Ligandbindingsdomene

Ligandbindingsdomene, often referred to as the ligand-binding domain (LBD), is a modular region in many proteins that binds ligands such as small molecules, ions, or peptides. As the functional contact point for recognizing specific ligands, the LBD modulates the activity, stability, localization, or protein–protein interactions of its host protein.

Structural features typically include a pocket or groove formed by a combination of alpha and beta elements. Ligand binding can induce conformational changes, such as domain closure or shifts in interaction surfaces, that propagate signals within the molecule. Binding mechanisms are described in terms of induced fit or conformational selection.

LBDs occur in diverse protein families. In nuclear hormone receptors, the LBD binds steroids and other lipophilic ligands and engages transcriptional regulators. Bacterial periplasmic binding proteins contain two-lobed LBDs that deliver ligands to transport systems. Extracellular ligand-binding domains of receptor tyrosine kinases and certain G protein–coupled receptors recognize growth factors or neurotransmitters. Other folds, such as the lipocalin or immunoglobulin-like domains, also serve as ligand-binding units in various contexts.

Studying LBDs relies on structural biology techniques such as X-ray crystallography, cryo-electron microscopy, and NMR, as well as biophysical binding assays and computational modeling. Understanding LBDs informs drug design, protein engineering, and the development of biosensors that detect specific ligands.