Catalyzes the conversion of (8S)-3',8-cyclo-7,8-dihydroguanosine 5'-triphosphate to cyclic pyranopterin monophosphate (cPMP) (By similarity). Probably plays a role in host phagosome maturation arrest (PubMed:20844580). (8S)-3',8-cyclo-7,8-dihydroguanosine 5'-triphosphate = cyclic pyranopterin phosphate + diphosphate Cofactor biosynthesis; molybdopterin biosynthesis. Homohexamer; trimer of dimers. Expression is positively regulated by the transcriptional regulator MoaR1. Grows normally in liquid culture, traffics into host (human and mouse) acidified compartments early after phagocytosis, suggesting it no longer arrests phagosome maturation as well as wild-type, impaired growth in mouse macrophages (PubMed:20844580). Belongs to the MoaC family.