Viral uncoating

Diana GD, Otto MJ, McKinlay MA. Inhibitors of viral uncoating. Pharmacol Ther 1985 24 287-297. 

De Clercq E, Yamamoto N, Pauwels R, Baba M, Schols D, Nakashima H, Balzarini J, Debyser Z, Murrer BA, Schwartz D, Thornton D, Bridger G, Fricker S, Henson G, Abrams M, Picker D. Potent and selective inhibition of human immunodeficiency virus (HIV)-l and HIV-2 replication by a class of bicyclams interacting with a viral uncoating event. Proc Natl Acad Sci USA 1992 89 5286-5290. 

Bayer N, Schober D, Prchla E, Murphy RE, Blaas D, Fuchs R. Effect of bafi-lotnycin Al and nocodazole on endocytic transport in HeLa cells implications for viral uncoating and infection. J Virol 1998 72(12) 9645-9655. 

Rozhon E, Cox S, Buontempo P, et al. SCH-38057—a picornavirus capsid-binding molecule with antiviral activity after the initial stage of viral uncoating. Antivir Res 1993 21(1) 15—35. 

Mode of action The precise antiviral mechanism of amantadine and rimantadine remains to be established. Recent evidence points to a blockade of the viral membrane matrix protein, M2, which functions as an ion channel. This channel is required for the fusion of the viral membrane with the cell membrane that ultimately forms the endosome (created when the virus is internalized by endocytosis). [Note The acid environment of the endosome is required for viral uncoating.] These drugs may also interfere with the release of new virions. 

With one exception (Smith et al, 1996), all the studies of complexes of viruses with other proteins are hybrids of cryo-EM for the complex and crystallography for its components. The fitting of atomic models within cryo-EM density maps has revealed the relative positioning of structural components of viruses, and their receptors or antibodies, and has afforded insights into the mechanisms of cell invasion, viral uncoating, and immune recognition. 

Rimantadine hydrochloride, an alpha-methyl derivative of amantadine (alpha-methyl-l-adamantane methylamine hydrochloride), is more active than amantadine against influenza A viruses in vitro and in laboratory animals. It is an alternative to amantadine for the prevention and treatment of influenza A virus infections in adults and for the prevention of influenza in children. Adverse effects have been considered to be less common with rimantadine (SEDA-8, 143), and it is generally tolerated better than amantadine, because it causes fewer nervous system adverse effects (1). Unfortunately, rimantadine is more costly, which has led many institutions to develop influenza treatment guidelines. Both drugs work by blocking the M2 ion channel, which is needed to affect a pH change that helps to initiate viral uncoating. 

Antiviral MEchaniyn noi htliy undemood—appears to blodc the viral uncoating of influenza. Antiparfcinson Mechanism not fully understood—appears to increase dopamine release, biock dopamine reuptake, and stimulate dopamine receptors. 

This drug interferes at virtually all stages of viral replication—viral uncoating. RNA transcription, protein synthesis, and the assembly of new virions. 

MECHANISMS OF ACTION AND RESISTANCE Amantadine and rimantadine inhibit an early step in viral replication, probably viral uncoating for some strains, they also have an effect on a late step in viral assembly probably mediated through altering hemagglutinin processing. The primary locus of action is the influenza A virus M2 protein, an integral membrane protein that functions as an ion channel. 

Figure 7. Proposed model for the role of N-formylated HIV-1 p24 . A fraction of the formylated HIV-1 p24 raises the possibility that N-formylation plays a promotion role in core disassembly during viral uncoating.

Both amantadiae and rknantadiae have been found to reduce the duration of influenza A-iaduced fever and malaise, and to lessen viral shedding. Prophylactic treatment has been recommended for high risk patients (95). It has been suggested that, ia the presence of amantadine, the influenza vims attaches normally to cells, but once iaside the ceU the vims fails to initiate repHcation. Thus amantadine appears to inhibit the initiation of transcription at an early stage between uncoating and viral-specific RNA synthesis (96). 

Other viral targets Attachment proteins Fusion proteins Disassembly/Uncoating... 

In general terms, four main stages can be recognized in the multiplication of human viruses, (i) attachment (ii) penetration and uncoating (iii) production of viral proteins and replication of viral nucleic acid, (iv) assembly and release of progeny viruses. 

Penetration. After fusion of viral and host membranes, or uptake into a phagosome, the virus particle is carried into the cytoplasm across the plasma membrane. This penetration process is an active one that requires expenditure of energy by the cell. At this stage the envelope and the capsid are shed, and the viral nucleic acids are released. The uncoating of virus accounts for the drop in infectious virus assayed, because the uncoated virus cannot withstand the assay conditions. 

Kundu et al.64 used MEKC conditions to assess the purity of two recombinant proteins a cytomegalovirus-CMP-KDO synthetase fusion protein expressed in E. coli and a hepatitis C viral protein expressed in CHO cells. Proteins were prepared in a 10-mM Tris-1% SDS buffer (pH 8.5) and analyzed in a 10-mM borate-100-mM SDS buffer (pH 9.5) in uncoated capillaries. The level of impurities, which varied with the method of protein production, agreed within 5% with results obtained by densitometric scanning of SDS-PAGE gels of the same materials. 

Amantadine (C) specifically affects the replication of influenza A (RNA) viruses, the causative agent of true influenza. These viruses are endocytosed into the cell. Release of viral DNA requires protons from the acidic content of endosomes to penetrate the virus. Presumably, amantadine blocks a channel protein in the viral coat that permits influx of protons thus, uncoating is prevented. Moreover, amantadine inhibits viral maturation. The drug is also used prophylactically and, if possible, must be taken before the outoreak of symptoms. It also is an antiparkinsonian... 

Although the specific details of replication vary among types of viruses, the overall process can be described as consisting of five phases (1) attachment and penetration, (2) uncoating, (3) synthesis of viral components, (4) assembly of virus particles, and (5) release of the... 

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