nonreceptor

Nonreceptors are molecular targets that produce biological effects without functioning as receptors for extracellular ligands in the classic sense. In cell biology and pharmacology, the term is used to describe proteins and other molecules that participate in signaling and cellular regulation but do not bind ligands as cell-surface receptors (such as GPCRs) do. Nonreceptors can act as enzymes, transporters, structural components, or scaffolds that influence signaling cascades and metabolic pathways.

Common classes of nonreceptors include nonreceptor tyrosine kinases (for example Src and Abl), serine/threonine kinases, phosphatases, proteasomes, and various metabolic enzymes. Other examples are membrane transporters and certain intracellular signaling proteins that modulate pathways without serving as ligand-binding receptors. By acting on substrates, post-translational modifiers, or transcriptional regulators, nonreceptors can alter cellular responses to stimuli initiated by receptors or other cues.

In pharmacology, nonreceptors are important drug targets. Inhibitors of kinases, proteases, or enzymes can modify disease processes even when the target is not a receptor. This contrasts with drugs that act primarily by activating or blocking receptor signaling. Understanding nonreceptor targets helps explain mechanisms of action for many therapeutics and highlights the diversity of cellular regulation beyond classical receptor biology.