How might substrate specificity, a protein's designed ability to interact only with very specific molecular shapes, play a role in the cell-cell identification process that features glycoproteins and receptors? What are the real-world human health consequences of this specificity?

A signal molecule must bind to its receptor to initiate a response. Receptors are proteins that bind to their signal molecule either externally (cell-surface receptors) or internally (nuclear receptors) within the cytoplasm or nucleus ... Once a ligand binds to its receptor, a series of reactions are initiated.