Understanding the function of the ribosome-associated molecular chaperone trigger factor in chloroplasts

• Applicant: Professor Dr. Felix Willmund
• Subject Area: Plant Biochemistry and Biophysics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565401467

Chloroplasts possess a semi-autonomous genome that encodes essential subunits of key complexes involved in photosynthetic light reactions, carbon fixation, gene expression, and metabolism. During gene expression, the maturation and folding of nascent polypeptides occur simultaneously with protein synthesis on ribosomes. In both bacteria and chloroplasts of the green lineage, one of the first factors involved in protein maturation is the ATP-independent molecular chaperone known as trigger factor. In bacteria, the role of trigger factor is well-characterized; it helps to prevent premature folding and avoids unwanted molecular interactions in the crowded cellular environment. In chloroplasts, the general process of nascent polypeptide maturation and the specific contribution of trigger factor is far less understood. In our previous work we began to uncover the function of chloroplast trigger factor. Our data suggest that this chaperone has diverged from its prokaryotic counterpart, likely adapting to its specialized role within the chloroplast. While it remains unclear which chloroplast-encoded proteins specifically require trigger factor during maturation, our preliminary findings indicate that the large subunit of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco), RbcL, may be a major substrate. This proposal aims to investigate the early steps of nascent polypeptide maturation in chloroplasts, with a focus on trigger factor. We seek to obtain a comprehensive understanding of the function of this chaperone in plastids, including how it structurally interacts with translating ribosomes and nascent polypeptides. Given the limited knowledge about the initial folding steps of RbcL, we will further explore the early folding cascade of RbcL and its dependence on chaperone-assisted maturation and the putative contribution of trigger factor. Studying these aspects of protein maturation in chloroplasts is crucial not only for advancing our understanding of fundamental biochemical processes within the organelle but also for unlocking the potential of metabolic engineering and synthetic biology within chloroplasts. Furthermore, insights into the biogenesis of Rubisco will be relevant for future efforts to reengineer this key enzyme of the global carbon cycle, one of the most abundant and essential enzymes on Earth.

• DFG Programme: Research Grants