2NXS

Structural and kinetic effects of hydrophobic mutations in the active site of human carbonic anhydrase II


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.80 Å
  • R-Value Free: 0.200 
  • R-Value Work: 0.178 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history


Literature

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, S.Z.Tu, C.K.Bhatt, D.Govindasamy, L.Agbandje-McKenna, M.McKenna, R.Silverman, D.N.

(2007) Biochemistry 46: 3803-3813

  • DOI: 10.1021/bi602620k
  • Structures With Same Primary Citation

  • PubMed Abstract: 
  • 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 facilita ...

    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.


    Organizational Affiliation

    Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610-0267, USA.



Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
carbonic anhydrase 2
A
260Homo sapiensMutation(s): 1 
Gene Names: CA2
EC: 4.2.1.1
Find proteins for P00918 (Homo sapiens)
Go to UniProtKB:  P00918
NIH Common Fund Data Resources
PHAROS  P00918
Protein Feature View
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
SO4
Query on SO4

Download CCD File 
A
SULFATE ION
O4 S
QAOWNCQODCNURD-UHFFFAOYSA-L
 Ligand Interaction
ZN
Query on ZN

Download CCD File 
A
ZINC ION
Zn
PTFCDOFLOPIGGS-UHFFFAOYSA-N
 Ligand Interaction
External Ligand Annotations 
IDBinding Affinity (Sequence Identity %)
SO4Ki:  183000000   nM  BindingDB
SO4Ki:  200000000   nM  BindingDB
SO4Ki:  300000000   nM  BindingDB
SO4Ki:  89000000   nM  BindingDB
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.80 Å
  • R-Value Free: 0.200 
  • R-Value Work: 0.178 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 42.888α = 90
b = 41.664β = 104.78
c = 72.953γ = 90
Software Package:
Software NamePurpose
CrystalCleardata collection
CNSrefinement
DENZOdata reduction
SCALEPACKdata scaling
CNSphasing

Structure Validation

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Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2007-04-24
    Type: Initial release
  • Version 1.1: 2008-05-01
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance