2nwo: Difference between revisions
No edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
[[Image:2nwo.gif|left|200px]] | [[Image:2nwo.gif|left|200px]] | ||
<!-- | |||
The line below this paragraph, containing "STRUCTURE_2nwo", creates the "Structure Box" on the page. | |||
You may change the PDB parameter (which sets the PDB file loaded into the applet) | |||
or the SCENE parameter (which sets the initial scene displayed when the page is loaded), | |||
or leave the SCENE parameter empty for the default display. | |||
--> | |||
{{STRUCTURE_2nwo| PDB=2nwo | SCENE= }} | |||
}} | |||
'''Structural and kinetic effect of hydrophobic mutations in the active site of human carbonic anhydrase II''' | '''Structural and kinetic effect of hydrophobic mutations in the active site of human carbonic anhydrase II''' | ||
| Line 31: | Line 28: | ||
[[Category: Fisher , S Z.]] | [[Category: Fisher , S Z.]] | ||
[[Category: McKenna, R.]] | [[Category: McKenna, R.]] | ||
[[Category: | [[Category: Carbonic anhydrase]] | ||
[[Category: | [[Category: Histidine 64]] | ||
[[Category: | [[Category: Proton transfer]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 10:00:19 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 10:00, 4 May 2008
Structural and kinetic effect of hydrophobic mutations in the active site of human carbonic anhydrase II
OverviewOverview
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.
DiseaseDisease
Known disease associated with this structure: Osteopetrosis, autosomal recessive 3, with renal tubular acidosis OMIM:[611492]
About this StructureAbout this Structure
2NWO is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.
ReferenceReference
Speeding up proton transfer in a fast enzyme: kinetic and crystallographic studies on the effect of hydrophobic amino acid substitutions in the active site of human carbonic anhydrase II., Fisher SZ, Tu C, Bhatt D, Govindasamy L, Agbandje-McKenna M, McKenna R, Silverman DN, Biochemistry. 2007 Mar 27;46(12):3803-13. Epub 2007 Mar 2. PMID:17330962 Page seeded by OCA on Sun May 4 10:00:19 2008