TY - JOUR
T1 - Structural analysis of Pseudomonas 1-aminocyclopropane-1-carboxylate deaminase complexes
T2 - Insight into the mechanism of a unique pyridoxal-5′- phosphate dependent cyclopropane ring-opening reaction
AU - Karthikeyan, Subramanian
AU - Zhou, Qingxian
AU - Zhao, Zongbao
AU - Kao, Chai Lin
AU - Tao, Zhihua
AU - Robinson, Howard
AU - Liu, Hung Wen
AU - Zhang, Hong
PY - 2004/10/26
Y1 - 2004/10/26
N2 - 1-Aminocyclopropane-1-carboxylate (ACC) deaminase is a pyridoxal 5′-phosphate (PLP) dependent enzyme catalyzing the opening of the cyclopropane ring of ACC to give α-ketobutyric acid and ammonia as the products. This ring cleavage reaction is unusual because the substrate, ACC, contains no abstractable α-proton and the carboxyl group is retained in the product. How the reaction is initiated to generate an α-carbanionic intermediate, which is the common entry for most PLP-dependent reactions, is not obvious. To gain insight into this unusual ring-opening reaction, we have solved the crystal structures of ACC deaminase from Pseudomonas sp. ACP in complex with substrate ACC, an inhibitor, 1-aminocyclopropane-1-phosphonate (ACP), the product α-ketobutyrate, and two D-amino acids. Several notable observations of these structural studies include the following: (1) a typically elusive gem-diamine intermediate is trapped in the enzyme complex with ACC or ACP; (2) Tyr294 is in close proximity (3.0 Å) to the pro-S methylene carbon of ACC in the gem-diamine complexes, implicating a direct role of this residue in the ring-opening reaction; (3) Tyr294 may also be responsible for the abstraction of the α-proton from D-amino acids, a prelude to the subsequent deamination reaction; (4) the steric hindrance precludes accessibility of active site functional groups to the L-amino acid substrates and may account for the stereospecificity of this enzyme toward D-amino acids. These structural data provide evidence favoring a mechanism in which the ring cleavage is induced by a nucleophilic attack at the pro-S β-methylene carbon of ACC, with Tyr294 as the nucleophile. However, these observations are also consistent with an alternative mechanistic possibility in which the ring opening is acid-catalyzed and may be facilitated by charge relay through PLP, where Tyr294 functions as a general acid. The results of mutagenesis studies corroborated the assigned critical role for Tyr294 in the catalysis.
AB - 1-Aminocyclopropane-1-carboxylate (ACC) deaminase is a pyridoxal 5′-phosphate (PLP) dependent enzyme catalyzing the opening of the cyclopropane ring of ACC to give α-ketobutyric acid and ammonia as the products. This ring cleavage reaction is unusual because the substrate, ACC, contains no abstractable α-proton and the carboxyl group is retained in the product. How the reaction is initiated to generate an α-carbanionic intermediate, which is the common entry for most PLP-dependent reactions, is not obvious. To gain insight into this unusual ring-opening reaction, we have solved the crystal structures of ACC deaminase from Pseudomonas sp. ACP in complex with substrate ACC, an inhibitor, 1-aminocyclopropane-1-phosphonate (ACP), the product α-ketobutyrate, and two D-amino acids. Several notable observations of these structural studies include the following: (1) a typically elusive gem-diamine intermediate is trapped in the enzyme complex with ACC or ACP; (2) Tyr294 is in close proximity (3.0 Å) to the pro-S methylene carbon of ACC in the gem-diamine complexes, implicating a direct role of this residue in the ring-opening reaction; (3) Tyr294 may also be responsible for the abstraction of the α-proton from D-amino acids, a prelude to the subsequent deamination reaction; (4) the steric hindrance precludes accessibility of active site functional groups to the L-amino acid substrates and may account for the stereospecificity of this enzyme toward D-amino acids. These structural data provide evidence favoring a mechanism in which the ring cleavage is induced by a nucleophilic attack at the pro-S β-methylene carbon of ACC, with Tyr294 as the nucleophile. However, these observations are also consistent with an alternative mechanistic possibility in which the ring opening is acid-catalyzed and may be facilitated by charge relay through PLP, where Tyr294 functions as a general acid. The results of mutagenesis studies corroborated the assigned critical role for Tyr294 in the catalysis.
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U2 - 10.1021/bi048878g
DO - 10.1021/bi048878g
M3 - Article
C2 - 15491139
AN - SCOPUS:6344228463
SN - 0006-2960
VL - 43
SP - 13328
EP - 13339
JO - Biochemistry
JF - Biochemistry
IS - 42
ER -