From Proteopediaproteopedia link
Carbonic anhydrase inhibitors. Comparison of chlorthalidone and indapamide X-ray crystal structures in adducts with isozyme II: when three water molecules make the difference
[CAH2_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.    
[CAH2_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. 
Publication Abstract from PubMed
Thiazide diuretics inhibit all mammalian isoforms of carbonic anhydrase (CA, EC 18.104.22.168) with a different profile as compared to classical inhibitors. Acting as moderate-weak inhibitors of CA II and CA I, chlorthalidone and indapamide considerably inhibit other isozymes among the 16 CAs present in vertebrates. These compounds show a different behavior against CAs I and II, with chlorthalidone being 18.3 times more potent against CA II and 150 times more potent against CA I, as compared to indapamide. In the X-ray crystal structures of the CA II-chlorthalidone adduct three active site water molecules interacting with the inhibitor scaffold were observed that lack in the corresponding indapamide adduct. Chlorthalidone bound within the active site is in an enolic tautomeric form, with the OH moiety participating in two strong hydrogen bonds with Asn67 and a water molecule. This binding mode may be exploited for designing better CA II inhibitors.
Carbonic anhydrase inhibitors. Comparison of chlorthalidone and indapamide X-ray crystal structures in adducts with isozyme II: when three water molecules and the keto-enol tautomerism make the difference.,Temperini C, Cecchi A, Scozzafava A, Supuran CT J Med Chem. 2009 Jan 22;52(2):322-8. PMID:19115843
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.