Transducer Mechanism: Enzyme-Linked Receptors

Enzyme-linked receptors are cell-surface receptors that mediate signaling pathways for cell division, differentiation, or immune response, which makes them unique drug targets.

They contain transmembrane helices that connect an extracellular ligand-binding domain to the cytosolic domain, which acts as an enzyme itself or forms a complex with an enzyme.

The enzyme component can be a kinase, transferring phosphate to serines, threonines, or tyrosines in substrates; a phosphatase, removing phosphates from targets; or a guanylyl cyclase, converting GTP to cyclic GMP.

Receptor tyrosine kinases, a prominent family of enzyme-linked receptors, bind growth factors and undergo a conformational change that leads to receptor dimerization. Once dimerized, one receptor phosphorylates tyrosine residues on the other.

The phosphorylated tyrosines bind and phosphorylate target proteins, relaying the signal downstream.

Drugs can target ligand binding and the enzymatic domains of these receptors. For example, imatinib inhibits the kinase domain and blocks the phosphorylation of target proteins, preventing cancer cell multiplication.