Dissection of a β-barrel motif leads to a functional dimer: The case of the intestinal fatty acid binding protein

Abstract

A lingering issue in the area of protein engineering is the optimal design of β motifs. In this regard, the framework provided by intestinal fatty acid binding protein (IFABP) was successfully chosen to explore the consequences on structure and function of the redesign of natural motifs. A truncated form of IFABP (Δ98Δ) served to illustrate the nonintuitive notion that the integrity of the β-barrel can indeed be compromised with no effect on the ability to attain a nativel-ike fold. This is most likely the outcome of the key role played by the preservation of essential core residues. In the search for the minimal structural determinants of this fold, Δ98Δ offered room for further intervention. A dissection of this protein leads to a new abridged variant, Δ78Δ, containing 60% of the amino acids of IFABP. Spectroscopic analyses indicate that Δ78Δ retains substantial β-sheet content and preserves tertiary interactions, displaying cooperative unfolding and binding activity. Most strikingly, this construct adopts a remarkably stable dimeric structure in solution. This phenomenon takes advantage of the inherent structural plasticity of this motif, likely profitting from edge-to-edge interactions between β-sheets, whereas avoiding the most commonly occurring outcome represented by aggregation. Published by Wiley-Blackwell. © 2009 The Protein Society.