Acidic dileucine motifs in the cylindrical inclusion protein of turnip mosaic virus are crucial for endosomal targeting and viral replication

Previously we reported that the multifunctional cylindrical inclusion (CI) protein of turnip mosaic virus (TuMV) is targeted to endosomes through the interaction with the medium subunit of adaptor protein complex 2 (AP2 beta), which is essential for viral infection. Although several functionally important regions in the CI have been identified, little is known about the determinant(s) for endosomal trafficking. The CI protein contains seven conserved acidic dileucine motifs [(D/E)XXXL(L/I)] typical of endocytic sorting signals recognized by AP2 beta. Here, we selected five motifs for further study and identified that they all were located in the regions of CI interacting with AP2 beta. Coimmunoprecipitation assays revealed that alanine substitutions in the each of these acidic dileucine motifs decreased binding with AP2 beta. Moreover, these CI mutants also showed decreased accumulation of punctate bodies, which enter endocytic-tracking styryl-stained endosomes. The mutations were then introduced into a full-length infectious clone of TuMV, and each mutant had reduced viral replication and systemic infection. The data suggest that the acidic dileucine motifs in CI are indispensable for interacting with AP2 beta for efficient viral replication. This study provides new insights into the role of endocytic sorting motifs in the intracellular movement of viral proteins for replication.

Automated summary

This study identified the importance of acidic dileucine motifs in the CI protein of Turnip mosaic virus for interaction with AP2 beta, which is crucial for efficient viral replication.