Lifetimes of intermediates in the beta-sheet to alpha-helix transition of beta-lactoglobulin by using a diffusional IR mixer

The extremely slow alpha -helix/beta -sheet transition of proteins is a cru cial step in amylogenic diseases and represents an internal rearrangement o f local contacts in an already folded protein. These internal structural re arrangements within an already folded protein are a critical aspect of biol ogical action and are a product of conformational flow along unknown metast able local minima of the energy landscape of the compact protein. We use a diffusional IR mixer with time-resolved Fourier transform IR spectroscopy c apable of 400-mus time resolution to show that the trifluoroethanol driven beta -sheet to a-helix transition of beta -lactoglobulin proceeds via a com pact beta -sheet intermediate with a lifetime of 7 ms, small compared with the overall folding time of beta -lactoglobulin.