Colloidal assembly of proteins with delaminated lamellas of layered metal hydroxide.

The colloidal LDH nanosheets have been assembled in aqueous medium with three proteins having different structures and surface charge distributions. In addition to the interfacial adsorption features, the secondary and/or higher level structures of surface-bound proteins are investigated by ATR-FTIR and fluorescence spectroscopic techniques. The structure and conformation of porcine pancreatic lipase (PPL), for which the negative charges are concentrated on the side surface opposite to active sites, are well retained, but the orientations of PPL molecules on two-dimensional LDH nanosheets could be lying flat or standing up depending on the PPL/LDH ratio. The bioactivity of PPL lying flat is enhanced in both the hydrolysis and kinetic resolution in comparison with its soluble counterpart. In the case of hemoglobin (Hb), a tetrameric hemeprotein with relatively uniform distribution of surface negative charges, the interfacial assembly might result in the unfolding of its tertiary or quaternary structure, but its secondary structure and redox-active heme groups are not denatured. Although the secondary structure of bovine serum albumin (BSA), for which the negative charges are distributed along the surfaces of linearly arranged domains I and II, is unfolded, the loss of the ordered structure is less than previously found owing to the less curvature of the two-dimensional LDH nanosheet surface. This is the first report related to the investigations of protein structures, conformations, and orientations in the biohybrids consisting of LDH nanosheets.