The trans-Golgi SNARE syntaxin 6 is recruited to the chlamydial inclusion membrane

Abstract

Chlamydia trachomatis is an obligate intracellular pathogen that replicates within a parasitophorous vacuole termed an inclusion. The chlamydial inclusion is isolated from the endocytic pathway but fusogenic with Golgi-derived exocytic vesicles containing sphingomyelin and cholesterol. Sphingolipids are incorporated into the chlamydial cell wall and are considered essential for chlamydial development and viability. The mechanisms by which chlamydiae obtain eukaryotic lipids are poorly understood but require chlamydial protein synthesis and presumably modification of the inclusion membrane to initiate this interaction. A polarized cell model of chlamydial infection has demonstrated that chlamydiae preferentially intercept basolaterally directed, sphingomyelin-containing exocytic vesicles. Here we examine the localization and potential function of trans-Golgi and/or basolaterally associated soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins in chlamydia-infected cells. The trans-Golgi SNARE protein syntaxin 6 is recruited to the chlamydial inclusion in a manner that requires chlamydial protein synthesis and is conserved among all chlamydial species examined. The localization of syntaxin 6 to the chlamydial inclusion requires a tyrosine motif or plasma membrane retrieval signal (YGRL). Thus in addition to expression of at least two inclusion membrane proteins that contain SNARE-like motifs, chlamydiae also actively recruit eukaryotic SNARE-family proteins.

Chlamydial Intracellular Survival Strategies

“…In support of this notion, at least two Golgi-specific SNARES, including Syntaxin 6 and GS15 (Moore et al 2011;Pokrovskaya et al 2012), as well as vesicles containing the endocytic SNARES, Vamp3, Vamp7, and Vamp8, are recruited to the inclusion (Delevoye et al 2008;Paumet et al 2009). Interestingly, a subset of Incs contains motifs that display similarities to eukaryotic SNAREs, including IncA, CT813, and CT223 (Delevoye et al 2008;Paumet et al 2009).…”

Manipulation of Host Vesicular Trafficking and Membrane Fusion During Chlamydia Infection

“…Treatment of the infected host cells with chloramphenicol to inhibit bacterial www.intechopen.com protein synthesis abrogated trafficking of Syntaxin 6 to the inclusion suggesting that bacterial effectors are necessary to induce this recruitment. The depletion of Syntaxin 6 by siRNA did not significantly affect the development of the inclusion nor change the recruitment of sphingomyelin to the inclusion [Moore et al, 2011]. Therefore, the role f Syntaxin6 during Chlamydia infection remains unclear.…”

“…Syntaxin 6 is a SNARE protein that localizes to the trans-Golgi network (TGN) and likely plays a role in mediating the fusion of Golgi-derived vesicles with endosomes and/or lysosomes [Bock et al, 1997]. Recently, Hackstadt and co-workers showed that Syntaxin 6 relocates to the inclusion in a 18 hours post-infection [Moore et al, 2011]. Neither Syntaxin 4 nor Syntaxin 16 were found to localize to the inclusion suggesting that the recruitment of Syntaxin 6 was specific.…”

“…Interestingly, the SNARE domain of Syntaxin 6 was not required for the recruitment to the inclusion. Instead, a small 10-amino acid "plasma membrane retrieval sequence" (TDRYGRLDRE) located N-terminal to the SNARE domain was found to be necessary for re-localization [Moore et al, 2011]. Deletion of this domain results in Syntaxin 6 being present in the cytosol in non-infected cells [Watson and Pessin, 2000].…”

Cloning, Expression, and Biophysical Investigations of Truncated Inclusion Protein A (IncA) from Chlamydia trachomatis

“…27,28,38 Previous studies show only the α-helical region facing the host cytoplasm is necessary for fusion 27 , however, biochemical properties and the structure of the soluble C-terminal domain of the IncA dimer have yet to characterized. …”