Protein O-glycosylation in Saccharomyces cerevisiae: the protein O-mannosyltransferases Pmt1p and Pmt2p function as heterodimer

AbstractThe protein O-mannosyltransferases Pmt1p and Pmt2p are catalyzing the O-glycosylation of serine and threonine residues in the endoplasmic reticulum of yeast. Deletion of each of these proteins by disruption of the corresponding gene leads to a dramatic decrease of mannosyltransferase activity in vitro. With an anti-Pmt1p immunoaffinity column a complex of Pmt1p and a second protein was purified; this protein turned out to be Pmt2p. Overexpression of Pmt1p or Pmt2p, respectively, does not increase mannosyltransferase activity in vitro. Overexpression of both mannosyltransferases together, however, raises in vitro activity threefold. These data indicate that Pmt1p and Pmt2p function as a complex catalyzing protein O-glycosylation in yeast

Membrane Transport Inhibition as Mode of Action of Polyene Antimycotics: Recent Data Supported by Old Ones

Novija istraživanja pokazuju da se antimikotična aktivnost poliena zasniva na njihovoj interakciji sa sterolima u staničnoj stijenci, a ne, kao što se prije vjerovalo, na njihovoj sposobnosti stvaranja pora. Stoga je zaključeno da steroli imaju važnu ulogu u aktivnosti stanične stijenke, te da je ona ozbiljno narušena nakon što se na njih vežu polieni. Steroli su neophodni za aktivnost esencijalnih proteina u staničnoj stijenci. U ovom su radu opisane različite interakcije proteina i ergosterola, a zaključeno je da polieni prvenstveno djeluju na proteine u staničnoj stijenci. Svi dostupni podaci koji potkrijepljuju ovu tezu sažeti su u ovom pregledu. Čak i podaci dobiveni prije gotovo 40 godina mogu poslužiti u planiranju budućih istraživanja.Recent studies demonstrate that the actual interactions of polyenes with membrane sterols are the basis for their antimycotic toxicity and not, as previously assumed, their potential to form pores. Therefore, sterols must play a vital role in membranes and this function is seriously disturbed once polyenes bind to and/or sequester them. Essential membrane proteins obviously require sterols for their activity. Among the various membrane protein/ergosterol interactions discussed herein, transport proteins of the plasma membrane are most likely the primary target for polyenes. All data available which support this notion are summarized in this review. Even data obtained almost 40 years ago could be useful in guiding future research

Membrane Transport Inhibition as Mode of Action of Polyene Antimycotics: Recent Data Supported by Old Ones

Novija istraživanja pokazuju da se antimikotična aktivnost poliena zasniva na njihovoj interakciji sa sterolima u staničnoj stijenci, a ne, kao što se prije vjerovalo, na njihovoj sposobnosti stvaranja pora. Stoga je zaključeno da steroli imaju važnu ulogu u aktivnosti stanične stijenke, te da je ona ozbiljno narušena nakon što se na njih vežu polieni. Steroli su neophodni za aktivnost esencijalnih proteina u staničnoj stijenci. U ovom su radu opisane različite interakcije proteina i ergosterola, a zaključeno je da polieni prvenstveno djeluju na proteine u staničnoj stijenci. Svi dostupni podaci koji potkrijepljuju ovu tezu sažeti su u ovom pregledu. Čak i podaci dobiveni prije gotovo 40 godina mogu poslužiti u planiranju budućih istraživanja.Recent studies demonstrate that the actual interactions of polyenes with membrane sterols are the basis for their antimycotic toxicity and not, as previously assumed, their potential to form pores. Therefore, sterols must play a vital role in membranes and this function is seriously disturbed once polyenes bind to and/or sequester them. Essential membrane proteins obviously require sterols for their activity. Among the various membrane protein/ergosterol interactions discussed herein, transport proteins of the plasma membrane are most likely the primary target for polyenes. All data available which support this notion are summarized in this review. Even data obtained almost 40 years ago could be useful in guiding future research

Plasma membrane microdomains regulate turnover of transport proteins in yeast

In this study, we investigate whether the stable segregation of proteins and lipids within the yeast plasma membrane serves a particular biological function. We show that 21 proteins cluster within or associate with the ergosterol-rich membrane compartment of Can1 (MCC). However, proteins of the endocytic machinery are excluded from MCC. In a screen, we identified 28 genes affecting MCC appearance and found that genes involved in lipid biosynthesis and vesicle transport are significantly overrepresented. Deletion of Pil1, a component of eisosomes, or of Nce102, an integral membrane protein of MCC, results in the dissipation of all MCC markers. These deletion mutants also show accelerated endocytosis of MCC-resident permeases Can1 and Fur4. Our data suggest that release from MCC makes these proteins accessible to the endocytic machinery. Addition of arginine to wild-type cells leads to a similar redistribution and increased turnover of Can1. Thus, MCC represents a protective area within the plasma membrane to control turnover of transport proteins

Distribution of Cortical Endoplasmic Reticulum Determines Positioning of Endocytic Events in Yeast Plasma Membrane

In many eukaryotes, a significant part of the plasma membrane is closely associated with the dynamic meshwork of cortical endoplasmic reticulum (cortical ER). We mapped temporal variations in the local coverage of the yeast plasma membrane with cortical ER pattern and identified micron-sized plasma membrane domains clearly different in cortical ER persistence. We show that clathrin-mediated endocytosis is initiated outside the cortical ER-covered plasma membrane zones. These cortical ER-covered zones are highly dynamic but do not overlap with the immobile and also endocytosis-inactive membrane compartment of Can1 (MCC) and the subjacent eisosomes. The eisosomal component Pil1 is shown to regulate the distribution of cortical ER and thus the accessibility of the plasma membrane for endocytosis