Thomas D, Morgan D G, DeRosier D J
W. M. Keck Institute for Cellular Visualization, Rosenstiel Basic Medical Sciences Research Center, and Department of Biology, Brandeis University, Waltham, Massachusetts 02454.
J Bacteriol. 2001 Nov;183(21):6404-12. doi: 10.1128/JB.183.21.6404-6412.2001.
Flagella purified from Salmonella enterica serovar Typhimurium contain FliG, FliM, and FliN, cytoplasmic proteins that are important in torque generation and switching, and FliF, a transmembrane structural protein. The motor portion of the flagellum (the basal body complex) has a cytoplasmic C ring and a transmembrane M ring. Incubation of purified basal bodies at pH 4.5 removed FliM and FliN but not FliG or FliF. These basal bodies lacked C rings but had intact M rings, suggesting that FliM and FliN are part of the C ring but not a detectable part of the M ring. Incubation of basal bodies at pH 2.5 removed FliG, FliM, and FliN but not FliF. These basal bodies lacked the C ring, and the cytoplasmic face of the M ring was altered, suggesting that FliG makes up at least part of the cytoplasmic face of the M ring. Further insights into FliG were obtained from cells expressing a fusion protein of FliF and FliG. Flagella from these mutants still rotated but cells were not chemotactic. One mutant is a full-length fusion of FliF and FliG; the second mutant has a deletion lacking the last 56 residues of FliF and the first 94 residues of FliG. In the former, C rings appeared complete, but a portion of the M ring was shifted to higher radius. The C-ring-M-ring interaction appeared to be altered. In basal bodies with the fusion-deletion protein, the C ring was smaller in diameter, and one of its domains occupied space vacated by missing portions of FliF and FliG.
从鼠伤寒沙门氏菌血清型鼠伤寒中纯化得到的鞭毛含有FliG、FliM和FliN，这些胞质蛋白在扭矩产生和转换中起重要作用，还含有跨膜结构蛋白FliF。鞭毛的马达部分（基体复合体）有一个胞质C环和一个跨膜M环。在pH 4.5条件下孵育纯化的基体可去除FliM和FliN，但不会去除FliG或FliF。这些基体缺乏C环，但M环完整，这表明FliM和FliN是C环的一部分，而不是M环可检测到的部分。在pH 2.5条件下孵育基体可去除FliG、FliM和FliN，但不会去除FliF。这些基体缺乏C环，且M环的胞质面发生了改变，这表明FliG至少构成了M环胞质面的一部分。通过表达FliF和FliG融合蛋白的细胞获得了对FliG的进一步认识。这些突变体的鞭毛仍能旋转，但细胞没有趋化性。一个突变体是FliF和FliG的全长融合体；第二个突变体缺失了FliF的最后56个残基和FliG的前94个残基。在前者中，C环似乎完整，但M环的一部分向更大半径移位。C环与M环的相互作用似乎发生了改变。在含有融合缺失蛋白的基体中，C环直径较小，其一个结构域占据了FliF和FliG缺失部分腾出的空间。
