Antagonist

Any substance that blocks agonist binding and/or inhibits an agonist-induced biological response. Many antagonists are structural analogues of the corresponding agonists, and molecular mimicry permits antagonists to bind at a receptor binding site in a manner that blocks or alters the typical agonist-induced response. Antagonists can sometimes also interfere with downstream steps in signal-transduction cascades triggered by an agonist. Some antagonists show no obvious structural similarity to the agonist, and antagonist binding to the receptor is thought to convert the occupied receptor to a conformation which blocks agonist binding.

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