Sensing and signaling for peroxisome autophagic degradation (pexophagy) in yeasts

Abstract

yeast cells, similarly to cells of other eukaryotic organisms, possess intracellular organelles, including that of peroxisomes also known as microbodies . Enzymes of oxidative metabolism, mainly hydrogen peroxide generating oxidases, catalase, some enzymes of glyoxylic cycle and enzymes involved in catabolism of unusual carbon sources (n-alkanes, methanol) are located in peroxisomes. Especially important role is played by peroxisomes in methylotrophic yeasts, unique eukaryotic organisms capable to utilize one-carbon compound, methanol. Active proliferation and biogenesis of peroxisomes occur on methanol, so these organelles can occupy between 30 and 80% of cellular volume. After shift of methanol-grown cells into media with multicarbon substrates, such as glucose or ethanol, an excess of peroxisomes degrades in the specific process known as autophagic degradation of peroxisomes or pexophagy. There are 36 AuTophaGy related genes, known as ATG genes, which products are also involved in pexophagy. At the same time, not much is known on mechanisms of glucose and ethanol sensing and signaling which initia te pexophagy process. Proteins Pfk1(α-subunit of phosphofructokinase), Slt2 (mitogen-activating protein kinase) Gpr1 and Gpa2 (components of GPCr system) and Snf3 and Ggt2 (highand low-affinity glucose sensors) were found to be involved in signaling of glucose-induced pexophagy in Saccharomyces cerevisiae. In the methylotrophic yeast Pichia pastoris, glucose sensing protein Gss1 was found to be important for glucose-induced pexophagy. Very few is known on mechanisms of ethanol sensing and signaling during pexophagy which is an important problem for future studies.