The sigA gene which is borne on the she pathogenicity island of Shigella flexneri 2a encodes an exported cytopathic protease involved in intestinal fluid accumulation

Abstract

In this study, the sigA gene situated on the she pathogenicity island of Shigella flexneri 2a was cloned and characterized. Sequence analysis showed that sigA encodes a 139.6-kDa protein which belongs to the SPATE (serine protease autotransporters of Enterobacteriaceae) subfamily of autotransporter proteins. The demonstration that SigA is autonomously secreted from the cell to yield a 103-kDa processed form and possesses a conserved C-terminal domain for export from the cell were consistent with the autotransporter pathway of secretion. Functional analysis showed that SigA is a secreted temperature- regulated serine protease capable of degrading casein. SigA was cytopathic for HEp-2 cells, s..