Abstract
Hepatitis B Virus (HBV) glycobiology has been an area of intensive research in the last decades and continues to be an attractive topic due to the multiple roles that N-glycosylation in particular plays in the virus life-cycle and its interaction with the host that are still being discovered. The three HBV envelope glycoproteins, small (S), medium (M) and large (L) share a very peculiar N-glycosylation pattern, which distinctly regulates their folding, degradation, assembly, intracellular trafficking and antigenic properties. In addition, recent findings indicate important roles of N-linked oligosaccharides in viral pathogenesis and evasion of the immune system surveillance. This review focuses on N-glycosylation’s contribution to HBV infection and disease, with implications for development of improved vaccines and antiviral therapies.
Highlights
Attachment of oligosaccharides to Asn residues within consensus sequences (Asn-X-Ser/Thr) of nascent polypeptides, known as N-linked glycosylation, is both a highly conserved and the most abundant protein modification occurring in the endoplasmic reticulum (ER) of eukaryotic cells [1].it is not surprising that this process has crucial consequences on the fate of resulting glycoproteins by regulating their folding into the native conformation, trafficking and stability.Most enveloped viruses take advantage of this host-specific pathway to glycosylate own surface proteins, with important consequences at different stages of their lifecycles.Hepatitis B Virus (HBV) is a human pathogen and a member of the Hepadnaviridae family of DNA viruses with liver tropism
I removes the remaining three α1-2-linked Man units, with formation of (GlcNAc)2 Man5-7 intermediates [13,14]. This trimming provides the substrates for subsequent processing by Golgi α-mannosidase II and various glycosyl-transferases in medial and trans-Golgi compartments, resulting in the complex N-glycan structures of mature viral particles and subviral particles (SVPs) leaving the cell via multivesicular bodies (MVBs) and the constitutive secretory pathway, respectively [26]
Lifecycle, we are able to understand, at least in part, the multiple facets of N-glycosylation and the role played in the HBV biology
Summary
Attachment of oligosaccharides to Asn residues within consensus sequences (Asn-X-Ser/Thr) of nascent polypeptides, known as N-linked glycosylation, is both a highly conserved and the most abundant protein modification occurring in the endoplasmic reticulum (ER) of eukaryotic cells [1]. HBV-infected hepatocytes produce 42 nm infectious virions, consisting in a nucleocapsid protected by a lipid membrane harboring the small (S), medium (M) and large (L) surface (envelope) glycoproteins. These transmembrane proteins are translated from the same open reading frame (ORF) and have a common carboxy-terminal end, corresponding to the S sequence. Asn-146 (N146) of the S domain; this is functional in about half of all envelope proteins, resulting in similar amounts of glycosylated and non-glycosylated S, M and L isoforms (Figure 1). 9, 1404 of 15 in the cytoplasm and the ER lumen [6,7] (Figure 1) These sites are conserved among all HBV genotypes, indicating instrumental roles in biosynthesis and function of the envelope proteins [8].
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