The physical state of the LDL core influences the conformation of apolipoprotein B-100 on the lipoprotein surface.

We assessed the influence of temperature on the secondary structure of apolipoprotein B-100 (apoB) in normal low-density lipoprotein (N-LDL) and triglyceride-rich LDL (T-LDL). Gradual heating from 7 degrees C to the phase-transition temperature of the lipoprotein core ( approximately 28 degrees C and approximately 15 degrees C for N-LDL and T-LDL, respectively) gradually altered the secondary structure of apoB, while further heating from the phase-transition temperature to 45 degrees C had no additional effect. Above the phase-transition temperature of the core, the apoBs of N-LDL and T-LDL had a similar secondary structure. These results indicate that the conformation of apoB on the LDL surface depends strongly on the physical state of the lipoprotein core, and less on the lipid composition of the core per se.