The bacterial photosynthetic reaction center as a model for membrane proteins.
The bacterial photosynthetic reaction center as a model for membrane proteins.
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细菌光合反应中心作为膜蛋白的模型。
DOI：
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发表时间：
1989
影响因子：
16.6
通讯作者：
G. Feher
中科院分区：
文献类型：
--
作者：
D. Rees;H. Komiya;T. Yeates;James P. Allen;G. Feher
膜蛋白参与许多基本的细胞过程。直到最近，由于缺乏原子水平的结构信息，对膜蛋白功能和特性的理解受到阻碍。在了解膜蛋白结构方面具有里程碑意义的成就是紫色细菌红假单胞菌（Rhodopseudomonas viridis）的光合反应中心（RC）的结晶(1)和结构测定（2-5），其次是球形红杆菌（Rhodobacter sphaeroides）的RC（6-17）。RC是一种完整的膜蛋白-色素复合物，它执行光合作用的初始步骤（见18）。紫色细菌的Rps。绿绿和Rb。球形植物由三种膜相关蛋白亚基（指定为L， M和H）和以下辅助因子组成：四种细菌叶绿素（Bchl或B），两种细菌叶绿素（Bphe或[phi]），两种醌和一种非血红素铁。辅因子被组织成两个对称分支，它们通过双重旋转轴（2,8）近似相关。RC结构组织的一个中心特征是存在11个疏水[α]-螺旋，大约有20-30个残基长，被认为代表RC的跨膜部分（3,9）。五个跨膜螺旋存在于L和M亚基中，而单个螺旋存在于H亚基中。L和M亚基的折叠相似，这与两条链之间显著的序列相似性一致（19-25）。L和M亚基通过与两个辅因子分支相关的相同的双旋转轴近似相关。
Membrane proteins participate in many fundamental cellular processes. Until recently, an understanding of the function and properties of membrane proteins was hampered by an absence of structural information at the atomic level. A landmark achievement toward understanding the structure of membrane proteins was the crystallization (1) and structure determination (2-5) the photosynthetic reaction center (RC) from the purple bacteria Rhodopseudomonas viridis, followed by that of the RC from Rhodobacter sphaeroides (6-17). The RC is an integral membrane protein-pigment complex, which carries out the initial steps of photosynthesis (reviewed in 18). RCs from the purple bacteria Rps. viridis and Rb. sphaeroides are composed of three membrane-associated protein subunits (designated L, M, and H), and the following cofactors: four bacteriochlorophylls (Bchl or B), two bacteriopheophytins (Bphe or [phi]), two quinones, and a nonheme iron. The cofactors are organized into two symmetrical branches that are approximately related by a twofold rotation axis (2, 8). A central feature of the structural organization of the RC is the presence of 11 hydrophobic [alpha]-helixes, approximately 20-30 residues long, which are believed to represent the membrane-spanning portion of the RC (3, 9). Five membrane-spanning helixes are present in both the L and M subunits, while a single helix is in the H subunit. The folding of the L and M subunits is similar, consistent with significant sequence similarity between the two chains (19-25). The L and M subunits are approximately related by the same twofold rotation axis that relates the two cofactor branches.
RCs are the first membrane proteins to be described at atomic resolution; consequently they provide an important model for discussing the folding of membrane proteins. The structure demonstrates that [alpha]-helical structures may be adopted by integral membrane proteins, and provides confirmation of the utility of hydropathy plots in identifying nonpolar membrane-spanning regions from sequence data. An important distinction between the folding environments of water-soluble proteins and membrane proteins is the large difference in water concentration surrounding the proteins. As a result, hydrophobic interactions (26) play very different roles in stabilizing the tertiary structures of these two classes of proteins; this has important structural consequences. There is a striking difference in surface polarity of membrane and water-soluble proteins. However, the characteristic atomic packing and surface area appear quite similar.
A computational method is described for defining the position of the RC in the membrane (10). After localization of the RC structure in the membrane, surface residues in contact with the lipid bilayer were identified. As has been found for soluble globular proteins, surface residues are less well conserved in homologous membrane proteins than the buried, interior residues. Methods based on the variability of residues between homologous proteins are described (13); they are useful (a) in defining surface helical regions of membrane and water-soluble proteins and (b) in assigning the side of these helixes that are exposed to the solvent. A unifying view of protein structure suggests that water-soluble proteins may be considered as modified membrane proteins with covalently attached polar groups that solubilize the proteins in aqueous solution.