A designed metal-binding protein with a novel fold

Abstract

A MAJOR challenge in protein design is to create stable scaffolds into which tailored functions can be introduced. Here we present the design, synthesis and characterization of a 61-residue all-β protein: the minibody. We used a portion of the heavy chain variable domain of an immunoglobulin as a template, obtaining a molecule with a novel β-sheet scaffold and two regions corresponding to the hypervariable loops HI and H2. To exploit the potential for creating functional centres in the minibody, we engineered a metal-binding site into it. This site is formed by one histidine in HI and two in H2. The protein is folded, compact and able to bind metal, thus representing the first designed β-protein with a novel fold and a tailored function. By randomizing the sequence of the hypervariable loops, we are using the minibody scaffold to construct a conformationally constrained peptide library displayed on phage.