SINGLE MOLECULE AND SAXS STUDIES OF EARLY COLLAPSE IN PROTEIN FOLDING

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Does the unfolded state contract at low-denaturant concentrations? Many single-molecule Forster Resonance Energy Transfer (sm-FRET) experiments suggest that unfolded, single domain proteins invariably collapse from random coil dimensions to a much more compact state as the denaturant concentration is reduced. However, the results of similarly numerous small angle X-ray scattering (SAXS) suggest instead that this effect may be rare. Here we explore this discrepancy via a detailed SAXS-based study of protein L, a protein that has been the subject of one previous SAXS study, which suggests the dimensions of the protein's unfolded state remain fixed between 6 and 1.4 guanidine hydrochloride (Gdm), and two prior sm-FRET studies, which suggest that the chain contracts by 20 to 30% over this same range.