D98D, A MINIMALIST MODEL OF ANTIPARALLEL B-SHEET PROTEINS BASED ON INTESTINAL FATTY ACID BINDING PROTEIN

CURTO, L.M.; CARAMELO, J.J.; FRANCHINI, G.R.; DELFINO, J.M.

PROTEIN SCIENCE

JOHN WILEY & SONS INC

Año: 2009 vol. 18 p. 735 - 746

0961-8368

The design of b-barrels has always been a formidable challenge for de novo protein design. For instance, a persistent problem is posed by the intrinsic tendency to associate given by free edges. From the opposite standpoint provided by the redesign of natural motifs, we believe that the IFABP framework allows room for intervention, giving rise to abridged forms from which lessons on b-barrel architecture and stability could be learned. In this context, D98D (encompassing residues 29-126 of IFABP) emerges as a monomeric variant that folds properly, retaining functional activity, despite lacking extensive stretches involved in the closure of the b-barrel. Spectroscopic probes (fluorescence and circular dichroism) support the existence of a form preserving the essential determinants of the parent structure, albeit endowed with enhanced flexibility. Chemical and physical perturbants reveal cooperative unfolding transitions, with evidence of significant population of intermediate species in equilibrium, structurally akin to those transiently observed in IFABP. The recognition by the natural ligand oleic acid exerts a mild stabilizing effect, being of a greater magnitude than that found for IFABP. In summary, D98D adopts a monomeric state with a compact core and a loose periphery, thus pointing to the non-intuitive notion that the integrity of the b-barrel can indeed be compromised with no consequence on the ability to attain a native-like and functional fold.