Structural Analysis of Baseplate Wedge Proteins of BacteriophageT4

Abstract

Gp10, gp11 and gp7 constitute part of the wedges, six of which surround the hub to form a baseplate. These proteins interact to form a precursor oligomer in the initial assembly process of the wedge. Recent 3D-image reconstruction of the baseplate before and after contraction (hexagon and star, respectively) together with crystal structures of gp11 and part of gp10 has revealed that these proteins play a central role during the conformational change. In order to fully understand the mechanism of the structural change, we need to determine the whole structure of gp10 and gp7, but it has been difficult. As we have recently succeeded in isolating gp7, we applied limited proteolysis of gp10 and its complex with gp11 or gp7 by lysyl endopeptidase. Gp10 alone, which is a trimer, is cleaved at Lys289, but when complexed with gp11, gp10 is then cleaved at Lys194 where gp11 remained intact. Gp10 consists of four domains, I through IV, where gp11 binds to domain III. Based on the results of limited proteolysis, the region between His195 and Lys289 (95 residues) is likely to belong to domain III. On the other hand, when gp10 is complexed with gp7 and subjected to limited proteolysis,gp10 becomes resistant to the protease, although gp7 was cleaved as in the same way as is proteolysed alone. The results indicated that that the resulting C-terminal 124 residues of gp7 form a stable complex with gp10. Crystallization of the protease-resistant region of gp10-gp11 complex is under way.