Outer membrane protein secretin of type III secretion system of Vibrio vulnificus: structure prediction and orientation

Abstract:

The marine organism Vibrio vulnificus causes seafood-borne infection and is a major cause of human mortality. Secretin, a major component of the type III secretion system (TTSS) virulence machinery, forms oligomeric rings in the outer membrane of many Gram- negative organisms. The secretin ring-shaped complexes possess pore-forming activity. The pores function as channels for transport of macromolecules across the complex. However, the TTSS secretin family has not been studied in V. vulnificus. The secretin of TTSS of V. vulnificus was identified and predicted to be homologous to secretin of Gram-negative organisms like Yersinia and Escherichia coli. It contained an amino-terminal signal peptide region for processing by the sec machinery. The homology model of secretin of V. vulnificus possessed the E. coli periplasmic domain specific to secretin of TTSS. Buried pore-lining residues in the homology model were identified by bioinformatics tools. Thus, secretin of V. vulnificus may function as channels to allow transport of molecules. The optimized pore axis with the biggest and longest cavity through the channel was detected which generated a guide to the orientation of secretin in V. vulnificus. Thus, the secretin of V. vulnificus has a conserved C-terminal domain enclosing a pore and a nonconserved lipolytic motif which may be involved in adherence to the chitinous surface.

Keywords::

• Vibrio vulnificus
• secretin
• virulence
• pore
• transport
• bioinformatics
• type III secretion system