Essential for the synthesis of the polyglutamate capsule of B.anthracis which is one of the principal virulence factors during anthrax infection. May form a polyglutamyl synthetase complex together with proteins CapA and CapB. CapC may be the endogenous acceptor of glutamyl residues. Capsule biogenesis; capsule polysaccharide biosynthesis. Capsule synthesis is transcriptionally regulated by AtxA, AcpA and AcpB.