Integrin-Targeting Fluorescent Proteins: Exploration of RGD Insertion Sites.

The potential of the fluorescent protein scaffold to control peptide sequence functionality is illustrated by an exploration of fluorescent proteins as novel probes for targeting integrins. A library of fluorescent mCitrine proteins with RGD motifs incorporated at several positions in loops within the protein main chain was generated and characterized. Amino acid mutations to RGD as well as RGD insertions were evaluated: both led to constructs with typical mCitrine fluorescent properties. Screening experiments against four human integrin receptors revealed two strong-binding constructs and two selective integrin binders. The effect of the site of RGD incorporation illustrates the importance of the protein scaffold on RGD sequence functionality, leading to fluorescent protein constructs with the potential for selective integrin targeting.