Fahrner K A, Block S M, Krishnaswamy S, Parkinson J S, Berg H C
Department of Cellular and Developmental Biology, Harvard University Cambridge, MA 02138-2020.
J Mol Biol. 1994 Apr 29;238(2):173-86. doi: 10.1006/jmbi.1994.1279.
Two mutants with defects in hook-associated protein 3 (HAP3) were isolated that exhibit impaired swimming only when they interact with a solid surface or a semisolid matrix. Motility and chemotaxis were normal in liquid media, even in media containing viscous agents, but cells failed to swarm in 0.28% agar. Mutants appeared to carry a full complement of flagella of normal configuration and length. However, filaments rotating counterclockwise close to a glass surface transformed from normal to straight, while filaments rotating clockwise transformed from curly to straight. Both transformations propagated from base to tip, as expected if torsionally induced. The mutations mapped to the middle of flgL, to structural gene for HAP3, and sequence analysis revealed the same coding change in both mutants: a substitution of cysteine for arginine 168. Our results show that the ability of a filament composed of normal flagellin subunits to resist mechanical stress depends on the structure of the protein (HAP3) to which it is attached at its base. The N-terminal sequence of HAP3 was found to be similar to the N-terminal sequence of flagellin, and the possibility that it provides a nucleation site for the C-terminal region of flagellin is discussed.
分离出了两个钩相关蛋白3（HAP3）有缺陷的突变体，它们仅在与固体表面或半固体基质相互作用时才表现出游泳能力受损。在液体培养基中，即使在含有粘性剂的培养基中，运动性和趋化性也是正常的，但细胞在0.28%的琼脂中无法群游。突变体似乎携带了完整的正常构型和长度的鞭毛。然而，靠近玻璃表面逆时针旋转的丝状体从正常变为笔直，而顺时针旋转的丝状体从卷曲变为笔直。这两种转变都从基部向顶端传播，正如扭转诱导时所预期的那样。这些突变定位于flgL的中部，即HAP3的结构基因，序列分析显示两个突变体的编码变化相同：第168位精氨酸被半胱氨酸取代。我们的结果表明，由正常鞭毛蛋白亚基组成的丝状体抵抗机械应力的能力取决于其基部所附着的蛋白质（HAP3）的结构。发现HAP3的N端序列与鞭毛蛋白的N端序列相似，并讨论了它为鞭毛蛋白的C端区域提供成核位点的可能性。
