Glycobiology Advance Access originally published online on January 26, 2005
Glycobiology 2005 15(6):655-666; doi:10.1093/glycob/cwi046
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Glycobiology vol. 15 no. 6 © Oxford University Press 2005; all rights reserved.
N-glycosylation at one rabies virus glycoprotein sequon influences N-glycan processing at a distant sequon on the same molecule
2 Department of Pathology, College of Physicians and Surgeons of Columbia University, 630 West 168th Street, New York, NY 10032; 3 Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-Mizuhoku, Nagoya 467-8603, Japan; 4 Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104; 5 Shoshin Group, 24 Milk Street, Newburyport, MA 01950; 6 Department of Anatomy and Cell Biology, University of Pennsylvania, School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104; and 7 The Wistar Institute, 3601 Spruce Street, Philadelphia, PA 19104
1 To whom correspondence should be addressed; e-mail: ss2479{at}columbia.edu
Received on December 28, 2004; revised on January 22, 2005; accepted on January 24, 2005
Rabies glycoprotein (RGP(WT)) contains N-glycosylation sequons at Asn37, Asn247, and Asn319, although Asn37 is not efficiently glycosylated. To examine N-glycan processing at Asn247 and Asn319, full-length glycosylation mutants, RGP(-2-) and RGP(--3), were expressed, and Endo H sensitivity was compared. When the Asn247 sequon is present alone in RGP(-2-), 90% of its N-glycans are high-mannose type, whereas only 35% of the N-glycans at Asn319 in RGP(--3) are high-mannose. When both sequons are present in RGP(-23), 87% of the N-glycans are of complex type. The differing patterns of Endo H sensitivity at sequons present individually or together suggests that glycosylation of one sequon affects glycosylation at another, distant sequon. To explore this further, we constructed soluble forms of RGP: RGP(WT)T441His and RGP(--3)T441His. Tryptic glycopeptides from these purified secreted proteins were isolated by HPLC and characterized by a 3D oligosaccharide mapping technique. RGP(WT)T441His had fucosylated, bi- and triantennary complex type glycans at Asn247 and Asn319. However, Asn247 had half as many neutral glycans, more monosialylated glycans, and fewer disialylated glycans when compared with Asn319. Moreover, when comparing the N-glycans at Asn319 on RGP(--3)T441His and RGP(WT)T441His, the former had 30% more neutral, 28% more monosialylated, and 33% fewer disialylated glycans. This suggests that the N-glycan at Asn247 allows additional N-glycan processing to occur at Asn319, yielding more heavily sialylated bi- and triantennary forms. The mechanism(s) by which glycosylation at one sequon influences N-glycan processing at a distant sequon on the same glycoprotein remains to be determined.
Key words: N-glycan processing / N-glycosylation / rabies virus glycoprotein / sequon N-glycosylation