When a protein adsorbs on the surface of a material that is curved on the nanoscale, the structure and function of the adsorbed protein can be markedly changed. For example, when proteins are adsorbed on silica nanoparticles and carbon nanotubes, which have a positive, convex curvature, changes in secondary structure of the protein have been noted, which result in a decrease in catalytic activity1,2. However, when proteins adsorb on nanoporous materials with a negative, concave local surface geometry, the behavior is different: we have noted a relative increase in enzymatic activity of adsorbed lysozyme and myoglobin on nanoporous SBA-15 with controlled pore sizes. This suggests a distinct interaction mechanism between these proteins and the nanopore surface.
Our preliminary studies of the enhanced catalytic activity of the adsorbed lysozyme and myoglobin on SBA-15, reported at the AIChE meeting in 2009, illustrated that confinement of mesopores can stabilize protein structures. Ordered mesoporous SBA-15 with carefully controlled surface geometries and different surface chemical properties were introduced to study the effects of the local surface geometry and surface chemistry on the conformation of the adsorbed protein. A decrease in catalytic activity of the same adsorbed proteins on SBA-15, of which the pore surface is modified with hydrophobic moieties, but which has a similar pore size to the original SBA-15, for which a remarkable increase in activity was noted, reveals that local surface chemistry also plays an important role on the function of the adsorbed proteins. Liquid phase ATR-FTIR spectroscopy with Fourier self-deconvolution and mathematical analysis were introduced to analyze the nature and the changes of the secondary structures of free and adsorbed protein molecules on mesopores with different pore sizes and surface properties3. Our studies show that the protein structures are perturbed to a different extent, depending on the surface interactions.
The results show that the activity and stability of adsorbed proteins inside the pores of SBA-15 are strongly correlated with the local geometry and the surface properties of the nanoporous materials. Strong surface interactions, and a confined space of the right geometry are essential to enhance the activity and stability of the adsorbed proteins.
(1) Vertegel, A. A.; Siegel, R. W.; Dordick, J. S. Langmuir 2004, 20, 6800-6807.
(2) Asuri, P.; Bale, S. S.; Karajanagi, S. S.; Kane, R. S. Current Opinion in Biotechnology 2006, 17, 562-568.
(3) Dong, A.; Malecki, J. M.; Lee, L.; Carpenter, J. F.; Lee, J. C. Biochemistry 2002, 41, 6660-6667.