1gex
From Proteopedia
(New page: 200px<br /><applet load="1gex" size="450" color="white" frame="true" align="right" spinBox="true" caption="1gex, resolution 2.2Å" /> '''CRYSTAL STRUCTURE OF ...) |
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caption="1gex, resolution 2.2Å" /> | caption="1gex, resolution 2.2Å" /> | ||
'''CRYSTAL STRUCTURE OF HISTIDINOL-PHOSPHATE AMINOTRANSFERASE COMPLEXED WITH HISTIDINOL-PHOSPHATE'''<br /> | '''CRYSTAL STRUCTURE OF HISTIDINOL-PHOSPHATE AMINOTRANSFERASE COMPLEXED WITH HISTIDINOL-PHOSPHATE'''<br /> | ||
==Overview== | ==Overview== | ||
| - | Histidinol-phosphate aminotransferase (HspAT) is a key enzyme on the | + | Histidinol-phosphate aminotransferase (HspAT) is a key enzyme on the histidine biosynthetic pathway. HspAT catalyzes the transfer of the amino group of L-histidinol phosphate (Hsp) to 2-oxoglutarate to form imidazole acetol phosphate (IAP) and glutamate. Thus, HspAT recognizes two kinds of substrates, Hsp and glutamate (double substrate recognition). The crystal structures of native HspAT and its complexes with Hsp and N-(5'-phosphopyridoxyl)-L-glutamate have been solved and refined to R-factors of 19.7, 19.1, and 17.8% at 2.0, 2.2, and 2.3 A resolution, respectively. The enzyme is a homodimer, and the polypeptide chain of the subunit is folded into one arm, one small domain, and one large domain. Aspartate aminotransferases (AspATs) from many species were classified into aminotransferase subgroups Ia and Ib. The primary sequence of HspAT is less than 18% identical to those of Escherichia coli AspAT of subgroup Ia and Thermus thermophilus HB8 AspAT of subgroup Ib. The X-ray analysis of HspAT showed that the overall structure is significantly similar to that of AspAT of subgroup Ib rather than subgroup Ia, and the N-terminal region moves close to the active site like that of subgroup Ib AspAT upon binding of Hsp. The folding of the main-chain atoms in the active site is conserved between HspAT and the AspATs, and more than 40% of the active-site residues is also conserved. The eHspAT recognizes both Hsp and glutamate by utilizing essentially the same active-site folding as that of AspAT, conserving the essential residues for transamination reaction, and replacing and relocating some of the active-site residues. The binding sites for the phosphate and the alpha-carboxylate groups of the substrates are roughly located at the same position and those for the imidazole and gamma-carboxylate groups at the different positions. The mechanism for the double substrate recognition observed in eHspAT is in contrast to that in aromatic amino acid aminotransferase, where the recognition site for the side chain of the acidic amino acid is formed at the same position as that for the side chain of aromatic amino acids by large-scale rearrangements of the hydrogen bond networks. |
==About this Structure== | ==About this Structure== | ||
| - | 1GEX is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with PLP and HSA as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Histidinol-phosphate_transaminase Histidinol-phosphate transaminase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.6.1.9 2.6.1.9] Full crystallographic information is available from [http:// | + | 1GEX is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=PLP:'>PLP</scene> and <scene name='pdbligand=HSA:'>HSA</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Histidinol-phosphate_transaminase Histidinol-phosphate transaminase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.6.1.9 2.6.1.9] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1GEX OCA]. |
==Reference== | ==Reference== | ||
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[[Category: pyridoxal-5'-phosphate]] | [[Category: pyridoxal-5'-phosphate]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 12:49:19 2008'' |
Revision as of 10:49, 21 February 2008
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CRYSTAL STRUCTURE OF HISTIDINOL-PHOSPHATE AMINOTRANSFERASE COMPLEXED WITH HISTIDINOL-PHOSPHATE
Overview
Histidinol-phosphate aminotransferase (HspAT) is a key enzyme on the histidine biosynthetic pathway. HspAT catalyzes the transfer of the amino group of L-histidinol phosphate (Hsp) to 2-oxoglutarate to form imidazole acetol phosphate (IAP) and glutamate. Thus, HspAT recognizes two kinds of substrates, Hsp and glutamate (double substrate recognition). The crystal structures of native HspAT and its complexes with Hsp and N-(5'-phosphopyridoxyl)-L-glutamate have been solved and refined to R-factors of 19.7, 19.1, and 17.8% at 2.0, 2.2, and 2.3 A resolution, respectively. The enzyme is a homodimer, and the polypeptide chain of the subunit is folded into one arm, one small domain, and one large domain. Aspartate aminotransferases (AspATs) from many species were classified into aminotransferase subgroups Ia and Ib. The primary sequence of HspAT is less than 18% identical to those of Escherichia coli AspAT of subgroup Ia and Thermus thermophilus HB8 AspAT of subgroup Ib. The X-ray analysis of HspAT showed that the overall structure is significantly similar to that of AspAT of subgroup Ib rather than subgroup Ia, and the N-terminal region moves close to the active site like that of subgroup Ib AspAT upon binding of Hsp. The folding of the main-chain atoms in the active site is conserved between HspAT and the AspATs, and more than 40% of the active-site residues is also conserved. The eHspAT recognizes both Hsp and glutamate by utilizing essentially the same active-site folding as that of AspAT, conserving the essential residues for transamination reaction, and replacing and relocating some of the active-site residues. The binding sites for the phosphate and the alpha-carboxylate groups of the substrates are roughly located at the same position and those for the imidazole and gamma-carboxylate groups at the different positions. The mechanism for the double substrate recognition observed in eHspAT is in contrast to that in aromatic amino acid aminotransferase, where the recognition site for the side chain of the acidic amino acid is formed at the same position as that for the side chain of aromatic amino acids by large-scale rearrangements of the hydrogen bond networks.
About this Structure
1GEX is a Single protein structure of sequence from Escherichia coli with and as ligands. Active as Histidinol-phosphate transaminase, with EC number 2.6.1.9 Full crystallographic information is available from OCA.
Reference
Structures of Escherichia coli histidinol-phosphate aminotransferase and its complexes with histidinol-phosphate and N-(5'-phosphopyridoxyl)-L-glutamate: double substrate recognition of the enzyme., Haruyama K, Nakai T, Miyahara I, Hirotsu K, Mizuguchi H, Hayashi H, Kagamiyama H, Biochemistry. 2001 Apr 17;40(15):4633-44. PMID:11294630[[Category: phosphoric acid mono-[2-amino-3-(3h-imidazol-4-yl)-propyl]ester]]
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