Molecular and functional characterization of a SUR1 mutation underlying dual glucose dysregulation

In this study, we describe molecular and functional characterization of the SUR1 missense variant Y123F, identified by whole-exome sequencing (WES) in a 6-year-old patient with alternating diabetic ketoacidosis (DKA) and dysglycemia, including hyperglycemia and postprandial hypoglycemia after high-protein meals. Evolutionary analysis revealed strong conservation of residue Y123. Structure-aware and energy-based in silico analyses predicted modest destabilization and increased local cavity volume at the mutation site, accompanied by reduced predicted SUR1-Kir6.2 interfacial contacts. Molecular dynamics simulations (MDS) further indicated increased local flexibility, altered solvation, and a reshaped free-energy landscape (FEL) in the mutant compared with the wild-type. Experimentally, the mature form of mutant SUR1 showed reduced steady-state abundance on immunoblots, and reconstituted SUR1-Kir6.2 complexes exhibited enhanced Rb⁺ efflux. Collectively, these findings support a model in which the Y123F substitution alters interactions between SUR1 and Kir6.2, resulting in increased ATP-sensitive potassium (K_ATP) channel gating activity that may contribute to the patient's hyperglycemia. On the other hand, the postprandial hypoglycemic episodes observed in the patient suggest that multiple physiological factors modulate the functional consequences of this mutation-effects not fully captured by the in vitro approaches used here. Therefore, further investigations, including comprehensive functional analyses and in vivo studies, are required to clarify its role in whole-body glucose regulation. Importantly, this study highlights the value of an integrated in silico-experimental pipeline for rigorous functional assessment of disease-associated protein variants, exemplified by diabetes-related mutations, to elucidate pathogenic mechanisms and inform therapeutic strategies and application.