The Histidine 382 Residue Influences the Thermal Stability and Binding Propensity of the E2 Domain of Amyloid Precursor Protein.

The E2 domain of amyloid precursor protein (APP_E2) plays a central role in the protein's function. We reinvestigate how the missense mutation, ΔH382L, affects the domain's thermal stability and ligand binding propensity through differential scanning fluorometry. We report that the ΔH382L significantly impacts the thermal stability of APP_E2 with a reduction in Tm of 10.1°C ± 0.8°C when compared to wild-type APP_E2. In the presence of Cu2+ ions, WT APP_E2 showed a significant increase in Tm of 2.3°C ± 0.4°C, indicative of binding, whereas the mutant exhibited a significant decrease in Tm of 9.5°C ± 0.4°C, suggesting that Cu2+-mediated stabilization of APP_E2 is highly dependent on specific interactions. We further observed that the mutation affected heparin binding, with the mutant protein showing a 9.9°C ± 0.7°C decrease in Tm and requiring lower NaCl concentrations for elution from heparin Sepharose compared with the wild-type protein. Lastly, through molecular dynamics simulations, native contacts, dynamic cross-correlation and network analyses, we demonstrated that this point mutation may induce rigidity to one of the helical subdomains of APP_E2, change native contacts and correlated motion across the domain and reroute possible established communication pathways from the mutation site to distal residues. The global perturbations predicted in the presence of mutation may provide possible mechanistic explanation of the observed reduced thermal tolerance. Overall, our data reported that a missense mutation to an uncharged amino acid at position 382 of APP_E2 significantly decreases the thermal stability and binding propensity of the domain.