7aeq
Human carbonic anhydrase II in complex with 2,3,5,6-tetrafluoro-4-(2-hydroxyethylsulfanyl)-N-methyl-benzenesulfonamide
Structural highlights
DiseaseCAH2_HUMAN Defects in CA2 are the cause of osteopetrosis autosomal recessive type 3 (OPTB3) [MIM:259730; also known as osteopetrosis with renal tubular acidosis, carbonic anhydrase II deficiency syndrome, Guibaud-Vainsel syndrome or marble brain disease. Osteopetrosis is a rare genetic disease characterized by abnormally dense bone, due to defective resorption of immature bone. The disorder occurs in two forms: a severe autosomal recessive form occurring in utero, infancy, or childhood, and a benign autosomal dominant form occurring in adolescence or adulthood. Autosomal recessive osteopetrosis is usually associated with normal or elevated amount of non-functional osteoclasts. OPTB3 is associated with renal tubular acidosis, cerebral calcification (marble brain disease) and in some cases with mental retardation.[1] [2] [3] [4] [5] FunctionCAH2_HUMAN Essential for bone resorption and osteoclast differentiation (By similarity). Reversible hydration of carbon dioxide. Can hydrate cyanamide to urea. Involved in the regulation of fluid secretion into the anterior chamber of the eye.[6] [7] Publication Abstract from PubMedZinc-containing metalloenzyme carbonic anhydrase (CA) binds primary sulfonamides with extremely high, up to picomolar, affinity by forming a coordination bond between the negatively charged amino group and the zinc ion and making hydrogen bonds and hydrophobic contacts with other parts of the inhibitor molecule. However, N-methyl-substituted, secondary or tertiary sulfonamides bind CA with much lower affinity. In search for an explanation for this diminished affinity, a series of secondary sulfonamides were synthesized and, together with analogous primary sulfonamides, the affinities for 12 recombinant catalytically active human CA isoforms were determined by the fluorescent thermal shift assay, stopped-flow assay of the inhibition of enzymatic activity and isothermal titration calorimetry. The binding profile of secondary sulfonamides as a function of pH showed the same U-shape dependence seen for primary sulfonamides. This dependence demonstrated that there were protein binding-linked protonation reactions that should be dissected for the estimation of the intrinsic binding constants to perform structure-thermodynamics analysis. X-ray crystallographic structures of secondary sulfonamides and computational modeling dissected the atomic contributions to the binding energetics. Secondary sulfonamides bind to carbonic anhydrases via coordination bond between the negatively charged nitrogen of alkylated amino group and Zn(II) in the active site of CA. The binding reaction is linked to deprotonation of the amino group and protonation of the Zn(II)-bound hydroxide. To perform the structure-thermodynamics analysis, contributions of these linked reactions must be subtracted to determine the intrinsic energetics. In this aspect, the secondary sulfonamides are similar to primary sulfonamides as CA inhibitors. Structure and mechanism of secondary sulfonamide binding to carbonic anhydrases.,Baronas D, Dudutiene V, Paketuryte V, Kairys V, Smirnov A, Juozapaitiene V, Vaskevicius A, Manakova E, Grazulis S, Zubriene A, Matulis D Eur Biophys J. 2021 Oct;50(7):993-1011. doi: 10.1007/s00249-021-01561-1. Epub, 2021 Jul 30. PMID:34328515[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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