GH31 glycosidases are widespread across organisms, but, remarkably, less than 1% have been biochemically characterized to date. Among them, human lysosomal acid α-glucosidase (GAA) is notable for its link to Pompe disease, a rare lysosomal storage disorder caused by its deficiency (1). This disease results in glycogen accumulation, severe cellular damage, motor impairment, and premature death. Structural and functional studies of GAA mutants are challenging due to their instability and lack of activity, hindering their expression and purification. Here, we explore MalA, a GH31 enzyme from the hyperthermophilic archaeon Saccharolobus solfataricus, as a stable homolog of GAA. Its exceptional thermal stability and robustness (2) make MalA an ideal scaffold for studying its less stable human homolog. The R400H mutant in MalA, corresponding to the pathogenic GAA R600H mutation, exhibited a 1200-fold drop in specificity constant and a >8 °C reduction in thermal stability. Furthermore, the pharmacological chaperones used in Pompe disease therapy exhibited a differential stabilizing effect on the mutant versus the wild-type enzyme, which is conventionally used to screen for the chaperoning activity of new molecules. These findings validate MalA as a powerful functional model that accurately mimics the destabilizing effects of pathogenic mutations. Furthermore, we propose the thermophilic enzyme MalA as a robust platform for investigating GAA-related mutations and for screening novel therapeutic chaperones (3).