Magnetic resonance imaging detects a specific peptide-protein binding event.

DOTA was conjugated to the N-terminus of a 12-mer peptide by using standard peptide synthesis chemistry. The peptide, first isolated by phage display, maintained a high affinity for its protein-binding target, Gal-80, even with GdDOTA attached. The high affinity constant (KA = 5 x 105 M-1) combined with the high relaxivity of the resulting GdDOTA-peptide.protein complex (r1bound = 44.8 +/- 1.7 mM-1 s-1) allowed detection of Gal-80 at muM levels using a standard magnetic resonance imaging protocol. This novel peptide-based, binding-activated MRI method could potentially be used to screen a wide variety of biomolecules.