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Structural and spectroscopic characterisation of a heme peroxidase from sorghum

DOI: 10.1007/s00775-015-1313-z DOI Help
PMID: 26666777 PMID Help

Authors: Chukwudi I. Nnamchi (University of Nigeria) , Gary Parkin (University of Leicester) , Igor Efimov (University of Leicester) , Jaswir Basran (University of Leicester) , Hanna Kwon (University of Leicester) , Dimitri A. Svistunenko (University of Essex) , Jon Agirre (The University of York) , Bartholomew N. Okolo (University of Nigeria) , Anene Moneke (University of Nigeria) , Bennett C. Nwanguma (University of Nigeria) , Peter Moody (University of Leicester) , Emma L. Raven (University of Leicester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Jbic Journal Of Biological Inorganic Chemistry

State: Published (Approved)
Published: December 2015
Diamond Proposal Number(s): 6388

Abstract: A cationic class III peroxidase from Sorghum bicolor was purified to homogeneity. The enzyme contains a high-spin heme, as evidenced by UV–visible spectroscopy and EPR. Steady state oxidation of guaiacol was demonstrated and the enzyme was shown to have higher activity in the presence of calcium ions. A FeIII/FeII reduction potential of −266 mV vs NHE was determined. Stopped-flow experiments with H2O2 showed formation of a typical peroxidase Compound I species, which converts to Compound II in the presence of calcium. A crystal structure of the enzyme is reported, the first for a sorghum peroxidase. The structure reveals an active site that is analogous to those for other class I heme peroxidase, and a substrate binding site (assigned as arising from binding of indole-3-acetic acid) at the γ-heme edge. Metal binding sites are observed in the structure on the distal (assigned as a Na+ ion) and proximal (assigned as a Ca2+) sides of the heme, which is consistent with the Ca2+-dependence of the steady state and pre-steady state kinetics. It is probably the case that the structural integrity (and, thus, the catalytic activity) of the sorghum enzyme is dependent on metal ion incorporation at these positions.

Journal Keywords: Heme · Porphyrin · X-ray crystallography · Sorghum · Peroxidase · Calcium

Subject Areas: Biology and Bio-materials

Instruments: I03-Macromolecular Crystallography

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