Design of Stable -Helical Arrays from an Idealized TPR Motif

a parallel array, to produce an extended molecule with an overall superhelical architecture. This can be visualized as a spiral staircase in which the individual TPR and Biochemistry motifs are the steps. Precisely how the TPR fold may mediate protein-pro-2 Howard Hughes Medical Institute 3 Department of Chemistry tein interactions was first revealed by the crystal structures of the two different three-TPR domains of Hop, TPR1 and TPR2A, bound to C-terminal peptides from Hsp70 and Hsp90, respectively [8]. The peptide binding site is presented on an inner concave surface, or cradle, which is formed by the three-TPR motif. In natural pro-Summary teins, the number of tandem TPR motifs varies from 3 to about 16, with 3 being the most common number The tetratricopeptide repeat (TPR) is a 34-amino acid (L.D.'A. and L.R., in preparation). The structures of the ␣-helical motif that occurs in over 300 different pro-Hop complexes suggest an explanation for the minimal teins. In the different proteins, three to sixteen or more number of repeats—less than three tandem repeats TPR motifs occur in tandem arrays and function to would not form a complete binding cradle. mediate protein-protein interactions. The binding TPR domains are of particular interest with respect to specificity of each TPR protein is different, although their folding, modular architecture, and range of binding the underlying structural motif is the same. Here we specificities. Designing idealized TPR motifs allows a describe a statistical approach to the design of an better understanding of how the amino acid sequence idealized TPR motif. We present the high-resolution specifies fold and function. The wealth of sequences X-ray crystal structures (to 1.55 and 1.6 A ˚) of designed available makes a statistical approach to design an ap-TPR proteins and describe their solution properties propriate strategy. Our aim, therefore, was to use a con-and stability. A detailed analysis of these structures sensus-based TPR design to engineer novel proteins provides an understanding of the TPR motif, how it is by arraying various numbers of an idealized TPR motif. repeated to give helical arrays with different superheli-Further, although TPR-containing domains in nature cal twists, and how a very stable framework may be rarely contain less than three TPR motifs, we wished constructed for future functional designs. to determine whether this number reflects a structural requirement or, rather, is necessary for function through Introduction the creation of a peptide binding site. Thus, three separate proteins were …