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

MATTERA, V; PARODI, AJ; MARINO-BUSJLE, C; BREDESTON, LM; D'ALESSIO, C

Cordoba

Congreso; 2nd Argentinean Symposyum on Glycobiology; 2016

The enzyme UDP-Glc:glycoprotein glucosiltransferase(UGGT) is a key player in quality control of glycoprotein folding process inthe endoplasmic reticulum (ER). It adds a Glc residue to misfoldedglycoproteins, tagging them to stay in the ER during the folding process. Itssubstrate the nucleotide-sugar UDP-Glc, is synthesized in citosol but its entrymechanism into the yeast ER is not yet known. We?ve identified 8 genes in thewhole fission yeast Schizosaccharomycespombe genome that belong to the three Pfam families in which allnucleotide-sugar transporters (NST) of the secretory pathway identified so farbelong. The products of two of them (hut1+and yea4+) localize to theER. Here we demonstrate that: 1) Dhut1 and Δgpt1(UGGT null) mutants share several phenotypic features; 2) Dhut1 mutants show a 50% reduction in UDP-Glctransport into ER-derived membranes; 3) deletion of each one of six of theeight 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 Δhut1Δvrg4double mutants could not be tested but we determined that vrg4+ codes for the GDP-Man transporter that localizesto the Golgi. We conclude that although the hut1+gene product appears to be somehow involved in UDP-Glc entrance into the ER, atleast another yet unknown unconventional transport mechanism operates in theyeast secretory pathway.