Copper, zinc superoxide dismutase from Caragana jubata: A thermostable enzyme that functions under a broad pH and temperature window

This study reports a thermostable Cu, Zn superoxide dismutase (SOD) obtained from a high-altitude plant Caragana jubata (Cj-Cu, Zn SOD). The expression of Cj-Cu, Zn SOD in Escherichia coli followed by purification yielded a 17.5 kDa protein with a specific activity of 1547 +/- 39 units/mg of protein at 0 degrees C. The enzyme (i) functioned across a temperature range of -10 to +80 degrees C with optimum activity at 0-4 degrees C; (ii) performed well in a pH range of 6-9 with optimum activity at pH 7.5; (iii) was resistant to denaturation by sodium dodecyl sulfate (SDS) and urea; and (iv) existed in both monomeric and dimeric forms, the latter being more active. The enzyme exhibited activity upto 80 degrees C (k(d) =8.00 +/- 0.17 x 10(-3) min(-1), t(1/2) = 95 +/- 21 min), and tolerated autoclaving (heating at 121 degrees C at a pressure of 1.1 kg/cm(2) for 20 min). Circular dichroic spectroscopy analysis confirmed the thermostable nature of Cj-Cu, Zn SOD. Analysis in 94 phylogenetically diverse plant species across varied habitat preferences revealed the presence of autoclavable SOD in 15 species. SODs with unique properties of thermo/kinetic stability can be exploited for various applications in cosmetic, food, and pharmaceutical industries. (C) 2016 Elsevier Ltd. All rights reserved.