Catalyzes a mechanistically unusual reaction, the ATP-dependent insertion of CO2 between the N7 and N8 nitrogen atoms of 7,8-diaminopelargonic acid (DAPA, also called 7,8-diammoniononanoate) to form a ureido ring. Only CTP can partially replace ATP while diaminobiotin is only 37% as effective as 7,8-diaminopelargonic acid (PubMed:4892372, PubMed:4921568). In another study both CTP and GTP (but not ITP, TTP or UTP) can partially replace ATP (PubMed:25801336). (7R,8S)-7,8-diammoniononanoate + ATP + CO2 = (4R,5S)-dethiobiotin + ADP + 3 H(+) + phosphate Binds 1 Mg(2+) per subunit, in one structure a second Mg(2+) was seen. Cofactor biosynthesis; biotin biosynthesis; biotin from 7,8-diaminononanoate: step 1/2. Homodimer. Belongs to the dethiobiotin synthetase family.