Fluorescence-based peptide screening using ligand peptides directly conjugated to a thiolated glass surface

Functional peptides from peptide libraries are frequently screened using an array format. We report here results of a feasibility study of fluorescence-based peptide screening using an array format on surface-modified glass. The surface of an amine-coated glass slide was modified to contain thiol groups by iminothiolane treatment. The epsilon-amine of the C-terminal lysine from a ligand peptide was iodinated and then spotted onto the thiolated glass surface to covalently conjugate the ligand peptide to the surface via a thioether bond. This covalent immobilization allowed the ligand peptides to withstand washing steps by tightly adhering to the glass surface and confining their subsequent binding reactions within a spotted area. Two representative peptides were used as the ligand peptides; a 'target' (positive) heptapeptide that could specifically bind to trypsin, and a 'control' (negative) hexapeptide that had no binding affinity with trypsin. When fluorescein isothiocyanate-labeled trypsin was reacted with the ligand peptides, the target peptide demonstrated distinctively higher (ca. 8.7-fold) fluorescence intensity that was easily differentiated from the control peptide by a fluorescence scanner. A separate experiment using a quartz crystal microbalance confirmed that the difference in binding mass (ca. 9.1-fold) was very close to that seen in fluorescence intensity. These results suggested a quantitative, 1:1 correlation between mass and fluorescence signals. Furthermore, a smaller spot volume and a higher ligand peptide concentration resulted in higher fluorescence signal intensity. This study provides information on the potential for using fluorescence-based screening of functional peptides on a glass array format.