ROLE OF GLYCOSYLATION IN THE LIPID-BINDING ACTIVITY OF THE EXCHANGEABLE APOLIPOPROTEIN, APOLIPOPHORIN-III

Non-glycosylated recombinant Locusta migratoria apolipophorin-III, apo Lp-III, was expressed in E. coli and its physical-chemical properties were compared to those of the glycosylated native apoLp-III. Fluoresce nce quantum yield and acrylamide quenching studies indicated a slightl y higher accessibility of the Trp residues in the recombinant apoLp-II I. Far-UV CD spectroscopy indicated that the recombinant apoLp-III has a lower alpha-helical content than the glycosylated apoLp-III. Both p roteins spontaneously formed discoidal recombinant lipoprotein particl es when incubated with dimyristoylphosphatidylcholine (DMPC). Interact ion with lipid promotes an increase in a-helical content. CD and fluor escence studies indicate that both proteins adopt the same conformatio n in the lipid-bound state. However, the kinetics of association of th e recombinant protein with DMPC is 5-fold faster than that of the nati ve protein. The results suggest that glycosylation inhibits the lipid binding activity by preventing the exposure of hydrophobic domains and /or decreasing the conformational flexibility of the protein. (C) 1998 Academic Press.