title: Glycosylation of BRI2 on asparagine 170 is involved in its trafficking to the cell surface but not in its processing by furin or ADAM10.
abstract: Two different mutated forms of BRI2 protein are linked with familial British and Danish dementias, which present neuropathological similarities with Alzheimer's disease. BRI2 is a type II transmembrane protein that is trafficked through the secretory pathway to the cell surface and is processed by furin and ADAM10 (a disintegrin and metalloproteinase domain 10) to release secreted fragments of unknown function. Its apparent molecular mass (42-44 kDa) is significantly higher than that predicted by the number and composition of amino acids (30 kDa) suggesting that BRI2 is glycosylated. In support, bioinformatics analysis indicated that BRI2 bears the consensus sequence Asn-Thr-Ser (residues 170-173) and could be N-glycosylated at Asn170. Given that N-glycosylation is considered essential for protein folding, processing and trafficking, we examined whether BRI2 is N-glycosylated. Treatment of HEK293 (human embryonic kidney) cells expressing BRI2 with the N-glycosylation inhibitor tunicamycin or mutation of Asn170 to alanine reduced its molecular mass by ~2 kDa. These data indicate that BRI2 is N-glycosylated at Asn170. To examine the effect of N-glycosylation on BRI2 trafficking at the cell surface, we performed biotinylation and (35)S methionine pulse-chase experiments. These experiments showed that mutation of Asn170 to alanine reduced BRI2 trafficking at the cell surface and its steady state levels at the plasma membrane. Furthermore, we obtained data indicating that this mutation did not affect cleavage of BRI2 by furin or ADAM10. Our results confirm the theoretical predictions that BRI2 is N-glycosylated at Asn170 and show that this post-translational modification is essential for its expression at the cell surface but not for its proteolytic processing.
authors.affiliation: Division of Animal and Human Physiology, Department of Biology, National and Kapodistrian University of Athens, 157 84 Panepistimiopolis, Ilisia, Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Tsachaki
authors.forename: Despina
authors.initials: D
authors.lastname: Serlidaki
authors.forename: Andriana
authors.initials: A
authors.lastname: Fetani
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Zarkou
authors.forename: Ismini
authors.initials: I
authors.lastname: Rozani
authors.forename: Jorge
authors.initials: J
authors.lastname: Ghiso
authors.forename: Spiros
authors.initials: S
authors.lastname: Efthimiopoulos
mesh_terms: D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism*; D000072197:ADAM10 Protein; D048868:Adaptor Proteins, Signal Transducing; D053829:Amyloid Precursor Protein Secretases / Q000235:genetics / Q000378:metabolism*; D001216:Asparagine / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D045683:Furin / Q000378:metabolism*; D006031:Glycosylation; D057809:HEK293 Cells; D006801:Humans; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C120083:ITM2B protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D001216:Asparagine; D053829:Amyloid Precursor Protein Secretases; D045683:Furin; D051722:ADAM Proteins; D000072197:ADAM10 Protein; C491236:ADAM10 protein, human