Our research is aimed at understanding the principles that govern the folding of globular proteins. The insight gained provides a rational basis for predicting the three-dimensional structure of proteins from sequence data. Understanding the structural basis of protein stability and folding also plays a critical role in efforts to design proteins with new or modified functional properties. Moreover, studies of protein folding in vitro provide the necessary framework for understanding the folding of proteins in their cellular environments and related cellular processes, including protein trafficking and degradation. Finally, a wide range of human disorders can be linked to aggregation of partially denatured or misfolded forms of proteins; the structural and kinetic properties of protein folding intermediates are thus directly relevant for understanding and treating such diseases.
Much of our research is focused on elucidating the structural properties and mechanistic role of early folding intermediates. Despite impressive advances in rapid kinetics and spectroscopic methods, much remains to be learned. While it is now widely accepted that many proteins undergo major conformational changes during early stages of folding, long before they cross the rate-limiting barrier to the native state, we know little about the tertiary structure and topological features of these early intermediates, and it remains unclear whether they facilitate or hinder the conformational search for the native structure. We are exploring the early stages of folding of a variety of proteins by coupling advanced rapid mixing methods with structurally informative conformational probes, such as intrinsic and extrinsic fluorescence probes, and protection of individual amide hydrogens from solvent exchange monitored by NMR. The involvement of specific residues and interactions in stabilizing transient states and barriers in folding are explored by combining these structural and kinetic methods with site-directed mutagenesis.
Our group also participates in collaborative studies involving NMR and other spectroscopic methods aimed at elucidating the structure, dynamics and macromolecular interactions of proteins and nucleic acids of biomedical interest, including a membrane-cytoskeleton scaffolding protein (with Z. Bu), modular domains involved in the innate immune response (Y.C. Park), HIV integrase (with A.M. Skalka), blood coagulation factor XI (with P.N. Walsh, Temple University), and de novo designed proteins (with W.F. DeGrado, University of Pennsylvania). Other activities include morphological and molecular imaging studies of small animals used in cancer research, using NMR and optical imaging methods.