Catalyzes cobalt insertion in the corrin ring. ATP + Co(2+) + H2O + hydrogenobyrinate a,c-diamide = ADP + cob(II)yrinate a,c diamide + 5 H(+) + phosphate Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from precorrin-2 (aerobic route): step 10/10. Heterotrimer of CobN, CobS and CobT. Belongs to the CobN family.