1.A.98 The Human T-Lymphotropic Virus 1 P13 protein (HTLV1-P13) Family Human T-cell leukemia virus type-1 (HTLV-1) encodes a mitochondrial protein named p13. p13 mediates an inward K⁺ current in isolated mitochondria that leads to mitochondrial swelling, depolarization, increased respiratory chain activity and reactive oxygen species (ROS) production. These effects trigger the opening of the permeability transition pore and are dependent on the presence of K⁺ and on the amphipathic α-helical domain of p13. In the context of cells, p13 acts as a sensitizer to selected apoptotic stimuli. It shares some structural and functional analogies with viroporins, a class of small integral membrane proteins that form pores and alter membrane permeability (Silic-Benussi et al. 2010). p13 is essential for the establishment and maintenance of HTLV-1 infection in vivo (Edwards et al. 2011).
References:
Edwards, D., C. Fenizia, H. Gold, M.F. de Castro-Amarante, C. Buchmann, C.A. Pise-Masison, and G. Franchini. (2011). Orf-I and orf-II-encoded proteins in HTLV-1 infection and persistence. Viruses 3: 861-885.
Georgieva, E.R., P.P. Borbat, C. Fanouraki, and J.H. Freed. (2020). High-yield production in E. coli and characterization of full-length functional p13 protein from human T-cell leukemia virus type 1. Protein Expr Purif 105659. [Epub: Ahead of Print]
Hyser, J.M. and M.K. Estes. (2015). Pathophysiological Consequences of Calcium-Conducting Viroporins. Annu Rev Virol 2: 473-496.
Silic-Benussi, M., O. Marin, R. Biasiotto, D.M. D''Agostino, and V. Ciminale. (2010). Effects of human T-cell leukemia virus type 1 (HTLV-1) p13 on mitochondrial K⁺ permeability: A new member of the viroporin family? FEBS Lett. 584: 2070-2075.
Examples:
TC#	Name	Organismal Type	Example
1.A.98.1.1	HTLV-1 P13 viroporin of 87 aas. Transports K⁺ (Hyser and Estes 2015). Large protein conformation changes occur upon transitioning from the soluble to the membrane-bound state. p13(II)-assisted transport of K⁺ suggests an involvement in the control of the transmembrane potential (*Georgieva et al.* 2020**).	Viruses	P13 of Human T-cell leukemia (lymphotropic) virus type-1 (C6L855)

1.A.98.1.2	The Tax protein of 58 aas.		Tax of Human T-cell leukemia virus 3 (HTLV-3) (Human T-lymphotropic virus 3)

1.A.98.1.3	p30 protein of 177 aas and 1 or 2 TMSs		p30 protein of Human T-cell leukemia virus type I