Native beta-lactoglobulin self-assembles into a hexagonal columnar phase on a solid surface

Using electron scanning microscopy, we have studied the protein deposit left on silicon and mica substrates by dried droplets of aqueous solutions of bovine ?-lactoglobulin at low concentration and pH = 2-7. We have observed different self-assembled structures: homogeneous layers, hexagonal platelets and flower-shaped patterns laying flat on thesurface,androdsformedbycolumns.Homogeneouslayerscoveredthelargestareaofthedropletdeposit.Theother structures were found in small isolated regions, where the protein solution dried in the form of microdroplets. The presence ofhexagonalplatelets, flower-shaped patterns andcolumnar rods shows that?-lactoglobulinself-assembles at the surface in a hexagonal columnar phase, which has never been observed in solution. A comparison with proteins showing similar aggregates suggests that ?-lactoglobulin structures grow from hexagonal germs composed of discotic nanometric building blocks, possibly possessing an octameric structure. We propose that discotic building blocks of ?- lactoglobulin may be produced by the anisotropic interaction with the solid surface.