ESR project MLU Halle, Germany

Establishing connections in the photosynthetic phosphoproteome network.

Plants use light at certain wavelengths with just the right amount of energy to produce sugars. Light intensity varies throughout the day, and the leaf must adjust how this energy is distributed among the light collecting systems in order to best use it.  The two light gathering protein complexes can each absorb a certain light quality, and the whole system works best when the amount of light that they each absorb is balanced.  For this to happen, many types of proteins will work together to control the energy distribution between the light harvesting systems in the leaf.  These proteins must also be regulated so that they do their job when required and stop when they are not needed. This is achieved by switching the proteins on or off using two chemical reactions called phosphorylation and de-phosphorylation. This means that a phosphate ion is either attached (phosphorylation) or removed (de-phosphorylation) from a protein by an enzyme that works to give or take away phosphate ions. Depending on the protein, the addition or removal of a phosphate ion will often change the properties of the protein, and this turns it on so that it can do its job, or turns it off so that it stops.

In this project, phosphate-adding enzymes, called kinases, and the phosphate-removing enzymes, called phosphatases are studied. The goal is to elucidate which proteins are turning on or off and under what light conditions this is happening. To this end, the modification of proteins will be analysed by a method called mass spectrometry. This method measures the masses of peptides and uses the fact that phosphate-carrying peptides are heavier than their non-phosphorylated counterparts to distinguish them.This type of analysis will be performed in the absence and the presence of a specific kinase or phosphatase, to identify the targets of these enzymes by finding the differences between these experimental conditions.