Humboldt-Universität zu Berlin - AG Pflanzenphysiologie

TPR Proteins and their Role in Chloroplasts

Josephine Herbst


Multi-step metabolic processes in living cells, like chlorophyll biosynthesis and photosynthesis in photoautotrophic organisms, are organized/associated in macromolecular complexes to ensure a smooth sequence of reactions. For a precise organization of the different steps, not only the catalytic proteins, but also mediator or scaffolding proteins are needed. Members of the tetratricopeptide repeat (TPR) proteins superfamily are known to contribute to protein association. Prominent examples for TPR proteins are YCF3 and YCF37, which play a role in PSI assembly; or the FLU protein, which is involved in regulation of ALA- and chlorophyll biosynthesis.

It is our goal to contribute to the exploration of assembly factors, scaffold proteins or chaperones for the coordination of chlorophyll synthesis with the subsequent supply and assembly of chlorophyll into photosynthetic proteins in the thylakoid membranes. We began our studies with the identification of an Arabidopsis homolog of the cyanobacterial Pitt (POR-interacting protein) protein, which is a TPR responsible i.a. for the stability of the protochlorophyllide oxidoreductase (POR). Then, we will examine Arabidopsis tpr mutants, which show deficiency of chloroplast-localized TPR proteins, for their impact on chlorophyll accumulation and photosynthesis as well as the accumulation and activity of enzymes involved in chlorophyll synthesis. It is intended to confirm reliable interaction of the higher plant TPR isoform(s) with enzymes of chlorophyll synthesis by applying additional independent biochemical approaches for specific protein-protein interactions in vitro and in planta.


TPR lines


Several of the chosen TPR lines showed a severe phenotype, when grown on agar plates in comparison to the wildtype (A). We intend to examine the cause of these phenotypic changes in pigment content and chloroplast biogenesis. For at least two of the investigated TPR proteins, an interaction to the protochlorophyllide oxidoreductase isoforms (PORA/B/C) could be confirmed via yeast-two-hybrid experiments (B).