Although enolase, other glycolytic enzymes, and a variety of cytoplasmic proteins lacking an N-terminal secretion signal have been widely described as located at the cell surface in yeast and in mammalian cells, their presence in this external location is still controversial. Here, we report that different experimental approaches (genetics, cellular biology and proteomics) show that yeast enolase can reach the cell surface and describe the protein regions involved in its cell surface targeting. Hybrid enolase truncates, fused at their C terminus with the yeast internal invertase or green fluorescent protein (GFP) as reporter proteins, proved that the 169 N-terminal amino acids are sufficient to target the protein to the cell surface. Furthermore, the enolase-GFP fusion co-localized with a plasma membrane marker. Enolase was also identified among membrane proteins obtained by a purification protocol that includes sodium carbonate to prevent cytoplasmic contamination. These proteins were analyzed by SDS-PAGE, trypsin digestion and LC-MS/MS for peptide identification. Elongation factors, mitochondrial membrane proteins and a mannosyltransferase involved in cell wall mannan biosynthesis were also identified in this fraction.
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