Architecture and Principle of Formation of the Baseplate of Bacteriophage T4

尾部溶菌酶gp5是一种结构上必需的成分，具有溶菌酶活性，能在感染后局部消化宿主大肠杆菌的肽聚糖，使尾管能够到达内膜。在加工过程中，gp5前体在Ser351和Ala352之间发生切割。然而，C-末端结构域作为复合体的一部分保留下来，只有在感染时才会分离。我们已经证明，C-末端结构域存在于尾巴和病毒粒子中。研究还表明，感染细胞的尾部也保留了C-末端结构域。最近，普渡大学博士后研究员Shuji Kanamaru在Michael G.Rossmann教授的实验室成功地从gp5-gp27杂六聚体的晶体中确定了衍射相。该复合体的结构现在正在解开，但它已经揭示了使gp5成为三聚体的细长的C-末端三重β-螺旋。本项目要解决的另一个结构是底板楔形的起爆复合体，即GP10-GP11复合体。它被认为构成了从底板底部伸出的六角形底板顶端的尾销。经SDS-PAGE、Edman降解和分析超速离心法测定，表明该络合物是一个亚基组成为(GP10)_3(GP11)_3的杂六角体。最近得到了适合于X射线分析的晶体，有待物相确定。作为第三个结晶的靶蛋白，尾部完成蛋白GP15也得到了过表达和结晶。它形成同六面体，很可能形成管环的最后一个环。人们正在努力获得更大的适合X射线衍射的晶体。

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.