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| - | [[Image:1tzm.gif|left|200px]] | + | {{Seed}} |
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| | {{STRUCTURE_1tzm| PDB=1tzm | SCENE= }} | | {{STRUCTURE_1tzm| PDB=1tzm | SCENE= }} |
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| - | '''Crystal structure of ACC deaminase complexed with substrate analog b-chloro-D-alanine'''
| + | ===Crystal structure of ACC deaminase complexed with substrate analog b-chloro-D-alanine=== |
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| - | ==Overview==
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| - | 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 alpha-ketobutyric acid and ammonia as the products. This ring cleavage reaction is unusual because the substrate, ACC, contains no abstractable alpha-proton and the carboxyl group is retained in the product. How the reaction is initiated to generate an alpha-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 alpha-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 A) 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 alpha-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 beta-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.
| + | The line below this paragraph, {{ABSTRACT_PUBMED_15491139}}, adds the Publication Abstract to the page |
| | + | (as it appears on PubMed at http://www.pubmed.gov), where 15491139 is the PubMed ID number. |
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| | + | {{ABSTRACT_PUBMED_15491139}} |
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| | ==About this Structure== | | ==About this Structure== |
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| | [[Category: Structure]] | | [[Category: Structure]] |
| | [[Category: Substrate]] | | [[Category: Substrate]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 10:33:43 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 07:02:06 2008'' |
Revision as of 04:02, 28 July 2008
Template:STRUCTURE 1tzm
Crystal structure of ACC deaminase complexed with substrate analog b-chloro-D-alanine
Template:ABSTRACT PUBMED 15491139
About this Structure
1TZM is a Single protein structure of sequence from Pseudomonas sp.. Full crystallographic information is available from OCA.
Reference
Structural analysis of Pseudomonas 1-aminocyclopropane-1-carboxylate deaminase complexes: insight into the mechanism of a unique pyridoxal-5'-phosphate dependent cyclopropane ring-opening reaction., Karthikeyan S, Zhou Q, Zhao Z, Kao CL, Tao Z, Robinson H, Liu HW, Zhang H, Biochemistry. 2004 Oct 26;43(42):13328-39. PMID:15491139
Page seeded by OCA on Mon Jul 28 07:02:06 2008
