4qk1
Structural and Catalytic Effects of Proline Substitution and Surface Loop Deletion in the Extended Active Site of Human Carbonic Anhydrase II - K170P
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 PubMedThe bioengineering of a thermophilic enzyme starting from a mesophilic scaffold has proven to be a significant challenge as several stabilizing elements have been proposed to be the foundation of thermal stability including disulfide bridges, surface loop reduction, ionic pair networks, proline substitutions, and aromatic clusters. This study emphasizes the impact of increasing the rigidity of human carbonic anhydrase II (HCA II) via incorporation of proline residues at positions 170 and 234, which are located in surface loops that are able to accommodate restrictive main-chain conformations without rearrangement of the surrounding peptide backbone. Additionally, the effect of compactness of HCA II was examined by way of deletion of a surface loop (residues 230 through 240), which had been previously identified as a possible source of thermal stability for the hyperthermophilic CA isolated from the bacterium Sulfurihydrogenibium yellowstonense YO3AOP1. Differential scanning calorimetry analysis of these HCA II variants revealed that these structural modifications had a minimum effect on the thermal stability of the enzyme while kinetic studies showed unexpected effects on the catalytic efficiency and proton transfer rates. X-ray crystallographic analysis of these HCA II variants showed the electrostatic potential and configuration of the highly acidic loop (residues 230 and 240) plays an important role in its high catalytic activity. Based on these observations and the literature, a picture is emerging of the various components within the general structural architecture of HCA II that are key to stability. These elements could provide the blueprints for the rational thermal stability engineering of other enzymes. This article is protected by copyright. All rights reserved. Structural and Catalytic Effects of Proline Substitution and Surface Loop Deletion in the Extended Active Site of Human Carbonic Anhydrase II.,Boone CD, Rasi V, Tu C, McKenna R FEBS J. 2015 Feb 13. doi: 10.1111/febs.13232. PMID:25683338[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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