Paper out: Absolute numbers for the peroxisomal yeast proteome

Yeast cells must react quickly and reliably to changes in environmental conditions, such as changes in nutrient requirements. For example, the switch from glucose as a carbon source to oleic acid, a long-chain fatty acid whose degradation requires special metabolic pathways of beta-oxidation, is accompanied by an increase in peroxisomes. However, it is not only the number and size of these cell organelles that changes, the protein composition must also be adapted. Until now, there has been no precise description of which proteins are expressed under the different conditions and, above all, in what numbers (copy number). The publication by Hirak Das and colleagues from Bettina Warscheid's working group now fills this gap using modern mass spectrometry: extensive pre-fractionation provides a particularly comprehensive picture of the proteome in the form of 4500 quantified proteins. Using a trick, the researchers were able to determine the absolute number of proteins: The number of histones is proportional to the amount of DNA and therefore to the number of cells and their total weight. Taking into account the molecular mass of each protein, the number of proteins per cell and thus the copy number can be determined. Das and colleagues were thus able to show drastic changes such as the increase in the peroxisomal protein number by a factor of nine or the increase in beta-oxidation enzymes by a factor of over 500. Interestingly, the number of import proteins, which are responsible for transport into the peroxisomes, hardly changed. These must therefore achieve a significantly higher throughput under oleate conditions. How exactly this happens is the subject of Prof Warscheid's current research.