Homma M, DeRosier D J, Macnab R M
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511.
J Mol Biol. 1990 Jun 20;213(4):819-32. doi: 10.1016/S0022-2836(05)80266-9.
Within the bacterial flagellum the basal-body rod, the hook, the hook-associated proteins (HAPs), and the helical filament constitute an axial substructure whose elements share structural features and a common export pathway. We present here the amino acid sequences of the hook protein and the three HAPs of Salmonella typhimurium, as deduced from the DNA sequences of their structural genes (flgE, flgK, flgL and fliD, respectively). We compared these sequences with each other and with those for the filament protein (flagellin) and four rod proteins, which have been described previously (Joys, 1985; Homma et al., 1990; Smith & Selander, 1990). Hook protein most strongly resembled the distal rod protein (FlgG) and the proximal HAP (HAP1), which are thought to be attached to the proximal and distal ends of the hook, respectively; the similarities were most pronounced near the N and C termini. Hook protein and flagellin, which occupy virtually identical helical lattices, did not resemble each other strongly but showed some limited similarities near their termini. HAP3 and HAP2, which form the proximal and distal boundaries of the filament, showed few similarities to flagellin, each other, or the other axial proteins. With the exceptions of the N-terminal region of HAP2, and the C-terminal region of flagellin, proline residues were absent from the terminal regions of the axial proteins. Moreover, with the exception of the N-terminal region of HAP2, the terminal regions contained hydrophobic residues at intervals of seven residues. Together, these observations suggest that the axial proteins may have amphipathic alpha-helical structure at their N and C termini. In the case of the filament and the hook, the terminal regions are believed to be responsible for the quaternary interactions between subunits. We suggest that this is likely to be true of the other axial structures as well, and specifically that interaction between N-terminal and C-terminal alpha-helices may be important in the formation of the axial structures of the flagellum. Although consensus sequences were noted among some of the proteins, such as the rod, hook and HAP1, no consensus extended to the entire set of axial proteins. Thus the basis for recognition of a protein for export by the flagellum-specific pathway remains to be identified.
在细菌鞭毛中，基体杆、钩形结构、钩相关蛋白（HAPs）和螺旋状细丝构成了一个轴向亚结构，其各个组成部分具有共同的结构特征和一条共同的输出途径。我们在此展示了鼠伤寒沙门氏菌的钩形蛋白和三种HAPs的氨基酸序列，这些序列是根据它们结构基因（分别为flgE、flgK、flgL和fliD）的DNA序列推导出来的。我们将这些序列相互进行了比较，并与之前已描述的细丝蛋白（鞭毛蛋白）和四种杆蛋白的序列进行了比较（乔伊斯，1985年；本间等人，1990年；史密斯和塞兰德，1990年）。钩形蛋白与远端杆蛋白（FlgG）和近端HAP（HAP1）最为相似，据认为它们分别附着在钩形结构的近端和远端；在N端和C端附近，相似性最为明显。钩形蛋白和鞭毛蛋白占据几乎相同的螺旋晶格，但彼此之间相似性不强，只是在它们的末端附近有一些有限的相似之处。形成细丝近端和远端边界的HAP3和HAP2与鞭毛蛋白、彼此或其他轴向蛋白几乎没有相似之处。除了HAP2的N端区域和鞭毛蛋白的C端区域外，轴向蛋白的末端区域没有脯氨酸残基。此外，除了HAP2的N端区域外，末端区域每隔七个残基就含有疏水残基。这些观察结果共同表明，轴向蛋白在其N端和C端可能具有两亲性α螺旋结构。就细丝和钩形结构而言，末端区域被认为负责亚基之间的四级相互作用。我们认为其他轴向结构可能也是如此，特别是N端和C端α螺旋之间的相互作用可能在鞭毛轴向结构的形成中很重要。尽管在一些蛋白质之间发现了共有序列，如杆蛋白、钩形蛋白和HAP1，但没有一个共有序列能扩展到整个轴向蛋白组。因此，通过鞭毛特异性途径识别用于输出的蛋白质的基础仍有待确定。
