Characterization of a cysteine-containing peptide tether immobilized onto a gold surface

One side of a triangular molecular tile has been successfully synthesized. The synthesized peptide contains two cysteines (Cys), two glutamic acids (Glu), and a p-aminomethylbenzoyl-p-benzoic acid (AMBBA). The cysteines anchor the peptide to a gold surface by formation of gold-thiolate bonds. The negatively charged glutamic acids should assist in the binding of positively charged proteins to the peptide. The rigid AMBBA provides a benzophenone group for photochemically tethering proteins to the peptide and also acts as the corner for the triangle. Electron spectroscopy for chemical analysis (ESCA) and near-edge X-ray absorption fine structure were used to characterize the composition and orientation of the AMBBA-Cys-Glu-Cys-Glu peptide on the gold surface. Adsorption from 7 muM solutions of the peptide in phosphate-buffered saline produced peptide overlayers with the thiol groups from both cysteines bound to the gold surface. The amide groups of the peptide backbone and the aromatic rings of the AMBBA groups were both oriented parallel to the gold surface. ESCA and fluorescence microscopy demonstrated that albumin could be successfully photoimmobilized to the adsorbed peptide tether. The AMBBA-Cys-Glu-Cys-Glu peptide on gold also could photochemically tether chymotrypsin. The tethered chymotrypsin was active and capable of cleaving a fluorogenic substrate. When the chymotrypsin was tethered as a positively charged protein, it exhibited higher enzyme activity than when it was tethered as a negatively charged protein. However, in all cases the activity of the bound chymotrypsin was lower than its activity in solution.