Nakai M, Goto A, Nohara T, Sugita D, Endo T
Department of Chemistry, Faculty of Science, Nagoya University, Japan.
J Biol Chem. 1994 Dec 16;269(50):31338-41.
Recently, we identified the SecA and SecY proteins in the cyanobacterium Synechococcus PCC7942. Antibodies raised against cyanobacterial SecA specifically reacted with a 110-kDa protein of pea chloroplasts, suggesting the presence of SecA in higher plant chloroplasts. A part of the pea secA cDNA was polymerase chain reaction-amplified with degenerated oligonucleotide primers and with pea cDNA as a template. The deduced amino acid sequence shows 62% identity with cyanobacterial SecA and 52% identity with Escherichia coli SecA. Antibodies raised against the pea SecA fragment, which was expressed in E. coli cells from the obtained polymerase chain reaction-amplified cDNA, reacted with the 110-kDa chloroplast protein; the 110-kDa protein was mainly found in the stroma but partly in the thylakoid membrane. The anti-pea SecA IgG inhibited the in vitro import of the 33-kDa protein of the oxygen-evolving complex, but not of the 23-kDa protein of the oxygen-evolving complex, into thylakoids. These results suggest that SecA facilitates transport of a subset of thylakoid lumenal proteins including the 33-kDa protein into thylakoids. We propose that a bacterial-type Sec protein-dependent transport system operates for protein transport into thylakoids in higher plant chloroplasts.
最近，我们在蓝藻聚球藻PCC7942中鉴定出了SecA和SecY蛋白。针对蓝藻SecA产生的抗体与豌豆叶绿体中的一种110 kDa蛋白发生特异性反应，这表明高等植物叶绿体中存在SecA。以豌豆cDNA为模板，用简并寡核苷酸引物通过聚合酶链反应扩增出豌豆secA cDNA的一部分。推导的氨基酸序列与蓝藻SecA的同一性为62%，与大肠杆菌SecA的同一性为52%。针对从获得的聚合酶链反应扩增cDNA在大肠杆菌细胞中表达的豌豆SecA片段产生的抗体，与110 kDa的叶绿体蛋白发生反应；110 kDa蛋白主要存在于基质中，但部分存在于类囊体膜中。抗豌豆SecA IgG抑制了放氧复合体33 kDa蛋白而非放氧复合体23 kDa蛋白向类囊体的体外导入。这些结果表明，SecA促进了包括33 kDa蛋白在内的一部分类囊体腔蛋白向类囊体的转运。我们提出，一种细菌型Sec蛋白依赖性转运系统在高等植物叶绿体中负责蛋白向类囊体的转运。
