Structural Biology on Molecular Mechanism of Low-Affinity Protein-Protein Interactions on the Cell Membrane

Protein-protein interactions are essential in diverse cellular processes including signal transduction. It is not uncommon for protein-protein interactions in the transmembrane signaling to exhibit low binding affinities with a dissociation constant in the μM range or higher. Presumably, membrane proteins can selectively bind with their binding partners via low-affinity interactions because they can only diffuse laterally in the membrane plane and interact with the partners within a limited space on the membrane surface or within the membrane. This review focuses on the crystallographic studies on cell-surface receptors and intramembrane proteases that perform the transmembrane signaling mediated by low-affinity protein-protein interactions.