Architecture and Principle of Formation of the Baseplate of Bacteriophage T4

尾部溶菌酶gp 5是结构上必需的组分，并且具有溶菌酶活性，其在感染时局部破坏宿主大肠杆菌的肽聚糖，使得尾管可以到达内膜。在加工过程中，gp 5前体的裂解发生在Ser 351和Ala 352之间。然而，C-末端结构域作为复合物的一部分保留下来，只有在感染时才会分离。我们已经证明，C-末端结构域是存在于两个尾巴和病毒粒子。还显示感染细胞中的尾部也保留C-末端结构域。最近，普渡大学Michael G.Rossmann教授实验室的博士后研究员Kanamaru成功地确定了gp 5-gp 27异源六聚体晶体的衍射相位。复合物的结构现在正在解决，但它已经揭示了使gp 5成为三聚体的细长C末端三倍螺旋。本项目中要解决的另一个结构是底板楔形体的起始复合体，gp 10-gp 11复合体。它被认为是构成六角底板顶点的尾销，从底板底部突出。SDS-聚丙烯酰胺凝胶电泳、Edman降解和超离心分析表明，该复合物为异源六聚体，亚基组成为（gp 10）_3（gp 11）_3。最近已获得适合于X射线分析的配合物晶体，其有待于物相测定。作为结晶的第三个靶蛋白，尾部完成蛋白gp 15也被过表达并结晶。它形成同源六聚体，并且很可能形成管环的最后一个环。正在努力获得适合于X射线衍射的较大晶体。

Tail lysozyme, gp5, is a structurally essential component and possesses lysozyme activity which locally digests peptidoglycan of the host E.coli upon infection so that the tail tube can reach the inner membrane. Cleavage of gp5 precursor takes place between Ser351 and Ala352 during processing. The C- terminal domain, however, stays as part of the complex and will be detached only upon infection. We have demonstrated that the C-terminal domain is present in both tails and the virion. It was also shown that the tails in infedted cells also retain the C-terminal domain. Very recently, Shuji Kanamaruwho is a post-doctoral fellow at Purdue in Prof. Michael G.Rossmann's lab succeeded in determining the phase of diffractions from the crystal of gp5-gp27 hetero-hexamer. The structure of the complex is now being solved, but it already revealed the slender C-terminal triple beta-helix that makes gp5 a trimer. Another structure to be solved in this project is the initiation complex of the wedge of the baseplate, gp10-gp11 complex. It is considered to constitute the tail pins at the vertices of the hexagonal baseplate, which protrude from the bottom of the baseplate. Based on SDS-PAGE and Edman degradation of the complex and also analytical ultracentrifugation, it was shown that the complex is a hetero-hexamer with the subunit composition of (gp10)_3(gp11)_3. Crystal of the complex suitable for X-ray analysis has been recently been obtained which awaits the phase determination. As the third target protein for crystallization, gp15, the tail completion protein, was also overexpressed and crystallized. It forms a homo-hexamer and it is likely to form the last annulus of the tube ring. Efforts is being made to obtain larger crystals suitable for X-ray diffraction.