2nwy: Difference between revisions
New page: left|200px<br /> <applet load="2nwy" size="450" color="white" frame="true" align="right" spinBox="true" caption="2nwy, resolution 1.65Å" /> '''Structural and kine... |
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caption="2nwy, resolution 1.65Å" /> | caption="2nwy, resolution 1.65Å" /> | ||
'''Structural and kinetic effects of hydrophobic mutations on the active site of human carbonic anhydrase II'''<br /> | '''Structural and kinetic effects of hydrophobic mutations on the active site of human carbonic anhydrase II'''<br /> | ||
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==Overview== | ==Overview== | ||
Catalysis of the hydration of CO2 by human carbonic anhydrase isozyme II, (HCA II) is sustained at a maximal catalytic turnover of 1 mus-1 by proton, transfer between a zinc-bound solvent and bulk solution. This mechanism of, proton transfer is facilitated via the side chain of His64, which is, located 7.5 A from the zinc, and mediated via intervening water molecules, in the active-site cavity. Three hydrophilic residues that have previously, been shown to contribute to the stabilization of these intervening waters, were replaced with hydrophobic residues (Y7F, N62L, and N67L) to determine, their effects on proton transfer. The structures of all three mutants were, determined by X-ray crystallography, with crystals equilibrated from pH, 6.0 to 10.0. A range of changes were observed in the ordered solvent and, the conformation of the side chain of His64. Correlating these structural, variants with kinetic studies suggests that the very efficient proton, transfer (approximately 7 micros-1) observed for Y7F HCA II in the, dehydration direction, compared with the wild type and other mutants of, this study, is due to a combination of three features. First, in this, mutant, the side chain of His64 showed an appreciable inward orientation, pointing toward the active-site zinc. Second, in the structure of Y7F HCA, II, there is an unbranched chain of hydrogen-bonded waters linking the, proton donor His64 and acceptor zinc-bound hydroxide. Finally, the, difference in pKa of the donor and acceptor appears favorable for proton, transfer. The data suggest roles for residues 7, 62, and 67 in fine-tuning, the properties of His64 for optimal proton transfer in catalysis. | Catalysis of the hydration of CO2 by human carbonic anhydrase isozyme II, (HCA II) is sustained at a maximal catalytic turnover of 1 mus-1 by proton, transfer between a zinc-bound solvent and bulk solution. This mechanism of, proton transfer is facilitated via the side chain of His64, which is, located 7.5 A from the zinc, and mediated via intervening water molecules, in the active-site cavity. Three hydrophilic residues that have previously, been shown to contribute to the stabilization of these intervening waters, were replaced with hydrophobic residues (Y7F, N62L, and N67L) to determine, their effects on proton transfer. The structures of all three mutants were, determined by X-ray crystallography, with crystals equilibrated from pH, 6.0 to 10.0. A range of changes were observed in the ordered solvent and, the conformation of the side chain of His64. Correlating these structural, variants with kinetic studies suggests that the very efficient proton, transfer (approximately 7 micros-1) observed for Y7F HCA II in the, dehydration direction, compared with the wild type and other mutants of, this study, is due to a combination of three features. First, in this, mutant, the side chain of His64 showed an appreciable inward orientation, pointing toward the active-site zinc. Second, in the structure of Y7F HCA, II, there is an unbranched chain of hydrogen-bonded waters linking the, proton donor His64 and acceptor zinc-bound hydroxide. Finally, the, difference in pKa of the donor and acceptor appears favorable for proton, transfer. The data suggest roles for residues 7, 62, and 67 in fine-tuning, the properties of His64 for optimal proton transfer in catalysis. | ||
==About this Structure== | ==About this Structure== | ||
2NWY is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with ZN as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Carbonate_dehydratase Carbonate dehydratase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.2.1.1 4.2.1.1] Full crystallographic information is available from [http:// | 2NWY is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with <scene name='pdbligand=ZN:'>ZN</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Carbonate_dehydratase Carbonate dehydratase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.2.1.1 4.2.1.1] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2NWY OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: proton transfer]] | [[Category: proton transfer]] | ||
''Page seeded by [http:// | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jan 23 15:35:44 2008'' | ||
