Anesthetic Binding Sites on Three-Helix Bundle Proteins

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The proposed research has the long-range goal of providing an understanding of how the inhaled general anesthetics interact with proteins, from structural and dynamic points of view, at the molecular level. This will be achieved using approaches developed in this laboratory to detect anesthetic binding to protein targets. The primary experimental focus will be synthetic three-alpha-helix bundles that can be structurally modified by established techniques. These synthetic proteins serve as simplified models for the bundles of transmembrane alpha-helices that are ubiquitous structural components of ion channels and neurotransmitter receptors in the central nervous system, and are the favored targets for general anesthetics at present. The current structural understanding of membrane proteins precludes their use to precisely examine anesthetic- protein complexation. However, the proposed use of simplified, well-defined, models of the transmembrane domains of native proteins lend themselves to the direct determination of the structural features of anesthetic binding sites using various spectroscopic approaches and X-ray crystallography. This will provide a detailed frame to evaluate hydrophobic, polar, and protein cavity contributions to anesthetic binding, providing insight into the relative importance of specific molecular interactions for anesthetic complexation. This information will provide guidelines for the structural composition of in vivo binding sites for volatile general anesthetics. The consequences of anesthetic binding to protein targets will be determined using measures of protein dynamics such as fluorescence anisotropy and protein thermodynamic stability, with the goal of furthering our understanding of how a bound anesthetic might alter protein function. The proposed studies build on the reported findings on halothane binding to dimeric four-alpha-helix bundles to (i) define the structure of the anesthetic binding site, and (ii) obtain atomic-level X-ray crystal structures of protein with bound anesthetic. Ultimately, the use of such model systems will provide fundamental information concerning how these important clinical compounds interact with potential target sites in the central nervous system at the molecular level, and will establish a framework for testing such associations, with natural membrane proteins. A precise structural description of the anesthetic binding site on this model system will allow a focused search of the Protein Data Bank for potential binding sites on existing- and future entries.