Aspartate dehydrogenase, a novel enzyme identified from structural and functional studies of TM1643
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TM1643 from Thermotoga maritima is an NAD/NADP-dependent L-aspartate dehydrogenase that produces iminoaspartate, representing an alternative to aspartate oxidase (NadB) for the first step of NAD biosynthesis.
"two different enzymes, an oxidase and a dehydrogenase, may have evolved to catalyze the first step of NAD biosynthesis in prokaryotes. TM1643 establishes a new class of amino acid dehydrogenases"
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The crystal structure reveals an N-terminal Rossmann fold domain with bound NAD+ and a C-terminal catalytic domain.
"The structure reveals the presence of an N-terminal Rossmann fold domain with a bound NAD(+) cofactor and a C-terminal alpha+beta domain"
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TM1643 has no aspartate oxidase activity, confirming it is a dehydrogenase and not an oxidase.
"The enzymatic characterization of TM1643 revealed that it possesses NAD or NADP-dependent dehydrogenase activity toward l-aspartate but no aspartate oxidase activity"
The first archaeal L-aspartate dehydrogenase from the hyperthermophile Archaeoglobus fulgidus: gene cloning and enzymological characterization.
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The A. fulgidus L-aspartate dehydrogenase is a homodimeric protein (~48 kDa) that is highly thermostable with optimum temperature of ~80 degrees C.
"a homodimeric protein with a molecular mass of about 48 kDa...The enzyme specifically utilized L-aspartate as the electron donor, while either NAD or NADP could serve as the electron acceptor"
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Homologs of L-aspartate dehydrogenase are found in many methanogenic archaea but not in Thermococcales or Sulfolobales.
"Within the archaeal domain, homologues of this enzyme occurred in many Methanogenic species, but not in Thermococcales or Sulfolobales species"
Crystal structure of archaeal highly thermostable L-aspartate dehydrogenase/NAD/citrate ternary complex
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The A. fulgidus L-aspDH crystal structure at 1.9 A resolution shows a dimeric enzyme with two domains per subunit separated by a deep active-site cleft.
"each subunit consists of two domains separated by a deep cleft containing an active site"
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Substrate binding induces a large conformational change with movement of two loops, and thermostability is achieved through inter- and intrasubunit ion pairs.
"A. fulgidus L-aspDH assumes a closed conformation and that a large movement of the two loops takes place during substrate binding"
Complete genome sequence of the methanogenic archaeon, Methanococcus jannaschii
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The complete genome sequence of M. jannaschii, which includes the MJ0915 locus (nadX).
"Complete genome sequence of the methanogenic archaeon, Methanococcus jannaschii"
Gene Ontology annotation through association of InterPro records with GO terms
Electronic Gene Ontology annotations created by transferring manual GO annotations between related proteins based on shared sequence features
Combined Automated Annotation using Multiple IEA Methods