Bidirectional electron transfer in photosystem I: accumulation of A0- in A-side or B-side mutants of the axial ligand to chlorophyll A0.
Bidirectional electron transfer in photosystem I: accumulation of A0- in A-side or B-side mutants of the axial ligand to chlorophyll A0.
复制标题
光系统 I 中的双向电子转移：A0- 在叶绿素 A0 轴向配体的 A 侧或 B 侧突变体中积累。
DOI：
10.1021/bi0354177
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发表时间：
2004
期刊：
影响因子：
2.9
通讯作者：
A. Webber
中科院分区：
文献类型：
--
作者：
V. M. Ramesh;K. Gibasiewicz;K. Gibasiewicz;Su Lin;S. Bingham;A. Webber
光系统I在P（700）和F（X）之间存在两条潜在的电子传递途径。这些分支由电子转移链组分A、A（0）和A（1）组成。初级电子受体A（0）是叶绿素a单体，其可以是在2.5 A分辨率结构中鉴定的两个叶绿素分子eC-A（3）/eC-B（3）中的一个或两个。eC-A（3）/eC-B（3）叶绿素均由甲硫氨酸的硫原子配位。这种配位是非常不寻常的，因为酸性Mg（2+）和软碱硫之间的相互作用很弱。eC-A（3）/eC-B（3）叶绿素也位于可能连接天线和电子转移链叶绿素的连接叶绿素之一附近。由于它们在结构中的位置，eC-A（3）/eC-B（3）叶绿素可能在激发能量转移和电子转移中起作用。为了测试eC-A（3）/eC-B（3）叶绿素在电子传递中的作用，PsaA的Met-684和PsaB的Met-664已被改变为His、Ser和Leu。M（A684）或M（B664）的替换导致生长表型的显著改变。His和Leu突变体在氧气存在下对光非常敏感。在B侧突变体中，生长受到更大程度的损害。然而，所有的突变体都能够以相当的速度厌氧生长。His和Ser突变体都以与野生型相似的水平积累PSI，而Leu突变体具有减少的PSI量。超快瞬态吸光度测量显示，在中性条件下，（A（0）（-）- A（0））差异信号在MH（A684）和MH（B664）突变体中积累，表明A（0）（-）和A（1）之间的电子转移被阻断或显著减慢。结果表明，在莱茵衣藻的PSI中，ETC的A支和B支都有活性。
Photosystem I contains two potential electron transfer pathways between P(700) and F(X). These branches are made up of the electron transfer chain components A, A(0), and A(1). The primary electron acceptor A(0) is a chlorophyll a monomer that could be one or both of the two chlorophyll molecules, eC-A(3)/eC-B(3), identified in the 2.5 A resolution structure. The eC-A(3)/eC-B(3) chlorophylls are both coordinated by the sulfur atom of a methionine. This coordination is highly unusual, as interactions between the acid Mg(2+) and the soft base sulfur are weak. The eC-A(3)/eC-B(3) chlorophylls also are located close to one of the connecting chlorophylls that may link the antenna and the electron transfer chain chlorophylls. Due to their location in the structure, the eC-A(3)/eC-B(3) chlorophylls may play a role in both excitation energy transfer and electron transfer. To test the role of the eC-A(3)/eC-B(3) chlorophylls in electron transfer, Met-684 of PsaA and Met-664 of PsaB have been changed to His, Ser, and Leu. Replacement of either M(A684) or M(B664) results in a significant alteration in growth phenotype. The His and Leu mutants are very light sensitive in the presence of oxygen. Growth is impaired to a greater extent in the B-side mutants. However, all of the mutants are able to grow anaerobically at comparable rates. The His and Ser mutants all accumulate PSI at a level similar to that of wild type, whereas the Leu mutants have reduced amounts of PSI. Ultrafast transient absorbance measurements show that the (A(0)(-) - A(0)) difference signal accumulates in the MH(A684) and MH(B664) mutants under neutral conditions, demonstrating that electron transfer between A(0)(-) and A(1) is blocked or significantly slowed. The results show that both the A-branch and the B-branch of the ETC are active in PSI from Chlamydomonas reinhardtii.