Oligomerization of the chitin synthase Chs 3 is monitored at the G olgi and affects its endocytic recycling

• Published in: Molecular microbiology Vol. 90; no. 2; pp. 252 - 266
• Main Authors: Sacristan, Carlos, Manzano‐Lopez, Javier, Reyes, Abigail, Spang, Anne, Muñiz, Manuel, Roncero, Cesar
• Format: Journal Article
• Language: English
• Published: 01.10.2013
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.12360

Chs 3, the catalytic subunit of chitin synthase III in S accharomyces cerevisiae, is a complex polytopic membrane protein whose plasma membrane expression is tightly controlled: export from the ER requires interaction with Chs 7; exit from the G olgi is dependent on the exomer complex, and precise bud neck localization relies on endocytosis. Moreover, Chs 3 is efficiently recycled from endosomes to the TGN in an AP ‐1‐dependent manner. Here we show that the export of Chs 3 requires the cargo receptor Erv 14, in a step that is independent of Chs 7. Chs 3 oligomerized in the ER through its N ‐terminal cytosolic region. However, the truncated Δ126 Chs 3 was still exported by Erv 14, but was sent back from the G olgi to the ER in a COPI ‐ and Rer 1‐dependent manner. A subset of the oligomerization‐deficient Chs 3 proteins evaded G olgi quality control and reached the plasma membrane, where they were enzymatically active but poorly endocytosed. This resulted in high CSIII levels, but calcofluor white resistance, explained by the reduced intercalation of calcofluor white between nascent chitin fibres. Our data show that the oligomerization of Chs 3 through its N ‐terminus is essential for proper protein trafficking and chitin synthesis and is therefore monitored intracellularly.