Endosomal transport function in yeast requires a novel AAA-type ATPase, Vps4p

Area of Science:

• Cell Biology
• Molecular Biology
• Yeast Genetics

Background:

• Vacuolar proteins in Saccharomyces cerevisiae are sorted via a pre-vacuolar endosome.
• Vacuolar Protein Sorting (VPS) mutants, like vps4, accumulate cargo in this compartment.
• The VPS4 gene encodes a AAA-type ATPase.

Purpose of the Study:

• To investigate the function of the VPS4 gene and its protein product (Vps4p) in yeast vacuolar protein transport.
• To characterize the role of Vps4p's ATPase activity in protein sorting.
• To elucidate the consequences of Vps4p dysfunction on endosome morphology and protein trafficking.

Main Methods:

• Gene cloning and protein purification of Vps4p.
• Biochemical assays to determine Vps4p ATPase activity.
• Site-directed mutagenesis to inactivate ATPase activity.
• Phenotypic analysis of vps4 mutants (including temperature-sensitive alleles) using microscopy and protein localization studies.

Main Results:

• Vps4p exhibits N-ethylmaleimide-sensitive ATPase activity.
• A catalytically inactive Vps4p mutant acts as a dominant-negative inhibitor of protein sorting.
• Loss of Vps4p function leads to defects in vacuolar protein delivery and the accumulation of aberrant endosomal structures.
• Vps4p is required for efficient transport out of the pre-vacuolar endosome.

Conclusions:

• Vps4p, a AAA-type ATPase, is essential for the final steps of vacuolar protein transport in yeast.
• Vps4p likely functions in vesicle-mediated transport or membrane remodeling at the pre-vacuolar endosome.
• Disruption of Vps4p function results in a characteristic endosomal trafficking block.