Early stages of LDL oxidation: apolipoprotein B structural changes monitored by infrared spectroscopy

Changes in the conformation of apoliprotein B-100 in the early stages of co pper-mediated low density lipoprotein oxidation have been monitored by infr ared spectroscopy. During the lag phase no variation in structure is observ ed, indicating that copper binding to the protein does not significantly af fect its structure. In the propagation phase, while hydroperoxides are form ed but the protein is not modified, no changes in secondary structure are o bserved, but the thermal profile of the band corresponding to alpha -helix is displaced in frequency, indicating changes in tertiary structure associa ted with this conformation but not with beta -sheet components. When aldehy de formation starts, a decrease of similar to3% in the area of bands corres ponding to alpha -helix and beta -sheet is produced, concomitantly with an increase in beta -turns and unordered structure. The two bands correspondin g to beta -turns vary as well under these conditions, indicating changes in these structures. Also at this stage the thermal profile shows variations in frequency for the bands corresponding to both alpha -helix and beta -she et. The results are consistent with the hypothesis that as soon as the poly unsaturated fatty acids from the particle core are modified, this change is reflected at the surface, in the alpha -helical components contacting the monolayer, - Chehin, R., D. Rengel, J. C. G. Milicua, F. M. Goni,J. L. R. A rrondo, and G. Pifat. Early stages of LDL oxidation: apolipoprotein B struc tural changes monitored by infrared spectroscopy.