Abstract
Peptides that recognize artificial materials including synthetic polymers and small molecules are drawing attention in the fields of biotechnology and chemical biology. In particular, reversible peptide aptamers that associate with the target molecules only under specific conditions are interesting. In this work, peptide aptamers that recognize a phenolphthalein derivative (PhP: a pH-sensitive organic dye) immobilized on a solid surface in a pH-dependent manner were selected using an in vitro display method (cDNA display). Considering the hydrophobic and aromatic nature of PhP, we prepared a biased DNA library (3A library) that encodes more aromatic amino acids than the standard random codon and performed seven rounds of selection from >1010 peptide species. The selected peptides including LVFLIWWM (LV59) associated with PhP-modified solid support (sepharose resin and magnetic beads) in neutral buffer but readily dissociated under basic conditions where PhP undergoes large structural change from lactone to quinoid, which is accompanied by increase of hydrophilicity and anionic charge. Control experiments suggested that LV59 recognized both phenol and lactone moieties, and the association under neutral pH is mainly driven by π-stacking and hydrophobic interaction between the peptide and PhP. Notably, however, total hydrophobicity and number of aromatic rings did not completely explain the affinity, and sequence specificity was observed to some extent. After further optimization, this interaction pair would be practically useful for protein purification.