Reversible thermal conformation changes in human serum low-density lipoprotein.

Human serum beta(1) (LDL(2)) lipoprotein was preparatively divided into three subfractions on the basis of density, and the protein conformation was investigated by optical rotatory dispersion and circular dichroism. The protein conformation was found to vary substantially as a function of lipid composition and temperature in a gradual and reversible manner. Surprisingly, the reversible temperature range includes physiological temperature. From the character of the spectra, it appears that alpha-helix, disordered, and beta conformations can be present in the protein moiety. The presence of these conformations and their distribution appears to depend upon both lipid content and temperature. The importance of this conformational flexibility in its relation to the role of the lipoprotein in lipid transport is discussed.