Complement receptor 1 2026-11-05
Complement receptor 1 is a membrane glycoprotein that recognizes C3b and participates in regulation and handling of complement-tagged material. It is distinct from complement receptor 3, the Mac-1 complex associated with recognition of iC3b. Naming a receptor by its complement ligand does not make all complement-receptor proteins or all cleaved complement fragments equivalent.[ref]
Identification of the membrane glycoprotein that is the C3b receptor of the human erythrocyte, polymorphonuclear leukocyte, B lymphocyte, and monocyte by D. T. Fearon. JEM 152,20–30(1980), abstract: membrane gp205 and C3b-receptor identification.
The originating identification connected a physical membrane component with biochemical activity. D. T. Fearon investigated an erythrocyte membrane glycoprotein, termed gp205, that could reduce activity of the alternative-pathway C3 convertase by displacing Bb from the complex. It also promoted cleavage-inactivation of C3b in the presence of the C3b-inactivating enzyme. These activities motivated testing whether the same membrane component was the C3b receptor on several blood-cell classes.[ref]
Identification of the membrane glycoprotein that is the C3b receptor of the human erythrocyte, polymorphonuclear leukocyte, B lymphocyte, and monocyte by D. T. Fearon. Abstract: convertase decay, inactivation cofactor activity and erythrocyte/leukocyte receptor identity.
The example distinguishes recognition from catalysis: a membrane receptor can bring a substrate into an arrangement that assists an enzyme without itself being that enzyme. Likewise, observing less complement activation after adding a membrane preparation does not alone identify the responsible protein. Purification and independent binding/function evidence link an inhibitory activity to a particular molecular component. The receptor's presence on red blood cells also shows why a complement-binding cell need not be a phagocyte.
D. T. Fearon 2026-11-05
D. T. Fearon authored a 1980 study identifying a membrane glycoprotein as the receptor for the complement fragment C3b on human red blood cells, B cells, monocytes and polymorphonuclear leukocytes. The molecule, called gp205 in the paper, is associated with the receptor now called complement receptor 1. The work connected a purified protein's biochemical activity with a receptor found on several classes of blood cells.[ref]
Identification of the membrane glycoprotein that is the C3b receptor of the human erythrocyte, polymorphonuclear leukocyte, B lymphocyte, and monocyte by D. T. Fearon. Abstract, Journal of Experimental Medicine 152 (1980), pp. 20–30; DOI 10.1084/jem.152.1.20.
The route to identification is instructive. The glycoprotein was investigated for its ability to inhibit a C3 convertase and to assist enzymatic inactivation of C3b. Those activities suggested a C3b-binding function, which the receptor experiments tested. Thus a cell membrane receptor need not merely initiate a response: recognition of a complement component can also help regulate the amplification system to which that component belongs.[ref]
Identification of the membrane glycoprotein that is the C3b receptor of the human erythrocyte, polymorphonuclear leukocyte, B lymphocyte, and monocyte by D. T. Fearon. Abstract: convertase destabilization, C3b-inactivator cofactor activity and receptor identification.