Williams K A, Glibowicka M, Li Z, Li H, Khan A R, Chen Y M, Wang J, Marvin D A, Deber C M
Division of Biochemistry Research, Research Institute Hospital for Sick Children, Toronto, Ontario, Canada.
J Mol Biol. 1995 Sep 8;252(1):6-14. doi: 10.1006/jmbi.1995.0469.
Filamentous bacteriophage M13, an important cloning and phage display vector, is encapsulated by ca 2700 copies of its 50-residue major coat protein (gene 8). This protein occurs as a membrane protein while stably inserted into its E. coli host inner membrane, and as a coat protein upon assembly and packing onto phage DNA in the lipid-free virion. To examine the specific protein-protein interactions underlying these processes, we used a combination of randomized and saturation mutagenesis of the entire gene 8 to assess the susceptibility of each position to mutation. In the resulting library of ca 100 viable M13 mutants, "small" residues (Ala,Gly,Ser), which constitute the non-polar face of the N-terminal amphipathic helical segment, and a face of the hydrophobic (effective transmembrane) helical segment, were found to be highly conserved. These results support a model in which coat protein packing is stabilized by the presence within each protein subunit of two "oligomerization segments", i.e. specific helical regions with faces rich in small residues which function to promote the close approach of alpha-helices.
丝状噬菌体M13是一种重要的克隆和噬菌体展示载体，由约2700个其50个氨基酸的主要外壳蛋白（基因8）拷贝包裹。该蛋白在稳定插入其大肠杆菌宿主内膜时以膜蛋白形式存在，而在脂质-free病毒粒子中组装并包装到噬菌体DNA上时则作为外壳蛋白。为了研究这些过程背后的特定蛋白质-蛋白质相互作用，我们对整个基因8进行了随机和饱和诱变的组合，以评估每个位置对突变的敏感性。在产生的约100个可行的M13突变体文库中，发现构成N端两亲性螺旋段非极性面以及疏水（有效跨膜）螺旋段一个面的“小”残基（丙氨酸、甘氨酸、丝氨酸）高度保守。这些结果支持了一个模型，即外壳蛋白的包装通过每个蛋白质亚基内两个“寡聚化段”的存在而稳定，即具有富含小残基面的特定螺旋区域，其作用是促进α-螺旋的紧密靠近。
