title: Crystal structure of E. coli beta-carbonic anhydrase, an enzyme with an unusual pH-dependent activity.
abstract: Carbonic anhydrases fall into three distinct evolutionary and structural classes: alpha, beta, and gamma. The beta-class carbonic anhydrases (beta-CAs) are widely distributed among higher plants, simple eukaryotes, eubacteria, and archaea. We have determined the crystal structure of ECCA, a beta-CA from Escherichia coli, to a resolution of 2.0 A. In agreement with the structure of the beta-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 beta-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 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.
authors.affiliation: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Cronk
authors.forename: J A
authors.initials: JA
authors.lastname: Endrizzi
authors.forename: M R
authors.initials: MR
authors.lastname: Cronk
authors.forename: J W
authors.initials: JW
authors.lastname: O'neill
authors.forename: K Y
authors.initials: KY
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D013329:Structure-Activity Relationship; D015032:Zinc / Q000378:metabolism
chemical_list: D002256:Carbonic Anhydrases; D015032:Zinc