Hansenula polymorpha Hac1p Is Critical to Protein N-Glycosylation Activity Modulation, as Revealed by Functional and...

Area of Science:

• * Molecular and Cellular Biology
• * Yeast Genetics
• * Protein Folding and Stress Response

Background:

• * Endoplasmic reticulum (ER) stress triggers the unfolded protein response (UPR) to manage misfolded proteins.
• * The UPR is regulated by transcription factors like Hac1p/Xbp1.
• * Hansenula polymorpha is a thermotolerant yeast model organism.

Purpose of the Study:

• * To identify and characterize the HAC1 homolog (HpHAC1) in Hansenula polymorpha.
• * To investigate the role of HpHAC1 in the UPR and cellular processes.
• * To explore the connection between HpHAC1 and protein glycosylation.

Main Methods:

• * Identification and molecular analysis of HpHAC1 in Hansenula polymorpha.
• * Construction and phenotypic analysis of H. polymorpha hac1-null (Hphac1Δ) mutant.
• * Comparative transcriptome analysis of wild-type (WT) and Hphac1Δ strains under ER stress conditions (DTT, TM).
• * Analysis of protein glycosylation patterns (carboxypeptidase Y).

Main Results:

• * HpHAC1 mRNA contains a unique intron regulating its translation.
• * Hphac1Δ mutant exhibits slow growth, reduced thermotolerance, and increased sensitivity to cell wall perturbing agents and UPR inducers.
• * HpHAC1 is essential for the expression of core UPR target genes, including those involved in N-linked protein glycosylation.
• * The Hphac1Δ mutant shows altered glycosylation and processing of carboxypeptidase Y.
• * Overexpression of HpHac1p enhances N-linked glycosylation efficiency and tunicamycin resistance.

Conclusions:

• * HpHAC1 is vital for UPR induction in Hansenula polymorpha.
• * HpHAC1 plays a significant role in efficient N-linked protein glycosylation.
• * The study elucidates the dual function of HpHac1p in stress response and glycosylation in this yeast species.