| GenProp0326 |
protein sorting system, PEP-CTERM/exosortase (generic)~This Genome Property describes a proposed protein sorting system associated with exopolysaccharide loci in many Gram-negative bacteria. One hallmark is the presence of a paralogous domain at the C-termini of a substantial number of proteins in a single genome, usually from four to sixty-five. Features of this domain, described by TIGRFAMs model TIGR02595, are a conserved motif PEP, a transmembrane domain, and a cluster of basic residues for a total length of about 24 amino acids. We call this domain PEP-CTERM, and note that is shares a number of properties with the the LPXTG-type Gram-positive cell-wall targeting sequence. Another hallmark of this system is the presence of one or more homologs of EpsH (TIGR02602), a highly hydrophobic protein that spans the membrane eight or more times. Its surrounding genes nearly always pertain to exopolysaccharide biosynthesis. We have proposed that TIGR02602 models a transpeptidase that cleaves PEP-CTERM proteins, attaches them transiently to an active site Cys, then attaches them covalently to an unknown substrate for sorting to the outer surface of the cell, closely analogous to the action of sortase in Gram-positive bacteria. We suggest the name exosortase for EpsH homologs involved in this process. In Proteobacterial species with a the PEP-CTERM/exsortase system, a sensor histidine kinase (TIGR02916) and a sigma-54-dependent DNA-binding response regulator (TIGR02915) are present and appear to bind a conserved regulatory site found upstream of most PEP-CTERM genes. |
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Unexplained |
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