Structural Analysis on the Early Intermediates of Protein Folding by X-Ray Solution Scattering with a Cryo-Stopped-Flow Method

Abstract

Early events of protein folding have been investigated by a cryo-stopped-flow method with ultraviolet circular dichroism, fluorescence and X-ray solution scattering as probes. We found that α-helices were formed very rapidly as a folding nucleus within the dead-time of the stopped-flow apparatus. In the case of ubiquitin containing α-helix and β-structure, the folding took place via α-helix-rich intermediate, contrary to the previous hypothesis of 2-state transition. This was also the case of Src SH3 domain protein containing only β-structure and other proteins so far investigated. The intermediate structure of Src SH3 domain protein folding was calculated by using a SAXS-MD program.
In the studies of three homologous SH3 domain proteins (Src, Fyn and PI3K), we found that these proteins are folded via a different folding pathways.