Hemagglutinin

Part of speech: noun

Definitions

1. A protein found on the surface of certain viruses that causes red blood cells to clump together and facilitates the virus's entry into host cells
2. A viral surface glycoprotein that binds to sialic acid on red blood cells, promoting their aggregation and enabling the virus to infect target cells
3. A molecule present on some viruses that induces the agglutination of erythrocytes and aids in attachment and penetration of host cells during infection

Etymology: Hemagglutinin is a compound built from two pieces. Its second part, "agglutinin," comes from Latin "agglutinare," meaning "to glue to," itself built from "ad-" ("to") and "gluten" ("glue"). That Latin root reaches back to an ancient word for glue, which is also the source of English "gluten." The word "agglutinin" was formed in English as a term for a substance that causes cells or particles to clump together, and "hem-" is simply the combining form of "haem," the blood, so the whole word means something like a blood-clumping agent. The clumping sense is the key. Hemagglutinin names a protein on the surface of a virus, such as influenza, that makes red blood cells stick together. That clumping is not an accident of the virus's chemistry: it is the mechanism by which the protein lets the virus attach to cells it infects. The "glue" in the word therefore describes a real biological function rather than a loose metaphor.

Synonyms: agglutinin, lectin, viral protein