A size filter at the Golgi regulates apical membrane protein sorting

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Apical sorting of epithelial membrane proteins is crucial for cell function but remains poorly understood.
• Apical proteins typically possess smaller cytoplasmic domains compared to basolateral proteins, but the underlying mechanism is unclear.

Purpose of the Study:

• To investigate if a size barrier at the Golgi apparatus influences apical sorting of epithelial membrane proteins.
• To determine the role of cytoplasmic domain size in apical protein localization.

Main Methods:

• Utilized a synthetic biology approach with a streptavidin-binding peptide system to control protein release from the endoplasmic reticulum.
• Engineered apical proteins (Crb3, Ace2, Muc1) with varying cytoplasmic domain sizes.
• Analyzed protein localization, Golgi departure, and N-glycosylation patterns.

Main Results:

• Increasing cytoplasmic domain size of apical proteins led to partial basolateral mislocalization and delayed Golgi exit.
• Altered N-glycosylation and Golgi segregation were observed for proteins with larger cytoplasmic domains.
• A non-dissociable Pals1 mutant impaired Crb3 exit, indicating its dissociation is critical for sorting.

Conclusions:

• A size-selective filter at the Golgi apparatus actively promotes apical sorting of proteins with small cytoplasmic domains.
• The timely dissociation of Pals1 from Crb3 is essential for reducing the effective cytoplasmic domain size and enabling normal apical sorting.