in both proteins can compensate each other, indicating an electrostatic interaction at an interface between the two proteins. The cytoplasmic domain of MotA contains two charged residues that interact with five charged residues in the C-terminal domain of FliG to generate torque ( Lloyd and Blair, 1997 Zhou and Blair, 1997 Zhou et al., 1998). The C-terminal periplasmic domain of MotB contains an essential peptidoglycan-binding motif. MotA/PomA and MotB/PomB have four and one membrane-spanning alpha helices and large cytoplasmic and periplasmic domains, respectively ( Chun and Parkinson, 1988 Dean et al., 1984 De Mot and Vanderleyden, 1994). However, extensive analysis using biochemical cross-linking and site-directed mutagenesis has identified their topology, stoichiometry, and likely active regions. A recent complete structure in situ of the flagellar motor of the spirochete Treponema primitia at 7 nm resolution shows 16 stators in an interconnected ring around the rotor, with most of the mass in the cytoplasmic membrane and periplasm ( Figure 4.2D Murphy et al., 2006).Ĭurrently, there are no atomic-level structures of any part of the stator complexes. coli, and Streptococcus ( Figure 4.2C), containing between 10 and 16 particles depending on the species and the individual motor ( Coulton and Murray, 1978 Khan et al., 1988, 1992). Freeze-fracture cryo-EM shows them located in rings at the periphery of the rotor in Aquaspirillum serpens, Bacillus species, E. ![]() Stator complexes anchor to the peptidoglycan cell wall and span the cytoplasmic membrane, forming ion channels ( Blair and Berg, 1990 De Mot and Vanderleyden, 1994 Sato and Homma, 2000). MotA/MotB and PomA/PomB appear to be very similar in sequence, topology, and function ( Asai et al., 1997 Yorimitsu and Homma, 2001). ![]() typhimurium, or PomA and PomB in Na +-driven motors such as the polar motors of V. The stators are a complex of two proteins: MotA and MotB in H +-driven flagellar motors such as those of E. Berry, in Single Molecule Biology, 2009 Stator
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