Which cell adhesion receptors display Ca2+ independent binding?

The correct choice is the immunoglobulin superfamily (IgSF) because these cell adhesion receptors utilize a mechanism for binding that does not depend on calcium ions (Ca2+). Instead, their adhesion is primarily mediated through the interaction of their immunoglobulin-like domains, which can interact with other proteins through non-covalent bonds such as hydrogen bonds, van der Waals forces, and ionic interactions.

Understanding the role of Calcium in other adhesion molecules reveals why IgSF is distinct. For example, cadherins require Ca2+ for their structural and functional integrity, as calcium ions stabilize the binding sites of cadherin molecules on adjacent cells. Integrins, on the other hand, also have Ca2+ dependent binding, relying on divalent cations for activation and stabilization of their ligand-binding sites. Selectins are another class of adhesion receptors that typically bind in a Ca2+-dependent manner as well, as their lectin-like domains require calcium to recognize specific carbohydrate ligands.

Therefore, the IgSF is unique in its ability to facilitate cell adhesion through mechanisms that do not require the presence of calcium ions, highlighting its importance in various biological processes, including immune responses and tissue development.