The Potyviridae family, named after its type member, Potato virus Y (PVY), is the largest of the 65 plant virus groups and families currently recognized. The coding region for P1 peptidase is located at the very beginning of the viral genome of the family Potyviridae. Until recently P1 was thought of as serine peptidase with RNA-binding activity and with possible influence in cell-to-cell viral spreading. This N-terminal protein, among all of the potyviruses, is the most divergent protein: varying in length and in its amino acid sequence. Nevertheless, P1 peptidase in many ways is still a mysterious viral protein. In this review, we would like to offer a comprehensive overview, discussing the proteomic, biochemical and phylogenetic views of the P1 protein.

Background: Pea seed-borne mosaic virus (PSbMV) is a member of the genus Potyvirus that can be transmitted by seeds, causing serious losses in legume crop yields. Its genome consists of 3 peptidases-P1, HC-Pro, and NIa. Interestingly, only the P1 peptidase, localized on the N-terminal portion of the viral polyprotein, still remains without any concrete function on influencing viral infections. Results: P1 peptidase consists of the originally-described C2H2 zinc finger motif. This newly revealed characteristic can help further clarify its true activity during viral infection. The truncated portion of P1 (Δ33-143) was expressed in bacteria and used for production of polyclonal antibody in rabbit. Using this antibody, it was shown that P1 (42 kDa) can be presented in infected plant also in a shorter form (30 kDa). Immunocytochemical localization of P1 in the protoplasts, obtained from the infected pea plant, demonstrated the localization of P1 in the cytoplasm, as well as in the nucleus. Moreover, newly found C2H2 motive can form active cavity according to in silico model of P1 molecule. Conclusions: Herein, it was described the C2H2 zinc finger motif (ZnF), which is non-standard compared to others present in the eukaryotic world. Moreover, the predicted protein models in silico of the ZnF found. Similar ZnF was also found in the P1 of another 5 viruses (3 Potyviruses, and 2 Tritimoviruses).