1.A.89 The Human Coronavirus 229E Viroporin (229E Viroporin) Family
A locus located between the spike and envelope genes is conserved in all coronaviruses and contains a complete or truncated open reading frame (ORF). Zhang et al. 2013 demonstrated that ORF4a of the human coroavirus 229E is similar to a viroporin, ORF3a, from the severe acute respiratory syndrome coronavirus (SARS-CoV). ORF4a forms ion channels and regulates virus release. When ORF4a proteins were expressed in infected cells, they localized to the endoplasmic reticulum/Golgi intermediate compartment (ERGIC) and formed homo-oligomers through disulfide bridges that possessed ion channel activity in both Xenopus oocytes and yeast. Based on the measurement of conductance to different monovalent cations, ORF4a appeared to form a non-selective channel for monovalent cations. Viral production decreased when ORF4a protein expression was suppressed by siRNA in infected cells. Thus, the HCoV-229E ORF4a protein is functionally analogous to the SARS-CoV ORF3a protein which also acts as a viroporin to regulates virus production.
References:
ORF4a viroporin of 133 aas and 3 TMSs (Zhang et al. 2013).
Virus
ORF4a of human coronavirus 229E
Viroporin of 222 aas and 3 strongly hydrophobic TMSs in the N-terminal half of the protein followed by a region of moderate hydrophobicity in the C-terminal half.
Virus
Viroporin of human coronavirus NL63
Non structural protein 3c, a viroporin of 237 aas with 3 stronly hydrophobic TMSs in the N-terminal half of the protein and a broad region of moderate hydrophobicity in the second half.
Virus
Viroporin 3c of feline coronavirus UUF
Viroporin ORF3-1 of 205 aas and 4 or more TMSs in a 3 + 1-3 TMS arrangement.
Viruses
Orf3-1 viroporin of porcine respiratory coronavirus
3a protein of 152 aas and 3 or 4 TMSs
Protein 3a of Bat coronavirus
ORF3 protein of 228 aas and 3 TMSs.
ORF3 of Chaerephon bat coronavirus/Kenya