STX17: an ancient SNARE protein whose roles have not been conserved

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mammalian syntaxin 17 (STX17) is involved in diverse cellular processes, including mitochondrial dynamics, lipid metabolism, and autophagy.
• STX17 possesses a conserved C-terminal hydrophobic domain (CHD) but a variable C-terminal tail (C-tail), suggesting evolutionary divergence in its functions.
• The protein's cellular localization and roles are known to be influenced by nutritional conditions.

Purpose of the Study:

• To investigate the conserved and divergent roles of STX17 homologs from different species.
• To compare the cellular localization and functional activities of fly and nematode STX17 in mammalian cells.
• To elucidate the evolutionary adaptations of STX17 in relation to its cellular functions.

Main Methods:

• Expression of fly (Syx17) and nematode (SYX-17) STX17 homologs in mammalian cells.
• Confocal microscopy to determine subcellular localization under various conditions.
• Functional assays to assess roles in mitochondrial fission and autophagy.

Main Results:

• Fly Syx17 localized to the cytosol and translocated to autophagosomes upon starvation, mimicking mammalian STX17's autophagy role.
• Nematode SYX-17 primarily localized to mitochondria, promoting mitochondrial fission but not participating in autophagy.
• In vivo studies confirmed that fly and nematode homologs did not perform the functions observed in mammalian cells, indicating species-specific roles.

Conclusions:

• STX17 homologs exhibit distinct subcellular localizations and functional specificities across eukaryotes.
• The C-tail of STX17 likely plays a crucial role in mediating species-specific interactions and functions.
• STX17 acts as a versatile molecular sensor, adapting its cellular roles based on evolutionary context and nutritional cues.