High conformational flexibility of phosphomannomutase 2: Implications for functioning mechanisms, stability and pharmacological chaperone design

Phosphomannomutase 2 (PMM2) is a critical enzyme in the N-glycosylation pathway, and its defect is the cause of the most common congenital disorder of glycosylation. Despite its biological relevance, the understanding of PMM2 is limited, as the catalytic mechanism and required conformational dynamics remain unknown. In this study, we investigated murine PMM2 (Pmm2) to elucidate its structural flexibility and functional insights. High-resolution crystal structures of Pmm2 in both apo and activator-bound forms provided a more detailed model of the protein, underscoring the role of three ionic cofactors that are essential for dimerization, catalysis, and stability. The Pmm2 structures also provided eight distinct conformations of the protein subunit, highlighting its dynamic nature. Structural comparisons among Pmm2, human PMM2 and other phosphomannomutases helped define the architecture of the enzyme as a dimer assembled by the rigid association of the cap domains, which provide a flat platform from which the core domains of each subunit protrude in a flexible manner. Molecular dynamics (MD) simulations of the human and murine PMM2s further emphasized the enzymes substantial conformational flexibility, revealing extensive core domain movements and suggesting potential inter-subunit communication within the dimer. This study refines the model of PMM2 function, demonstrating its dynamic role in substrate binding, intermediate reorientation, and product release. The observed flexibility provides new opportunities to target specific enzyme states, enabling the development of pharmacological chaperones.