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Superoxide dismutases are important group of antioxidant metallozyme and play important role in ROS homeostasis in salinity stress. The present study reports the biochemical properties of a salt-tolerant Cu, Zn-superoxide from Avicennia marina (Am_SOD). Am_SOD was purified from the leaf and identified by mass-spectrometry. Recombinant Am_SOD cDNA was bacterially expressed as a homodimeric protein. Enzyme kinetics revealed a high substrate affinity and specific activity of Am_SOD as compared to many earlier reported SODs. An electronic transition in 360–400 nm spectra of Am_SOD is indicative of Cu2+-binding. Am_SOD activity was potentially inhibited by diethyldithiocarbamate and H2O2, a characteristic of Cu, Zn-SOD. Am_SOD exhibited conformational and functional stability at high NaCl concentration as well in alkaline pH. Introgression of Am_SOD in E. coli conferred tolerance to oxidative stress under highly saline condition. Am_SOD was moderately thermostable and retained functional activity at ~ 60 °C. In-silico analyses revealed 5 solvent-accessible N-terminal residues of Am_SOD that were less hydrophobic than those at similar positions of non-halophilic SODs. Substituting these 5 residues with non-halophilic counterparts resulted in > 50% reduction in salt-tolerance of Am_SOD. This indicates a cumulative role of these residues in maintaining low surface hydrophobicity of Am_SOD and consequently high salt tolerance. The molecular information on antioxidant activity and salt-tolerance of Am_SOD may have potential application in biotechnology research. To our knowledge, this is the first report on salt-tolerant SOD from mangrove. [ABSTRACT FROM AUTHOR]

Sunflower pollen was reported to contain respiratory allergens responsible for occupational allergy and pollinosis. The present study describes the comprehensive characterization of a major sunflower allergen Hel a 6. Natural Hel a 6 was purified from sunflower pollen by anion exchange and gel filtration chromatography. Hel a 6 reacted with IgE-antibodies from 57% of 39 sunflower-sensitized patient sera suggesting it to be a major allergen. The patients were of Indian origin and suffering from pollinosis and allergic rhinitis. Hel a 6 exhibited allergenic activity by stimulating mediator release from basophils. Monomeric Hel a 6 displayed pectate lyase activity. The effect of various physicochemical parameters such as temperature, pH, and calcium ion on the functional activity of Hel a 6 revealed a stable nature of the protein. Hel a 6 was folded, and its melting curve showed reversible denaturation in which it refolded back to its native conformation from a denatured state. Hel a 6 displayed a high degree of sequence conservation with the pectate lyase allergens from related taxonomic families such as Amb a 1 (67%) and Art v 6 (57%). The IgE-cross reactivity was observed between Hel a 6 and its ragweed and mugwort homologs. The cross-reactivity was further substantiated by the mediator release when Hel a 6-sensitized effector cells were cross-stimulated with Art v 6 and Amb a 1. Several putative B cell epitopes were predicted and mapped on these 3 allergens. Two antigenic regions were found to be commonly shared by these 3 allergens, which could be crucial for cross-reactivity. In conclusion, Hel a 6 serves as a candidate molecule for diagnosis and immunotherapy for weed allergy. [ABSTRACT FROM AUTHOR]