| Biomembranes are functional structures responsible for controlling numerous cellular functions. In this work, a synthetic membrane-based recognition system capable of reproducing important features of biological targeting and assembly was developed. Proteins are targeted to membranes through the affinity of surface histidine side chains for transition metal ions immobilized in the lipid headgroups. A set of metal-chelating lipids for this purpose has previously been synthesized. Through measurement of the lipid surface pressure-molecular area ({dollar}pi{dollar}-A) isotherms, the capability of the iminodiacetate (IDA) headgroups to chelate Cu{dollar}sp{lcub}2+{rcub}{dollar} was demonstrated. In addition, to tailor the density of metal sites on the membrane, mixing of a pyrene-labeled IDA lipid with two phosphocholine lipids was investigated.; The binding of myoglobin to IDA-Cu lipid monolayers by naturally occurring histidines was observed through changes in the lipid {dollar}pi{dollar}-A isotherms. Targeting of cytochrome b{dollar}sb5{dollar}, engineered to display a hexa-histidine affinity tag at the C-terminus, to IDA-Cu lipid monolayers was also demonstrated. The hexa-histidine tag was found to provide an apparent affinity for IDA-Cu lipid binding of at least {dollar}rm Ksb{lcub}a{rcub} = 2times 10sp7 Msp{lcub}-1{rcub}{dollar}. A Frumkin-type adsorption isotherm was developed to describe the binding of proteins to lipid monolayers.; Synthetic lipid monolayers can induce growth of 2D protein crystals at the air-water interface. For the first time, growth of 2D protein crystals on metal-chelating lipid monolayers via coordination of naturally occurring surface histidines was demonstrated. Two-dimensional crystals of the protein streptavidin, grown on IDA-Cu lipid monolayers, were observed using Brewster angle and polarization fluorescence microscopies. The IDA-Cu-histidine interaction may provide a general route to the growth of 2D protein crystals.; Finally, mimicking ligand-induced assembly, and subsequent signaling, can produce functional materials such as an IDA lipid-based metal-ion sensor (Sasaki, et al. Angew. Chem. Int. Ed. Engl. 34, 905-907, 1995). In order to probe similar ligand-induced reorganization of a pyrene-labeled TDA lipid monolayer, a UV-vis fluorescence microphotometer was constructed. As a demonstration of its utility, the instrument was used to quantitate fluorescence from a pyrene IDA lipid monolayer and estimate a diffusion coefficient for the lipids. In addition, reorganization of the IDA lipids by binding of a multivalent ligand, poly(histidine), was observed. |
