Basic amino acids as modulators of an O-linked glycosylation signal of the herpes simplex virus type 1 glycoprotein gC: functional roles in viral infectivity.
The herpes simplex virus type 1 (HSV-1) glycoprotein gC-1 is engaged both in viral attachment and viral immune evasion mechanisms in the infected host. Besides several N-linked glycans, gC-1 contains numerous O-linked glycans, mainly localized in two pronase-resistant clusters in the N-terminal domain of gC-1. In the present study we construct and characterize one gC-1 mutant virus, in which two basic amino acids (114K and 117R) in a putative O-glycosylation sequon were changed to alanine. We found that this modification did not modify the N-linked glycosylation but increased the content of O-linked glycans considerably. Analysis of the O-glycosylation capacity of wild-type and mutant gC-1 was performed by in vitro glycosylation assays with synthetic peptides derived from the mutant region predicted to present new O-glycosylation sites. Thus the mutant peptide region served as a better substrate for polypeptide GalNAc-transferase 2 than the wild-type peptide, resulting in increased rate and number of O-glycan attachment sites. The predicted increase in O-linked glycosylation resulted in two modifications of the biological properties of mutant virus-that is, an impaired binding to cells expressing chondroitin sulfate but not heparan sulfate on the cell surface and a significantly reduced plaque size in cultured cells. The results suggested that basic amino acids present within O-glycosylation signals may down-regulate the amount of O-linked glycans attached to a protein and that substitution of such amino acid residues may have functional consequences for a viral glycoprotein involving virus attachment to permissive cells as well as viral cell-to-cell spread.
Mårdberg
Kristina
K
Department of Virology, University of Göteborg, Guldhedsgatan 10B; S-413 46 Göteborg, Sweden.
Nyström
Kristina
K
Tarp
Mads Agervig
MA
Trybala
Edward
E
Clausen
Henrik
H
Bergström
Tomas
T
Olofsson
Sigvard
S
D000818:Animals; D002460:Cell Line; D002809:Chondroitin Sulfates / Q000378:metabolism*; D005700:Galactosyltransferases / Q000737:chemistry; D006031:Glycosylation; D006497:Heparan Sulfate / Q000378:metabolism*; D018259:Herpesvirus 1, Human / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D051379:Mice; D011134:Polysaccharides / Q000378:metabolism*; D011402:Pronase / Q000737:chemistry; D011499:Protein Processing, Post-Translational / Q000235:genetics / Q000502:physiology*; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014774:Virulence / Q000235:genetics / Q000502:physiology
D002809:Chondroitin Sulfates; D005700:Galactosyltransferases; D006497:Heparan Sulfate; D011134:Polysaccharides; D011402:Pronase; D014759:Viral Envelope Proteins; C038535:glycoprotein gC, herpes simplex virus type 1; C032545:UDPgalactose-N-acetylgalactosamine galactosyltransferase