Yeast Cell Protein Complex Study

[molecule2005]

The first quantitative study of protein complexes that communicate pheromone signals in living yeast cells gives a valuable insight into a crucial signalling process also found in humans.

Scientists from the European Molecular Biology Laboratory (EMBL) recently gained a greater understanding of the cellular signal chain through which pheromones stimulate mating in yeast. Similar signal chains are found in humans, where they take part in many important processes including the differentiation of nerve cells and the development of cancer. For the first time, researchers used a sophisticated microscopy technique to observe the interaction of signalling molecules in living yeast cells, in order to understand how they pass on a signal through the cell.


Scientists labelled parts of the MAP kinase signalling chain with fluorescent molecules and observed their diffusion and interaction in living yeast cells stimulated by pheromones. A novel microscopy technique was used that does not disrupt the natural state of the cell.

'Our method is so precise that we could virtually count the molecules and the interactions between chain components,' says one of the group leaders, Michael Knop. 'To our surprise, the observed proteins in the cell's interior did not interact more after stimulation by the pheromone. This means changes in interaction are not the way by which the signal is transmitted through the interior of the cell.'

The research team demonstrated that the actual signal is not produced uniformly throughout the cell but only by the few chain components found in the mating projection. These components activate a protein known as Fus3, which diffuses into the centre of the cell, spreading the signal. However, whilst travelling, Fus3 is constantly deactivated by proteins found in the cell’s interior.

'We found that the concentration of Fus3 activity is very high at the tip of the developing mating organ and then gradually gets less towards the centre of the cell,' claims researcher Celine Maeder. 'This sets up a gradient of Fus3 activity, which might allow the signal to have different effects in different parts of the cell.'