Orientation distributions of hydrated protein films

Abstract

The objective of this research was to measure orientation distributions in protein films as a function of immobilization chemistry to determine what conditions lead to ordered films. The hypothesis was that an ordered film could be achieved using a site-directed approach to immobilize a protein to a surface via a unique functional group. In order to accomplish this goal, a novel combination of absorbance linear dichroism performed in a integrated optical waveguide total internal reflectance geometry and total internal reflection fluorescence anisotropy (IOW-ATR+TIRF) was used to measure the orientation distribution of protein films in situ. The development of this combined technique included the synthesis of a mathematical theory to relate measured spectroscopic parameters to the orientation distribution. This was followed by testing on model molecular assemblies of Langmuir-Blodgett films doped with fluorescent amphiphiles with known orientations. Past the development phase, the IOW-ATR+TIRF technique was used to measure the first orientation distributions for protein films. This represents a significant advance in the study of protein film assemblies. The results of this research indicate that the hypothesis is correct and that ordered protein films can result from site-directed methodologies. This was demonstrated by the narrow orientation distributions of yeast cytochrome c covalently bound to phospholipid bilayers and biospecifically bound to streptavidin films. This research also indicates that of equal importance to a site-directed approach is the ability to tailor a surface to prevent unwanted non-specific adsorption interactions. This type of behavior was observed for horse heart cytochrome c adsorbed to bare hydrophilic glass surfaces which exhibited a broad orientation distribution. However, it should also be pointed out that adsorption processes can lead to ordered protein films as demonstrated by cytochrome c adsorbed to arachidic acid LB films. It can be broadly stated that ordered protein films result from situations where a single high energy binding mechanism immobilizes a protein to the surface and non-specific interactions are prevented. This conclusion is certainly not novel, but the fact it has been demonstrated to be true by the direct measurement of orientation distributions is revolutionary in the development of protein thin film devices.