PDBsum entry 1fql

Lyase

PDB id: 1fql

Contents

Protein chain

256 a.a. *

Metals

_HG

_ZN

Waters ×60

* Residue conservation analysis

PDB id:

1fql

Name:

Lyase

Title:

X-ray crystal structure of zinc-bound f95m/w97v carbonic anhydrase (caii) variant

Structure:

Carbonic anhydrase. Chain: a. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Expressed in: escherichia coli. Expression_system_taxid: 562

Resolution:

2.00Å R-factor: 0.179 R-free: 0.255

Authors:

J.D.Cox,J.A.Hunt,K.M.Compher,C.A.Fierke,D.W.Christianson

Key ref:

J.D.Cox et al. (2000). Structural influence of hydrophobic core residues on metal binding and specificity in carbonic anhydrase II. Biochemistry, 39, 13687-13694. PubMed id: 11076507 DOI: 10.1021/bi001649j

Date:

05-Sep-00 Release date: 17-Jan-01

Protein chain

P00918  (CAH2_HUMAN) -  Carbonic anhydrase 2 from Homo sapiens

Seq: 260 a.a.

Struc: 256 a.a.*

* PDB and UniProt seqs differ at 2 residue positions (black crosses)

Enzyme reactions

• Enzyme class 2: E.C.4.2.1.1 - carbonic anhydrase.
• Reaction: hydrogencarbonate + H⁺ = CO2 + H2O
• Cofactor: Zn(2+)
• Enzyme class 3: E.C.4.2.1.69 - cyanamide hydratase.
• Reaction: urea = cyanamide + H2O

Note, where more than one E.C. class is given (as above), each may correspond to a different protein domain or, in the case of polyprotein precursors, to a different mature protein.

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

DOI no: 10.1021/bi001649j

Biochemistry 39:13687-13694 (2000)

PubMed id: 11076507

Structural influence of hydrophobic core residues on metal binding and specificity in carbonic anhydrase II.

J.D.Cox, J.A.Hunt, K.M.Compher, C.A.Fierke, D.W.Christianson.

ABSTRACT

Aromatic residues in the hydrophobic core of human carbonic anhydrase II (CAII) influence metal ion binding in the active site. Residues F93, F95, and W97 are contained in a beta-strand that also contains two zinc ligands, H94 and H96. The aromatic amino acids contribute to the high zinc affinity and slow zinc dissociation rate constant of CAII [Hunt, J. A., and Fierke, C. A. (1997) J. Biol. Chem. 272, 20364-20372]. Substitution of these aromatic amino acids with smaller side chains enhances Cu(2+) affinity while decreasing Co(2+) and Zn(2+) affinity [Hunt, J. A., Mahiuddin, A., & Fierke, C. A. (1999) Biochemistry 38, 9054-9062]. Here, X-ray crystal structures of zinc-bound F93I/F95M/W97V and F93S/F95L/W97M CAIIs reveal the introduction of new cavities in the hydrophobic core, compensatory movements of surrounding side chains, and the incorporation of buried water molecules; nevertheless, the enzyme maintains tetrahedral zinc coordination geometry. However, a conformational change of direct metal ligand H94 as well as indirect (i.e., "second-shell") ligand Q92 accompanies metal release in both F93I/F95M/W97V and F93S/F95L/W97M CAIIs, thereby eliminating preorientation of the histidine ligands with tetrahedral geometry in the apoenzyme. Only one cobalt-bound variant, F93I/F95M/W97V CAII, maintains tetrahedral metal coordination geometry; F93S/F95L/W97M CAII binds Co(2+) with trigonal bipyramidal coordination geometry due to the addition of azide anion to the metal coordination polyhedron. The copper-bound variants exhibit either square pyramidal or trigonal bipyramidal metal coordination geometry due to the addition of a second solvent molecule to the metal coordination polyhedron. The key finding of this work is that aromatic core residues serve as anchors that help to preorient direct and second-shell ligands to optimize zinc binding geometry and destabilize alternative geometries. These geometrical constraints are likely a main determinant of the enhanced zinc/copper specificity of CAII as compared to small molecule chelators.