Impact of missense mutations on the structure–function relationship of human succinyl-CoA synthetase using in silico analysis

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The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with succinyl-CoA synthetase (SCS) deficiency caused by pathogenic variants in genes encoding its two subunits. SCS is a mitochondrial enzyme involved in several metabolic pathways and acts as a heterodimer composed of α and β subunits encoded by SUCLG1 and SUCLA2 genes, respectively. The purpose of this study was to analyze the effects of the most pathogenic non-synonymous single nucleotide polymorphisms (nsSNPs) by applying, using different prediction tools, a filtering strategy, on the 343 and 365 nsSNPs found in SUCLG1 and SUCLA2 genes, respectively, retrieved from the databases, then to evaluate their structural and functional effects using homology modeling and molecular docking. Results showed that most deleterious mutations selected for structural analysis were located in loop regions critical for protein stability and function, especially, variants altering glycine and proline residues in these regions supporting their importance. We also showed that variants leading to hydrophobic and hydrophilic residues can destabilize the folding and binding of the protein. Molecular docking has also been used to identify the most important regions of ligand binding site (CoA binding site, ADP-Mg2+ binding site and phosphate ion binding site) and between the two subunits themselves, which mainly involving the ligase CoA domain. Our structural analysis, performed on selected nsSNP, are in accordance with experimental studies reported in the literature and predicted that they would responsible to either nonfunctional protein, subunit instability resulting in reduced amounts of misassembled protein, or in a protein unable to phosphorylate ADP.