scholarly journals SciN Is an Outer Membrane Lipoprotein Required for Type VI Secretion in Enteroaggregative Escherichia coli

2008 ◽  
Vol 190 (22) ◽  
pp. 7523-7531 ◽  
Author(s):  
Marie-Stéphanie Aschtgen ◽  
Christophe S. Bernard ◽  
Sophie De Bentzmann ◽  
Roland Lloubès ◽  
Eric Cascales
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Biofilm Formation ◽  
Cell Envelope ◽  
Gene Clusters ◽  
Type Vi Secretion ◽  
Outer Membrane Lipoprotein ◽  
In Vivo Labeling ◽  
Membrane Lipoprotein

ABSTRACT Enteroaggregative Escherichia coli (EAEC) is a pathogen implicated in several infant diarrhea or diarrheal outbreaks in areas of endemicity. Although multiple genes involved in EAEC pathogenesis have been identified, the overall mechanism of virulence is not well understood. Recently, a novel secretion system, called type VI secretion (T6S) system (T6SS), has been identified in EAEC and most animal or plant gram-negative pathogens. T6SSs are multicomponent cell envelope machines responsible for the secretion of at least two putative substrates, Hcp and VgrG. In EAEC, two copies of T6S gene clusters, called sci-1 and sci-2, are present on the pheU pathogenicity island. In this study, we focused our work on the sci-1 gene cluster. The Sci-1 apparatus is probably composed of all, or a subset of, the 21 gene products encoded on the cluster. Among these subunits, some are shared by all T6SSs identified to date, including a ClpV-type AAA+ ATPase (SciG) and an IcmF (SciS) and an IcmH (SciP) homologue, as well as a putative lipoprotein (SciN). In this study, we demonstrate that sciN is a critical gene necessary for T6S-dependent secretion of the Hcp-like SciD protein and for biofilm formation. We further show that SciN is a lipoprotein, as shown by the inhibition of its processing by globomycin and in vivo labeling with [3H]palmitic acid. SciN is tethered to the outer membrane and exposed in the periplasm. Sequestration of SciN at the inner membrane by targeting the +2 residue responsible for lipoprotein localization (Gly2Asp) fails to complement an sciN mutant for SciD secretion and biofilm formation. Together, these results support a model in which SciN is an outer membrane lipoprotein exposed in the periplasm and essential for the Sci-1 apparatus function.

scholarly journals Deletion of lolB, Encoding an Outer Membrane Lipoprotein, Is Lethal for Escherichia coli and Causes Accumulation of Lipoprotein Localization Intermediates in the Periplasm

2001 ◽  
Vol 183 (22) ◽  
pp. 6538-6542 ◽  
Author(s):  
Kimie Tanaka ◽  
Shin-Ichi Matsuyama ◽  
Hajime Tokuda
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Temperature Sensitive ◽  
Helper Plasmid ◽  
Inner Membrane ◽  
Outer Membrane Lipoprotein ◽  
Lipoprotein Complex ◽  
Membrane Lipoprotein

ABSTRACT Outer membrane lipoproteins of Escherichia coli are released from the inner membrane upon the formation of a complex with a periplasmic chaperone, LolA, followed by localization to the outer membrane. In vitro biochemical analyses revealed that the localization of lipoproteins to the outer membrane generally requires an outer membrane lipoprotein, LolB, and occurs via transient formation of a LolB-lipoprotein complex. On the other hand, a mutant carrying the chromosomal lolB gene under the control of thelac promoter-operator grew normally in the absence of LolB induction if the mutant did not possess the major outer membrane lipoprotein Lpp, suggesting that LolB is only important for the localization of Lpp in vivo. To examine the in vivo function of LolB, we constructed a chromosomal lolB null mutant harboring a temperature-sensitive helper plasmid carrying the lolBgene. At a nonpermissive temperature, depletion of the LolB protein due to loss of the lolB gene caused cessation of growth and a decrease in the number of viable cells irrespective of the presence or absence of Lpp. LolB-depleted cells accumulated the LolA-lipoprotein complex in the periplasm and the mature form of lipoproteins in the inner membrane. Taken together, these results indicate that LolB is the first example of an essential lipoprotein for E. coliand that its depletion inhibits the upstream reactions of lipoprotein trafficking.

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