Kojima Kouji, Nakamoto Hitoshi
Department of Biochemistry and Molecular Biology, Saitama University, Saitama, 338-8570, Japan.
Curr Microbiol. 2005 May;50(5):272-6. doi: 10.1007/s00284-005-4486-9. Epub 2005 Apr 11.
In cyanobacteria, a disruptant of hspA encoding a small heat shock protein homologue, shows decreased cell growth rates at moderately high temperatures, and loss of both basal and acquired thermo-tolerances, which resemble the phenotype of an htpG disruptant. In vitro studies have shown that both small heat shock protein and Hsp90 can bind and keep non-native proteins in a refolding-competent state under denaturing conditions. The aim of the present study is to elucidate whether constitutive expression of HspA can functionally replace HtpG, a prokaryotic homolog of Hsp90, in the cyanobacterium Synechococcus sp. PCC 7942. HspA did not improve the viability of the htpG disruptant at a lethal temperature, although it did that of the wild type. It did not improve an iron-starved phenotype of the mutant under normal growth conditions, a novel phenotype found in the present study. These results suggest that cellular function of HtpG may differ significantly from that of HspA.
在蓝细菌中,编码小热激蛋白同源物的hspA的破坏突变体在适度高温下细胞生长速率降低,并且丧失了基础耐热性和获得性耐热性,这与htpG破坏突变体的表型相似。体外研究表明,小热激蛋白和Hsp90在变性条件下都能结合并使非天然蛋白质保持在可重折叠的状态。本研究的目的是阐明HspA的组成型表达是否能在集胞藻属PCC 7942蓝细菌中功能性替代Hsp90的原核同源物HtpG。HspA在致死温度下并未提高htpG破坏突变体的活力,尽管它提高了野生型的活力。在正常生长条件下,它也未改善本研究中发现的突变体的铁饥饿表型。这些结果表明,HtpG的细胞功能可能与HspA的细胞功能有显著差异。