From Proteopediaproteopedia link
Mutant carbonic anhydrase II in complex with an azide and an alkyne
[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
The carbonic anhydrase II mutant His64Cys was prepared and applied to tethered alkyne/azide cycloaddition reactions. The azide component could be tethered to the enzyme surface through a disulfide bridge, while the alkyne component was reversibly coordinated through a sulfonamide anchor to the zinc ion in the original catalytic center of the enzyme. The incipient orientation of the reactants in the binding site and of the formed triazole product were characterized by crystallography. The reaction progression could be monitored by HPLC-MS analysis.
Stereo- and Regioselective Azide/Alkyne Cycloadditions in Carbonic Anhydrase II via Tethering, Monitored by Crystallography and Mass Spectrometry.,Schulze Wischeler J, Sun D, Sandner NU, Linne U, Heine A, Koert U, Klebe G Chemistry. 2011 May 16;17(21):5842-51. doi: 10.1002/chem.201002437. Epub, 2011 Apr 19. PMID:21506176
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.