Integrated Approach for Biochemical and Functional Characterization of Six Clinical Variants of Glucose-6-Phosphate...

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a widespread enzymopathy affecting approximately 500 million individuals that represents a significant global health issue. Among the more than 230 identified mutations in the G6PD gene, six class A variants-G6PD Utrecht (Pro409Ser), G6PD Suwalki (Pro409Arg), G6PD Merlo (Pro409Gln), G6PD Kawasaki (Gly410Ala), G6PD Shinagawa (Gly410Asp), and G6PD Riverside (Gly410Cys)-are located in the beta-loop near the NADP⁺ binding site. These mutations are of particular interest due to their association with severe hematologic phenotypes, including chronic hemolytic anemia, as well as their proposed role in the allosteric regulation of G6PD multimerization. This study presents a comprehensive biochemical and functional characterization of these clinically relevant G6PD variants. The variant enzymes were cloned, expressed, and purified for characterization. Kinetic parameters and thermal stability assays, complemented by molecular dynamics simulations (MDS), were employed to elucidate the structural impacts of the mutations. Our results demonstrate that these mutations significantly impair protein function, characterized by reduced affinity for glucose-6-phosphate (G6P) and NADP⁺, as well as altered thermal stability compared with wild-type G6PD. MDS revealed that point mutations in the βN- and βM-sheets in the NADP⁺_s region propagate subtle conformational changes, ultimately affecting the NADP⁺c region and the G6P binding cavity. Furthermore, secondary structure element analyses of the simulation data showed that Pro409 and Gly410 point mutations propagate several changes around residues 195-210 (G6P binding site) and 380-400 (NADP⁺_s), explaining their effect on overall catalytic performance. These findings enhance our understanding of the molecular mechanisms underlying G6PD deficiency and its clinical implications, providing a foundation for future therapeutic strategies aimed at mitigating the effects of these variants.