Site-directed mutagenesis in loop ۶ of human superoxide dismutase ۱ to investigate characterization of mutant enzyme

Human superoxide dismutase ۱ (hSOD۱) is an antioxidant enzyme that converts superoxide radicals to hydrogen peroxide and oxygen. More than ۱۰۰ mutations have been founded in this enzyme to cause amyotrophic lateral sclerosis (ALS). The aim of this study was to investigate the effect of L۱۰۶V mutation, which is located in Ⅵ loop of superoxide dismutase on its structure and activity. The superoxide dismutase gene in plasmid pET-۲۸a (+) was used as a template for targeted mutagenesis by Quick-change PCR. After confirmation of the mutation, the plasmid containing the mutation was transferred to the E.coli expression bacterium strain BL۲۱ (DE۳). IPTG and lactose inducers were used to express the protein. Purification of the protein was performed by nickel-sepharose affinity chromatography and SDS_PAGE gel, which was used to determine the purity of the protein. Specific activity of mutant and wild enzymes were determined using pyrogallol substrate at ۴۲۰ nm by spectrophotometry. Structural studies were performed using intrinsic fluorescence and external fluorescence techniques with ANS marker. The results of this study show that the specific activity of wild type and mutant enzyme (L۱۰۶V) were ۷۰۳۱.۲۵ U / mg and ۷۲۳۸.۶۵ mg, respectively. Structural studies with intrinsic fluorescence showed that the emission intensity of L۱۰۶V mutant was slightly lower than wild type. Increased intensity of extrinsic fluorescence emission L۱۰۶V mutant compared to the wild type indicates exposes more hydrophobic surfaces to ANS. Thus, the L۱۰۶V mutation in the superoxide dismutase gene is a genetic factor associated with the inherited form of amyotrophic lateral sclerosis.

کلیدواژه ها:

L۱۰۶V mutant enzyme ، affinity chromatography ، intrinsic and extrinsic Fluorescence ، Amyotrophic lateral sclerosis