title: The macrophage cell surface glycoprotein F4/80 is a highly glycosylated proteoglycan.
abstract: Molecules whose expression is limited to particular leukocyte populations are of interest since they may perform unique functions for these cells. We therefore examined the biochemical nature of the F4/80 molecule, which is expressed solely on macrophage and dendritic cell subpopulations. Our study clearly indicates that post-translational modifications, which can influence both a protein's structural and functional features, constitute a major component of the 160-kDa cell-surface F4/80 molecule. The F4/80 molecule is synthesized as a single polypeptide chain which acquires numerous intramolecular disulfide bonds and requires an extended time period (T1/2 = 60 min) for transport to an endoglycosidase H-resistant form. The F4/80 molecule contains extensive N-linked glycosylation which contributes approximately 40 kDa to the mature molecule. The N-linked carbohydrates are of the branched, complex type, containing repeating N-acetylglycosamine or N-acetyllactosamine units which mediate the reactivity of the F4/80 molecule with Datura stramonium lectin. O-linked glycosylation is also present and contributes approximately 10 kDa to the F4/80 molecule. Furthermore, the sialic acid modifications of the F4/80 molecule are primarily through alpha 2-6 linkages to galactose. Finally, we demonstrate that the F4/80 molecule is a proteoglycan modified by chondroitin sulfate glycosaminoglycans. In addition to clarifying the nature of the F4/80 molecule biochemically, these post-translational modifications have specific implications for molecular recognition processes. We conclude that the modifications of the F4/80 molecule may mediate cell-cell recognition, cell adhesion, or ligand binding independently of the F4/80 molecule protein core.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
authors.forename: I D
authors.initials: ID
authors.lastname: Haidl
authors.forename: W A
authors.initials: WA
authors.lastname: Jefferies
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000276:immunology; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D006031:Glycosylation; D037102:Lectins / Q000737:chemistry; D017737:Macrophages, Peritoneal / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding; D011499:Protein Processing, Post-Translational / Q000276:immunology; D011509:Proteoglycans / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*
chemical_list: D037102:Lectins; D008562:Membrane Glycoproteins; D011509:Proteoglycans