Effects of missense R84Q mutation on human Pyrroline-5-carboxylate synthase enzyme properties, an in-silico analysis

Mammalian Δ-(1)-Pyrroline-5-carboxylate synthase (P5CS) enzyme catalyzes the coupled phosphorylation and reduction-conversion of glutamate to Δ-(1)- pyrroline-5- carboxylate (P5C), a critical step in the proline, ornithine, citrulline and arginine biosynthesis. In plants and mammals, P5CS consists of two separate enzymatic domains: N-terminal γ-glutamyl kinase (γ-GK) and C-terminal γ-glutamyl phosphate reductase (γ–GPR). Hyperammonemia has been reported as a new inborn disorder, with a range of clinical symptoms which is associated with a reduced synthesis of proline, ornithine, citruline and arginine. A missense mutation, R84Q, which alters the conserved residue in γ-GK domain, is responsible for this disorder. In this study using in-silico approaches as a new bioinformatics method, sequence analysis was performed and the tertiary structure of γ-GK domain of human P5CS, which includes the R84Q missense mutation, was predicted and the mutation effects on structural and functional features of P5CS enzyme were analyzed. Our analysis showed that this substitution has an affect on the molecular surface accessibility and total energy of the modeled structure. We conclude that this mutation results in a reduced activity of P5CS enzyme and an impaired synthesis of these amino acids.