Library-Based Development of New Optical Imaging Probes

Young-Tae Chang’s group has expanded their library of novel rosamine fluorophore analogs synthesized by combinatorial solid-phase chemistry. These probes display a wide range of quantum efficiencies, and absorbance and emission wavelengths. The rosamine library has been screened in cell imaging and bio-analyte response assays (Wang et al., JACS, 2006). A major effort has been directed towards screening this library against a bead-attached peptide library, in order to identify specific and high affinity fluorophore-peptide pairs, to be eventually used for site-specific protein labeling in living cells. A 10-member library of 10-mer peptides was screened against the rosamine library, and the brightest peptide beads were selected on a fluorescence scanner with UV irradiation. These peptides were sequenced, re-synthesized on a large scale, and tested again for binding to the rosamine compound. One peptide-rosamine pair has been found with 4 μM dissociation constant and a 15-fold increase in fluorescence intensity upon binding. We are now optimizing the peptide sequence and length and completing our characterization of this labeling system.