Probing Phosphorylation-Induced Vibrational Couplings in CFTR by 2D IR Spectra Simulations

Phosphorylation of the regulator (R) domain underlies the basis for gating in the human cystic fibrosis transmembrane conductance regulator (CFTR), malfunction or down regulation of CFTR leads to defective apical chloride transport. The biophysical mechanism that underlies the regulatory effect of R domain is still unclear. Here, we utilize a combination of molecular dynamics simulations and theoretically calculated two-dimensional infrared (2D IR) spectra to probe both the structure and spectral signature of phosphorylated and unphosphorylated CFTR. We uncover an ATP-independent asymptotic movement of nucleotide binding domains (NBDs) driven by phosphorylated R domain. Utilizing non-rephasing cross ground-state bleach infrared (GB IR) spectra simulation, we overcome the interpretation hurdle caused by overlaps of multiple vibrational modes, and find distinct vibrational couplings induced by phosphorylation. By calculating exciton eigenfrequencies, we pinpoint specific vibrational couplings to individual amide I modes (carbonyl stretches), unveiling a critical role of serine residues in modulating the coupling state of neighboring amino acids. Our findings offer a bond-specific perspective on how intramolecular interactions within the R domain translate into its broader regulatory function.