1BV3

HUMAN CARBONIC ANHYDRASE II COMPLEXED WITH UREA


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.85 Å
  • R-Value Free: 0.213 
  • R-Value Work: 0.171 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

Carbonic anhydrase catalyzes cyanamide hydration to urea: is it mimicking the physiological reaction?

Briganti, F.Mangani, S.Scozzafava, A.Vernaglione, G.Supuran, C.T.

(1999) J.Biol.Inorg.Chem. 4: 528-536


  • PubMed Abstract: 
  • The interaction of human carbonic anhydrase (hCA) isozymes I and II with cyanamide, a linear molecule isoelectronic with the main physiological substrate of the enzyme, CO(2), was investigated through spectroscopic, kinetic, and X-ray crystallographi ...

    The interaction of human carbonic anhydrase (hCA) isozymes I and II with cyanamide, a linear molecule isoelectronic with the main physiological substrate of the enzyme, CO(2), was investigated through spectroscopic, kinetic, and X-ray crystallographic studies. We show here that cyanamide is hydrated to urea in the presence of CAs, and that it also acts as a weak non-competitive inhibitor (K(I)=61+/-3 mM and 238+/-9 mM for hCA II and hCA I, respectively) towards the esterasic activity of these enzymes, as tested with 4-nitrophenyl acetate. Changes in the spectrum of the Co(II)-hCA II derivative observed in the presence of cyanamide suggest that it likely binds the metal ion within the CA active site, adding to the coordination sphere, not substituting the metal-bound solvent molecule. It thereafter undergoes a nucleophilic attack from the metal-bound hydroxide ion, forming urea which remains bound to the metal, as observed in the X-ray crystal structure of hCA II soaked in cyanamide solutions for several hours. The urea molecule is directly coordinated to the active site Zn(II) ion through a protonated nitrogen atom. Several hydrogen bonds involving active site residues Thr199 and Thr200 as well as three water molecules (Wat99, Wat122, and Wat123) further stabilize the urea-hCA II adduct. Kinetic studies in solution further proved that urea acts as a tight binding inhibitor of the two isozymes hCA I and hCA II, with very slow binding kinetics (k(on) = 2.5 x 10(-5)s(-1)M(-1)). A mechanism to explain the hydration process of cyanamide by CAs, as well as the tight binding of urea in the active site, is also proposed based on the hypothesis that urea is deprotonated when bound to the enzyme. Cyanamide is thus the first true suicide substrate of this enzyme for which binding has been documented by means of X-ray crystallographic and spectroscopic studies.


    Organizational Affiliation

    Università di Firenze, Laboratorio di Chimica Inorganica e Bioinorganica, Via Gino Capponi 7, I-50121 Florence, Italy.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
PROTEIN (CARBONIC ANHYDRASE II)
A
259Homo sapiensGene Names: CA2
EC: 4.2.1.1
Find proteins for P00918 (Homo sapiens)
Go to Gene View: CA2
Go to UniProtKB:  P00918
Small Molecules
Ligands 3 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
ZN
Query on ZN

Download SDF File 
Download CCD File 
A
ZINC ION
Zn
PTFCDOFLOPIGGS-UHFFFAOYSA-N
 Ligand Interaction
URE
Query on URE

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Download CCD File 
A
UREA
C H4 N2 O
XSQUKJJJFZCRTK-UHFFFAOYSA-N
 Ligand Interaction
HGB
Query on HGB

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Download CCD File 
A
4-(HYDROXYMERCURY)BENZOIC ACID
C7 H6 Hg O3
WMHRYLDWLOGHSG-UHFFFAOYSA-M
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.85 Å
  • R-Value Free: 0.213 
  • R-Value Work: 0.171 
  • Space Group: P 1 21 1
Unit Cell:
Length (Å)Angle (°)
a = 42.820α = 90.00
b = 42.020β = 104.26
c = 73.030γ = 90.00
Software Package:
Software NamePurpose
CCP4refinement
SAINTdata reduction
CCP4model building
SAINTdata scaling
CCP4phasing

Structure Validation

View Full Validation Report or Ramachandran Plots



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 1999-09-28
    Type: Initial release
  • Version 1.1: 2007-10-16
    Type: Version format compliance
  • Version 1.2: 2011-07-13
    Type: Version format compliance