MUTATIONAL ANALYSIS OF PHOTOSYSTEM-I POLYPEPTIDES IN THE CYANOBACTERIUM SYNECHOCYSTIS SP, PCC-6803 - TARGETED INACTIVATION OF PSAI REVEALS THE FUNCTION OF PSAI IN THE STRUCTURAL ORGANIZATION OF PSAL

被引:77
作者
XU, Q [1 ]
HOPPE, D [1 ]
CHITNIS, VP [1 ]
ODOM, WR [1 ]
GUIKEMA, JA [1 ]
CHITNIS, PR [1 ]
机构
[1] KANSAS STATE UNIV AGR & APPL SCI, DIV BIOL, MANHATTAN, KS 66506 USA
关键词
D O I
10.1074/jbc.270.27.16243
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
We cloned, characterized, and inactivated the psaI gene encoding a 4-kDa hydrophobic subunit of photosystem I from the cyanobacterium Synechocystis sp. PCC 6803, The peal gene is located 90 base pairs downstream from psaL, and is transcribed on 0,94- and 0,SB-kilobase transcripts, To identify the function of psaI, we generated a cyanobacterial strain in which psaI has been interrupted by a gene for chloramphenicol resistance. The wild-type and the mutant cells showed comparable rates of photoautotrophic growth at 25 degrees C, However, the mutant cells grew slower and contained less chlorophyll than the wild-type cells, when grown at 40 degrees C. The PsaI-less membranes from cells grown at either temperature showed a small decrease in NADP(+) photoreduction rate when compared to the wild-type membranes. Inactivation of psaI led to an 80% decrease in the PsaL level in the photosynthetic membranes and to a complete loss of PsaL in the purified photosystem I preparations, but had little effect on the accumulation of other photosystem I subunits, Upon solubilization with nonionic detergents, photosystem I trimers could be obtained from the wild-type, but not from the PsaI-less membranes, The PsaI-less photosystem I monomers did not contain detectable levels of PsaL. Therefore, a structural interaction between PsaL and PsaI may stabilize the association of PsaL with the photosystem I core. PsaL in the mild-type and PsaI-less membranes showed equal resistance to removal by chaotropic agents. However, PsaL in the PsaI-less strain exhibited an increased susceptibility to proteolysis. From these data, we conclude that PsaI has a crucial role in aiding normal structural organization of PsaL within the photosystem I complex and the absence of PsaI alters PsaL organization, leading to a small, but physiologically significant, defect in photosystem I function.
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页码:16243 / 16250
页数:8
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