Perturbation of the internal water chain in cytochrome f of oxygenic photosynthesis: loss of the concerted reduction of cytochromes f and b6.
Perturbation of the internal water chain in cytochrome f of oxygenic photosynthesis: loss of the concerted reduction of cytochromes f and b6.
复制标题
含氧光合作用细胞色素 f 内部水链的扰动：细胞色素 f 和 b6 协同还原的丧失。
DOI：
10.1021/bi981814j
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Cramer,WA
中科院分区：
文献类型：
--
作者：
Ponamarev,MV;Cramer,WA
萝卜细胞色素的1.96°结构形成了一个H2O分子的线性内链，链上的氧原子具有与邻近原子相当的占有率和“B”因子[Martinez等人]。(1996)蛋白质科学。5,1081−1092.]四种水从血红素延伸到细胞色素表面的Lys66。所有为5个内部H2O分子的15个氢键贡献一个原子的残基在23个细胞色素序列中基本上是保守的。由于只有谷氨酰胺和天冬氨酸侧链参与氢键，所以水链就像一根“质子线”。通过对这些天冬氨酸和谷氨酰胺残基进行定点突变，验证了保守的H2O链的功能。在莱茵衣藻产生的6个突变株中，5个保守的Asn/Gln残基中有4个发生了改变。除N168F突变体外，其余均为光合作用生长。细胞氧化速率和细胞色素b6还原速率(野生型为5−6ms)虽未受到明显影响，但细胞还原速率和电致变色慢带移位的产生(ΔψS)明显降低，半衰期分别增加到38ms和18ms。因此，在这些突变体中，Cytb6的还原明显先于Cytf的还原。在没有明显变化的情况下，Δψ的延迟意味着突变体中H+的移位率降低，电子传递也随之减慢，很可能是在isp和cytf之间。结论如下： (I)质子和电子转移在细胞色素f的还原中耦合，细胞水链在H+转移中起作用；(Ii)水链突变体中b6f复合体的高、低势链的还原不协调；(Iii)喹酚去质子化和电子转移是由一个早期事件启动的，可能是由细胞色素f的氧化引发的isp的运动。
The 1.96 Å structure of turnip cytochromefrevealed a linear internal chain of H2O molecules with the oxygen atoms of the chain having occupancies and “B” factors comparable to those of neighboring atoms [Martinez et al. (1996)Protein Sci. 5, 1081−1092.]. Four waters extend 11 Å from the heme toward Lys66 on the cytochrome surface. All residues that contribute an atom to the 15 H-bonds of five internal H2O molecules are essentially conserved in 23 cytochrome sequences. With only Gln and Asn side chains involved in H-bonding, the water chain resembles a “proton wire”. The function of the conserved H2O chain was tested through site-directed mutagenesis of these Asn and Gln residues. Four of the five conserved Asn/Gln residues were changed in six mutants generated in the green alga,Chlamydomonas reinhardtii. Except for the N168F mutant, all grew photosynthetically. Although the rates of oxidation of cytfoxidation and of reduction of cytb6(5−6 ms in the wild type) were not significantly affected, the rates of cytfreduction and generation of the slow electrochromic band shift (Δψs) were markedly decreased, the half-times increasing to as much as 38 and 18 ms, respectively. Thus, in these mutants, reduction of cytb6reduction clearly precedes that of cytf. Retardation of Δψsin the absence of an observable change in the rate of cytb6reduction implied that the rate of H+translocation decreased in the mutants, and electron transfer was concomitantly retarded, most likely between the ISP and cytf. The following was concluded: (i) proton and electron transfer are coupled in reduction of cytf, and the cytfwater chain functions in H+transfer; (ii) reduction of the high- and low-potential chains in theb6fcomplex is not concerted in the water chain mutants; and (iii) quinol deprotonation and electron transfer from reduced quinone are initiated by an early event, probably the movement of the ISP triggered by oxidation of cytf.