1FSN

X-RAY CRYSTAL STRUCTURE OF METAL-FREE F93S/F95L/W97M CARBONIC ANHYDRASE (CAII) VARIANT

Summary for 1FSN

• Entry DOI: 10.2210/pdb1fsn/pdb
• Related: 1FQL 1FQM 1FQN 1FQR 1FR4 1FR7 1FSQ 1FSR
• Descriptor: CARBONIC ANHYDRASE II (2 entities in total)
• Functional Keywords: carbonic anhydrase, metal binding, metal specificity, lyase
• Biological source: Homo sapiens (human)
• Cellular location: Cytoplasm: P00918
• Total number of polymer chains: 2
• Total formula weight: 58279.87

Authors

Cox, J.D.,Hunt, J.A.,Compher, K.M.,Fierke, C.A.,Christianson, D.W. (deposition date: 2000-09-11, release date: 2001-01-17, Last modification date: 2024-02-07)

Primary citation

Cox, J.D.,Hunt, J.A.,Compher, K.M.,Fierke, C.A.,Christianson, D.W.
Structural influence of hydrophobic core residues on metal binding and specificity in carbonic anhydrase II.
Biochemistry, 39:13687-13694, 2000

PubMed 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.

PubMed: 11076507
DOI: 10.1021/bi001649j

Experimental method

X-RAY DIFFRACTION (2 Å)