Phosphate forms an unusual tripodal complex with the Fe–Mn center of sweet potato purple acid phosphatase
AUTOR(ES)
Schenk, Gerhard
FONTE
National Academy of Sciences
RESUMO
Purple acid phosphatases (PAPs) are a family of binuclear metalloenzymes that catalyze the hydrolysis of phosphoric acid esters and anhydrides. A PAP in sweet potato has a unique, strongly antiferromagnetically coupled Fe(III)–Mn(II) center and is distinguished from other PAPs by its increased catalytic efficiency for a range of activated and unactivated phosphate esters, its strict requirement for Mn(II), and the presence of a μ-oxo bridge at pH 4.90. This enzyme displays maximum catalytic efficiency (kcat/Km) at pH 4.5, whereas its catalytic rate constant (kcat) is maximal at near-neutral pH, and, in contrast to other PAPs, its catalytic parameters are not dependent on the pKa of the leaving group. The crystal structure of the phosphate-bound Fe(III)–Mn(II) PAP has been determined to 2.5-Å resolution (final Rfree value of 0.256). Structural comparisons of the active site of sweet potato, red kidney bean, and mammalian PAPs show several amino acid substitutions in the sweet potato enzyme that can account for its increased catalytic efficiency. The phosphate molecule binds in an unusual tripodal mode to the two metal ions, with two of the phosphate oxygen atoms binding to Fe(III) and Mn(II), a third oxygen atom bridging the two metal ions, and the fourth oxygen pointing toward the substrate binding pocket. This binding mode is unique among the known structures in this family but is reminiscent of phosphate binding to urease and of sulfate binding to λ protein phosphatase. The structure and kinetics support the hypothesis that the bridging oxygen atom initiates hydrolysis.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=544300Documentos Relacionados
- Structure and Phase Transition of Fe-Mn Alloy Powders Prepared by Gas Atomization
- Characterization of manganese alloy residues for the recycling of FeSiMn and high-carbon FeMn fines
- An FeIVO complex of a tetradentate tripodal nonheme ligand
- Composition and color stability of anthocyanin-based extract from purple sweet potato
- The Glycosylphosphatidylinositol-Anchored Phosphatase from Spirodela oligorrhiza Is a Purple Acid Phosphatase1