Y. Liu et al., CATALYTIC MECHANISM OF THE ADENYLYL AND GUANYLYL CYCLASES - MODELING AND MUTATIONAL ANALYSIS, Proceedings of the National Academy of Sciences of the United Statesof America, 94(25), 1997, pp. 13414-13419
The adenylyl and guanylyl cyclases catslyze the formation of 3 ',5 ' c
yclic adenosine or guanosine monophosphate from the corresponding nucl
eoside 5 '-triphosphate. The guanylyl cyclases, the mammalian adenylyl
cyclases, and their microbial homologues function as pairs of homolog
ous catalytic domains. The crystal structure of the rat type II adenyl
yl cyclase C-2 catalytic domain was used to model by homology a mammal
ian adenylyl cyclase C-1-C-2 domain pair, a homodimeric soluble cyclas
e of dictyostelium discoideum, a heterodimeric soluble guanylyl cyclas
e, and a homodimeric membrane guanyly cyclase. Mg(2+)ATP or Mg(2+)GTP
were docked into the active sites based on known stereochemical constr
aints on their conformation. The models are consistent with the activi
ties of seven active-site mutants. Asp-310 and Glu-432 of type 1 adeny
lyl cyclase coordinate a Mg(2+)ion. The D310S and D310A mutants have l
O-fold reduced V-max and altered [Mg2+] dependence. The NTP purine moi
eties bind in mostly hydrophobic pockets. Specificity is conferred by
a Lys and an Asp in adenylyl cyclase, and a Glu, an Arg, and a Cys in
guanyly cyclase. The models predict that an Asp from one domain is a g
eneral base in the reaction, and that the transition state is stabiliz
ed by a conserved Asn-Arg pair on the other domain.