Conformational stability of the polypeptide components of human high density serum lipoprotein.

An investigation of the denaturation of the major polypeptides from human serum high density lipoprotein by guanidine hydrochloride reveals that the lipid-free, water-soluble states are minimally stable relative to the random coil states. These findings are in direct contrast to the resistance of intrinsic membrane proteins (in the absence of ligand) to complete unfolding by the same denaturant. Consideration of the denaturation data for the apolipoproteins together with previously published data from this laboratory on ligand-induced conformational changes indicate that these polypeptides possess several similar conformational states which are readily interconvertible.