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This document uses the citation format from Journal of Virology (JVI).
The ubiquitin-proteasome system is a common target of several unrelated viruses that have evolved convergent strategies to redirect host ubiquitin machinery to serve their own needs. Members of the genus Chlorovirus, a group of large dsDNA viruses that infect certain freshwater chlorella-like green algae, encode a conserved Skp1 homolog and ankyrin-repeat (ANK) proteins, some of which contain C-terminal domains characteristic of cellular F-boxes or related viral PRANC domains. These observations suggested that this unique combination of chlorovirus proteins either interact with or imitate the key components of the SCF (Skp1-Cul1-F-box) ubiquitin ligases. Using mass spectrometry, we identified two functional classes of ANK proteins from prototype chlorovirus PBCV-1 as binding partners for the virus-encoded Skp1: (i) cellular F-box-like ANK proteins (e.g., ank-A682L); and (ii) core ANK proteins (e.g., ank-A607R). The former ANK class contains a C-terminal F-box-like motif that is recognized by cellular Skp1 proteins from widely divergent species. Yeast two-hybrid analysis confirmed putative F-box-dependent protein interaction of PBCV-1 ank-A682L by constructing serial domain deletions. The other class of viral ANK proteins constitutes a core ANK family with one member represented in all 41 sequenced chloroviruses. A comprehensive phylogenetic analysis of these core 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 core ANK and Skp1 proteins across three chlorovirus genera. Our results indicate that chloroviruses have evolved complimenting Skp1 and ANK proteins that mimic cellular SCF-associated proteins.
Advisor: James Van Etten