There's a catch

Leukocytes are more likely to grab onto a vascular surface when under flow than in the absence of flow. This counterintuitive behavior relies on bonds between transmembrane selectins on the blood cell and their vascular ligands. These so-called “catch bonds” get stronger because flow flips open selectin into a binding-ready conformation, Lou et al. show on page 1107.

The authors have solved the structure of L-selectin, which can now be added to previous structures of P- and E-selectin. The extracellular domains of all three have an N-terminal lectin domain and an EGF-like domain that are separated by a hinge. In L- and E-selectin, the two sides of this hinge are connected by a hydrogen bond between...