 |
PDBsum entry 3k5h
|
|
|
|
References listed in PDB file
|
 |
|
Key reference
|
|
|
Title
|
|
Structural and functional studies of aspergillus clavatus n(5)-Carboxyaminoimidazole ribonucleotide synthetase .
|
|
|
Authors
|
|
J.B.Thoden,
H.M.Holden,
H.Paritala,
S.M.Firestine.
|
|
|
Ref.
|
|
Biochemistry, 2010,
49,
752-760.
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
Abstract
|
|
|
N(5)-Carboxyaminoimidazole ribonucleotide synthetase (N(5)-CAIR synthetase), a
key enzyme in microbial de novo purine biosynthesis, catalyzes the conversion of
aminoimidazole ribonucleotide (AIR) to N(5)-CAIR. To date, this enzyme has been
observed only in microorganisms, and thus, it represents an ideal target for
antimicrobial drug development. Here we report the cloning, crystallization, and
three-dimensional structural analysis of Aspergillus clavatus N(5)-CAIR
synthetase solved in the presence of either Mg(2)ATP or MgADP and AIR. These
structures, determined to 2.1 and 2.0 A, respectively, revealed that AIR binds
in a pocket analogous to that observed for other ATP-grasp enzymes involved in
purine metabolism. On the basis of these models, a site-directed mutagenesis
study was subsequently conducted that focused on five amino acid residues
located in the active site region of the enzyme. These investigations
demonstrated that Asp 153 and Lys 353 play critical roles in catalysis without
affecting substrate binding. All other mutations affected substrate binding and,
in some instances, catalysis as well. Taken together, the structural and kinetic
data presented here suggest a catalytic mechanism whereby Mg(2)ATP and
bicarbonate first react to form the unstable intermediate carboxyphosphate. This
intermediate subsequently decarboxylates to CO(2) and inorganic phosphate, and
the amino group of AIR, through general base assistance by Asp 153, attacks
CO(2) to form N(5)-CAIR.
|
|
|
|
|
|
|
