title: Analysis and function of prototype foamy virus envelope N glycosylation.
abstract: The prototype foamy virus (PFV) glycoprotein, which is essential for PFV particle release, displays a highly unusual biosynthesis, resulting in posttranslational cleavage of the precursor protein into three particle-associated subunits, i.e., leader peptide (LP), surface (SU), and transmembrane (TM). Glycosidase digestion of metabolically labeled PFV particles revealed the presence of N-linked carbohydrates on all subunits. The differential sensitivity to specific glycosidases indicated that all oligosaccharides on LP and TM are of the high-mannose or hybrid type, whereas most of those attached to SU, which contribute to about 50% of its molecular weight, are of the complex type. Individual inactivation of all 15 potential N-glycosylation sites in PFV Env demonstrated that 14 are used, i.e., 1 out of 2 in LP, 10 in SU, and 3 in TM. Analysis of the individual altered glycoproteins revealed defects in intracellular processing, support of particle release, and infectivity for three mutants, having the evolutionarily conserved glycosylation sites N8 in SU or N13 and N15 in the cysteine-rich central "sheets-and-loops" region of TM inactivated. Examination of alternative mutants with mutations affecting glycosylation or surrounding sequences at these sites indicated that inhibition of glycosylation at N8 and N13 most likely is responsible for the observed replication defects, whereas for N15 surrounding sequences seem to contribute to a temperature-sensitive phenotype. Taken together these data demonstrate that PFV Env and in particular the SU subunit are heavily N glycosylated and suggest that although most carbohydrates are dispensable individually, some evolutionarily conserved sites are important for normal Env function of FV isolates from different species.
authors.affiliation: Institut für Virologie, Medizinische Fakultät "Carl Gustav Carus," Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lüftenegger
authors.forename: Marcus
authors.initials: M
authors.lastname: Picard-Maureau
authors.forename: Nicole
authors.initials: N
authors.lastname: Stanke
authors.forename: Axel
authors.initials: A
authors.lastname: Rethwilm
authors.forename: Dirk
authors.initials: D
authors.lastname: Lindemann
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D006031:Glycosylation; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D016092:Spumavirus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D013696:Temperature; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014771:Virion / Q000378:metabolism
chemical_list: D014759:Viral Envelope Proteins