Influenza virus, M2 protein

Pinto EH, Holsinger LJ, Lamb RA (1992) Influenza virus M2 protein has ion channel activity. Cell 69 517-528... 

Channel-forming proteins exhibit a number of structural motifs the influenza virus M2 proton channel and voltage-gated channels for K+, Na+ and Ca2+are all composed of four identical subunits that aggregate to form a central pore as shown in Fig. 5.7 an acid sensing Na+ ion channel has a similar structure but with threefold symmetry Ca2+ release channels, the divalent metal ion transporter CorA, the... 

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. 

C. Wang, K. Takeuchi, L. Pinto, and R. Lamb. Ion channel activity of influenza A virus M2 protein — Characterization of the amantadine block. J. Virology, 67 (1993) 5585-5594. 

Currently, two classes of drugs are available with antiviral activity against influenza viruses inhibitors of the ion channel activity of the M2 membrane protein, amantadine and rimantadine, and the neuraminidase inhibitors oseltamivir, and zanamivir. H5N1 viruses isolated from poultry and humans in Thailand and Viet Nam in 2004 invariably showed an amantadine-resistance indicating that amantadine treatment is not an option during the ongoing outb-treak in South-East Asia. 

Budding and release of progeny virus. B. Replicative cycle of an influenza virus, an example of an RNA virus. 1. Attachment. 2. Endocytosis. 3. Influx of H+ through M2 protein. 4. Fusion of the viral envelope with the endosomes membrane, dissociation of the RNP complex, and entry of viral RNA into the nucleus. 5. Synthesis of viral mRNA by viral RNA polymerase. 6. Translation of viral mRNA by host cell s ribosomes. 7. Replication of viral RNA, using viral RNA polymerase, via cRNA replicative form. 8. Assembly of virus particles, and 9. Budding and release of progeny virus. 

Mechanism of Action A dopaminergic agonist that blocks the uncoating of influenza A virus, preventing penetration into the host and inhibiting M2 protein in the assembly of progeny virions. Amantadine also blocks the reuptake of dopamine into presyn-aptic neurons and causes direct stimulation of postsynaptic receptors. Therapeutic Effect Antiviral and antiparkinsonian activity. 

Channels internal walls and external mouths contain groups that are easily ionized, such as tyrosine, or protonated, such as tryptophan, and are likely to be affected by changes in pH. The M2 transmembrane protein, encoded by influenza viruses, forms a tetrameric transmembrane channel for protons when it infects cells [15]. 

Fluorotryptophan (F-Trp) was one of the first labels used for investigation of peptides and proteins by 19F NMR. Both 5- and 6-fluorotryptophan are commercially available. In this case, orientational constraints and distance measurements are very useful for obtaining information about the side-chain conformation [74, 75], The tryptophan side-chain is often found to anchor transmembrane helices in the lipid head-group region of the membrane and it often plays a functional role in peptides that form channels in the membrane, such as gramicidin A [74, 76] or the influenza virus peptide M2 [75], Fluorotryptophans are easily incorporated into peptides and proteins using biosynthetic and SPPS protocols. 

The influenza virus is an RNA-(—)- virus and possesses its own RNA polymerase enzyme. The complete RNA genome codes for eight proteins - two structural (matrix) proteins M, and M2, haemagglutinin, and neuraminidase and four proteins involved in replication, three of which make up the polymerase enzyme. Substrates for this are the usual ribonucleosides and there has been some success with the use of nucleoside analogues as inhibitors of the enzyme. The drug ribavirin has been the most successful, although this has to be administered by aerosol. These days, its major use is for the treatment of infections caused by respiratory syncytial viruses (especially in children), since these can cause long-term morbidity. 

The transmembrane portion of the M2 protein from the influenza A virus has been studied in hydrated DMPC lipid bilayers with solid-state NMR.209 Orientational constraints are obtained from the isotopically labeled peptide samples mechanically aligned between thin glass plates. I5N chemical shifts from single-site labeled samples constrain the molecular frame with respect to... 

Amantadine (Scheme 8,3), and rimantadine (Scheme 8,4) are active against influenza A viruses. The action of these closely related agents is complex and incompletely understood, but they are believed to block cellular membrane ion channels [37,38], Both drugs target the influenza A matrix protein (M2). Drug-treated cells are unable to lower the pH of the endosomal compartment (a function normally controlled by the M2 gene product), a process which is essential to induce conformational changes in the HA protein to permit membrane fusion. 

Chekmenev, E.Y., Hu, J., Gor kov, P.L. et al. 2005. N and P solid-state NMR study of transmembrane domain alignment of M2 protein of influenza A virus in hydrated cylindrical lipid bilayers confined to anodic aluminum oxide nanopores. J. Magn. Reson. 173 322-327. 

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