Crystal structure of E-coli beta-carbonic anhydrase, an enzyme with an unusual pH-dependent activity

Cronk, JD Endrizzi, JA Cronk, MR O'Neill, JW Zhang, KYJ

Jd. Cronk et al., Crystal structure of E-coli beta-carbonic anhydrase, an enzyme with an unusual pH-dependent activity, PROTEIN SCI, 10(5), 2001, pp. 911-922

51

INGLESE

Article

Biochemistry & Biophysics

PROTEIN SCIENCE

0961-8368 → ACNP

10

5

2001

911 - 922

ISI

0961-8368(200105)10:5<911:CSOEBA>2.0.ZU;2-S

Carbonic anhydrases fall into three distinct evolutionary and structural cl asses: alpha, beta, and gamma. The beta -class carbonic anhydrases (beta -C As) are widely distributed among higher plants, simple eukaryotes, eubacter ia, and archaea. We have determined the crystal structure of ECCA, a beta - CA from Escherichia coli, to a resolution of 2.0 Angstrom. In agreement wit h the structure of the beta -CA from the chloroplast of the red alga Porphy ridium purpureum, the active-site zinc in ECCA is tetrahedrally coordinated by the side chains of four conserved residues, These results confirm the o bservation of a unique pattern of zinc ligation in at least some beta -CAs. The absence of a water molecule in the inner coordination sphere is incons istent with known mechanisms of CA activity, ECCA activity is highly pH-dep endent in the physiological range, and its expression in yeast complements an oxygen-sensitive phenotype displayed by a beta -CA-deletion strain. The structural and biochemical characterizations of ECCA presented here and the comparisons with other beta -CA structures suggest that ECCA can adopt two distinct conformations displaying widely divergent catalytic rates.