Glycosylation influences the lectin activities of the macrophage mannose receptor.
The mannose receptor (MR) is a heavily glycosylated endocytic receptor that recognizes both mannosylated and sulfated ligands through its C-type lectin domains and cysteine-rich (CR) domain, respectively. Differential binding properties have been described for MR isolated from different sources, and we hypothesized that this could be due to altered glycosylation. Using MR transductants and purified MR, we demonstrate that glycosylation differentially affects both MR lectin activities. MR transductants generated in glycosylation mutant cell lines lacked most mannose internalization activity, but could internalize sulfated glycans. Accordingly, purified MR bearing truncated Man5-GlcNAc2 glycans (Man5 -MR) or non-sialylated complex glycans (SA0-MR) did not bind mannosylated glycans, but could recognize SO4-3-Gal in vitro. Additional studies showed that, although mannose recognition was largely independent of the oligomerization state of the protein, recognition of sulfated carbohydrates was mostly mediated by self-associated MR and that, in SA0-MR, there was a higher proportion of oligomeric MR. These results suggest that self-association could lead to multiple presentation of CR domains and enhanced avidity for sulfated sugars and that non-sialylated MR is predisposed to oligomerize. Therefore, the glycosylation of MR, terminal sialylation in particular, could influence its binding properties at two levels. (i) It is required for mannose recognition; and (ii) it modulates the tendency of MR to self-associate, effectively regulating the avidity of the CR domain for sulfated sugar ligands.
Glycobiology Institute and the Biochemistry Department, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
Yunpeng
Y
Su
Talitha
T
Bakker
James
J
Harris
Clarence
C
Tsang
Gordon D
GD
Brown
Mark R
MR
Wormald
Siamon
S
Gordon
Raymond A
RA
Dwek
Pauline M
PM
Rudd
Luisa
L
Martinez-Pomares
D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002241:Carbohydrates / Q000737:chemistry; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D002850:Chromatography, Gel; D006224:Cricetinae; D004705:Endocytosis; D005434:Flow Cytometry; D006031:Glycosylation; D037102:Lectins / Q000737:chemistry*; D037181:Lectins, C-Type / Q000737:chemistry*; D008024:Ligands; D008264:Macrophages / Q000378:metabolism*; D008358:Mannose / Q000737:chemistry; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000737:chemistry*; D051379:Mice; D018613:Microscopy, Confocal; D008958:Models, Molecular; D009154:Mutation; D011134:Polysaccharides / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry*; D012190:Retroviridae / Q000235:genetics; D013455:Sulfur / Q000737:chemistry; D020349:Surface Plasmon Resonance; D013997:Time Factors; D014018:Tissue Distribution
D002241:Carbohydrates; D037102:Lectins; D037181:Lectins, C-Type; D008024:Ligands; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011134:Polysaccharides; D011956:Receptors, Cell Surface; D013455:Sulfur; D008358:Mannose