Chemisorption of the Dipeptide Arg-Cys on a Gold Surface and the Selectivity of G-Protein Adsorption

Arginine- l -cysteine dipeptide adsorbates are used in this study as a model system for G-protein-coupled receptors (GPCRs). An arginine-containing model molecule is chosen because the GPCR α 2 A has been shown to include an arginine-rich region in the G-protein-binding part of the third intracellular loop, and the role of arginines by means of recognition is believed to exceed their positive charge. The dipeptide Arg-Cys is adsorbed to gold surfaces and the peptide monolayers are characterized. These peptide monolayers are then used for G-protein adsorption experiments to study the molecular interaction and binding. The molecular adsorption, orientation, and chemical binding of the peptide to the surface are studied by X-ray photoelectron spectroscopy and infrared reflection−absorption spectroscopy. A chemical shift in the S(2p) core level spectrum of the peptide adsorbate on gold shows that there is a strong molecular surface interaction consistent with a chemical binding of the peptide to the surface through the sulfur atom. With the cysteine part linked to the surface, the arginine part of the molecule is available for further adsorption processes. Monolayers of Arg-Cys, l -cysteine, and cysteamine are used for G-protein adsorption experiments. Adsorption of human serum albumin and human immunoglobulins on the same monolayers are studied for comparison. The analytical tool is surface plasmon resonance. Two different buffers are used for the adsorption studies, and the influence of buffer composition on protein adsorption is discussed.