Structure and secretion of CofJ , a putative colonization factor of enterotoxigenic E scherichia coli

Summary Enterotoxigenic E scherichia coli ( ETEC ) colonize the human gut, causing severe cholera‐like diarrhoea. ETEC utilize a diverse array of pili and fimbriae for host colonization, including the T ype IVb pilus CFA / III . The CFA / III pilus machinery is encoded on the cof operon, which is similar in gene sequence and synteny to the tcp operon that encodes another T ype IVb pilus, the V ibrio cholerae toxin co‐regulated pilus ( TCP ). Both pilus operons possess a syntenic gene encoding a protein of unknown function. In V . cholerae , this protein, TcpF , is a critical colonization factor secreted by the TCP apparatus. Here we show that the corresponding ETEC protein, CofJ , is a soluble protein secreted via the CFA / III apparatus. We present a 2.6 Å resolution crystal structure of CofJ , revealing a large β‐sandwich protein that bears no sequence or structural homology to TcpF . CofJ has a cluster of exposed hydrophobic side‐chains at one end and structural homology to the pore‐forming proteins perfringolysin O and α‐haemolysin. CofJ binds to lipid vesicles and epithelial cells, suggesting a role in membrane attachment during ETEC colonization.