Interview for Faculty Position

Biophysics of intrinsically unfolded proteins

Loren Hough

Rockefeller University

Intrinsically unfolded proteins lack a well-defined three-dimensional structure, behaving like a flexible polymer rather than a typical folded protein. Despite their prevalence (about thirty percent of human proteins contain significant unfolded regions), these proteins have seen relatively little study, in large part because of a lack of appropriate tools. We are therefore developing methods to understand the physical properties and biological function of unfolded proteins. I study the FG Nups, intrinsically unfolded proteins that form the filter controlling protein transport between a cell's cytoplasm and nucleus. In order for this transport to occur, cargo-carrying transport factors must bind to FG Nups in the nuclear pore complex (NPC). We are using nuclear magnetic resonance (NMR) spectroscopy to characterize the behavior FG Nups and their interaction with transport factors. In order to capture the dynamic atomic scale behavior of these proteins in their physiological state, we are using an NMR technique whereby we study the proteins within a living cell. We found that the behavior of FG Nups in cells is very different from when purified, showing that they are highly sensitive to their environment. The cell appears to be a good solvent for FG Nups, where every residue is in rapid motion; while typical buffers are bad solvents, leading to collapse of the polymer. Initial indications are that transport factor-FG Nup interactions are dynamic, consistent with the rapid exchange of cargoes across the NPC. Our results may explain previous contradictory measurements of FG Nup behavior, and help us to design artificial NPC-based filters. Our approaches should also help develop a toolkit to study other intrinsically unfolded proteins.