Tracing Putative Trafficking of the Glycolytic Enzyme Enolase via SNARE-Driven Unconventional Secretion

Glycolytic enzymes are cytosolic proteins, but they also play important extracellular roles in cell-cell communication and infection. We usedSaccharomyces cerevisiae to analyze the secretory pathway of some of these enzymes, including enolase, phosphoglucose isomerase, triose phosphate isomerase, and fructose 1,6-bisphosphate aldolase. Enolase, phosphoglucose isomerase, and an N-terminal 28-amino-acid-long fragment of enolase were secreted in asec23 -independent manner. The enhanced green fluorescent protein (EGFP)-conjugated enolase fragment formed cellular foci, some of which were found at the cell periphery. Therefore, we speculated that an overview of the secretory pathway could be gained by investigating the colocalization of the enolase fragment with intracellular proteins. The DsRed-conjugated enolase fragment colocalized with membrane proteins at thecis -Golgi complex, nucleus, endosome, and plasma membrane, but not the mitochondria. In addition, the secretion of full-length enolase was inhibited in a knockout mutant of the intracellular SNARE protein-coding geneTLG2 . Our results suggest that enolase is secreted via a SNARE-dependent secretory pathway inS. cerevisiae .