Double-ring chaperonin complexes are key mediators of cellular protein folding. Their essential function results from the cytosolic conditions of high protein concentration and volume occupancy, which present an unfavorable environment for spontaneous protein folding. Based on their ability to bind unfolded polypeptides within their ring cavities, chaperonins prevent off-pathway reactions and promote productive protein folding to the native state in an ATP-dependent manner. The homo-oligomeric E. coli complex GroEL acts in concert with the single-ring protein GroES. Unlike GroEL, the recently discovered eukaryotic cytosolic chaperonin TRiC is hetero-oligomeric. TRiC appears to function without a GroES-like cofactor. Its role as a general eukaryotic chaperonin remains to be established, as well as its mechanism in comparison to GroEL/GroES.

During her post-doctoral work Dr. Frydman identified and characterized the basic composition and function of the TRiC. The biochemical characterization of TRiC is central to the elucidation of its function in vivo. The ubiquity and conservation of the TRiC complex across eukaryotic cells suggests that it plays an essential role in polypeptide folding in the cytosol. We are thus interested in understanding the molecular mechanism by which TRiC mediates protein folding in the eukaryotic cytosol. There are three main questions the lab wants to explore:

1) What is the role of individual TRiC subunits in nucleotide and substrate binding?

2) how does nucleotide binding and hydrolysis drive the folding reaction?

3) how does the chaperonin interact with the substrate?

The results of our studies should clarify and define the mechanism of TRiC action. The characterization of nucleotide and substrate binding to the TRiC complex should lead to the elucidation of its mechanism of action. At a molecular level they will give insight into the fundamental process of cytosolic protein folding.

The subunit heterogeneity of TRiC may also reflect its potential to interact with other proteins in a highly regulated chaperone pathway. This possibility would open many avenues of research. Conditional mutants of TRiC will allow me to investigate its biological function through the use of genetic screens for other components of the system. For example, synthetic lethal screens and multicopy suppressor screens may uncover other chaperone systems, substrates, or regulatory proteins that interact with the complex. Thus, a combination of biochemical and genetic approaches will open the way to understanding the cellular role of TRiC.