The phosphorylation of Ser221 in VP2 of mink enteritis virus and its roles in virus amplification

- In the present study, we provide evidence that the MEV VP2 is phosphorylated during infection of feline F81 cells. Making use of mass spectrometry, we demonstrate that 3 threonines and 1 serine form the main phosphorylated domain of the MEV VP2 molecule.
- We find that mutant viruses containing an S221A non-phosphorylatable alanine substitution, or an S221E glutamic acid substitution to mimic serine phosphorylation, were able to express VP2 but had either limited ability or were unable to propagate in feline F81 cells.
- We show that the replication ability of an MEV-S221A mutant is reduced compared with wt MEV, thereby providing further evidence that phosphorylation in VP2 is important to a productive viral life cycle.
- We also predict and simulate the tertiary structure of MEV VP2 using Discovery Studio™ software.

Recent reports have indicated that phosphorylation of capsid proteins plays an important role in virion assemblage. Autonomous parvoviruses are among the smallest known viruses with an ssDNA genome enclosed within an icosahedral capsid. Here, we demonstrate that a structural protein (VP2) of one member, mink enteritis virus (MEV), is phosphorylated at serine-221 (Ser221) in vivo. Mutant viruses containing an S221A non-phosphorylatable alanine substitution, or an S221E glutamic acid substitution to mimic serine phosphorylation, were able to express VP2 but had either limited ability or were unable to propagate in feline F81 cells. We propose a new mechanism whereby VP2 phosphorylation plays an essential role in amplification during MEV infection.