Molecular investigation of protein maturation and quality control in the chloroplast of the green alga Chlamydomonas reinhardtii

• Applicant: Professor Dr. Felix Willmund
• Subject Area: Plant Biochemistry and Biophysics
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 248903262

Chloroplasts are organelles harboring essential and complex biochemical pathways that provide the basis for almost all life on our planet. Despite the importance of these processes, little is known about how proteins are folded and functionally maintained in plastids. The biogenesis and functional integration of newly synthesized proteins is particularly challenging within the chloroplast since its proteome consists of nuclear and chloroplast encoded proteins, which often constitute heterogenic complexes such as the photosystems or RuBisCo. To cope with these challenges, chloroplasts possess a network of molecular chaperones, similar to those found in other cellular compartments. While chaperones are well understood in bacteria, the eukaryotic cytosol, the endoplasmic reticulum (ER) and mitochondria, relatively little is known about their function in the chloroplast. Interestingly, chloroplast chaperones show certain peculiarities distinct from other chaperone systems, representing a functional adaptation to the challenges of folding the chloroplast proteome. The goal of this proposal is to shed light on the process of protein biogenesis in the chloroplast. We will analyze the role of individual chaperone components in the maturation of newly synthesized proteins. To this end, global approaches such as the identification of overall chaperone substrates and ribosome profiling of the plastidic translational apparatus will be applied as well as detailed biochemical investigation of individual chaperone components. In a conceptually related but separate project, mechanisms of chloroplast protein quality control will be illuminated. We will identify and analyze players that cope with intrinsically instable or aberrant proteins and investigate factors involved in the clearance of aggregated proteins. Studying such central questions in modern biology is key to understand principles governing protein homeostasis under physiological conditions as well as under stress conditions. A better understanding of protein biogenesis in the chloroplast is also essential to improve the potential of this compartment for biotechnological applications such as the heterologous expression of therapeutic proteins or metabolic engineering of biochemical pathways.

• DFG Programme: Research Grants
• International Connection: France, USA
• Participating Persons: Professor Dr. Udo Johanningmeier; Dr. Sebastian Pechmann; Professor Dr. Michael Schroda; Dr. Olivier Vallon