Molecular and in vivo Functions of the Chloroplast Chaperonins

We present here the final report for our research project entitled "The molecular and in vivo functions of the chloroplast chaperonins”. Over the past few decades, intensive investigation of the bacterial GroELS system has led to a basic understanding of how chaperonins refold denatured proteins. However, the parallel is limited in its relevance to plant chaperonins, since the plant system differs from GroEL in genetic complexity, physiological roles of the chaperonins and precise molecular structure. Due to the importance of plant chaperonins for chloroplast biogenesis and Rubisco assembly, research on this topic will have implications for many vital applicative fields such as crop hardiness and efficiency of plant growth as well as the production of alternative energy sources. In this study, we set out to investigate the structure and function of chloroplast chaperonins from A. thaliana. Most plants harbor multiple genes for chaperonin proteins, making analysis of plant chaperonin systems more complicated than the GroEL-GroES system. We decided to focus on the chaperonins from A. thaliana since the genome of this plant has been well defined and many materials are available which can help facilitate studies using this system. Our proposal put forward a number of goals including cloning, purification, and characterization of the chloroplast cpn60 subunits, antibody preparation, gene expression patterns, in vivo analysis of oligomer composition, preparation and characterization of plant deletion mutants, identification of substrate proteins and biophysical studies. In this report, we describe the progress we have made in understanding the structure and function of chloroplast chaperonins in each of these categories.