Our research is directed towards obtaining a molecular understanding of some processes involving membrane proteins, using the physical techniques of x-ray diffraction and crystallographic electron microscopy. Concurrently, we are developing a new structural approach - electron microscopy of frozen, wet specimens - that will allow more accurate description of the molecular details. Work will focus on the following projects: (a) the gap junction channel and cell-cell communication. We have learned about the quaternary configurations of the protein around this channel and the principle by which the channel may open and close. We plan now to extend this analysis in order to identify the parts which are instrumental in causing and controlling channel dimensions and to relate more closely the observed details to the physiology. This knowledge will help in understanding the design of cell-cell channels and the mechanism by which communication between cells is regulated. It would ultimately provide us with a rational basis for correcting communication defects, as are associated with malignant tissue. (b) Quaternary structure and action of an acetylcholine receptor. The nicotinic acetylcholine receptor is unique among all receptors/channels in the extent to which its biochemical and pharmacological properties have been characterized, yet little direct information is available concerning its quaternary structure. We have succeeded in growing tubular crystals of this molecule from which we plan to derive a map of the quaternary structure and investigate conformational changes. This map would provide the framework upon which a refined molecular picture could be built up based on the extensive biochemical data (including amino acid sequences) now available. (c) Interaction of ribosomes with intracellular membranes. A detailed picture of the RNA and protein distribution in the 80S ribosome is emerging from electron microscopy of crystalline arrays in frozen K+ and Mg2+ containing solutions. We plan next to use this information as a basis for understanding the structural aspects of functioning ribosomal particles on endoplasmic reticulum membranes and the nuclear envelope.
