title: The Structure of Carbonic Anhydrase IX Is Adapted for Low-pH Catalysis.
abstract: Human carbonic anhydrase IX (hCA IX) expression in many cancers is associated with hypoxic tumors and poor patient outcome. Inhibitors of hCA IX have been used as anticancer agents with some entering Phase I clinical trials. hCA IX is transmembrane protein whose catalytic domain faces the extracellular tumor milieu, which is typically associated with an acidic microenvironment. Here, we show that the catalytic domain of hCA IX (hCA IX-c) exhibits the necessary biochemical and biophysical properties that allow for low pH stability and activity. Furthermore, the unfolding process of hCA IX-c appears to be reversible, and its catalytic efficiency is thought to be correlated directly with its stability between pH 3.0 and 8.0 but not above pH 8.0. To rationalize this, we determined the X-ray crystal structure of hCA IX-c to 1.6 Å resolution. Insights from this study suggest an understanding of hCA IX-c stability and activity in low-pH tumor microenvironments and may be applicable to determining pH-related effects on enzymes.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Mahon
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Avni
authors.initials: A
authors.lastname: Bhatt
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Lilien
authors.initials: L
authors.lastname: Socorro
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Jenna M
authors.initials: JM
authors.lastname: Driscoll
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Okoh
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Carrie L
authors.initials: CL
authors.lastname: Lomelino
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Mam Y
authors.initials: MY
authors.lastname: Mboge
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Kurian
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Chingkuang
authors.initials: C
authors.lastname: Tu
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Mavis
authors.initials: M
authors.lastname: Agbandje-McKenna
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Susan C
authors.initials: SC
authors.lastname: Frost
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine , Gainesville, Florida 32610, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
mesh_terms: D000071231:Carbonic Anhydrase IX / Q000737:chemistry* / Q000235:genetics; D002384:Catalysis; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D000071231:Carbonic Anhydrase IX