Biomembrane Technology and Biomolecular Photonics
The design of a new generation of materials based on biomembrane components holds promise in diverse areas including optical recording media, chemical sensors, nanometer lithography, energy transducers, and enzyme catalysts. A variety of membrane proteins, including bacteriorhodopsin, rhodopsin, and acetylcholine receptor, exhibit active properties such as energy transduction, active and passive transport, chemical sensing, voltage channel gating, signal transduction, and self-assembly, which could find important uses in such materials. However, future progress will depend on the development of new methods for engineering such biomolecules with properties including enhanced stability and the ability to exist in a solid-state environment so that they are suitable for use in biomolecular devices.
In this project, the biophysics group is developing new methods based on molecular genetics and advanced biophysical techniques that will provide the capability to modify membrane proteins at the molecular level. Key among these techniques will be site-directed non-native amino acid replacement (SNAAR). This approach will provide a new dimension in protein engineering, enabling the replacement of native amino acid residues with custom designed residues. Current studies are aimed at incorporating photoactive non-native residues that will alter the electro-optical properties of bacteriorhodopsin. In this regard, recent studies have demonstrated that films produced from bacteriorhodopsin can be used for optical information processing.
The group has also demonstrated recently that self-assembled biomembranes can be used as molecular templates for nanostructure material fabrication. In one set of experiments, in collaboration with N. Clark and K. Douglas at the University of Colorado, 2-dimensionally crystalline S-layers were used as templates to produce patterned thin metal films with nanometer-sized holes and wires. In a different study (in collaboration with C. Safinya at the University of California Santa Barbara), the group recently reported the discovery that dry films of bacteriorhodopsin are structurally stable up to 140oC. Studies are being conducted to produce heatproof arrays of other proteins.
Energy Transduction, Ion Transport, and Signal Recognition
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.