SECONDARY STRUCTURE OF THE PARTICLE ASSOCIATING DOMAIN OF APOLIPOPROTEIN-B-100 IN LOW-DENSITY-LIPOPROTEIN BY ATTENUATED TOTAL-REFLECTION INFRARED-SPECTROSCOPY

The secondary structure of the human low-density lipoprotein (LDL) apo B-100 fragment embedded in the lipid domain of the particle has been investigated by Fourier transform attenuated total reflection infrared spectroscopy (FTIR-ATR). The solvent-exposed region of the protein wa s hydrolyzed by using different proteases (alpha-chymotrypsin, trypsin , proteinase K) for incubation times varying between 24 min and 48 h. Analysis of the FTIR-ATR spectra after repurification of the digested LDL particle indicates the same trend for all the hydrolysis condition s tested: the peptides remaining associated with the particle are rich in beta-sheet structure. Dichroism spectra reveal that at least part of the beta-sheets is associated with the phospholipid component of th e particle.