THE HTRA FAMILY OF SERINE PROTEASES

HtrA, also known as DegP and probably identical to the Do protease, is a heat shock-induced serine protease that is active in the periplasm of Escherichia coli, Homologues of HtrA have been described in a wide range of bacteria and in eukaryotes. Its chief role is to degrade misf olded proteins in the periplasm, Substrate recognition probably involv es the recently described PDZ domains in the C-terminal half of HtrA a nd, we suspect, has much in common with the substrate recognition syst em of the tail-specific protease, Prc (which also possesses a PDZ doma in). The expression of htrA is regulated by a complex set of signal tr ansduction pathways, which includes an alternative sigma factor, RpoE, an anti-sigma factor, RseA, a two-component regulatory system, CpxRA, and two phosphoprotein phosphatases, PrpA and PrpB. Mutations in the htrA genes of Salmonella, Brucella and Yersinia cause decreased surviv al in mice and/or macrophages, and htrA mutants can act as vaccines, a s cloning hosts and as carriers of heterologous antigens.