Molecular mechanism of secreted amyloid-β precursor protein in binding and modulating GABABR1a

A recent phenomenal study discovered that the extension domain of secreted amyloid-beta precursor protein (sAPP) can bind to the intrinsically disordered sushi 1 domain of the gamma-aminobutyric acid type B receptor subunit 1a (GABA(B)R1a) and modulate its synaptic transmission. The work provided an important structural foundation for the modulation of GABA(B)R1a; however, the detailed molecular interaction mechanism, crucial for future drug design, remains elusive. Here, we further investigated the dynamical interactions between sAPP peptides and the natively unstructured sushi 1 domain using all-atom molecular dynamics simulations, for both the 17-residue sAPP peptide (APP 17-mer) and its minimally active 9 residue segment (APP 9-mer). We then explored mutations of the APP 9-mer with rigorous free energy perturbation (FEP) calculations. Our in silico mutagenesis studies revealed key residues (D4, W6, and W7) responsible for the binding with the sushi 1 domain. More importantly, one double mutation based on different vertebrate APP sequences from evolution exhibited a stronger binding (Delta Delta G = -1.91 +/- 0.66 kcal mol(-1)), indicating a potentially enhanced GABA(B)R1a modulator. These large-scale simulations may provide new insights into the binding mechanism between sAPP and the sushi 1 domain, which could open new avenues in the development of future GABA(B)R1a-specific therapeutics.