Early steps in O-linked glycosylation and clustered O-linked glycans of herpes simplex virus type 1 glycoprotein C: effects on glycoprotein properties.
The pathogenesis of herpes simplex virus type 1 (HSV-1) implies the sequential infection of many cell types from mucosal cells to neurons, each having a unique pattern of protein glycosylation. The HSV-1 glycoprotein gC-1 is highly glycosylated and contains not only N-linked glycans but also a large number of O-linked glycans, some of which are clustered into two pronase-resistant arrays in the vicinity of the HSV-1 receptor-binding domain of gC-1. The aim of the present study was to characterize gC-1 signals for addition of clustered glycans, to determine the efficacy of synthetic peptides, representing putative O-glycosylation signals, as substrates for a panel of GalNAc transferases, and to identify possible effects of early O-linked glycosylation on the biological functions of gC-1. Gel filtration analysis of the pronase-resistant gC-1 O-glycan clusters from a glycoprotein mutant, lacking a site for N-linked glycosylation at Asn 73 in the vicinity of the O-glycosylation signal, suggested that one function of this N-linked glycan was to modulate the access for GalNAc transferases to one particular O-glycosylation peptide signal (aa 80-104). The ability of four GalNAc-transferase isoenzymes with different cell type expression patterns to initialize O-glycosylation of synthetic gC-1 derived peptides was analyzed. Two synthetic gC-1 peptides (aa 55-69 and aa 80-104) were excellent substrates for all four GalNAc-transferases, suggesting that cell types expressing less frequent GalNAc transferase species with unusual acceptor peptide sequence specificities may also produce a highly O-glycosylated gC-1 after HSV-1 infection. The O-linked glycans were not essential for cell surface expression of gC-1, but monoclonal antibody-assisted epitope analysis of N-acetylgalactosaminidase-treated gC-1 showed that the O-linked monosaccharide GalNAc contributed to expression of a three-dimensional epitope overlapping the heparan sulfate-binding domain of gC-1.
Biller
M
M
Department of Virology, University of Göteborg, Guldhedsgatan 10B, S-413 46 Göteborg, Sweden.
Mårdberg
K
K
Hassan
H
H
Clausen
H
H
Bolmstedt
A
A
Bergström
T
T
Olofsson
S
S
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002522:Chlorocebus aethiops; D006031:Glycosylation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011134:Polysaccharides / Q000378:metabolism*; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D011134:Polysaccharides; D014759:Viral Envelope Proteins; C038535:glycoprotein gC, herpes simplex virus type 1