@article {2018|2059, title = {A Streamlined, General Approach for Computing Ligand Binding Free Energies and Its Application to GPCR-Bound Cholesterol.}, journal = {Journal of Chemical Theory and Computation}, volume = {14}, year = {2018}, pages = {6560{\textendash}6573}, abstract = {

The theory of receptor-ligand binding equilibria has long been well-established in biochemistry, and was primarily constructed to describe dilute aqueous solutions. Accordingly, few computational approaches have been developed for making quantitative predictions of binding probabilities in environments other than dilute isotropic solution. Existing techniques, ranging from simple automated docking procedures to sophisticated thermodynamics-based methods, have been developed with soluble proteins in mind. Biologically and pharmacologically relevant protein-ligand interactions often occur in complex environments, including lamellar phases like membranes and crowded, nondilute solutions. Here, we revisit the theoretical bases of ligand binding equilibria, avoiding overly specific assumptions that are nearly always made when describing receptor-ligand binding. Building on this formalism, we extend the asymptotically exact Alchemical Free Energy Perturbation technique to quantifying occupancies of sites on proteins in a complex bulk, including phase-separated, anisotropic, or nondilute solutions, using a thermodynamically consistent and easily generalized approach that resolves several ambiguities of current frameworks. To incorporate the complex bulk without overcomplicating the overall thermodynamic cycle, we simplify the common approach for ligand restraints by using a single distance-from-bound-configuration (DBC) ligand restraint during AFEP decoupling from protein. DBC restraints should be generalizable to binding modes of most small molecules, even those with strong orientational dependence. We apply this approach to compute the likelihood that membrane cholesterol binds to known crystallographic sites on three GPCRs (β -adrenergic, 5HT-2B, and μ-opioid) at a range of concentrations. Nonideality of cholesterol in a binary cholesterol:phosphatidylcholine (POPC) bilayer is characterized and consistently incorporated into the interpretation. We find that the three sites exhibit very different affinities for cholesterol: The site on the adrenergic receptor is predicted to be high affinity, with 50\% occupancy for 1:10 CHOL:POPC mixtures. The sites on the 5HT-2B and μ-opioid receptor are predicted to be lower affinity, with 50\% occupancy for 1:10 CHOL:POPC and 1:10 CHOL:POPC, respectively. These results could not have been predicted from the crystal structures alone.

}, issn = {1549-9626}, doi = {10.1021/acs.jctc.8b00447}, author = {Salari, Reza and Joseph, Thomas and Lohia, Ruchi and J{\'e}r{\^o}me H{\'e}nin and Brannigan, Grace} } @article {2012|1960, title = {General Anesthetics Predicted to Block the {GLIC} Pore with Micromolar Affinity}, journal = {Plos Comput. Biol.}, volume = {8}, number = {5}, year = {2012}, pages = {e1002532}, publisher = {Public Library of Science}, abstract = {

Author Summary

Although general anesthesia is performed every day on thousands of people, its detailed microscopic mechanisms are not known. What is known is that general anesthetic drugs modulate the activity of ion channels in the central nervous system. These channels are proteins that open in response to binding of neurotransmitter molecules, creating an electric current through the cell membrane and thus propagating nerve impulses between cells. One possible mechanism for ion channel inhibition by anesthetics is that the drugs bind inside the pore of the channels, blocking ion current. Here we investigate such a pore block mechanism by computing the strength of the drugs{\textquoteright} interaction with the pore {\textendash} and hence the likelihood of binding, in the case of GLIC, a bacterial channel protein. The results, obtained from numerical simulations of atomic models of GLIC, indicate that the anesthetics isoflurane and propofol have a tendency to bind in the pore that is strong enough to explain blocking of the channel, even at low concentration of the drugs.

}, doi = {10.1371/journal.pcbi.1002532}, url = {http://dx.doi.org/10.1371\%2Fjournal.pcbi.1002532}, author = {LeBard, David N. and J{\'e}r{\^o}me H{\'e}nin and Roderic G Eckenhoff and Michael L Klein and Brannigan, Grace} }