HcPro, a multifunctional protein encoded by a plant RNA virus, targets the 20S proteasome and affects its enzymic activities

Abstract

The proteasome is a multicatalytic complex involved in many cellular processes in eukaryotes, such as protein and RNA turnover, cell division, signal transduction, transcription and translation. Intracellular pathogens are targets of its enzymic activities, and a number of animal viruses are known to interfere with these activities. The first evidence that a plant virus protein, the helper component-proteinase (HcPro) ofLettuce mosaic virus(LMV; genusPotyvirus), interferes with the 20S proteasome ribonuclease is reported here. LMV infection caused an aggregation of the 20S proteasome to high-molecular mass structuresin vivo, and specific binding of HcPro to the proteasome was confirmedin vitrousing two different approaches. HcPro inhibited the 20S endonuclease activityin vitro, while its proteolytic activities were unchanged or slightly stimulated. This ability of HcPro, a pathogenicity regulator of potyviruses, to interfere with some of the catalytic functions of the 20S proteasome suggests the existence of a novel type of defence and counter-defence interplay in the course of interaction between potyviruses and their hosts.