A STRUCTURAL STUDY OF LOW-DENSITY LIPOPRO TEIN-GANGLIOSIDE COMPLEXES USING THE INDUCTIVE RESONANCE ENERGY-TRANSFER FROM TRYPTOPHAN RESIDUESTO PYRENE

The interaction of low density lipoproteins (LDL) with ganglioside GM( 3) immobilized on plastic was shown to result in the formation of LDL- GM(3) complexes. It has been shown that pyrene incorporates into these complexes in the same way as in native lipoproteins. Using the phenom enon of inductive resonance energy transfer from excited tryptophan re sidues to pyrene, it has been established that tryptophan residues of the apo-B molecule in the LDL-GM(3) complex are more deeply immersed i n the lipid phase than those of LDL. The degree of immersion was propo rtional to the ganglioside content of the complex. Estimation of the d egree of accessibility of tryptophyls to pyrene (fluorescence quenchin g) has shown that, when LDL interact with GM(3), a structural reconstr uction of the protein occurs with the formation of domains more than 3 7 Angstrom in size (1.2 Forster's radios).