The binding of human serum transferrin to its specific receptor reconstituted into liposomes.
Human placental transferrin receptor (HPTR), purified following a procedure based on affinity chromatography step, was reconstituted by the detergent dialysis method into various kinds of phosphatidylcholine vesicles and the receptor ability to bind 125I-labelled human serum transferrin (HST) was then evaluated. In our experimental conditions, the binding of the labelled protein to its specific receptor showed several features, in particular: (1) in cholesterol/1-alpha-dipalmitoylphosphatidyl choline (CHO/DPPC) liposomes, a positive cooperatively of the transferrin binding resulted at the lowest cholesterol/phospholipids (C/P) ratio; 1-alpha-dioleylphosphatidyl choline (DOPC) and phosphatidic acid (PA) containing liposomes showed an opposite binding curve trend; (2) the apparent dissociation constant (K'd) did not change significantly as a function of the lipid composition, being always around 1.00 x 10(-6) M; (3) the encapsulation capacity of liposomes decreased from 27% to about 13% with increasing amounts of cholesterol and was around 20% in the presence of DOPC or PA; about 8-13% of this receptor was found to be functional; (4) receptor-loaded liposomes treated with polyclonal anti-HPTR rabbit antibodies showed a remarkable binding decrease for transferin. All these results seem to point out the crucial role played by the environment in the binding behaviour of the transferrin receptor.
Dipartimento di Scienze e Tecnologie Biomediche e di Biometria Università dell'Aquila, Italy.
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Di Giulio
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G
D'Andrea
M A
MA
Saletti
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Impagnatiello
A M
AM
D'Alessandro
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Oratore
D000818:Animals; D001667:Binding, Competitive; D002846:Chromatography, Affinity; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D010713:Phosphatidylcholines; D010920:Placenta / Q000737:chemistry; D011817:Rabbits; D011990:Receptors, Transferrin / Q000302:isolation & purification / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
D007074:Immunoglobulin G; D008081:Liposomes; D010713:Phosphatidylcholines; D011990:Receptors, Transferrin; D014168:Transferrin