A novel heterodimeric transferrin receptor encoded by a pair of VSG expression site-associated genes in T. brucei.
In T. brucei, a transferrin-binding protein has been found to share sequence homology with pESAG-7 and -6, the products of two related genes present in the VSG gene polycistronic transcription unit. When expressed in Xenopus oocytes, they appear as N-glycosylated proteins secreted in the medium (pESAG-7) and GPI anchored to the membrane (pESAG-6). These proteins are able to homo- or heterodimerize, probably through association in the same orientation. Only heterodimers can bind Tf, possibly two molecules per dimer. A comparison of Tf binding to pESAG-7/6-expressing oocytes and trypanosomes suggests that pESAG-7/6 is the Tf receptor of the parasite. In trypanosomes, the majority of pESAG-7/6 is released from the membrane and associates, together with Tf, with a glycosylated matrix present in the lumen of the flagellar pocket. Both pESAG-7/6 and Tf are internalized via coated pits and vesicles. These observations suggest a novel mode of Tf binding and uptake in trypanosomes.
Department of Molecular Biology, University of Brussels, Rhode St. Genèse, Belgium.
D
D
Salmon
M
M
Geuskens
F
F
Hanocq
J
J
Hanocq-Quertier
D
D
Nolan
L
L
Ruben
E
E
Pays
D000595:Amino Acid Sequence; D000818:Animals; D000913:Antibodies, Protozoan; D003593:Cytoplasm / Q000737:chemistry; D004705:Endocytosis; D017125:Genes, Protozoan; D006023:Glycoproteins; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D009865:Oocytes; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D011485:Protein Binding; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000276:immunology; D014346:Trypanosoma brucei brucei / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000032:analysis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014982:Xenopus laevis
D000913:Antibodies, Protozoan; D006023:Glycoproteins; D008565:Membrane Proteins; D010455:Peptides; D015800:Protozoan Proteins; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D014643:Variant Surface Glycoproteins, Trypanosoma; C078011:ESAG 7 protein, Trypanosoma brucei