MEASURING COLLAPSE KINETICS OF LAMBDA REPRESSOR

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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. Protein folding is usually slowed down by a free energy barrier, yet proteins can be designed to be very stable and to fold rapidly without a significant barrier. Such hyperstable proteins could serve as "scaffolds" for introducing new function and make "designer proteins." We are studying the formation of structure in one such unusual protein, engineered lambda repressor. Although the protein folds very rapidly, by cooling it down in viscous solutions, we can follow the formation of compact structure by time-resolved X-ray scattering at the BioCAT beamline at Argonne, the brightest source for aqueous protein scattering studies. We have conducted initial studies of the protein and our new stopped-low apparatus to optimize signals, and are continuing our studies in 2005 with three protein variants, the wildtype, one containing a D14A mutation, the third a A37G/A49G mutation. These were chosen to cover a range of stabilities and aggregation propensities. The default hypothesis for the folding of small proteins is that X-ray scattering, fluorescence and infrared spectroscopies will yield identical folding times (so-called two-state folding). We believe that the D14A mutant will violate this hypothesis, while the other two will conform, based on our design.