Tame J R, Dodson E J, Murshudov G, Higgins C F, Wilkinson A J
Department of Chemistry, University of York, UK.
Structure. 1995 Dec 15;3(12):1395-406. doi: 10.1016/s0969-2126(01)00276-3.
The periplasmic oligopeptide-binding protein OppA has a remarkably broad substrate specificity, binding peptides of two or five amino-acid residues with high affinity, but little regard to sequence. It is therefore an ideal system for studying how different chemical groups can be accommodated in a protein interior. The ability of the protein to bind peptides of different lengths has been studied by co-crystallising it with different ligands.
Crystals of OppA from Salmonella typhimurium complexed with the peptides Lys-Lys-Lys (KKK) and Lys-Lys-Lys-Ala (KKKA) have been grown in the presence of uranyl ions which form important crystal contacts. These structures have been refined to 1.4 A and 2.1 A, respectively. The ligands are completely enclosed, their side chains pointing into large hydrated cavities and making few strong interactions with the protein.
Tight peptide binding by OppA arises from strong hydrogen bonding and electrostatic interactions between the protein and the main chain of the ligand. Different basic side chains on the protein form salt bridges with the C terminus of peptide ligands of different lengths.
周质寡肽结合蛋白OppA具有非常广泛的底物特异性，能以高亲和力结合两个或五个氨基酸残基的肽，而对序列的要求很少。因此，它是研究不同化学基团如何容纳在蛋白质内部的理想系统。通过将该蛋白与不同配体共结晶，研究了其结合不同长度肽的能力。
在形成重要晶体接触的铀离子存在下，已培养出与肽赖氨酸 - 赖氨酸 - 赖氨酸（KKK）和赖氨酸 - 赖氨酸 - 赖氨酸 - 丙氨酸（KKKA）复合的鼠伤寒沙门氏菌OppA晶体。这些结构分别已精修至1.4埃和2.1埃。配体被完全包裹，其侧链指向大的水合腔，与蛋白质几乎没有强相互作用。
OppA对肽的紧密结合源于蛋白质与配体主链之间强烈的氢键和静电相互作用。蛋白质上不同的碱性侧链与不同长度肽配体的C末端形成盐桥。
