Structure and function of non-native metal clusters in human arginase I

Biochemistry. 2012 Oct 23;51(42):8399-409. doi: 10.1021/bi301145n. Epub 2012 Oct 12.

Abstract

Various 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+) ≈ Co(2+) ≫ Zn(2+). Therefore, Mn(2+) is required for optimal catalysis by human arginase I.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aminocaproates / chemistry
  • Aminocaproates / metabolism
  • Arginase / antagonists & inhibitors
  • Arginase / chemistry*
  • Arginase / metabolism
  • Boron Compounds / chemistry
  • Boron Compounds / metabolism
  • Catalytic Domain
  • Crystallography, X-Ray
  • Humans
  • Manganese / chemistry
  • Models, Molecular
  • Nickel / chemistry
  • Zinc / chemistry

Substances

  • 2-amino-6-boronohexanoic acid
  • Aminocaproates
  • Boron Compounds
  • Manganese
  • Nickel
  • Arginase
  • Zinc

Associated data

  • PDB/4GSM
  • PDB/4GSV
  • PDB/4GSZ
  • PDB/4GWC
  • PDB/4GWD