Conformational Dynamics and Binding Free Energies of Inhibitors of BACE-1: From the Perspective of Protonation Equilibria.
BACE-1 is the β-secretase responsible for the initial amyloidogenesis in Alzheimer's disease, catalyzing hydrolytic cleavage of substrate in a pH-sensitive manner. The catalytic mechanism of BACE-1 requires water-mediated proton transfer from aspartyl dyad to the substrate, as well as structural flexibility in the flap region. Thus, the coupling of protonation and conformational equilibria is essential to a full in silico characterization of BACE-1. In this work, we perform constant pH replica exchange molecular dynamics simulations on both apo BACE-1 and five BACE-1-inhibitor complexes to examine the effect of pH on dynamics and inhibitor binding properties of BACE-1. In our simulations, we find that solution pH controls the conformational flexibility of apo BACE-1, whereas bound inhibitors largely limit the motions of the holo enzyme at all levels of pH. The microscopic pKa values of titratable residues in BACE-1 including its aspartyl dyad are computed and compared between apo and inhibitor-bound states. Changes in protonation between the apo and holo forms suggest a thermodynamic linkage between binding of inhibitors and protons localized at the dyad. Utilizing our recently developed computational protocol applying the binding polynomial formalism to the constant pH molecular dynamics (CpHMD) framework, we are able to obtain the pH-dependent binding free energy profiles for various BACE-1-inhibitor complexes. Our results highlight the importance of correctly addressing the binding-induced protonation changes in protein-ligand systems where binding accompanies a net proton transfer. This work comprises the first application of our CpHMD-based free energy computational method to protein-ligand complexes and illustrates the value of CpHMD as an all-purpose tool for obtaining pH-dependent dynamics and binding free energies of biological systems.
Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.
M Olivia
MO
Kim
Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.
Patrick G
PG
Blachly
Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America; Department of Pharmacology, University of California San Diego, La Jolla, California, United States of America; Howard Hughes Medical Institute, University of California San Diego, La Jolla, California, United States of America; National Biomedical Computation Resource, University of California San Diego, La Jolla, California, United States of America.
J Andrew
JA
McCammon
D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors* / Q000648:ultrastructure*; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors* / Q000648:ultrastructure*; D001665:Binding Sites; D004735:Energy Transfer; D004791:Enzyme Inhibitors / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D011485:Protein Binding; D011487:Protein Conformation; D011522:Protons; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D004791:Enzyme Inhibitors; D011522:Protons; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human