Cyclic adenosine monophosphate (cAMP, cyclic AMP or 3'-5'-cyclic adenosine monophosphate) is an important signaling molecule in virtually all prokaryotic and eukaryotic cells. It activates diverse bacterial cAMP receptor proteins such as transcription factors and protein kinases. cAMP is derived from adenosine triphosphate (ATP) in reaction catalyzed by adenylate cyclase (AC). There are six distinct non-homologous classes of ACs. The majority of enzymes belong to class III which converts ATP to cAMP in a catalytic center formed by an interface of protein homodimers. GBAA_1210 protein monomer structure has the same fold as class IV AC from Yersinia pestis (3N10 deposit in PDB); however, it displays a different dimer organization at least inside crystals. The Y. pestis AC monomer forms an antiparallel eight-stranded barrel which binds ligands inside the barrel.