Determination of an Atomic-level Description of Protein Structure and Function

Research in my laboratory addresses three questions.

How do proteins evolve?
How proteins fold?
How do folded proteins assemble into regulated multiprotein complexes?
To address the questions of how proteins evolved and how they fold, we are studying a class of modular proteins that contain simple, repetitive architectures. These proteins are built from simple units of supersecondary structure that are repeated in multiple, tandem copies. Examples include ankyrin repeats and leucine-rich repeats.

This simple architecture suggests a major simplification to the evolutionary origins of proteins. Through recombination events, the simple building blocks illustrated above can be duplicated, fused, and mixed, providing a route to large proteins with diverse sequences, bypassing the need to start from large (and improbable) folded domains. We are currently looking at the effects of deletion, insertion, and recombination on stability and structure formation in repeat proteins. These measurements will provide us with an assessment of the fitness of such recombinant constructs.

In addition to the evolutionary implications of repeat architecture, repeat proteins provide a unique framework in which to understand protein folding thermodynamics and kinetics. Since repeat-proteins are linear, they provide an excellent system to determine the maximum radius of coupling between elements of protein structure, and are amenable to statistical thermodynamic modeling to help us quantify the origin and extent of coupling. And since the close contacts in repeat-proteins are made exclusively from neighboring segments of the polypeptide, their kinetics of folding should be fast, based on current ideas relating topology to folding rates. We are using deletion and point substitutions to map the equilibrium energy landscape of repeat proteins, and map kinetic flux onto these surfaces.

We are studying how proteins assemble into regulated multiprotein complexes using a system that is critical for transmembrane signal transduction, the Notch pathway. The Notch pathway controls cellular differentiation during development, and disruption of normal function in humans has been implicated in stroke, dementia, and in certain forms of leukemia. Our goal is to determine how the Notch receptor and its intracellular effectors interact, both structurally and thermodynamically, using techniques such as spectroscopy, light-scattering, calorimetry, and x-ray crystallography. Through studies of interactions between different components of this pathway, we hope to identify key allosteric regulatory mechanisms that control signaling, with the ultimate goal of describing the signal transduction process in terms of a binding partition function.