SAXS-DETECTED DYNAMICS OF FAST-FOLDING PROTEINS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This ongoing project follows up on a previous BioCAT project to study fast folding dynamics of lambda repressor by a combination of small angle X-ray scattering and circular dichroism spectroscopy (Dumont et al., Protein Science 15, 2596-2604 (2006)). We are examining the aggregation of lambda repressor and of fyn SH3 to obtain the potential of mean force between molecules and hence the size of the critical aggregation nucleus. The critical nucleus is an important measure of protein aggregation, but difficult to determine. We are also studying the folding dynamics of a downhill-folding mutant of lambda repressor by stopped-flow small angle X-ray scattering. The goal is to test the hypothesis that loss of the hydrophobic interaction eventually leads to a "turn-around" in the folding rate. We recently had our first beam time for this project, with the next planned time coming up in February 2007. We have completed radiation damage test on the proteins, all the concentration studies needed for the aggregation study (which is now in a phase of modeling the data to prepare for publication), and some of the kinetics measurements for the downhill lambda repressor mutants. More kinetics, including measurements at different final denaturant concentrations will be taken for both proteins next, to provide a complete map of the temperature dependence and time dependence of the radius of gyration.