Williams S G, Varcoe L T, Attridge S R, Manning P A
Department of Microbiology and Immunology, University of Adelaide, Australia.
Infect Immun. 1996 Jan;64(1):283-9. doi: 10.1128/iai.64.1.283-289.1996.
Hcp is a 28-kDa secreted protein of Vibrio cholerae regulated coordinately with the hemolysin, HlyA. Both proteins show a dependence on HlyU for expression, suggesting that Hcp may be secreted by V. cholerae in vivo. We have identified and sequenced two genes for Hcp, designated hcpA and hcpB (hemolysin-coregulated protein). The genes encode identical amino acid sequences. Both express a 28-kDa protein, despite open reading frames with only a 19-kDa capacity, suggesting that the Hcp protein runs aberrantly on polyacrylamide gel electrophoresis. There is no cleavage involved in secretion of Hcp from the cell, suggesting a novel mechanism of secretion. An hcp null mutant was constructed, and this strain displayed no deficiency in virulence or colonization in the infant mouse cholera model. From sequence data and primer extension analysis, we predict that the hcp promoter is the sigma 54 type, with a candidate integration host factor binding site upstream. Although hcp and hlyA are coregulated by HlyU, there are no obvious similarities between their promoters. We predict that an intermediate regulator may be involved in the activation of hcp by HlyU. This raises the possibility that HlyU is part of a regulatory cascade.
Hcp是霍乱弧菌一种28千道尔顿的分泌蛋白，与溶血素HlyA协同调节。这两种蛋白的表达均依赖于HlyU，提示Hcp可能在霍乱弧菌体内被分泌。我们已鉴定并测序了两个Hcp基因，命名为hcpA和hcpB（溶血素共调节蛋白）。这两个基因编码相同的氨基酸序列。尽管开放阅读框仅具有19千道尔顿的容量，但二者均表达一种28千道尔顿的蛋白，提示Hcp蛋白在聚丙烯酰胺凝胶电泳上迁移异常。Hcp从细胞中分泌时不涉及切割，提示一种新的分泌机制。构建了一个hcp缺失突变体，该菌株在幼鼠霍乱模型中未表现出毒力或定殖缺陷。根据序列数据和引物延伸分析，我们预测hcp启动子为σ54型，上游有一个候选整合宿主因子结合位点。尽管hcp和hlyA由HlyU共同调节，但其启动子之间无明显相似性。我们预测一种中间调节因子可能参与HlyU对hcp的激活。这增加了HlyU是调节级联反应一部分的可能性。
