UDP-Glc TRANSPORT MECANISM INTO THE ENDOPLASMIC RETICULUM OF FISSION YEAST: THE RULE?S EXCEPTION?

VANESA SOLEDAD MATTERA; LUIS BREDESTON; CRISTINA MARINO-BUSLJE; ARMANDO PARODI; CECILIA DALESSIO

Villa General Belgrano, Córdoba

Simposio; 2nd Argentinean Glycobiology Symposium; 2016

IBYME, CIQUIBIC (UNC), Instituto Leloir.

The enzyme UDP-Glc:glycoprotein glucosiltransferase (UGGT) is a key player in quality control of glycoprotein folding process in the endoplasmic reticulum (ER). It adds a Glc residue to misfolded glycoproteins, tagging them to stay in the ER during the folding process. Its substrate the nucleotide-sugar UDP-Glc, is synthesized in citosol but its entry mechanism into the yeast ER is not yet known. We?ve identified 8 genes in the whole fission yeast Schizosaccharomyces pombe genome that belong to the three Pfam families in which all nucleotide-sugar transporters (NST) of the secretory pathway identified so far belong. The products of two of them (hut1+ and yea4+) localize to the ER. Here we demonstrate that: 1) hut1 and Δgpt1 (UGGT null) mutants share several phenotypic features; 2) hut1 mutants show a 50% reduction in UDP-Glc transport into ER-derived membranes; 3) deletion of each one of six of the eight genes in combination with Δhut1 mutation did not abolish in vivo UDP-Glc entrance into the ER, 4) in vivo entrance of UDP-Glc into the ER of Δhut1Δvrg4 double mutants could not be tested but we determined that vrg4+ codes for the GDP-Man transporter that localizes to the Golgi. We conclude that although the hut1+ gene product appears to be somehow involved in UDP-Glc entrance into the ER, at least another yet unknown unconventional transport mechanism operates in the yeast secretory pathway. enzyme UDP-Glc:glycoprotein glucosiltransferase (UGGT) is a key player in quality control of glycoprotein folding process in the endoplasmic reticulum (ER). It adds a Glc residue to misfolded glycoproteins, tagging them to stay in the ER during the folding process. Its substrate the nucleotide-sugar UDP-Glc, is synthesized in citosol but its entry mechanism into the yeast ER is not yet known. We?ve identified 8 genes in the whole fission yeast Schizosaccharomyces pombe genome that belong to the three Pfam families in which all nucleotide-sugar transporters (NST) of the secretory pathway identified so far belong. The products of two of them (hut1+ and yea4+) localize to the ER. Here we demonstrate that: 1) hut1 and Δgpt1 (UGGT null) mutants share several phenotypic features; 2) hut1 mutants show a 50% reduction in UDP-Glc transport into ER-derived membranes; 3) deletion of each one of six of the eight genes in combination with Δhut1 mutation did not abolish in vivo UDP-Glc entrance into the ER, 4) in vivo entrance of UDP-Glc into the ER of Δhut1Δvrg4 double mutants could not be tested but we determined that vrg4+ codes for the GDP-Man transporter that localizes to the Golgi. We conclude that although the hut1+ gene product appears to be somehow involved in UDP-Glc entrance into the ER, at least another yet unknown unconventional transport mechanism operates in the yeast secretory pathway.