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Glycosylation and processing of prepro-alpha-factor through the yeast secretory pathway
Cell
|February 1, 1984
Summary
Investigating yeast secretory pathway mutants reveals key steps in prepro-alpha-factor processing. Specific mutations block protein transport, affecting glycosylation and proteolytic events before mature pheromone formation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The yeast secretory pathway is crucial for protein synthesis, modification, and transport.
- Understanding the sequential events of protein processing is vital for cell function.
- Prepro-alpha-factor serves as a model protein to study these complex pathways.
Purpose of the Study:
- To elucidate the specific stages of prepro-alpha-factor synthesis and processing.
- To identify the roles of different yeast secretory pathway mutants in protein maturation.
- To map the temporal order of glycosylation and proteolytic cleavage events.
Main Methods:
- Utilized various yeast secretory pathway mutants (sec53, sec59, sec18, sec7, sec1, sec2, sec3, sec5) blocked at distinct cellular compartments.
- Analyzed protein molecular weight and modifications (glycosylation) using tunicamycin treatment and in vitro synthesis.
- Assessed the accumulation of precursor and mature forms of prepro-alpha-factor.
Main Results:
- A tunicamycin-sensitive precursor, identical to the in vitro product, accumulates in normal cells and early mutants (sec53).
- Endoplasmic reticulum mutants (sec59, sec18) accumulate a glycosylated precursor with an uncleaved signal peptide.
- Proteolytic processing initiates at the Golgi apparatus (sec7), and mature pheromone accumulates in secretory vesicle mutants (sec1, sec2, sec3, sec5).
Conclusions:
- The study maps the sequential steps of prepro-alpha-factor processing within the yeast secretory pathway.
- Signal peptide removal occurs after initial glycosylation and ER translocation.
- Proteolytic maturation and vesicle transport are distinct, later stages in the pathway.
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