Syntaxin-17 (STX17) belongs to the syntaxin family, which is a group of the membrane integrated proteins participating in exocytosis. Syntaxins are associated with various intracellular membrane compartments and have been implicated in various physiological processes such as axonal growth and cell division [].STX17 is required to maintain the architecture of ER-Golgi intermediate compartment and Golgi []. STX17 is also involved in the fusion of autophagosomes with endosomes/lysosomes. Its unique C-terminal hairpin structure mediated by two tandem transmembrane domains is essential for its association with the autophagosomal membrane [, ].
This family includes serine proteases such as L. pneumophila effector Lpg1137 []. Lpg1137, is a serine protease that targets the mitochondria-associated ER membrane (MAM) and degrades STX17 (syntaxin 17), a SNARE implicated in macroautophagy/autophagy as well as mitochondria dynamics and membrane trafficking in fed cells. Lpg1137 has a sequence (-Gly-Leu-Ser68-Gly-Gly-) that matches the consensus sequence for the active site of serine proteases (Gly-X-Ser-X-Gly/Ala, where X is any residue). It exhibits proteolytic activity toward STX17 in vitro, whereas an active site mutant in which Ser68 is replaced by Ala does not. Expressed Lpg1137 localizes to the MAM and mitochondria, in addition to the cytosol, and binds to STX17 [].
