Development of effective and safe medication for the treatment of viral infections remains a major challenge for the pharmaceutical industry in the 21st Century. There are numerous problems with the existing antiviral treatments both in terms of their safety and, in some cases, their cost, and they cannot be used generally but only in special circumstances. However, the threat of viral diseases ranging from AIDS and hepatitis C to influenza is increasing each year and there is considerable interest in safer and more generally applicable alternative treatments. It has been recognized for some time that some viruses have glycosylation features that are essential to their infectivity, but a means of providing a therapeutic route that is based on this has not been easy to exploit. In recent years, a number of possible approaches have been investigated and some of these are now considered to be realistic forms of therapy. Generally, approaches based on inhibition of the host machinery to glycosylate viral proteins or the ability of compounds to mimic the surface glycosylation of the virus seem to offer the best potential approaches. In this mini-review article, we look at recent advances in both of these areas and their potential to provide a new arsenal of antiviral therapeutics for AIDS, hepatitis C and influenza. Some of these are now entering clinical trials and others are at an advanced stage of preclinical development, but all of them represent good candidates for a therapy that could be more resilient to the problems of viral mutation and diversity.
Glycoproteins are proteins that contain covalently bound oligosaccharides (glycans). Although there are structural features of N ‐ and O ‐linked glycans common to all eukaryotes, species‐specific glycosylation reactions create a wide diversity of structures. This is particularly relevant to cell surface glycoproteins although intracellular and even nuclear proteins may be glycosylated. The factors controlling glycosylation are complex and include the protein sequence and structure, specificity of relevant transferase enzymes, availability of donor sugars and other environmental factors. These may all interact so it is not surprising that there is great variety in glycosylation even on the same protein. Glycosylation of proteins is important in such areas as development and interaction with pathogens and provides a means of modifying the function of proteins that is not directly dependent on their deoxyribonucleic acid (DNA) template. Interest in the field is growing and advances in analytical technology now make the field accessible to a wider community. Key Concepts: Proteins are frequently modified posttranslationally, the most frequent modification being glycosylation. Glycosylation may play an important role in protein folding through interaction with the chaperones calnexin and calreticulin. It has been calculated that as many as 70% of all proteins may be glycosylated. The glycosylation of a protein may vary extensively depending on the cell in which it is produced which may enable the same protein to function in different ways depending where it is expressed. On the cell surface, glycoprotein glycans are frequently involved in cell–cell interactions. Glycosylation of the same protein may change during development or in maturation, for example in cells of the immune system. Glycosylation differs between species even if they are closely related, for example between great apes and man. Analysis of glycosylation has progressed in recent years and is now almost a routine procedure. Particular features of glycosylation may only have functional significance in a particular time and place but can be widely distributed which can make assignment of function to glycan structure difficult.
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