4gsm | pdb_00004gsm
Crystal Structure of Ni2+2-Human Arginase I
Structural highlights
Disease[ARGI1_HUMAN] Defects in ARG1 are the cause of argininemia (ARGIN) [MIM:207800]; also known as hyperargininemia. Argininemia is a rare autosomal recessive disorder of the urea cycle. Arginine is elevated in the blood and cerebrospinal fluid, and periodic hyperammonemia occurs. Clinical manifestations include developmental delay, seizures, mental retardation, hypotonia, ataxia, progressive spastic quadriplegia.[1] [2] Publication Abstract from PubMedVarious binuclear metal ion clusters and complexes have been reconstituted in crystalline human arginase I by removing the Mn(2+)(2) cluster of the wild-type enzyme with metal chelators and subsequently soaking the crystalline apoenzyme in buffer solutions containing NiCl(2) or ZnCl(2). X-ray crystal structures of these metal ion variants are correlated with catalytic activity measurements that reveal differences resulting from metal ion substitution. Additionally, treatment of crystalline Mn(2+)(2)-human arginase I with Zn(2+) reveals for the first time the structural basis for inhibition by Zn(2+), which forms a carboxylate-histidine-Zn(2+) triad with H141 and E277. The imidazole side chain of H141 is known to be hyper-reactive, and its chemical modification or mutagenesis is known to similarly compromise catalysis. The reactive substrate analogue 2(S)-amino-6-boronohexanoic acid (ABH) binds as a tetrahedral boronate anion to Mn(2+)(2), Co(2+)(2), Ni(2+)(2), and Zn(2+)(2) clusters in human arginase I, and it can be stabilized by a third inhibitory Zn(2+) ion coordinated by H141. Because ABH binds as an analogue of the tetrahedral intermediate and its flanking transition states in catalysis, this implies that the various metallo-substituted enzymes are capable of some level of catalysis with an actual substrate. Accordingly, we establish the following trend for turnover number (k(cat)) and catalytic efficiency (k(cat)/K(M)): Mn(2+) > Ni(2+) approximately Co(2+) >> Zn(2+). Therefore, Mn(2+) is required for optimal catalysis by human arginase I. Structure and function of non-native metal clusters in human arginase I.,D'Antonio EL, Hai Y, Christianson DW Biochemistry. 2012 Oct 23;51(42):8399-409. doi: 10.1021/bi301145n. Epub 2012 Oct , 12. PMID:23061982[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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