The Small Cysteine-Rich Protein of Potato Mop-Top Virus Exhibits Viroporin Activity.

Potato mop-top virus (PMTV) is the causal agent of potato tuber spraing disease, which causes significant economic losses to potato production worldwide. The 3'-proximal end of PMTV genomic RNA3 encodes an 8 kDa cysteine-rich protein (8K) that is not essential for replication and movement but contributes to virus infection and symptom development. Here, we demonstrate that PMTV 8K forms endomembrane multimers, alters the membrane permeability of Escherichia coli, and possesses potassium and proton conductance activity. In addition, our data reveal that two conserved cysteine residues in the central hydrophobic α-helix are essential for the viroporin activity. These results not only deepen our understanding of the function of PMTV 8K but also provide new insights into the diversity and origin of plant viral viroporins.