title: Crystal structure of the archaeal asparagine synthetase: interrelation with aspartyl-tRNA and asparaginyl-tRNA synthetases.
abstract: Asparagine synthetase A (AsnA) catalyzes asparagine synthesis using aspartate, ATP, and ammonia as substrates. Asparagine is formed in two steps: the β-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 α-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 α-carboxylate group into an enzyme that is able to activate the β-carboxylate group of aspartate, which can react with ammonia instead of tRNA.
authors.affiliation: Architecture et Réactivité de l'ARN, Université de Strasbourg, CNRS, Institut de Biologie Moléculaire et Cellulaire, UPR 9002, 15 rue René Descartes, 67084 Strasbourg Cedex, France. mick@mb.au.dk
authors.forename: Mickaël
authors.initials: M
authors.lastname: Blaise
authors.forename: Mathieu
authors.initials: M
authors.lastname: Fréchin
authors.forename: Vincent
authors.initials: V
authors.lastname: Oliéric
authors.forename: Christophe
authors.initials: C
authors.lastname: Charron
authors.forename: Claude
authors.initials: C
authors.lastname: Sauter
authors.forename: Bernard
authors.initials: B
authors.lastname: Lorber
authors.forename: Hervé
authors.initials: H
authors.lastname: Roy
authors.forename: Daniel
authors.initials: D
authors.lastname: Kern
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D000641:Ammonia / Q000737:chemistry / Q000378:metabolism; D001216:Asparagine / Q000737:chemistry / Q000378:metabolism; D001217:Aspartate-Ammonia Ligase / Q000737:chemistry* / Q000378:metabolism; D001226:Aspartate-tRNA Ligase / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D043903:Pyrococcus abyssi / Q000737:chemistry / Q000201:enzymology*; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry
chemical_list: D012346:RNA, Transfer, Amino Acyl; D001224:Aspartic Acid; D001216:Asparagine; D000641:Ammonia; D000255:Adenosine Triphosphate; D001226:Aspartate-tRNA Ligase; C029194:asparaginyl-tRNA synthetase; D001217:Aspartate-Ammonia Ligase