Biogenesis of chlorophyll binding electron transfer complexes

How is the binding of Chlorophyll to proteins of photosynthetic complexes regulated in plants Photosystems contain chlorophyll binding protein complexes for physical and chemical transformation of light energy into a chemical storage form. How the chlorophyll molecules that serve as primary sites for both processes are assembled in the photosynthetic machinery is unknown. We have established an in vitro model to study the binding of chlorophyll to protein complexes and especially to photosystem complexes. In the project, a site for binding of chlorophyll a has been identified in the light-harvesting like protein three, LIL3 immediately upon its synthesis. A model for transfer of chlorophyll to the photosystem complexes has been established and is verified experimentally.

The project has opened new possibilities for the work career of two postdoctoral scientists in the field of protein biochemistry. The technologies developed in the project are now applied for investigations in the area of medicine and industry. The postdocs have in part reached a developmental status to now apply for Professorship positions. The institute profits from the extended collaborative network established by the researchers. The local industry profits from the knowledge gain to extend and shape new products.

Since more than 10E9 years, nature operates endosymbiotic metabolic pathways in eukaryotic host cells. In plants, maintenance of the cells metabolism is compartmentalized. The metabolic stage of a family of plastid organelles defines the metabolic developmental stage of the plant. The chlorophyll binding electron transport protein complexes in the endosymbiontic chloroplast are the cornerstone in the evolutionary invention of nature to maintain a photoautotrophic metabolism and are the central regulatory process for survival of the plant. However, very little is known about the coordinated biogenesis of chlorophyll and of the chlorophyll binding proteins and their assembly. We established an experimental system using etioplasts from barley and mutants from Arabidopsis that provide excellent biochemical and genetic systems to characterize the complex biogenetic processes. Upon illumination, the switch in the developmental program can be studied in vivo and in vitro top down down to the molecular level. A novel method developed throughout the last two years has demonstrated that a fast and high-resolution isolation of native assemblies of multienzyme complexes is now possible. The method is key to isolate the hypercomplex assemblies for chlorophyll and protein synthesis, assembly of the chlorophyll binding proteins of the electron transfer chain and for the study of their coordinated action. We will focus on the isolation and characterization of the enzymatic activity of the assemblies in developmental and mutant studies using plants, bacteria and algae. Structural and special functional characterizations of the recently identified complexes for Chl and electron transfer will be conducted by single particle electron tomography and femtosecond crystallography in collaboration with our partners on site. The laboratory has developed an exciting degree of compentence for resolving this most extraordinary and essential regulatory biochemical pathway.