Nazanin Gholampour-Faroji , Monir-sadat Shakeri , Jafar Hemmat , Mohammad Rastegar-Moghadam Aliakbar Haddad-Mashadrizeh
Iranian J Biotech. 2020 January;18(1)

Background: Characterizing the structure and function of superoxide dismutase (SOD), as an antioxidant enzyme providing opportunities for its application in food supplements. Objectives: In this study, the features of the Manganese-SOD of Lactococcus lactis (SDLL), subsp. cremoris MG1363, as probiotic bacteria, were determined on the basis of the computational methods. Materials and Methods: The protein’s physicochemical properties and the prediction of its secondary structure were determined via the ProtParam server and the GOR program respectively. Moreover, the 3D structures of the proteins were constructed via the MODELLER on the basis of the homology method and the threading algorithm MUSTER. On the other hand, the structural stability of the models was assayed under the quasi-physiological conditions by the GROMACS program via the GROMOS96 43a1 force field in Linux system. Finally, using the Molecular Docking Studies, the functionality features of the models were predicted through their affinity with the corresponding substrates. Results: The results revealed the physicochemical properties of the SDLL and a 3D model of a chain of the enzyme being similar to the SOD from the Bacillus Subtilis (SDBS). The model of the SDLL was checked for quality control purposes including the Ramachandran plot, the ERRAT and the Verifiy3D. The model was suggestive of the structural stability in quasi-physiological conditions; yet, less than that of the SDBS. Assessing the cause of the instability in the SDLL model was indicative of two unstable regions in the area far from the enzyme’s active position, they were considered suitable for mutagenesis. Accordingly, the loop substitution for the corresponding region of SDBS and the deletion of the loop positioned at the C terminal of SDLL resulted in a mutant of SDLL with more stability and appropriate affinity with the corresponding substrate. Conclusion: In general, the study provides a new model of SDLL with certain thermostable features, and a new mutant with suitable stability and functionality on the basis of the direct mutagenesis being used in different applications. Keywords: Antioxidant enzymes, food supplements, thermostability, direct Mutagenesis

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