Characterization of SrgA, a Salmonella enterica serovar typhimurium virulence plasmid-encoded paralogue of the disulfide oxidoreductase DsbA, essential for biogenesis of plasmid-encoded fimbriae
Characterization of SrgA, a Salmonella enterica serovar typhimurium virulence plasmid-encoded paralogue of the disulfide oxidoreductase DsbA, essential for biogenesis of plasmid-encoded fimbriae
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DOI：
10.1128/jb.185.3.991-1000.2003
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发表时间：
2003-02-01
影响因子：
3.2
通讯作者：
Martin, NL
中科院分区：
文献类型：
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作者：
Bouwman, CW;Kohli, M;Martin, NL
二硫键氧化还原酶被视为折叠酶，通过催化掺入二硫键来提高蛋白质折叠速率，从而帮助维持蛋白质的有效折叠途径。 SrgA 是一种二硫键氧化还原酶，由鼠伤寒沙门氏菌的毒力质粒 pStSR100 编码，位于质粒携带的菌毛操纵子的下游。序列分析表明，SrgA 与来自大肠杆菌等的 DsbA 相似，但不像来自肠杆菌科成员的大多数染色体编码的二硫键氧化还原酶那么高度保守。 SrgA 定位于周质，其二硫键氧化还原酶活性取决于功能性 DsbB 的存在，该蛋白质还负责主要二硫键氧化还原酶 DsbA 的再氧化。对SrgA二硫键氧化还原酶活性的定量分析表明，SrgA在将二硫键引入底物碱性磷酸酶方面的效率低于DsbA，这表明SrgA比DsbA更具底物特异性。还证明 SrgA 的二硫键氧化还原酶活性对于质粒编码菌毛的产生是必需的。质粒编码菌毛的主要结构亚基 PefA 含有一个二硫键，必须将其氧化才能保持 PefA 稳定性并组装质粒编码菌毛。 SrgA 能有效氧化 PefA 的二硫键，而鼠伤寒沙门氏菌染色体编码的二硫键氧化还原酶 DsbA 则不能。 pefA和srgA也在pH 5.1下特异性表达，但在pH 7.0下不表达，这表明涉及pef基因表达的调控机制也涉及srgA表达。因此，SrgA 似乎是底物特异性二硫键氧化还原酶，从而解释了除了鼠伤寒沙门氏菌血清型 DsbA 之外还需要额外的二硫键形成催化剂的需要。
Disulfide oxidoreductases are viewed as foldases that help to maintain proteins on productive folding pathways by enhancing the rate of protein folding through the catalytic incorporation of disulfide bonds. SrgA, encoded on the virulence plasmid pStSR100 of Salmonella enterica serovar Typhimurium and located downstream of the plasmid-borne fimbrial operon, is a disulfide oxidoreductase. Sequence analysis indicates that SrgA is similar to DsbA from, for example, Escherichia coli, but not as highly conserved as most of the chromosomally encoded disulfide oxidoreductases from members of the family Enterobacteriaceae. SrgA is localized to the periplasm, and its disulfide oxidoreductase activity is dependent upon the presence of functional DsbB, the protein that is also responsible for reoxidation of the major disulfide oxidoreductase, DsbA. A quantitative analysis of the disulfide oxidoreductase activity of SrgA showed that SrgA was less efficient than DsbA at introducing disulfide bonds into the substrate alkaline phosphatase, suggesting that SrgA is more substrate specific than DsbA. It was also demonstrated that the disulfide oxidoreductase activity of SrgA is necessary for the production of plasmid-encoded fimbriae. The major structural subunit of the plasmid-encoded fimbriae, PefA, contains a disulfide bond that must be oxidized in order for PefA stability to be maintained and for plasmid-encoded fimbriae to be assembled. SrgA efficiently oxidizes the disulfide bond of PefA, while the S. enterica serovar Typhimurium chromosomally encoded disulfide oxidoreductase DsbA does not. pefA and srgA were also specifically expressed at pH 5.1 but not at pH 7.0, suggesting that the regulatory mechanisms involved in pef gene expression are also involved in srgA expression. SrgA therefore appears to be a substrate-specific disulfide oxidoreductase, thus explaining the requirement for an additional catalyst of disulfide bond formation in addition to DsbA of S. enterica serovar Typhimurium.