Photocontrolled Folding and Unfolding of a Collagen Triple Helix

At the flick of a switch: Two side chains of a collagen peptide containing (2S,4S)-mercaptoproline at two defined positions are linked with a diiodo azobenzene derivative. With the trans isomer of the azobenzene clamp (orange), the peptide folds into the collagen triple helix (green, blue, gray), which unfolds upon irradiation at 330 nm. The light-controlled folding/unfolding processes are fully reversible, making this system well-suited for ultrafast spectroscopic analysis.