receptorfamilies

Receptor families are groups of receptor proteins that detect specific extracellular signals, such as hormones, neurotransmitters, or environmental cues, and translate them into cellular responses. Members within a family share structural features, conserved sequence motifs, and related signaling strategies, which reflect common evolutionary origin. Receptors can be transmembrane proteins that span the cell membrane or intracellular receptors that act within the nucleus or cytoplasm. Families are commonly defined by topology, domain organization, and functional properties rather than by exact ligand identity alone.

Major receptor families include G protein-coupled receptors (GPCRs), characterized by seven transmembrane helices and coupling to heterotrimeric G proteins; receptor tyrosine kinases (RTKs), which have an extracellular ligand-binding domain and an intracellular tyrosine kinase; ligand-gated ion channels, which control ion flux in response to ligand binding; and nuclear receptors, which function as transcription factors after ligand binding. Additional examples include cytokine receptors and serine/threonine kinases, as well as plant receptor-like kinases with extracellular sensing domains.

Activation of a receptor family typically begins with ligand binding, triggering conformational changes that propagate signals through intracellular partners. GPCRs activate G proteins to regulate second messengers; RTKs trigger phosphorylation cascades; LGICs alter ion permeability; nuclear receptors modulate gene expression. Receptor families expand through gene duplication and diversification, contributing to physiological complexity and pharmacological diversity. Many receptor families are major drug targets in medicine.

Classification relies on sequence similarity, domain architecture, and functional assays, complemented by structural biology and phylogenetic analyses. Studying receptor families illuminates how cells perceive signals and coordinate responses across tissues and species.