Mutations Alter Conformations and Dynamics of APP‐TMDs: An RDC Analysis

Cleavage by γ‐secretase within the transmembrane domain (TMD) of amyloid precursor protein (APP) generates Aβ peptides that can accumulate in amyloid plaques in Alzheimer's disease pathogenesis. How γ‐secretase selects its substrates has been an enigma as they do not have a consensus sequence. In our previous study, we discussed a dynamic signature that controls internal bending/kinking and orientation of the two halves of the TMD. The extent, however, had remained ambiguous due to limitations of NOE‐based NMR structure determination. To solve this question, we measured residual dipolar couplings (RDCs) of APP‐TMD, using a polyethylene glycol gel‐based alignment medium with TFE/water mixtures. Using 1 H 15 N RDCs, we analyzed the conformations of APP‐TMD and two mutants, G38L and G38P, which previously had differed significantly in bend and orientation and cleavage efficiency by γ‐secretase. By fitting snapshots from a molecular dynamics trajectory, we analyzed how well structures matched the measured RDC values. This indicated that G38L retained mainly its relatively straight conformation, whereas bent and—in the case of G38P—locally unfolded structures likewise contribute dynamically to the other two. The RDC selected structures thus reproduce the features of the NOE‐derived structures, but show that all three TMDs retain some conformational adaptability.