The MyD116 African swine fever virus homologue interacts with the catalytic subunit of protein phosphatase 1 and activates its phosphatase activity

The DP71L protein of African swine fever virus (ASFV) shares sequence similarity with the herpes simplex virus ICP34.5 protein over a C-terminal domain. We showed that the catalytic subunit of protein phosphatase 1 (PP1) interacts specifically with the ASFV DP71L protein in a yeast two-hybrid screen. The chimeric full-length DP71L protein, from ASFV strain Badajoz 71 (BA71V), fused to glutathione S-transferase (DP71L-GST) was expressed in Escherichia coli and shown to bind specifically to the PP1-alpha catalytic subunit expressed as a histidine fusion protein (6 X His-PP1 alpha) in E. coli. The functional effects of this interaction were investigated by measuring the levels of PP1 and PP2A in ASFV-infected Vero cells. This showed that infection with wild-type ASFV strain BA71V activated PP1 between two- and threefold over that of mock-infected cells. This activation did not occur in cells infected with the BA71V isolate in which the DP71L gene had been deleted, suggesting that expression of DP71L leads to PP1 activation. In contrast, no effect was observed on the activity of PP2A following ASFV infection. We showed that infection of cells with wild-type BA71V virus resulted in decreased phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha). ICP34.5 recruits PP1 to dephospborylate the alpha subunit of eukaryotic translational initiation factor 2 (also known as eIF-2 alpha); possibly the ASFV DP71L protein has a similar function.