Haag E, Eaton-Rye J J, Renger G, Vermaas W F
Department of Botany, Arizona State University, Tempe 85287.
Biochemistry. 1993 Apr 27;32(16):4444-54. doi: 10.1021/bi00067a037.
The chlorophyll a-binding protein CP47 serves as core antenna to photosystem II (PS II). The predicted topology of CP47 exhibits six membrane-spanning regions and a large hydrophilic loop (loop E) which roughly includes 200 residues (255-455) and is presumably exposed to the lumenal side of the thylakoid membrane. Several lines of experimental evidence suggest that loop E might be involved in binding or stabilizing functional manganese in the catalytic site of water oxidation or in interacting with the extrinsic PS II-O protein (the 33-kDa manganese-stabilizing protein). To scan loop E for functionally important domains, oligonucleotide-directed mutagenesis has been used to introduce deletions of 3-8 residues in conserved and charged regions of loop E. In addition, one single-site mutation of the only histidine present in loop E was created (H343L). Domains deleted in delta 1 (I265-F268), delta 2 (T271-K277), delta 4 (T304-L309), delta 5 (F311-N317), and delta 12 (D440-P447) are required for stable assembly of functional PS II complexes. Deletion of domains delta 3 (K277-E283) and delta 11 (R422-E428) significantly reduces the level of assembled PS II and impairs photoautotrophic growth and oxygen evolution. Deletion of domain delta 8 (A373-D380) enhances the susceptibility to photoinhibition. In contrast, deletion of domains delta 6 (G333-I336), delta 7 (K347-R352), delta 9 (V392-Q394), and delta 10 (D416-F420) and mutation of H343 to leucine do not seem to severly interrupt PS II structure and function, although all mutants exhibit a slightly decreased stability of PS II as compared to the wild type. Thus, selected domains of the large hydrophilic loop of CP47 are important for PS II structure and function. With respect to possible sites of interaction between loop E of CP47 and the extrinsic PS II-O protein, our results indicate that none of the deletions in the region from residue 330 to 420 (delta 6, delta 7, delta 8, delta 9, delta 10) completely interrupts a functional association of the manganese-stabilizing protein to PS II, although the binding characteristics might be changed in some cases.
叶绿素a结合蛋白CP47作为光系统II（PS II）的核心天线。CP47的预测拓扑结构显示有六个跨膜区域和一个大的亲水环（环E），该亲水环大致包含200个残基（255 - 455），可能暴露于类囊体膜的腔侧。几条实验证据表明，环E可能参与在水氧化催化位点结合或稳定功能性锰，或与外在的PS II - O蛋白（33 kDa的锰稳定蛋白）相互作用。为了扫描环E中的功能重要结构域，已使用寡核苷酸定向诱变在环E的保守和带电区域引入3 - 8个残基的缺失。此外，还产生了环E中唯一组氨酸的单点突变（H343L）。δ1（I265 - F268）、δ2（T271 - K277）、δ4（T304 - L309）、δ5（F311 - N317）和δ12（D440 - P447）中缺失的结构域是功能性PS II复合物稳定组装所必需的。δ3（K277 - E283）和δ11（R422 - E428）结构域的缺失显著降低了组装的PS II水平，并损害光合自养生长和氧气释放。δ8（A373 - D380）结构域的缺失增强了对光抑制的敏感性。相比之下，δ6（G333 - I336）、δ7（K347 - R352）、δ9（V392 - Q394）和δ10（D416 - F420）结构域的缺失以及H343突变为亮氨酸似乎并没有严重中断PS II的结构和功能，尽管与野生型相比，所有突变体的PS II稳定性均略有下降。因此，CP47大亲水环的选定结构域对PS II的结构和功能很重要。关于CP47的环E与外在的PS II - O蛋白之间可能的相互作用位点，我们的结果表明，从残基330到420区域（δ6、δ7、δ8、δ9、δ10）的缺失均未完全中断锰稳定蛋白与PS II的功能关联，尽管在某些情况下结合特性可能会改变。
