The general perspective of this project is that an understanding of the motifs and chemical principles that govern helix-helix interactions in membrane proteins will serve as a basis for understanding and predicting structure, oligomerization, and function. Given the genomic abundance of sequences that appear to encode helical membrane proteins and the paucity of detailed high resolution structures, our alternative approach should prove valuable in providing working models for structures as well as in guiding thoughts concerning functional states. The key is to develop connections between structural and thermodynamic descriptions of helix-helix interactions. Additionally, motifs may be identified that allow simple approaches using straightforward sequence analysis. Progress during the first two years of the program has resulted in a number of promising directions, which we plan to exploit during the next grant period. An important development that serves as a cornerstone for our plan is the emergence of two genetic screens for helix interaction in E. coli membranes. These will be exploited to search the E. coli genome for naturally occurring interactions and to screen random libraries to obtain global views for interacting sequences. A second platform for our future studies is provided by the determination of the glycophorin A transmembrane helix dimer structure. Using the structure, we are testing ideas concerning the energy terms important in the interaction by redesigning the interface and studying structural and energetic properties of different designs. Additionally, we are exploring the use of natural motifs, such as the leucine zipper, to design interacting transmembrane helices. Computational chemistry and genomic database studies will be used to refine chemical ideas and document the occurrence of specific interactions in naturally occurring membrane proteins. The properties of helix interaction interfaces appear encouraging with regard to new avenues for drug discovery.
