红细菌光合作用反应中心与双氨基酸取代 I（L177）H+H（M182）L 的特性。

Properties of Rhodobacter sphaeroides photosynthetic reaction center with double amino acid substitution I(L177)H+H(M182)L.

机构信息

Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, Russia.

出版信息

Biochemistry (Mosc). 2011 Apr;76(4):450-4. doi: 10.1134/s0006297911040079.

Abstract

Histidine M182 in the reaction center (RC) of Rhodobacter sphaeroides serves as the fifth ligand of the bacteriochlorophyll (BChl) B(B) Mg atom. When this His is substituted by an amino acid that is not able to coordinate Mg, bacteriopheophytin appears in the B(B) binding site instead of BChl (Katilius, E., et al. (1999) J. Phys. Chem. B, 103, 7386-7389). We have shown that in the presence of the additional mutation I(L177)H the coordination of the BChl B(B) Mg atom in the double mutant I(L177)H+H(M182)L RC still remains. Changes in the double mutant RC absorption spectrum attributed to BChl absorption suggest that BChl B(B) Mg atom axial ligation might be realized not from the usual α-side of the BChl macrocycle, but from the opposite, β-side. Weaker coordination of BChl B(B) Mg atom compared to the other mutant RC BChl molecules suggests that not an amino acid residue but a water molecule might be a possible ligand. The results are discussed in the light of the structural changes that occurred in the RC upon Ile/His substitution in the L177 position.

摘要

红细菌反应中心（RC）中的组氨酸 M182 充当细菌叶绿素（BChl）B（B）Mg 原子的第五个配体。当这个 His 被不能配位 Mg 的氨基酸取代时，细菌原叶绿素会出现在 B（B）结合位点，而不是 BChl（Katilius，E.等人，1999 年，J. Phys. Chem. B，103，7386-7389）。我们已经表明，在存在额外突变 I（L177）H 的情况下，双突变体 I（L177）H+H（M182）L RC 中 BChl B（B）Mg 原子的配位仍然存在。双突变体 RC 吸收光谱中归因于 BChl 吸收的变化表明，BChl B（B）Mg 原子轴向配位可能不是来自 BChl 大环的通常α侧，而是来自相反的β侧。与其他突变 RC BChl 分子相比，BChl B（B）Mg 原子的配位较弱表明，可能的配体不是氨基酸残基而是水分子。这些结果是根据在 L177 位置发生的 Ile/His 取代后 RC 中发生的结构变化进行讨论的。