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Crystal structure of E. coli β–carbonic anhydrase, an enzyme with an unusual pH–dependent activity
Author(s) -
Cronk Jeff D.,
Endrizzi James A.,
Cronk Michelle R.,
O'neill Jason W.,
Zhang Kam Y.J.
Publication year - 2001
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.46301
Subject(s) - carbonic anhydrase , archaea , active site , escherichia coli , chemistry , crystallography , crystal structure , enzyme , zinc , biochemistry , biology , stereochemistry , gene , organic chemistry
Carbonic anhydrases fall into three distinct evolutionary and structural classes: α, β, and γ. The β‐class carbonic anhydrases (β‐CAs) are widely distributed among higher plants, simple eukaryotes, eubacteria, and archaea. We have determined the crystal structure of ECCA, a β‐CA from Escherichia coli, to a resolution of 2.0 Å. In agreement with the structure of the β‐CA from the chloroplast of the red alga Porphyridium purpureum , the active‐site zinc in ECCA is tetrahedrally coordinated by the side chains of four conserved residues. These results confirm the observation of a unique pattern of zinc ligation in at least some β‐CAs. The absence of a water molecule in the inner coordination sphere is inconsistent with known mechanisms of CA activity. ECCA activity is highly pH‐dependent in the physiological range, and its expression in yeast complements an oxygen‐sensitive phenotype displayed by a β‐CA‐deletion strain. The structural and biochemical characterizations of ECCA presented here and the comparisons with other β‐CA structures suggest that ECCA can adopt two distinct conformations displaying widely divergent catalytic rates.