Abstract
The tetratricopeptide repeat (TPR) motif is a degenerate 34 amino acid sequence identified in a wide variety of proteins. It is present in tandem arrays of 3-16 motifs that form scaffolds in order to mediate protein-protein interaction. Three-dimensional structural data have shown that a TPR motif contains two antiparallel α-helices such that tandem arrays of TPR motifs generate a right-handed helical structure with an amphipathic channel that might accommodate the complementary region of a target protein. Most TPR-containing proteins are associated with multi-protein complexes, and there is extensive evidence indicating that TPR motifs are important to the functioning of chaperone, cell-cycle, transcription and protein transport complexes. In the present works, our goal is to identify biophysical characteristics of TPR motifs not only as an important step towards understanding the role of tetratricopeptide repeats in the chaperone regulation but also to explore the structural properties. From the CD spectra, TPR1 forms an α-helical conformation that exhibits a cooperative two-state folding-unfolding transition. Thermal melting of TPR1 in phosphate buffer at pH7.5 indicated unfolding of the secondary structure with a Tm of 42.4℃. GdmCl denaturation suggests that TPR1 exhibits low structural stability with Gibbs free energy of 1.63 kcal/mol. These unstable features may be essential for the tetratricopeptide-repeat-containing proteins to mediate a wide range of protein-protein interactions. Further CD experiments were used to evaluate the binding of TPR1 to the c-terminal peptides of hsc70 and hsc90. Size exclusion column and DSS cross-linking have shown that TPR1 essentially self-associates to form dimmers.