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莱茵衣藻突变体的生物物理、生化和生理特性研究,这些突变体的D1蛋白中Ala251残基发生氨基酸替换,导致光合能力水平各异。

Biophysical, biochemical, and physiological characterization of Chlamydomonas reinhardtii mutants with amino acid substitutions at the Ala251 residue in the D1 protein that result in varying levels of photosynthetic competence.

作者信息

Lardans A, Förster B, Prásil O, Falkowski P G, Sobolev V, Edelman M, Osmond C B, Gillham N W, Boynton J E

机构信息

Department of Botany, Duke University, Durham, North Carolina 27708-1000, USA.

出版信息

J Biol Chem. 1998 May 1;273(18):11082-91. doi: 10.1074/jbc.273.18.11082.

Abstract

The QB binding site of the D1 reaction center protein, located within a stromal loop between transmembrane helices IV and V formed by residues Ile219 to Leu272, is essential for photosynthetic electron transport through photosystem II (PSII). We have examined the function of the highly conserved Ala251 D1 residue in this domain in chloroplast transformants of Chlamydomonas reinhardtii and found that Arg, Asp, Gln, Glu, and His substitutions are nonphotosynthetic, whereas Cys, Ser, Pro, Gly, Ile, Val, and Leu substitutions show various alterations in D1 turnover, photosynthesis, and photoautotrophic growth. The latter mutations reduce the rate of QA to QB electron transfer, but this is not necessarily rate-limiting for photoautotrophic growth. The Cys mutant divides and evolves O2 at wild type rates, although it has slightly higher rates of D1 synthesis and turnover and reduced electron transfer between QA and QB. O2 evolution, D1 synthesis, and accumulation in the Ser, Pro, and Gly mutants in high light is reduced, but photoautotrophic growth rate is not affected. In contrast, the Ile, Val, and Leu mutants are impaired in photoautotrophic growth and photosynthesis in both low and high light and have elevated rates of D1 synthesis and degradation, but D1 accumulation is normal. While rates of synthesis/degradation of the D1 protein are not necessarily correlated with alterations in specific parameters of PSII function in these mutants, bulkiness of the substituted amino acids is highly correlated with the dissociation constant for QB in the seven mutants examined. These observations imply that the Ala251 residue plays a key role in D1 protein.

摘要

D1反应中心蛋白的QB结合位点位于由异亮氨酸219至亮氨酸272残基形成的跨膜螺旋IV和V之间的基质环内,对于通过光系统II(PSII)的光合电子传递至关重要。我们已经在莱茵衣藻的叶绿体转化体中研究了该结构域中高度保守的丙氨酸251 D1残基的功能,发现用精氨酸、天冬氨酸、谷氨酰胺、谷氨酸和组氨酸替代是非光合性的,而用半胱氨酸、丝氨酸、脯氨酸、甘氨酸、异亮氨酸、缬氨酸和亮氨酸替代则在D1周转、光合作用和光自养生长方面表现出各种改变。后一种突变降低了QA到QB的电子转移速率,但这不一定是光自养生长的限速因素。半胱氨酸突变体以野生型速率分裂并释放氧气,尽管它的D1合成和周转速率略高,并且QA和QB之间的电子转移减少。高光下丝氨酸、脯氨酸和甘氨酸突变体中的氧气释放、D1合成和积累减少,但光自养生长速率不受影响。相反,异亮氨酸、缬氨酸和亮氨酸突变体在低光和高光下的光自养生长和光合作用均受损,并且D1合成和降解速率升高,但D1积累正常。虽然这些突变体中D1蛋白的合成/降解速率不一定与PSII功能的特定参数改变相关,但在所研究的七个突变体中,取代氨基酸的体积与QB的解离常数高度相关。这些观察结果表明丙氨酸251残基在D1蛋白中起关键作用。

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