Prof. SUN Bing’s research group at Institut Pasteur of Shanghai, CAS, found that ORF3 gene of Porcine epidemic diarrhea virus (PEDV) encodes an ion channel protein. This research entitled "PEDV ORF3 encodes an ion channel protein and regulates virus production." was published in FEBS Letter on Feb. 17, 2012.

PEDV is a member of the family Coronaviridae, which causes diarrhea，vomiting and dehydration in pigs and fatality in neonates. Institut Pasteur of Shanghai, in collaboration with Harbin Veterinary Research Institute, Yang-Ming University in Taiwan and other research units studied the function of PEDV ORF3 protein. They proposed a structure model the ORF3 protein consisting of four TM domains and forming a tetrameric assembly. TEVC on Xenopus laevis oocytes and yeast potassium uptake complementation experiments showed that wild-type (virulent strain) PEDV ORF3 protein has ion channel activity, which was similar to 3a protein of SARS-CoV. However, the ORF3 gene from an attenuated PEDV encodes a truncated protein with 49 nucleotide deletions, which lacks the ion channel activity. Furthermore, viral production is reduced in infected Vero cells when ORF3 gene is silenced by siRNA. This study suggested that ion channel proteins play an important role in coronavirus life cycle, and may be an appropriate drug target against coronaviruses.

This project was supported by grants from CAS, Ministry of Science and Technology, National Natural Science Foundation of China，Shangahi Pasteur Health Research Foundation and Li Ka-Shing Foundation.

PEDV ORF3 encodes an ion channel protein and regulates virus production. （FEBS Lett. 2012 Feb 17;586(4):384-91.）

The PEDV CV777 ORF3 protein forms an ion channel. (A) ORF3 protein was tested in PEDV infected cells by western blot. (B) Water-injected and PEDV ORF3-cRNA-injected oocytes are immunolabeled with anti-HA and monitored by confocal microscopy. (C) Typical current traces that can be detected by two-electrode voltage clamp (TEVC) in these PEDV CV777 ORF3 (wt) expressed oocytes, compared with water injected control oocytes. (D) PEDV CV777 ORF3 (wt) shows larger current in 100 mM K+ bath solution than in barium ions containing standard bath solution. (E) PEDV ORF3 channel can complement K+ channel deficient yeast. Growth phenotype of yeast Δtrk1Δtrk2 mutants transformed with PEDV CV777 ORF3 genes and pYES2 vector, respectively.