NMR Studies of Anesthetic Interactions witli lon Channels and Receptors.

University Of Pennsylvania, Philadelphia PA

Investigators

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Abstract

Project 3 will study anesthetic effects on protein global dynamics and test the central hypothesis that only those binding sites at which anesthetic binding can cause global dynamics changes are essential for mediating anesthetic action on proteins. Solution-state NMR in lyso-lipid micelles and high-resolution magicangle spinning (MAS) NMR in low-q lipid bicelles will be used to study a member ofthe Cys-loop ligandgated ion channel (LGIC) family (specific aim #1) and a member ofthe voltage-gated ion channel (VGIC) family (specific aim 2). We will focus on the transmembrane (TM) domain of nAChR a7 subunit in the functional homopentameric form with and without the intracellular (IC) domain, and the bacterial voltagegated sodium channel NaChBac. An anesthetic binding site will be engineered near the TM2-TM3 linker in nAChR a7 TM domain to turn this inhaled anesthetic-insensitive channel into an anesthetic sensitive channel. High-resolution TM domain structure of nAChR-a7 and the voltage-sensing domain (VSD), the pore domain (PD), and the 84-85 linker of NaChBac will be determined. Strategic ^^F probe placements, one or a few at a time, will be implemented to selectively label Phe, Lys, or site-directed Cys mutations to generate structural constraints. A model-based structure refinement approach will be taken through iterative interaction with Project 4 and Project 5 to refine the full-length receptor structures in the functional forms. The same ^¿F labels will also be used to determine slow domain dynamics through ^^F T2 dispersion measurements in the solution state. To complement the photoaffinity binding analyses in Project 1, intermolecular ^^F-^¿F NOESY and ^^F-^H HOESY between fluorinated anesthetics (halothane, isoflurane, sevoflurane, and fluorinated propofol) and the ^^F labels at various sites in the proteins will be used to determine anesthetic binding sites and affinities. We will classify and characterize at least two types of anesthetic binding sites: Type I where anesthetic binding can cause global dynamics changes and Type II where anesthetic binding produces only local effects. Through interaction with Project 2, we will seek correlations between anesthetic binding at Type I versus Type II sites and the effects of anesthetic binding on channel function. This project will provide new mechanistic insights into the down-stream events of anesthetic binding in modulating changes in channel activation and function.