SAXS STUDIES OF PROTEIN FOLDING INTERMEDIATES

Stanford University, Stanford CA

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Abstract

We propose to study protein folding intermediates at two levels (a) under suitable equilibrium conditions where we can stabilize partially folded states of proteins and (b) by direct kinetic measurements using stopped-flow time-resolved SAXS. SAXS data yield overall size and shape indication of the conformational state of a protein. High-quality, high-angle scattering profiles for cytochrome c have been measured at varying denaturant concentrations. We will use the combination of singular value decomposition analysis and a denaturant binding model to determine whether an equilibrium intermediate state exists. This analysis follows the method used to distinguish a folding intermediate for lysozyme (Chen, J. Mol. Biol. 261, 658-671). The A-states, partially folded intermediate states obtained at low pH with the addition of salt, of apomyoglobin have been characterized with SAXS. The apomyoglobin A-states stabilized with TFA, TCA, and KCl demonstrated different degrees of compaction, suggesting that there is not a unique A-state.