Cofactor-free detection of phosphatidylserine with cyclic peptides mimicking lactadherin

Cyclic peptides (cLacs) are designed to mimic the natural phosphatidylserine (PS) binding protein lactadherin. Unlike annexin V or its small molecule mimics, the cLac peptides selectively target PS-presenting membranes with no need for metal cofactors. We further show that a fluorophore-labeled cLac effectively stains early apoptotic cells. The small size and facile conjugation with a variety of imaging tracers make the cLac design promising for imaging cell death in vitro as well as in living organisms.