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1.A.41 The Avian Reovirus p10 Viroporin (p10 Viroporin) Family

Structure-function traits common to all viroporins are their small sizes (ca. 60-120 aa), high hydrophobicities, and the presence of helical domains that transverse the membrane and assemble into oligomeric-permeating structures (Largo et al. 2016).  The p10 protein is a membrane fusion/permeabilization protein encoded within the genomes of avian reoviruses. It is required for the virus to permeabilize cells during late infection and plays a role in virus-host interactions. Expression in bacterial cells arrests cell growth and enhances membrane permeability (Bodelón et al., 2002). The fusogenic extracellular N-terminal domain is not required for permeability. Therefore, it is a bifunctional protein where the two functions are associated with different domains. It is a small type I protein with 1 TMS (residues 43-63), its N-terminus out and its C-terminus in. 

Novel pathways leading to disease stimulated by viroporin ion conduction, such as inflammasome driven immunopathology have been described (Nieto-Torres et al. 2015).  A two stage folding/insertion mechanism for viroporins has been suggested (Martinez-Gil and Mingarro 2015).  These proteins are crucial for the pathogenicity and replication of viruses as they aid in various stages of the viral life cycle, from genome uncoating to viral release. In addition, the ion channel activities of viroporins cause disruption of cellular ion (Ca2+) homeostasis. Fluctuation in the calcium level triggers activation of host defensive programmed cell death pathways as well as the inflammasome, which in turn are being subverted for the viruses' replication benefits (Sze and Tan 2015).  The involvement of viroporins in virus-induced ER stress and autophagy has been discussed (Fung et al. 2015).

The reaction catalyzed by p10 is:

Ions (in)  ions (out)

References associated with 1.A.41 family:

Bodelón, G., L. Labrada, J. Martínez-Costas, and J. Benavente. (2002). Modification of late membrane permeability in avian reovirus-infected cells. J. Biol. Chem. 277: 17789-17796. 11893756
Fung, T.S., J. Torres, and D.X. Liu. (2015). The Emerging Roles of Viroporins in ER Stress Response and Autophagy Induction during Virus Infection. Viruses 7: 2834-2857. 26053926
Largo, E., C. Verdiá-Báguena, V.M. Aguilella, J.L. Nieva, and A. Alcaraz. (2016). Ion channel activity of the CSFV p7 viroporin in surrogates of the ER lipid bilayer. Biochim. Biophys. Acta. 1858: 30-37. 26464198
Martinez-Gil, L. and I. Mingarro. (2015). Viroporins, Examples of the Two-Stage Membrane Protein Folding Model. Viruses 7: 3462-3482. 26131957
Nieto-Torres, J.L., C. Verdiá-Báguena, C. Castaño-Rodriguez, V.M. Aguilella, and L. Enjuanes. (2015). Relevance of Viroporin Ion Channel Activity on Viral Replication and Pathogenesis. Viruses 7: 3552-3573. 26151305
Sze, C.W. and Y.J. Tan. (2015). Viral Membrane Channels: Role and Function in the Virus Life Cycle. Viruses 7: 3261-3284. 26110585