Interaction of beta2-glycoprotein 1 with phosphatidylserine-containing membranes: ligand-dependent conformational alterations initiate bivalent binding.
Beta2-glycoprotein 1 (beta2GP1), a 50 kDa serum glycoprotein that binds anionic phospholipid-containing membranes, plays a regulatory role in physiology and pathology. The protein is a member of the short consensus repeat (SCR) superfamily containing four typical repeating domains and an aberrant fifth domain constructed into an SCR-like core at the C-terminus. To investigate the contribution of the individual domains to the binding of beta2GP1, a series of sequential domain-deleted recombinant protein fragments were generated and assessed for their interaction with PS-containing vesicles. Spectral analyses of lipid binding-dependent alterations in tryptophan emission spectra revealed that the (single) tryptophan residues of the individual domains underwent binding-dependent conformational alterations. Depending on the ionic strength, some domains moved from polar to nonpolar environments, while others moved from less polar to more polar environments. Analysis of a series of acrylamide quenching and resonance energy transfer experiments indicated that the binding of N-terminal domain 1 to PS membranes exists in two, ionic strength-dependent, conformations. At low ionic strengths, domain 1 bound to the vesicles and induced their precipitation and/or aggregation. At physiologic ionic strengths, domain 1 detached from the membrane surface while the remaining domains maintained their association with the membrane. Under these conditions, membrane-bound conformationally altered domain 1 projects away from the membrane surface, enabling it to interact with other proteins and/or cell surface ligands or receptors.
Hamdan
Randala
R
Department of Cancer Biology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030-4095, USA.
Maiti
Sourindra N
SN
Schroit
Alan J
AJ
D000818:Animals; D002417:Cattle; D011232:Chemical Precipitation; D004591:Electrophoresis, Polyacrylamide Gel; D004735:Energy Transfer; D006801:Humans; D007700:Kinetics; D008024:Ligands; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014364:Tryptophan; D053835:Unilamellar Liposomes / Q000378:metabolism*; D053482:beta 2-Glycoprotein I / Q000737:chemistry* / Q000378:metabolism*
D008024:Ligands; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D011994:Recombinant Proteins; D053835:Unilamellar Liposomes; D053482:beta 2-Glycoprotein I; D014364:Tryptophan