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Publication Abstract from PubMed

Asparagine synthetase A (AsnA) catalyzes asparagine synthesis using aspartate, ATP, and ammonia as substrates. Asparagine is formed in two steps: the beta-carboxylate group of aspartate is first activated by ATP to form an aminoacyl-AMP before its amidation by a nucleophilic attack with an ammonium ion. Interestingly, this mechanism of amino acid activation resembles that used by aminoacyl-tRNA synthetases, which first activate the alpha-carboxylate group of the amino acid to form also an aminoacyl-AMP before they transfer the activated amino acid onto the cognate tRNA. In a previous investigation, we have shown that the open reading frame of Pyrococcus abyssi annotated as asparaginyl-tRNA synthetase (AsnRS) 2 is, in fact, an archaeal asparagine synthetase A (AS-AR) that evolved from an ancestral aspartyl-tRNA synthetase (AspRS). We present here the crystal structure of this AS-AR. The fold of this protein is similar to that of bacterial AsnA and resembles the catalytic cores of AspRS and AsnRS. The high-resolution structures of AS-AR associated with its substrates and end-products help to understand the reaction mechanism of asparagine formation and release. A comparison of the catalytic core of AS-AR with those of archaeal AspRS and AsnRS and with that of bacterial AsnA reveals a strong conservation. This study uncovers how the active site of the ancestral AspRS rearranged throughout evolution to transform an enzyme activating the alpha-carboxylate group into an enzyme that is able to activate the beta-carboxylate group of aspartate, which can react with ammonia instead of tRNA.

Crystal Structure of the Archaeal Asparagine Synthetase: Interrelation with Aspartyl-tRNA and Asparaginyl-tRNA Synthetases.,Blaise M, Frechin M, Olieric V, Charron C, Sauter C, Lorber B, Roy H, Kern D J Mol Biol. 2011 Sep 23;412(3):437-52. Epub 2011 Jul 28. PMID:21820443^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.