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Superoxide dismutases (SODs) protect the cells by catalyzing the dismutation of harmful superoxide radicals (O2•-) into molecular oxygen (O2) and hydrogen peroxide (H2O2). Here, a Cu, Zn SOD (WT) from a high altitude plant (Potentilla atrosanguinea) was engineered by substituting a conserved residue proline to glycine at position 61 (P61G). The computational analysis showed higher structural flexibility and clusters in P61G than WT. The P61G exhibited moderately higher catalytic efficiency (Km = 0.029 μM, Vmax = 1488) than WT protein (Km = 0.038 μM, Vmax = 1290.11). P61G showed higher thermostability as revealed from residual activity (72.25% for P61G than 59.31% for WT after heating at 80 °C for 60 min), differential calorimetry scanning and CD-spectroscopic analysis. Interestingly, the P61G mutation also resulted in enhanced tolerance to H2O2 inactivation than WT protein. The finding on enhancing the biophysico-chemical properties by mutating conserved residue could stand as an example to engineer other enzymes. Also, the reported mutant can be exploited in food and pharmaceutical industries.

Superoxide dismutases are the enzymes involved in dismutation of superoxide radicals into oxygen and hydrogen peroxide. The present work reports a thermostable Fe/Mn SOD of Geobacillus sp. strain PCH100 (GsSOD) isolated from glacial soil. Purified recombinant GsSOD is a dimeric protein of ~57 kDa that exhibited highest activity at a temperature of 10 °C and pH of 7.8. Maximum enzyme velocity and Michaelis constant of the GsSOD were 1098.90 units/mg and 0.62 μM, respectively. At 80 °C, thermal inactivation rate constant and half-life of GsSOD were 3.33 × 10−3 min−1 and 208 min, respectively. Interestingly, GsSOD tolerated a temperature of 100 °C and 130 °C up to 15 min and 5 min, respectively. Circular dichroism and differential scanning calorimetry confirmed thermostable nature of GsSOD. Apoenzyme of GsSOD regained enzymatic activity in the presence of Fe2+ and Mn2+ as metal ion cofactors. GsSOD was stable under varying concentrations of chemicals, namely ethylenediaminetetraacetic acid, potassium cyanide, hydrogen peroxide, chloroform-ethanol, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate, Tween-20, Triton X-100, urea, and guanidine hydrochloride. The enzyme exhibited >70% activity in presence of 10 mM metal ions. Owing to its thermostable nature and resistance to chemical inhibitors, GsSOD is a potential enzyme for industrial applications.

Superoxide dismutases (SODs) protect the cells by catalyzing the dismutation of harmful superoxide radicals (O

Superoxide dismutase (SOD) leads the front line of defense against injuries mediated by the reactive oxygen species (ROS). The SOD from a high-altitude plant Potentilla atrosanguinea is a unique thermostable enzyme. In this study, we applied a structure-guided consensus approach on Cu,Zn SOD from Potentilla atrosanguinea plant, to improve its enzymatic properties. The polar uncharged amino acid (threonine) at position 97 of wild-type (WT) SOD was selected as a target residue for substitution by aspartate (T97D) through site-directed mutagenesis. The WT and T97D were examined by a combinative approach consisting of robust computational and experimental tools. The in-silico analysis indicated improved dimeric stability in T97D as compared to the WT. The strong interactions between the monomers were related to improved dimerization and enhanced catalytic efficiency of T97D. These results were validated by in-vitro assays showing improved dimer stability and catalytic efficiency in T97D than WT. Moreover, the mutation also improved the thermostability of the enzyme. The combined structural and functional data described the basis for improved specific activity and thermostability. This study could expand the scope of interface residue to be explored as targets for designing of SODs with improved kinetics.

Superoxide dismutase (SOD) enzyme has implications in modulating the cell’s redox state. The study aims to explore the host genetic factors that limit the heterologous expression of a thermostable SOD from Potentilla atrosanguinea (Pa-SOD) in E. coli. It was observed that the heterologous expression of Pa-SOD in E. coli did not exhibit any enhancement after 1 h of induction. This led to the alteration in cell morphology and an increase in the doubling time of E. coli cells expressing Pa-SOD. Label-free quantification and MALDI-TOF/TOF-MS/MS analysis suggested differential expression of 81 proteins, of which 77 proteins were found to be downregulated and 4 were found to be upregulated in Pa-SOD expressing cells as compared to uninduced E. coli cells. Functional analysis of downregulated proteins shows involvement in molecular function, biological process, and were the part of a cellular component. The STRING database revealed interaction of an essential autoregulatory protein, RNase E with other proteins involved in biosynthetic processes, protein biosynthesis and folding, and cell division. Further, validation of RNase E protein revealed upregulation of rne at transcript level and downregulation of RNase E at protein level as compared to uninduced cells. The observations suggested the operation of multifaceted mechanisms with a key role of RNase E that regulated the expression of Pa-SOD at the physiological and molecular level. Since Pa-SOD has commercial applications, identification and manipulation of these networked genetic factors could lead to improvement of host strain for large-scale production of biologically active Pa-SOD and other heterologous proteins.

Oxygen (O2) is an essential component of all living aerobic organisms. It acts as an acceptor of energy and electrons during electron transport reactions, generating various reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide anion (O2 −), hydrogen peroxide (H2O2), and hydroxyl anion (HO ) as byproducts. The ROS are highly reactive and, therefore, cause extensive damage to the cellular system. However, over recent years, several studies have witnessed an essential role of ROS in plant growth and development and mediating response to biotic and abiotic stresses, which is strictly determined by the ROS levels themselves. Therefore, various enzymatic and non-enzymatic antioxidant mechanisms maintain ROS homeostasis, ensuring plant survival. Adverse environments, including temperature extremes, desiccation, high salinity, and metals, exacerbate ROS production. While such extreme environments are lethal, some plants called extremophytes sustain the adverse conditions. These extremophytes promptly sense the environment and undergo various morphological, physiological, and biochemical changes complemented with the genetic features, to minimize ROS generation and scavenge the excess ROS produced. The present review discusses different types of ROS, their production in subcellular compartments, and their management in plants. Besides, various survival strategies of extremophytes are also compiled. An emphasis has been given to high-altitude extremophytes, especially from the Himalayas, to understand their mechanism for managing ROS. Understanding of those adaptive mechanisms could be extrapolated to engineer stress resilience in other plants.