Dancing water molecules on the surface of soluble proteins provide the essential lubricant for macromolecular function. Surprisingly, polymers attached to protein surfaces have been reported to replace hydration water and bring inactive dry proteins back to life. The mechanism behind polymer-assisted functional protein motions has now been revealed by researchers from the Institut de Biologie Structurale in Grenoble, the Universities of Bordeaux, of California Irvine, of Bristol and of Perugia and from the Heinz-Maier Leibnitz Zentrum in Garching. The consortium applied neutron spectroscopy and molecular dynamics simulations to shed light on the motions animating proteins and polymers in the water-free hybrid. Separating them was possibly by selectively masking the signal from either the polymer or the protein by replacing hydrogen by deuterium atoms, the latter scattering neutrons two orders of magnitude less than the former in spectroscopy experiments. Surprisingly, protein and polymer motions turned out to be qualitatively similar, in stark contrast to protein and water motions being qualitatively different ; segmental polymer motions appear to substitute for hydration-water translational motions. Even if this substitution keeps dry proteins biologically active, certain dynamical modes are suppressed in the protein, possibly explaining the generally observed decrease in activity when hydration water is substituted by polymer coating. The study suggests ways to fine-tune polymer properties so that the loss in protein activity can be minimized. This will be particularly important for rationally designing protein-polymer hybrids for specific biotechnological applications, such as in medicine and cosmetics.
Diffusive-like motions in a solvent free protein-polymer hybrid. Schirò G, Fichou Y, Brogan APS, Sessions R, Lohstroh W, Zamponi M, Schneider GJ, Gallat F-X, Paciaroni A, Tobias DJ, Perriman A, Weik M. Physical Review Letters 126, 088102