Formation of hydrogen bonds precedes the rate-limiting formation of persistent structure in the folding of ACBP

A burst phase in the early folding of the four-helix two-state folder prote in acyl-coenzyme A binding protein (ACBP) has been detected using quenched- flow in combination with site-specific NMR-detected hydrogen exchange. Seve ral of the burst phase structures coincide with a structure consisting of e ight conserved hydrophobic residues at the interface between the two N and C-terminal helices. Previous mutation studies have shown that the formation of this structure is rare limiting for the final folding of ACBP. The burs t phase structures observed in ACBP are different from the previously repor ted collapsed types of burst phase intermediates observed in the folding of other proteins. (C) 2000 Academic Press.