Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Bacteriol. 2011 Aug;193(15):3748-56. doi: 10.1128/JB.05070-11. Epub 2011 Jun 3.
Autotransporters are a superfamily of virulence factors produced by Gram-negative bacteria that are comprised of an N-terminal extracellular domain (passenger domain) and a C-terminal β barrel domain (β domain) that resides in the outer membrane (OM). The β domain promotes the translocation of the passenger domain across the OM by an unknown mechanism. Available evidence indicates that an α-helical segment that spans the passenger domain-β domain junction is embedded inside the β domain at an early stage of assembly. Following its secretion, the passenger domain of the serine protease autotransporters of the Enterobacteriaceae (SPATEs) and the pertactin family of Bordetella pertussis autotransporters is released from the β domain through an intrabarrel autoproteolytic cleavage of the α-helical segment. Although the mutation of conserved residues that surround the cleavage site has been reported to impair both the translocation and cleavage of the passenger domain of a SPATE called Tsh, we show here that the mutation of the same residues in another SPATE (EspP) affects only passenger domain cleavage. Our results strongly suggest that the conserved residues are required to position the α-helical segment for the cleavage reaction and are not required to promote passenger domain secretion.
自动转运蛋白是革兰氏阴性细菌产生的一类毒力因子超家族，由 N 端细胞外结构域（载体结构域）和 C 端β桶结构域（β 结构域）组成，后者位于外膜（OM）中。β 结构域通过未知机制促进载体结构域穿过 OM 的易位。现有证据表明，跨越载体结构域-β 结构域连接的α-螺旋片段在组装的早期阶段嵌入β 结构域内部。在分泌后，肠杆菌科的丝氨酸蛋白酶自动转运蛋白（SPATE）和百日咳博德特氏菌 pertactin 家族的 pertactin 自动转运蛋白的载体结构域通过α-螺旋片段的桶内自蛋白水解切割从β 结构域中释放出来。尽管已经报道了围绕切割位点的保守残基的突变会损害称为 Tsh 的 SPATE 的载体结构域的易位和切割，但我们在这里表明，另一个 SPATE（EspP）中的相同残基的突变仅影响载体结构域的切割。我们的结果强烈表明，保守残基是用于切割反应的α-螺旋片段的定位所必需的，而不是促进载体结构域分泌所必需的。
