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1.A.99 The Infectious Bronchitis Virus Envelope Small Membrane Protein E (IBV-E) Family. 

The E protein is a 108 aa, 2 TMS protein belived to be a viroporin.  It interacts with the membrane (M) protein (Lim et al. 2001). The E protein is a component of the viral envelope that plays a central role in virus morphogenesis and assembly. It seems to be important for creating the membrane curvature needed to acquire the rounded, stable and infectious particle phenotype. The E protein acts as a viroporin, inducing the formation of hydrophilic pores in cellular membranes, and it induces apoptosis.

References associated with 1.A.99 family:

Li, S., L. Yuan, G. Dai, R.A. Chen, D.X. Liu, and T.S. Fung. (2019). Regulation of the ER Stress Response by the Ion Channel Activity of the Infectious Bronchitis Coronavirus Envelope Protein Modulates Virion Release, Apoptosis, Viral Fitness, and Pathogenesis. Front Microbiol 10: 3022. 32038520
Lim, K.P., H.Y. Xu, and D.X. Liu. (2001). Physical interaction between the membrane (M) and envelope (E) proteins of the coronavirus avian infectious bronchitis virus (IBV). Adv Exp Med Biol 494: 595-602. 11774531
Pendleton, A.R. and C.E. Machamer. (2008). Generating antibodies to the gene 3 proteins of infectious bronchitis virus. Methods Mol Biol 454: 163-189. 19057877