Premium
Structural analysis of the zinc hydroxide–Thr‐199–Glu‐106 hydrogen‐bond network in human carbonic anhydrase II
Author(s) -
Xue Yafeng,
Liljas Anders,
Jonsson BengtHarald,
Lindskog Sven
Publication year - 1993
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.340170112
Subject(s) - carbonic anhydrase ii , zinc , chemistry , carbonic anhydrase , mutant , hydrogen bond , bicarbonate , zinc hydroxide , molecule , active site , stereochemistry , hydroxide , crystallography , inorganic chemistry , enzyme , biochemistry , organic chemistry , gene
The singnificance of the zinc hydroxide–Thr‐199–Glu‐106 hydrogen‐bond network in the active site of human carbonic anhydrase II has been examined by X‐ray crystallographic analyses of site‐specific mutants. Mutants with Ala‐199 and Ala‐106 or Gln‐106 have low catalytic activities, while a mutant with Asp‐106 has almost full CO 2 hydration activity. The structures of these four mutants, as well as that of the bicarbonate complex of the mutant with Ala‐199, have been determined at 1.7 to 2.2 Å resolution. Removal of the γ atoms of residue 199 leads to distorted tetrahedral geometry at the zine ion, and a catalytically important zinc‐bound water molecule has moved towards Glu‐106. In the bicarbonate complex of the mutant with Ala‐199 one oxygen atom from bicarbonate binds to zinc without displacing this water molecule. Tetrahedral coordination geometries are retained in the mutants at position 106. The mutants with Ala‐106 and Gln‐106 have a zinc‐bound sulfate ion, whereas this sulfate site is only partially occupied in the mutant with Asp‐106. The hydrogen‐bond network seems to be “reversed” in the mutants with Ala‐106 and Gln‐106. The network is preserved as in native enzyme in the mutant with Asp‐106 but the side chain of Asp‐106 is more extended than that of Glu‐106 in the native enzyme. These results illustrate the importance of Glu‐106 and Thr‐199 for controlling the precise coordination geometry of the zinc ion and its ligand preferences with results in an optimal orientation of a zine‐bound hydroxide ion for an attack on the CO 2 substrate. © 1993 Wiley‐Liss, Inc.