Qin Ling, Hiser Carrie, Mulichak Anne, Garavito R Michael, Ferguson-Miller Shelagh
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Proc Natl Acad Sci U S A. 2006 Oct 31;103(44):16117-22. doi: 10.1073/pnas.0606149103. Epub 2006 Oct 18.
Well ordered reproducible crystals of cytochrome c oxidase (CcO) from Rhodobacter sphaeroides yield a previously unreported structure at 2.0 A resolution that contains the two catalytic subunits and a number of alkyl chains of lipids and detergents. Comparison with crystal structures of other bacterial and mammalian CcOs reveals that the positions occupied by native membrane lipids and detergent substitutes are highly conserved, along with amino acid residues in their vicinity, suggesting a more prevalent and specific role of lipid in membrane protein structure than often envisioned. Well defined detergent head groups (maltose) are found associated with aromatic residues in a manner similar to phospholipid head groups, likely contributing to the success of alkyl glycoside detergents in supporting membrane protein activity and crystallizability. Other significant features of this structure include the following: finding of a previously unreported crystal contact mediated by cadmium and an engineered histidine tag; documentation of the unique His-Tyr covalent linkage close to the active site; remarkable conservation of a chain of waters in one proton pathway (D-path); and discovery of an inhibitory cadmium-binding site at the entrance to another proton path (K-path). These observations provide important insight into CcO structure and mechanism, as well as the significance of bound lipid in membrane proteins.
来自球形红杆菌的细胞色素c氧化酶（CcO）排列有序、可重复的晶体，在2.0埃分辨率下产生了一种以前未报道过的结构，该结构包含两个催化亚基以及一些脂质和去污剂的烷基链。与其他细菌和哺乳动物的CcO晶体结构进行比较后发现，天然膜脂和去污剂替代物所占据的位置以及它们附近的氨基酸残基高度保守，这表明脂质在膜蛋白结构中的作用比通常设想的更为普遍和具体。发现定义明确的去污剂头部基团（麦芽糖）以类似于磷脂头部基团的方式与芳香族残基相关联，这可能是烷基糖苷去污剂在支持膜蛋白活性和结晶性方面取得成功的原因。该结构的其他显著特征包括：发现了一种以前未报道过的由镉和工程化组氨酸标签介导的晶体接触；记录了靠近活性位点的独特的His-Tyr共价连接；在一条质子通道（D通道）中一串水分子的显著保守性；以及在另一条质子通道（K通道）入口处发现了一个抑制性镉结合位点。这些观察结果为CcO的结构和机制以及结合脂质在膜蛋白中的重要性提供了重要的见解。
