The Physics department colloquia are usually on Friday afternoons at 3:30 pm in Lapham Hall Room 160. Coffee and cookies are served at 3:15 pm in the same room. Anyone is welcome.

Quaternary Structure and Binding Interfaces of the M₂ Muscarinic Receptor as Determined from FRET Measurements in Living Cells and Molecular Dynamics Simulations
Koki Yokoi, PhD Candidate, UWM Physics

G-protein coupled receptors (GPCRs) are the largest and most diverse family of membrane proteins that play roles in mediating signal transduction between outside and inside of a cell. Oligomerization of GPCRs and its possible role in function and signaling currently constitute an exciting area of research, with implications development of therapeutic regimens. We performed molecular dynamics (MD) simulations of fluorescent proteins attached through short linkers to GPCRs, in order to obtain distances between them and orientation factors of their transition dipole moments. Used in conjunction with Förster resonance energy transfer (FRET) experiments, this information is used for determination of binding interfaces between GPCR protomers (i.e., single molecules) within an oligomer. We simulated, with coarse-grained resolution, several configurations of dimers and tetramers of the M₂ muscarininc acetylcholine receptor fused to the green fluorescent protein (GFP, a donor of energy in FRET) and yellow fluorescent protein (YFP, an acceptor of energy). From simulated distances and orientation factors for oligomers with different relative orientation of the protomers, we computed apparent FRET efficiencies for mixtures of monomers, dimers and tetramers based on the simulated data, and then compared them to experimental FRET data. Comparing the fitting residuals obtained for all tested oligomer configurations, we were able to determine, for the first time, the most probable quaternary structure of the M₂ muscarinic receptor in living cells.