receptorcoreceptor

A receptor-coreceptor is a molecular complex formed by two or more membrane proteins that work together to bind a ligand and initiate signal transduction. In such complexes, a primary receptor directly recognizes the ligand, while one or more coreceptors enhance binding, determine specificity, help recruit signaling proteins, or enable receptor activation. Coreceptors can modulate affinity, promote receptor clustering, or facilitate conformational changes that propagate a cellular response. Depending on context, a receptor may rely on different coreceptors or function without one.

Examples illustrate the diversity of receptor-coreceptor systems. In HIV infection, CD4 acts as the primary receptor for the viral envelope, while coreceptors such as CCR5 or CXCR4 are required to trigger membrane fusion and entry. In B cells, the co-receptor trio CD19, CD21, and CD81 lowers the threshold for B cell receptor signaling and shapes responses to antigens. In developmental signaling, Wnt proteins engage Frizzled receptors together with LRP5/6 as coreceptors to transmit the signal through beta-catenin. Other systems involve receptor complexes in which a coreceptor modulates ligand binding, receptor localization, or downstream kinase recruitment.

Clinical and research relevance includes the influence of coreceptors on infection susceptibility and disease progression. Genetic variants, such as CCR5-Δ32, can confer resistance to certain viral strains. Therapeutic strategies have targeted coreceptors, exemplified by CCR5 antagonists in HIV treatment. Terminology can vary by field, and some proteins act only as co-receptors, while others participate directly in signaling through their intracellular domains. The concept highlights the cooperative nature of many signaling pathways.