Novel heat shock protein HspQ stimulates the degradation of mutant DnaA protein in Escherichia coli
Novel heat shock protein HspQ stimulates the degradation of mutant DnaA protein in Escherichia coli
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DOI：
10.1111/j.1365-2443.2004.00800.x
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发表时间：
2004-12-01
期刊：
影响因子：
2.1
通讯作者：
Katayama, T
中科院分区：
文献类型：
--
作者：
Shimuta, T;Nakano, K;Katayama, T
大肠杆菌DnaA蛋白启动染色体复制，是复制周期中重要的调控靶点。在这项研究中，发现通过转座子突变分离的抑制突变允许温度敏感性dnaA508和dnaA167突变体在40摄氏度下生长。该抑制因子由先前注释的ORF中的转座子插入组成，此处称为hspQ，其是一种新的热休克基因，其启动子被主要热休克因子sigma识别（32）。hspQ在pBR 322衍生物上的表达在30 ℃抑制dnaA 508和dnaA 167突变体的生长，而dnaA 46和其它dnaA突变体的生长对hspQ水平的变化不敏感。细胞DnaA508蛋白在高温下迅速降解，但hspQ破坏阻碍了这一过程。相反，DnaA46蛋白以不依赖hspQ的方式快速降解。凝胶过滤和化学交联实验表明，HspQ在溶液中形成稳定的同源二聚体，并且可以形成由约四个单体组成的同源多聚体。热休克诱导的蛋白酶如Clp含有亚基蛋白的同源多聚体。我们认为HspQ是一个新的蛋白质质量控制因子，它的功能是排除变性蛋白。
Escherichia coli DnaA protein initiates chromosomal replication and is an important regulatory target during the replication cycle. In this study, a suppressor mutation isolated by transposon mutagenesis was found to allow growth of the temperature-sensitive dnaA508 and dnaA167 mutants at 40 degreesC. The suppressor consists of a transposon insertion in a previously annotated ORF, here termed hspQ, a novel heat shock gene whose promoter is recognized by the major heat shock sigma factor sigma(32). Expression of hspQ on a pBR322 derivative inhibits growth of the dnaA508 and dnaA167 mutants at 30 degreesC, whereas growth of dnaA46 and other dnaA mutants is insensitive to changes in the level of hspQ. Cellular DnaA508 protein is degraded rapidly at elevated temperature, but hspQ disruption impedes this process. In contrast, DnaA46 protein is rapidly degraded in an hspQ-independent manner. Gel-filtration and chemical cross-linking experiments suggest that HspQ forms a stable homodimer in solution and can form homomultimers consisting of about four monomers. Heat-shock induced proteases such as Clp contain homomultimers of subunit proteins. We propose that HspQ is a new factor involved in the quality control of proteins and that it functions by excluding denatured proteins.