Energy Transduction, Ion Transport, and Signal Recognition

Kenneth Rothschild

Membrane proteins facilitate many key cellular processes, including energy transduction, ion transport, and signal recognition. Because these proteins are often difficult to crystallize for x-ray analysis, little is known about their structures and molecular mechanisms. For this reason, a combination of advanced spectroscopic and recombinant DNA techniques are being developed to investigate how these membrane proteins function.

A key focus of research is the light-driven proton pump, bacteriorhodopsin. Since the early 1970’s, this protein has become a focus for understanding the molecular mechanisms of active ion transport and energy transduction in biological systems. Two other proteins being investigated are rhodopsin, the primary receptor in vision, and acetylcholine receptor, which is involved in the transmission of the nerve impulses.

A central approach is the use of Fourier transform infrared (FTIR) difference spectroscopy. The group has shown that this method can be used to detect small conformational changes in membrane proteins. By combining this approach with site-directed mutagenesis, they have been able to construct a model for the key molecular events that occur during proton pumping in bacteriorhodopsin. A more advanced method for assigning bands and conducting structure-function studies which involves the site-directed isotope labeling of proteins using in vitro expression and supressor tRNAs is also under development. In a related approach, the substitution of non-native amino acids is being used to produce new forms of membrane proteins that will be useful in biotechnology.