Stabilization of the membrane protein bacteriorhodopsin to 140 °C in two-dimensional films

TWO-DIMENSIONAL assemblies of membrane proteins (see ref. 1, for example) such as bacteriorhodopsin are of current interest because of their potential application in technological areas as diverse as molecular electronics and optical switching2, molecular sieves3,4 and the lithographic fabrication of nanometre-scale patterns5,6. Here we report that bacteriorhodopsin7–9 can retain its folded native structure to temperatures as high as 140 °C when incorporated in multilayer structures of self-assembled, ordered films. Synchrotron X-ray scattering reveals that, under hydrated conditions, the two-dimensional lattice in multilayer films exhibits a reversible solid–liquid transition at about 69 °C, followed by irreversible denaturing of the bacteriorhodopsin at about 90 °C. But in dry films the melting transition and denaturation are suppressed up to 140 °C. These results suggest that it may be feasible to use multilayer assemblies of functional proteins and enzymes10,11 in high-temperature applications.