title: Carbon Dioxide "Trapped" in a β-Carbonic Anhydrase.
abstract: Carbonic anhydrases (CAs) are enzymes that catalyze the hydration/dehydration of CO2/HCO3(-) with rates approaching diffusion-controlled limits (kcat/KM ∼ 10(8) M(-1) s(-1)). This family of enzymes has evolved disparate protein folds that all perform the same reaction at near catalytic perfection. Presented here is a structural study of a β-CA (psCA3) expressed in Pseudomonas aeruginosa, in complex with CO2, using pressurized cryo-cooled crystallography. The structure has been refined to 1.6 Å resolution with R(cryst) and R(free) values of 17.3 and 19.9%, respectively, and is compared with the α-CA, human CA isoform II (hCA II), the only other CA to have CO2 captured in its active site. Despite the lack of structural similarity between psCA3 and hCA II, the CO2 binding orientation relative to the zinc-bound solvent is identical. In addition, a second CO2 binding site was located at the dimer interface of psCA3. Interestingly, all β-CAs function as dimers or higher-order oligomeric states, and the CO2 bound at the interface may contribute to the allosteric nature of this family of enzymes or may be a convenient alternative binding site as this pocket has been previously shown to be a promiscuous site for a variety of ligands, including bicarbonate, sulfate, and phosphate ions.
authors.affiliation: Division of Biology and Soft Matter, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Mayank
authors.initials: M
authors.lastname: Aggarwal
authors.affiliation: Cornell High Energy Synchrotron Source (CHESS), Cornell University , Ithaca, New York 14853, United States.
authors.forename: Teck Khiang
authors.initials: TK
authors.lastname: Chua
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida , Gainesville, Florida 32610, United States.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Pinard
authors.affiliation: Cornell High Energy Synchrotron Source (CHESS), Cornell University , Ithaca, New York 14853, United States.
authors.forename: Doletha M
authors.initials: DM
authors.lastname: Szebenyi
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida , Gainesville, Florida 32610, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D024402:Carbonic Anhydrase II / Q000737:chemistry / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D011550:Pseudomonas aeruginosa / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D011994:Recombinant Proteins; D002245:Carbon Dioxide; D024402:Carbonic Anhydrase II; D002256:Carbonic Anhydrases