Characterization of Substrate Binding to the Group II Archael Chaperonin from Methanococcus maripaludis (Mm-Cpn)

Abstract

Molecular chaperones are important for the proper folding and function of many proteins, and malfunction of chaperone-assisted folding has been implicated in several protein aggregation diseases. For this reason, chaperones have been identified as a potential area for drug development. An important step in developing specific therapeutic targets is the identification of the recognition site on the substrate as well as the binding site on the chaperone. In this study, we use a number of biophysical and biochemical methods to elucidate the binding site on a Human γ-Crystallin substrate and the recognition site on the Methanococcus maripaludis chaperonin (Mm-Cpn). A homologue of human chaperonins, Mm-Cpn has been shown to bind and inhibit the aggregation of several closely related members of the Human γ-Crystallin protein family including HγD- and HγC-crystallins. Although members of this protein family share a high degree of homology, Mm-Cpn suppression of HγD aggregation is twice as efficient as the suppression of HγC aggregation. It remains unclear whether this difference in suppression efficiency is linked to sequence-determined substrate binding kinetics or to differences in substrate aggregation kinetics. To better understand how sequence difference may affect aggregation and chaperone binding, we studied the chaperone-induced aggregation suppression for the isolated N-terminal and C-terminal domains of both HγD and HγC. Supported by an NIH Roadmap Award to the Center for Protein Folding Machinery (http://ncmi.bcm.tmc.edu/nanomedicine).