RUI: The Chemical Basis for Protein Self-assembly and Polymerization

Haverford College, Haverford PA

Investigators

Abstract

The objective of this project is to study the molecular and chemical role of the amino acid, glutamine, in the process of misfolding and aggregation of proteins containing long glutamine repeats. This aberrant process, resulting in the formation of large fibrils, is a general molecular problem common to all organisms and can lead to metabolic and structural deficiencies. Recently, the process of this aggregation has come under scrutiny since the intermediates formed during fibril growth can themselves persist in the organism and interfere with normal cellular processes. Stretches of glutamine repeats fold into a b-sheet structure, which then acts as a template for aggregation by the further addition of polypeptide strands to form a long filament. Individual filaments can further associate to form multi-filament fibrils. The glutamines are thought to stabilize these structures through mechanisms involving hydrogen bonding and hydrophobic interactions, although the details of these interactions and their respective roles during the self-assembly process are still controversial. The PI has developed a peptide model system that can form a prototypical b-sheet, called a b-hairpin, that can be studied using a variety of biophysical methods to probe the role of the glutamines in fostering b-sheet, filament, and fibril formation. Three specific goals are: (1) finding conditions to stabilize intermediates in the fibril assembly pathway so that the role of glutamine interactions on growth and stability can be assessed; (2) measuring the effects of amino acid mutations on these processes to probe chemical mechanism; and (3) isotope-labeling of specific glutamines to probe directly for stable hydrogen bonding in the various intermediates. The outcome of these studies will help to understand a fundamental problem in protein misfolding and to test a variety of structural models that have been proposed for proteins containing poly-glutamine repeats. This research has been developed as a set of projects suitable for undergraduates since the primary research efforts will be undertaken by students working to complete their thesis requirements in biology. Students engaged in this work will gain training in interdisciplinary research. This necessitates collaborative work and students will be working closely with colleagues in the Chemistry Department and collaborators at the University of Pennsylvania. Work on this project has led to the creation of lectures in protein folding and misfolding for an introductory course, more advanced lectures for an upper-level course in protein structure and function, and the development of a 7-week primary-literature-based course on protein misfolding and aggregation. The PI has a long-standing commitment to improving access to research for under-represented groups. In addition to a long-term commitment to an existing outreach program for science and writing for K-12 students from Philadelphia, he has regularly reserved space in his research lab over the summer and during the academic year for at least one student self-identified as belonging to an under-represented group. More broadly, as the director of the HHMI-sponsored programs at Haverford College, the PI is responsible for awarding student interdisciplinary research fellowships and funding internal and external research opportunities for students belonging to under-represented groups, administering several outreach programs, and supporting faculty development seminars and workshops to enhance the overall research program in the sciences.