Ermler U, Fritzsch G, Buchanan S K, Michel H
Max-Planck-Institut für Biophysik, Frankfurt/Main, Germany.
Structure. 1994 Oct 15;2(10):925-36. doi: 10.1016/s0969-2126(94)00094-8.
Photosynthetic reaction centres (RCs) catalyze light-driven electron, transport across photosynthetic membranes. The photosynthetic bacterium Rhodobacter, sphaeroides is often used for studies of RCs, and three groups have determined the structure of its reaction centre. There are discrepancies between these structures, however, and to resolve these we have determined the structure to higher resolution than before, using a new crystal form.
The new structure provides a more detailed description of the Rb. sphaeroides RC, and allows us to compare it with the structure of the RC from Rhodopseudomonas viridis. We find no evidence to support most of the published differences in cofactor binding between the RCs from Rps. viridis and Rb. sphaeroides. Generally, the mode of cofactor binding is conserved, particularly along the electron transfer pathway. Substantial differences are only found at ring V of one bacteriochlorophyll of the 'special pair' and for the secondary quinone, QB. A water chain with a length of about 23 A including 14 water molecules extends from the QB to the cytoplasmic side of the RC.
The cofactor arrangement and the mode of binding to the protein seem to be very similar among the non-sulphur bacterial photosynthetic RCs. The functional role of the displaced QB molecule, which might be present as quinol, rather than quinone, is not yet clear. The newly discovered water chain to the QB binding site suggests a pathway for the protonation of the secondary quinone QB.
光合反应中心（RCs）催化光驱动的电子在光合膜上的运输。光合细菌球形红杆菌常用于研究反应中心，已有三个研究小组确定了其反应中心的结构。然而，这些结构之间存在差异，为了解决这些差异，我们使用一种新的晶体形式，以比以往更高的分辨率确定了其结构。
新结构对球形红杆菌反应中心提供了更详细的描述，并使我们能够将其与绿假单胞菌反应中心的结构进行比较。我们没有发现证据支持已发表的关于绿假单胞菌和球形红杆菌反应中心辅因子结合方面的大多数差异。一般来说，辅因子的结合模式是保守的，特别是沿着电子传递途径。仅在“特殊对”的一个细菌叶绿素的环V以及次级醌QB处发现了显著差异。一条包含14个水分子、长度约为23埃的水链从QB延伸至反应中心的细胞质侧。
在非硫细菌光合反应中心中，辅因子的排列及其与蛋白质的结合模式似乎非常相似。移位的QB分子可能以氢醌而非醌的形式存在，其功能作用尚不清楚。新发现的通往QB结合位点的水链为次级醌QB的质子化提供了一条途径。
