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Molecular Cloning and Biochemical Characterization of the Iron Superoxide Dismutase from the Cyanobacterium Nostoc punctiforme ATCC 29133 and Its Response to Methyl Viologen-Induced Oxidative Stress.

Molecular biotechnology (2015-10-07)
Lakshmipyari Devi Moirangthem, Kalibulla Syed Ibrahim, Rebecca Vanlalsangi, Karin Stensjö, Peter Lindblad, Jyotirmoy Bhattacharya
ABSTRACT

Superoxide dismutase (SOD) detoxifies cell-toxic superoxide radicals and constitutes an important component of antioxidant machinery in aerobic organisms, including cyanobacteria. The iron-containing SOD (SodB) is one of the most abundant soluble proteins in the cytosol of the nitrogen-fixing cyanobacterium Nostoc punctiforme ATCC 29133, and therefore, we investigated its biochemical properties and response to oxidative stress. The putative SodB-encoding open reading frame Npun_R6491 was cloned and overexpressed in Escherichia coli as a C-terminally hexahistidine-tagged protein. The purified recombinant protein had a SodB specific activity of 2560 ± 48 U/mg protein at pH 7.8 and was highly thermostable. The presence of a characteristic iron absorption peak at 350 nm, and its sensitivity to H2O2 and azide, confirmed that the SodB is an iron-containing SOD. Transcript level of SodB in nitrogen-fixing cultures of N. punctiforme decreased considerably (threefold) after exposure to an oxidative stress-generating herbicide methyl viologen for 4 h. Furthermore, in-gel SOD activity analysis of such cultures grown at increasing concentrations of methyl viologen also showed a loss of SodB activity. These results suggest that SodB is not the primary scavenger of superoxide radicals induced by methyl viologen in N. punctiforme.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Isopropyl β-D-thiogalactopyranoside solution, ReadyMade IPTG solution for Blue-white screening
Sigma-Aldrich
IPTG, ≥99% (TLC), ≤0.1% Dioxane
Sigma-Aldrich
Isopropyl β-D-1-thiogalactopyranoside, ≥99% (TLC)
SAFC
Isopropyl β-D-1-thiogalactopyranoside