The ubiquitin-proteasome system is targeted by many viruses that have evolved strategies to redirect host ubiquitination machinery. Members of the genus Chlorovirus are proposed to share a common ancestral lineage with a broader group of related viruses, Nucleo-Cytoplasmic Large DNA Viruses (NCLDV). Chloroviruses encode a Skp1 homolog and ankyrin-repeat (ANK) proteins. Several chlorovirus encoded ANK-repeats contain C-terminal domains characteristic of cellular F-boxes or related NCLDV chordopox PRANC domains. These observations suggested that this unique combination of Skp1 and ANK-repeat proteins might form complexes analogous to the cellular Skp1-Cul1-F-box (SCF) ubiquitin ligase complex. We identified two A... More
The ubiquitin-proteasome system is targeted by many viruses that have evolved strategies to redirect host ubiquitination machinery. Members of the genus Chlorovirus are proposed to share a common ancestral lineage with a broader group of related viruses, Nucleo-Cytoplasmic Large DNA Viruses (NCLDV). Chloroviruses encode a Skp1 homolog and ankyrin-repeat (ANK) proteins. Several chlorovirus encoded ANK-repeats contain C-terminal domains characteristic of cellular F-boxes or related NCLDV chordopox PRANC domains. These observations suggested that this unique combination of Skp1 and ANK-repeat proteins might form complexes analogous to the cellular Skp1-Cul1-F-box (SCF) ubiquitin ligase complex. We identified two ANK proteins from the prototypic chlorovirus PBCV-1 that functioned as binding partners for the virus-encoded Skp1, proteins A682L and A607R. These ANK proteins had a C-terminal Skp1 interactional motif that functioned like cellular F-box domains. A C-terminal motif of ANK protein A682L binds Skp1 proteins from widely divergent species. Yeast two-hybrid analyses using serial domain deletion constructs confirmed the C-terminal localization of the Skp1 interactional motif in PBCV-1 A682L. ANK protein A607R represents an ANK family with one member present in all 41 sequenced chloroviruses. A comprehensive phylogenetic analysis of these related ANK and viral Skp1 proteins suggested partnered function tailored to the host alga or common ancestral heritage. Here, we show protein-protein interaction between corresponding family clusters of virus-encoded ANK and Skp1 proteins from three chlorovirus genera. Collectively, our results indicate that chloroviruses have evolved complimenting Skp1 and ANK proteins that mimic cellular SCF-associated proteins.