Taxonomic distribution of proteins containing PGA_cap domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing PGA_cap domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Poly-gamma-glutamate in bacteria.

Candela T, Fouet A
Mol Microbiol. 2006; 60: 1091-8

Poly-gamma-glutamate (PGA), a natural polymer, is synthesized by severalbacteria (all Gram-positive), one archaea and one eukaryote. PGA hasdiverse biochemical properties, enabling it to play different roles,depending on the organism and its environment. Indeed, PGA allows bacteriato survive at high salt concentrations and may also be involved invirulence. The minimal gene sets required for PGA synthesis were recentlydefined. There are currently two nomenclatures depending on the PGA finalstatus: cap, for 'capsule', when PGA is surface associated or pgs, for'polyglutamate synthase', when PGA is released. The minimal gene setscontain four genes termed cap or pgs B, C, A and E. The PGA synthesiscomplex is membrane-anchored and uses glutamate and ATP as substrates.Schematically, the reaction may be divided into two steps, PGA synthesisand PGA transport through the membrane. PGA synthesis depends primarily onCapB-CapC (or PgsB-PgsC), whereas PGA transport requires the presence, orthe addition, of CapA-CapE (or PgsAA-PgsE). The synthesis complex isprobably responsible for the stereochemical specificity of PGAcomposition. Finally, PGA may be anchored to the bacterial surface orreleased. An additional enzyme is involved in this reaction: either CapD,a gamma-glutamyl-transpeptidase that catalyses anchorage of the PGA, orPgsS, a hydrolase that facilitates release. The anchoring of PGA to thebacterial surface is important for virulence. All cap genes are thereforepotential targets for inhibitors specifically blocking PGA synthesis oranchorage.