Biochemical and molecular analyses of copper-zinc superoxide dismutase from a C4 plant Pennisetum glaucum reveals an adaptive role in response to oxidative stress.

Superoxide dismutases (SODs) form the foremost line of defense against ROS in aerobes. Pennisetum glaucum cDNA library is constructed to isolate superoxide dismutase cDNA clone (PgCuZnSOD) of 798 bp comprising 5'UTR (111 bp), an ORF (459 bp) and 3'UTR (228 bp). Deduced protein of 152 amino acids (16.7 kDa) with an estimated isoelectric point of 5.76 shared highest homology to cytoplasmic CuZnSODs from monocots i.e., maize, rice. Predicted 3D model reveals a conserved eight-stranded ß-barrel with active site held between barrel and two surface loops. Purified recombinant protein is relatively thermo-stable with maximal activity at pH 7.6 and shows inhibition with H(2)O(2) (4.3 mM) but not with azide (10 mM). In Pennisetum seedlings, abiotic stress induced PgCuZnSOD transcript up-regulation directly correlates to high protein and activity induction. Overexpression of PgCuZnSOD confers comparatively enhanced tolerance to methyl viologen (MV) induced oxidative stress in bacteria. Results imply that PgCuZnSOD plays a functional role in conferring oxidative stress tolerance to prokaryotic system and may hold significant potential to impart oxidative stress tolerance in higher plants through transgenic approach.