No abstract

In yeast, functions of the endoplasmic reticulum (ER) depend on the Golgi apparatus Ca2+ pool, which is replenished by the medial-Golgi ion pump Pmr1p. Here, to dissect the role of the Golgi Ca2+ pool in protein folding and elimination of unfolded proteins in the ER, the manifestations of the pmr1 mutation in yeast Hansenula polymorpha were studied. The PMR1 gene was disrupted in a H. polymorpha diploid strain. Haploid segregants of this diploid bearing the disruption allele were viable, though they showed a severe growth defect on synthetic medium and rapidly died during storage at low temperature. Disruption of H. polymorpha PMR1 led to defects of the Golgi-hosted protein glycosylation and vacuolar protein sorting. This mutation increased the survival rate of H. polymorpha cells upon treatment with the proapoptotic drug amiodarone. Unlike Saccharomyces cerevisiae, the H. polymorpha pmr1 mutant was not hypersensitive to chemicals that induce the accumulation of unfolded proteins in the ER, indicating that the elimination of unfolded proteins from the ER was not essentially affected. At the same time, the pmr1 mutation improved the secretion of human urokinase and decreased its intracellular aggregation, indicating an influence of the mutation on the protein folding in the ER.

No abstract

Proteins binding thioflavin T leading to its specific fluorescence were discovered in a fraction of noncovalently bound Saccharomyces cerevisiae yeast cell wall mannoproteins. Thioflavin-binding proteins display high resistance to trypsin digestion in solution. These data are the first experimental evidence for the presence of proteins whose properties are characteristic of amyloids in yeast cell wall, except for data on glucanotransferase Bgl2p that has amyloid properties. Our data suggest the anchoring of these proteins in the cell wall by a trypsin-sensitive part of the protein molecule. Experiments with a mutant strain devoid of the BGL2 gene suggest the compensation of absent amyloid-like protein Bgl2p by increase in contents of thioflavin-binding proteins in the cell wall.