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| {{STRUCTURE_1jfl| PDB=1jfl | SCENE= }} | | {{STRUCTURE_1jfl| PDB=1jfl | SCENE= }} |
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| '''CRYSTAL STRUCTURE DETERMINATION OF ASPARTATE RACEMASE FROM AN ARCHAEA'''
| | ===CRYSTAL STRUCTURE DETERMINATION OF ASPARTATE RACEMASE FROM AN ARCHAEA=== |
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| ==Overview==
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| There exists a d-enantiomer of aspartic acid in lactic acid bacteria and several hyperthermophilic archaea, which is biosynthesized from the l-enantiomer by aspartate racemase. Aspartate racemase is a representative pyridoxal 5'-phosphate (PLP)-independent amino acid racemase. The "two-base" catalytic mechanism has been proposed for this type of racemase, in which a pair of cysteine residues are utilized as the conjugated catalytic acid and base. We have determined the three-dimensional structure of aspartate racemase from the hyperthermophilic archaeum Pyrococcus horikoshii OT3 at 1.9 A resolution by X-ray crystallography and refined it to a crystallographic R factor of 19.4% (R(free) of 22.2%). This is the first structure reported for aspartate racemase, indeed for any amino acid racemase from archaea. The crystal structure revealed that this enzyme forms a stable dimeric structure with a strong three-layered inter-subunit interaction, and that its subunit consists of two structurally homologous alpha/beta domains, each containing a four-stranded parallel beta-sheet flanked by six alpha-helices. Two strictly conserved cysteine residues (Cys82 and Cys194), which have been shown biochemically to act as catalytic acid and base, are located on both sides of a cleft between the two domains. The spatial arrangement of these two cysteine residues supports the "two-base" mechanism but disproves the previous hypothesis that the active site of aspartate racemase is located at the dimeric interface. The structure revealed a unique pseudo mirror-symmetry in the spatial arrangement of the residues around the active site, which may explain the molecular recognition mechanism of the mirror-symmetric aspartate enantiomers by the non-mirror-symmetric aspartate racemase.
| | The line below this paragraph, {{ABSTRACT_PUBMED_12051922}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 12051922 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_12051922}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Homo-dimer]] | | [[Category: Homo-dimer]] |
| [[Category: Homologous domain]] | | [[Category: Homologous domain]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 21:09:55 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 20:10:19 2008'' |