1tz2: Difference between revisions

[[Image:1tz2.gif|left|200px]]<br /><applet load="1tz2" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1TZ2 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Pseudomonas_sp. Pseudomonas sp.] with <scene name='pdbligand=PLP:'>PLP</scene> and <scene name='pdbligand=1AC:'>1AC</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/1-aminocyclopropane-1-carboxylate_deaminase 1-aminocyclopropane-1-carboxylate deaminase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.5.99.7 3.5.99.7] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1TZ2 OCA].  

[[Category: Kao, C L.]]

[[Category: Liu, H W.]]

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