Legionella RavZ Plays a Role in Preventing Ubiquitin Recruitment to Bacteria-Containing Vacuoles

Abstract

Bacterial pathogens like <i>Salmonella</i> and <i>Legionella</i> establish intracellular niches in host cells known as bacteria-containing vacuoles. In these vacuoles, bacteria can survive and replicate. Ubiquitin-dependent selective autophagy is a host defense mechanism to counteract infection by invading pathogens. The <i>Legionella</i> effector protein RavZ interferes with autophagy by irreversibly deconjugating LC3, an autophagy-related ubiquitin-like protein, from a phosphoglycolipid phosphatidylethanolamine. Using a co-infection system with <i>Salmonella</i>, we show here that <i>Legionella</i> RavZ interferes with ubiquitin recruitment to the <i>Salmonella</i>-containing vacuoles. The inhibitory activity is dependent on the same catalytic residue of RavZ that is involved in LC3 deconjugation. In semi-permeabilized cells infected with <i>Salmonella</i>, external addition of purified RavZ protein, but not of its catalytic mutant, induced removal of ubiquitin associated with <i>Salmonella</i>-containing vacuoles. The RavZ-mediated restriction of ubiquitin recruitment to <i>Salmonella</i>-containing vacuoles took place in the absence of the host system required for LC3 conjugation. These observations suggest the possibility that the targets of RavZ deconjugation activity include not only LC3, but also ubiquitin.