Phosphorylation of Chs2p regulates interaction with COPII

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Chitin synthase Chs2p is essential for cell wall formation.
• Chs2p transport from the ER to the bud-neck is cell-cycle regulated.
• Phosphorylation of Chs2p impacts its trafficking.

Purpose of the Study:

• To investigate the role of Chs2p phosphorylation in its interaction with COPII.
• To elucidate the mechanism regulating Chs2p ER exit.

Main Methods:

• Yeast two-hybrid assays.
• In vitro ER vesicle formation assays.
• Analysis of cdc5(ts) mutant and phosphomimetic substitutions.

Main Results:

• Chs2p accumulates at ER exit sites in metaphase-arrested cells.
• CDK1 phosphorylation prevents Chs2p packaging into COPII vesicles.
• Cdc14p dephosphorylation stimulates Chs2p selection into COPII vesicles.
• Chs2p N-terminus interacts with COPII component Sec24p, reduced by phosphomimetic substitutions.

Conclusions:

• Dephosphorylation of Chs2p acts as a molecular switch for regulated ER exit.
• Phosphorylation state of Chs2p dictates its COPII vesicle packaging.
• This mechanism ensures proper localization of chitin synthase during mitosis.