Proteases Produced by Vibrio cholerae and Other Pathogenic Vibrios: Pathogenic Roles and Expression

Abstract

Pathogenic vibrios produce various pathogenic factors such as enterotoxin, hemolysin, cytotoxin, protease, siderophore, adhesive factor, and hemagglutinin. Direct toxic factors such as enterotoxin, hemolysin, and cytotoxin are related to the symptoms, whereas siderophore and adhesive factors may cause indirect factors, which play roles in the establishment of the infection. The proteases produced by pathogenic vibrios are long recognized to play pathogenic roles in the infection. Zn metalloprotease produced by Vibrio cholerae is thought to play indirect pathogenic roles such as processing other protein toxin(s) or supporting bacterial growth in the digestive tract. Hemagglutinin/protease (HA/P) produced by V. cholerae was the one first noticed which has 609 amino acid residues and a molecular size of 69.3 kDa. Further characterization of this protein revealed that the C-terminal peptide mediates hemagglutination or binding to the cell surface in many vibrios. HA/P is secreted via the type II secretion pathway at the cell pole and thought to play a role by promoting mucin gel penetration, detachment, and the spread of infection along the gastrointestinal tract. Special interaction of HA/P on chironomid egg masses was shown to be an important factor for the survival of V. cholerae in aquatic environments. Vibrios have a complex quorum-sensing system containing three kinds of autoinducers. In some, HA/P plays a role in controlling the quorum-sensing machinery. A cysteine protease domain was found in repeat in toxin (RTX) of V. cholerae. RTX is a large multifunctional toxin that causes actin cross-linking and is processed by proteolytic action during translocation into host cells. Other proteases such as Vibrio vulnificus protease (VVP) is well known for cell damage and association with major virulence. Thus, proteases produced by pathogenic vibrios play a variety of pathological roles.