Biochemical properties and oxalate-degrading activity of oxalate decarboxylase from bacillus subtilis at neutral pH.

Carolina Conter,Mauro Magnani,Mirco Dindo,Barbara Cellini,Luigia Rossi,Elisa Oppici

doi:10.1002/iub.2027

Abstract

Oxalate decarboxylase (OxDC) from Bacillus subtilis is a Mn‐dependent hexameric enzyme that converts oxalate to carbon dioxide and formate. OxDC has greatly attracted the interest of the scientific community, mainly due to its biotechnological and medical applications in particular for the treatment of hyperoxaluria, a group of pathologic conditions caused by oxalate accumulation. The enzyme has an acidic optimum pH, but most of its applications involve processes occurring at neutral pH. Nevertheless, a detailed biochemical characterization of the enzyme at neutral pH is lacking. Here, we compared the structural–functional properties at acidic and neutral pH of wild‐type OxDC and of a mutant form, called OxDC‐DSSN, bearing four amino acid substitutions in the lid (Ser161‐to‐Asp, Glu162‐to‐Ser, Asn163‐toSer, and Ser164‐to‐Asn) that improve the oxalate oxidase activity and almost abolish the decarboxylase activity. We found that both enzymatic forms do not undergo major structural changes as a function of pH, although OxDC‐DSSN displays an increased tendency to aggregation, which is counteracted by the presence of an active‐site ligand. Notably, OxDC and OxDC‐DSSN at pH 7.2 retain 7 and 15% activity, respectively, which is sufficient to degrade oxalate in a cellular model of primary hyperoxaluria type I, a rare inherited disease caused by excessive endogenous oxalate production. The significance of the data in the light of the possible use of OxDC as biological drug is discussed. © 2019 IUBMB Life, 1–11, 2019

Highlights

Oxalate decarboxylase (OxDC) from Bacillus subtilis requires Mn and O2 to catalyze the conversion of oxalate to formate and CO2 [1, 2]
Since these enzymes derive from plant sources and their purification is not suitable for large-scale applications, we thought to the possibility that the oxalate oxidase activity of OxDC-DSSN could be exploited as an alternative option to degrade oxalate under physiological conditions
In this work we investigated the molecular properties of OxDC and OxDC-DSSN at neutral pH

Summary

INTRODUCTION

Oxalate decarboxylase (OxDC) from Bacillus subtilis requires Mn and O2 to catalyze the conversion of oxalate to formate and CO2 [1, 2]. The crystal structure of OxDC-DSSN is not remarkably different with respect to the wild type, except for the conformation of the lid, which is intermediate between the open and the closed form [7]. Some oxalate oxidases display an optimum pH around 7 [23, 24], and a recent study reports that the encapsulation of oxalate oxidase from barley into polymeric zwitterionic capsules increases by twofold its activity at neutral pH [25] Since these enzymes derive from plant sources and their purification is not suitable for large-scale applications, we thought to the possibility that the oxalate oxidase activity of OxDC-DSSN could be exploited as an alternative option to degrade oxalate under physiological conditions. The possible implications of the results for the biotechnological applications of the enzyme are discussed

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSIONS