The chaperone Chs7 forms a stable complex with Chs3 and promotes its activity at the cell surface

Area of Science:

• Cell biology
• Protein folding and transport
• Yeast genetics

Background:

• Chitin synthase III (Chs3) is essential for yeast cell wall synthesis.
• Chs3 requires the chaperone Chs7 for proper folding, ER exit, and cell surface localization.
• Chs7 was previously thought to be an ER-resident protein with an uncharacterized role in Chs3 transport.

Purpose of the Study:

• To investigate the localization and function of the Chs7 chaperone in Chs3 transport.
• To elucidate the distinct roles of Chs7 in Chs3 folding, ER exit, and activity regulation.

Main Methods:

• Yeast genetics and molecular biology techniques.
• Analysis of Chs7 localization using microscopy.
• Characterization of Chs3 folding and activity in Chs7 mutants.

Main Results:

• Chs7 exits the ER and co-localizes with Chs3 at the bud neck and intracellular compartments.
• Mutations in Chs7's C-terminal domain disrupt its association with Chs3 post-ER.
• Disruption of Chs7-Chs3 association allows cell surface delivery but reduces Chs3 catalytic activity.

Conclusions:

• Chs7 plays dual roles: promoting Chs3 folding and ER exit, and subsequently regulating its activity at the plasma membrane.
• Chs7's interaction with Chs3 is dynamically regulated during Chs3 transport and function.