Dr. Hannah Birke
Dr. Hannah Birke
hannah.birke AET anu.edu.au
Evolution of Cysteine Synthesis in Phototrophic Organisms
Cysteine is the pivotal source of reduced sulfur for all organic compounds. In higher plants it is produced in a two step reaction from serine, acetyl-CoA, and sulfide by the enzymes serine acetyltransferase (SAT) and O-acetylserine(thiol)lyase (OAS-TL). SAT and OAS-TL form the so-called cysteine synthase complex (CSC). Remarkably, the function of complex formation is not substrate channeling but constitutes the basis for demand-driven regulation of cysteine synthesis. Additionally, SAT and OAS-TL in cytosol, plastids, and mitochondria contribute to a different extend to total cellular cysteine production. The regulatory function of complex formation and functional compartmentation of cysteine synthesis in higher plants seem to facilitate a delicate but efficient mechanism to adjust cysteine production to the demands of the cell and subcellular compartments. The significance of both CSC formation and compartmentation in higher plants is addressed by an evolutionary approach.!
To this end, conservation of SAT and OAS-TL protein structures as well as composition of the CSC is analyzed in Arabidopsis thaliana and Glycine max in comparison to eubacterial and cyanobacterial proteins. Evolutionary conservation of compartmentation is investigated using the moss Physcomitrella patens as a representative of early land plants. Finally, a special focus concentrates on the function of compartmentation in A. thaliana and the significance of sulfide consumption by cysteine production in a specific subcellular compartment. In this context, effects of excess sulfide on sulfur metabolism are analyzed in wild type plants and plants lacking cysteine production in specific subcellular compartments.
aided by Schmeil Stiftung, Heidelberg