Modeling of possible subunit arrangements in the eukaryotic chaperonin TRiC

The eukaryotic cytosolic chaperonin TRiC (TCP-1 Ring Complex), also known as CCT (Cytosolic Chaperonin containing TCP-1), is a hetero-oligomeric complex consisting of two back-to-back rings of eight different subunits each. The general architecture of the complex has been determined, but the arrangement of the subunits within the complex remains an open question. By assuming that the subunits have a defined arrangement within each ring, we constructed a simple model of TRiC that analyzes the possible arrangements of individual subunits in the complex. By applying the model to existing data, we find that there are only four subunit arrangements consistent with previous observations. Our analysis provides a framework for the interpretation and design of experiments to elucidate the quaternary structure of TRiC/CCT. This in turn will aid in the understanding of substrate binding and allosteric properties of this chaperonin.