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PDBsum entry 1awk
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References listed in PDB file
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Key reference
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Title
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Catalytic mechanism of the adenylyl and guanylyl cyclases: modeling and mutational analysis.
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Authors
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Y.Liu,
A.E.Ruoho,
V.D.Rao,
J.H.Hurley.
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Ref.
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Proc Natl Acad Sci U S A, 1997,
94,
13414-13419.
[DOI no: ]
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PubMed id
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Abstract
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The adenylyl and guanylyl cyclases catalyze the formation of 3', 5'-cyclic
adenosine or guanosine monophosphate from the corresponding nucleoside
5'-triphosphate. The guanylyl cyclases, the mammalian adenylyl cyclases, and
their microbial homologues function as pairs of homologous catalytic domains.
The crystal structure of the rat type II adenylyl cyclase C2 catalytic domain
was used to model by homology a mammalian adenylyl cyclase C1-C2 domain pair, a
homodimeric adenylyl cyclase of Dictyostelium discoideum, a heterodimeric
soluble guanylyl cyclase, and a homodimeric membrane guanylyl cyclase. Mg2+ATP
or Mg2+GTP were docked into the active sites based on known stereochemical
constraints on their conformation. The models are consistent with the activities
of seven active-site mutants. Asp-310 and Glu-432 of type I adenylyl cyclase
coordinate a Mg2+ ion. The D310S and D310A mutants have 10-fold reduced Vmax and
dependence. The NTP purine moieties 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 guanylyl cyclase. The models predict that an Asp from
one domain is a general base in the reaction, and that the transition state is
stabilized by a conserved Asn-Arg pair on the other domain.
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Figure 2.
Fig. 2. Sequence alignment colored by residue function. Based
on modeling, catalytic, Me^2+, pyrophosphate ligands are red;
forskolin, magenta; adenine, dark green; and guanine, gold. The
Gs  binding
site is gray (20), and G   is blue
(21). Dimer interface: blue underscores; h, hydrophobic pocket.
The C-terminal 60 aa are omitted.
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Figure 7.
Fig. 7. Hypothetical reaction mechanism, using AC1 as an
example.
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