A METAL-CHELATING LIPID FOR 2D PROTEIN CRYSTALLIZATION VIA COORDINATION OF SURFACE HISTIDINES

Two-dimensional protein crystallization on lipid monolayers is becomin g a powerful technique for structure determination as well as material s applications. However, progress has been hindered by the requirement of a unique affinity lipid for each new protein of interest. Metal io n coordination by surface-accessible histidine side chains provides a convenient and general method for targeting of proteins to surfaces. H ere we present the synthesis and characterization of a metal-chelating lipid which has been designed to target proteins to Langmuir monolaye rs and promote their two-dimensional crystallization based on histidin e coordination. The lipid utilizes the metal chelator iminodiacetate ( IDA) as the hydrophilic headgroup and contains unsaturated, oleyl tail s to provide the fluidity necessary for two-dimensional protein crysta llization. The lipid is shown to bind copper from the subphase strongl y when incorporated in Langmuir monolayers. In addition, it is possibl e to form copper-containing monolayers by spreading. the premetalated lipid on the subphase in the absence of copper. Fluorescence microscop y reveals the binding and crystallization of the protein streptavidin, promoted by the simultaneous coordination of two surface-accessible h istidine side chains to the IDA-Cu lipid.