STRUCTURAL STUDIES ON THE CONTRACTILE TAIL SHEATH PROTEIN OF BACTERIOPHAGE T4

为了阐明噬菌体T4尾鞘组装和收缩的分子机制，我们对尾鞘蛋白gp 18的结构进行了研究。Gp 18的分子量为71，160，具有658个氨基酸残基。1)用TNM硝化gp 18的酪氨酸残基（四硝基甲烷）揭示了10或11个酪氨酸残基在31个酪氨酸中，Tyr 63/73、254、270、455、460、493、523、535、569和590是可修饰的，无论是单体状态还是尾鞘的延伸形式，但这些残基中只有5个是可修饰的（Tyr 254、270、455、460和493）在鞘管收缩形式下进行了修改。特别地，Tyr 270和455的硝化独立于sp 18的缔合状态进行。另一方面，通过巯基特异性试剂ABD-F（4-氨基磺酰基）-7-氟-2，1，3-苯并恶二唑）对Cys残基进行修饰，发现gp 18的5个半胱氨酸残基中的Cys 377、Cys 477和Cys 607具有巯基。Cys 402和406很可能通过二硫键连接，Cys 607可以在单体和缔合状态下被修饰，而Cys 477仅在gp 18的单体状态下可被修饰。2)有限的蛋白水解、免疫印迹和免疫电子显微镜显示，胰蛋白酶抗性片段是Ala 82-Lys 316，并且当结合上文和下文所述的数据时，残基250至410的区域似乎形成尾鞘的突出部分，如Amos和Klug（1975）的三维图像重建所揭示的。3)铜绿假单胞菌噬菌体PS 17的尾鞘基因的序列测定显示尾鞘蛋白具有385个氨基酸，并且T4噬菌体gp 18中的相应序列被分成两个部分并且存在于一级结构中的两个独立的位置。

In order to elucidate the molecular mechanism of assembly and contraction of the tail sheath of bacteriophage T4, we have studieed the structure of the tail sheath protein, gp18. Gp18 has a molecular weight of 71,160 with 658 amino acid residues. 1)Nitration of tyrosine residues of gp18 by TNM (tetranitromethane) has revealed that 10 or 11 tyrosine residues (Tyr63/73, 254,270,455,460,493,523,535,569 and 590) out of 31 tyrosines were modifiable either in the monomeric state or the extended form of the tail sheath, but only five of these residues (Tyr254,270,455,460 and 493) were modified in the contracted form of the sheath. Especially, the nitration of Tyr270 and 455 proceeded independent of the association state of sp18. On the other hand, modification of Cys residues by a sulfhydryl group-specific reagent, ABD-F (4-aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole), has revealed that Cys377, Cys477 and Cys607, among 5 cysteine residues in gp18, have a sulfhydryl group. Cys402 and 406 are very likely connected by a disulfide bond.Cys607 can be modified n monomeric and associated states, whereas Cys477 is modifiable only in the monomeric state of gp18. 2) Limited proteolysis, immunoblotting and immuno-electron microscopy have shown that the trypsin-resistant fragment is Ala82-Lys316 and that, when combined with the data described above and below, the region of residues 250 through 410 appears to form the protruding part of the tail sheath as revealed by three-dimensional image reconstruction by Amos and Klug (1975). 3) Sequence determination of the tail sheath gene of Pseudomonas aeruginosa phage PS17 revealed that the tail sheath protein has 385 amino acids and that the corresponding sequence in T4 phage gp18 was split into two parts and present in two separate places in the primary structure.