A bipartite signal mediates the transfer of type IV secretion substrates of Bartonella henselae into human cells

Abstract

Bacterial type IV secretion (T4S) systems mediate the transfer of macromolecular substrates into various target cells, e.g., the conjugative transfer of DNA into bacteria or the transfer of virulence proteins into eukaryotic host cells. The T4S apparatus VirB of the vascular tumor-inducing pathogen Bartonella henselae causes subversion of human endothelial cell (HEC) function. Here we report the identification of multiple protein substrates of VirB, which, upon translocation into HEC, mediate all known VirB-dependent cellular changes. These Bartonella-translocated effector proteins (Beps) A-G are encoded together with the VirB system and the T4S coupling protein VirD4 on a Bartonella-specific pathogenicity island. The Beps display a modular architecture, suggesting an evolution by extensive domain duplication and reshuffling. The C terminus of each Bep harbors at least one copy of the Bepintracellular delivery domain and a short positively charged tail sequence. This biparte C terminus constitutes a transfer signal that is sufficient to mediate VirB͞VirD4-dependent intracellular delivery of reporter protein fusions. The Bep-intracellular delivery domain is also present in conjugative relaxases of bacterial conjugation systems. We exemplarily show that the C terminus of such a conjugative relaxase mediates protein transfer through the Bartonella henselae VirB͞VirD4 system into HEC. Conjugative relaxases may thus represent the evolutionary origin of the here defined T4S signal for protein transfer into human cells.conjugative relaxase ͉ effector protein ͉ endothelial cell ͉ protein translocation ͉ antiapoptosis

The mating pair formation system of conjugative plasmids—A versatile secretion machinery for transfer of proteins and DNA

“…The interaction is mediated by the C-terminal domain of VirE2 (Atmakuri et al, 2003). The C-termini of several T4SS-translocated substrates have been identiWed as the signals mediating secretion by their associated secretion systems (Nagai et al, 2005;Schulein et al, 2005;Simone et al, 2001;Vergunst et al, 2000Vergunst et al, , 2003Vergunst et al, , 2005. It therefore seems probable that substrate recognition by the CPs, as a general rule, occurs via speciWc interactions between the CPs and the C-termini of their associated substrates.…”

“…The existence of a C-terminal signal mediating translocation of dedicated T4SS protein substrates has been discovered in three diVerent T4SS: the VirB/VirD4 systems of B. henselae and A. tumefaciens, and the Dot/Icm system of L. pneumophila (Atmakuri et al, 2003;Nagai et al, 2005;Schulein et al, 2005;Simone et al, 2001;Vergunst et al, 2000Vergunst et al, , 2003Vergunst et al, , 2005. Evidence is accumulating that these secretion systems have evolved from conjugation systems and that the C-terminal secretion signal of their secreted protein substrates originates from a relaxase ancestor (Schulein et al, 2005).…”

Bartonella and Brucella--Weapons and Strategies for Stealth Attack

“…As a canonical T4SS, the Bartonella VirB system comprises an effectorrecognition component: the coupling protein VirD4 , which has no homolog in Brucella, and which instead expresses the unique VirB12 (O'Callaghan et al 1999). The genes of the VirB T4SSs are encoded as operons (Berger and Christie 1994), which either locate together with effector genes (Bartonella lineage 4) or not (Bartonella lineage 3 and Brucella) (Schulein et al 2005;Engel et al 2011;de Jong and Tsolis 2012). Because biosynthesis of the multiprotein VirB T4SS and its translocated effectors is costly for the bacterial cells, expression is tightly regulated on the transcriptional level.…”

“…The VirB-translocated Bartonella effector proteins (Bep; named BepA-BepG in B. henselae) display a composite domain architecture characterized by an amino-terminal effector domain and a carboxy-terminal secretion signal (Schmid et al 2004;Dehio 2005;Schulein et al 2005;Engel et al 2011). The carboxy-terminal secretion signal is bipartite and composed of a Bep intracellular delivery domain (BID) of approximately 140 amino acids and a short, nonconserved, positively charged tail sequence (Schulein et al 2005).…”

“…The carboxy-terminal secretion signal is bipartite and composed of a Bep intracellular delivery domain (BID) of approximately 140 amino acids and a short, nonconserved, positively charged tail sequence (Schulein et al 2005). Besides mediating T4SS-dependent translocation into host cells, some BID domains can also directly modulate hostcellular pathways.…”