Proteins associated with activity of Fc receptors on isolated human placental syncytiotrophoblast microvillous plasma membranes.
To identify Fc receptors from human placental microvilli, proteins that were liberated by detergents from human placental synctiotrophoblast microvillous membranes (StMPM) were characterized by their abilities to bind human IgG in immune complexes with sheep or goat anti-human IgG and to monomeric rabbit anti-dinitrophenol (DNP) IgG bound to DNP-lysine Sepharose. Three placental IgG-binding proteins coprecipitated with immune complexes (Mr = 68,000, 52,000-56,000, 40,000) and were designated pIBP68, pIBP56 and pIBP40, respectively. Of the three proteins only pIBP56 bound to immobilized monomeric rabbit IgG. It was isolated from detergent lysates of StMPM and LDS/phenol glycoprotein extracts of placental plasma membranes suggesting that pIBP56 was a glycoprotein FcR previously reported (Mikulska et al, 1982). The binding specificities of pIBP56 and pIBP40 appeared to be detergent dependent. Photoaffinity crosslinking of StMPM surface proteins in situ to monomeric rabbit derivatized with N-succinimidyl(4-azidophenyl)-I, 3-dithiopropionate identified IgG-binding proteins identical in size to pIBP56 and pIBP40. Crosslinking further suggested that monomeric IgG covalently bound to a complex of StMPM proteins with a total size of 110,000-120,000 Mr. The findings suggest that pIBP68, pIBP56 and pIBP68 are responsible for IgG binding activity of placental StMPM.
Department of Immunology, University of Toronto, Canada.
J A
JA
Down
M
M
Kawakami
M H
MH
Klein
K J
KJ
Dorrington
D001345:Autoradiography; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis*; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000648:ultrastructure; D008970:Molecular Weight; D011257:Pregnancy Proteins / Q000032:analysis* / Q000648:ultrastructure; D011961:Receptors, Fc / Q000032:analysis*
D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; D011257:Pregnancy Proteins; D011961:Receptors, Fc