RBDs

Receptor-binding domains (RBDs) are regions on the surface proteins of many viruses that mediate attachment to host cells by recognizing specific cellular receptors. RBDs are central to viral entry and can influence host range and tissue tropism. In coronaviruses, the RBD is part of the spike glycoprotein and binds to receptors such as ACE2, enabling subsequent membrane fusion after conformational changes. RBDs are a common feature across diverse virus families and are frequent targets of neutralizing antibodies.

Structure and dynamics: RBDs often exhibit conformational flexibility, exposing the receptor-binding site in some states while occluding it in others. They typically contain loops and motifs that form a pocket or interface for the receptor. Mutations within an RBD can alter binding affinity and specificity, potentially expanding host range or affecting transmissibility and immune recognition. Comparative analysis of RBD sequences helps track evolution and variant lineages.

Research methods: Structural approaches such as cryo-electron microscopy and X-ray crystallography reveal RBD architecture. Biophysical assays, including surface plasmon resonance and biolayer interferometry, measure receptor affinity. Functional assays assess viral entry and neutralization by antibodies. Studies often combine structural, biochemical, and clinical data to understand how RBD variation shapes infectivity and immune escape.

Impact and applications: Knowledge of RBDs informs public health responses, surveillance for new variants, and design of vaccines and therapeutics. Many vaccines and monoclonal antibodies target RBD epitopes to block receptor engagement. Because RBDs balance functional constraints with selective pressure from the host immune system, they remain a focal point in the study of viral evolution and pathogenesis.