Hemagglutinin (H5N1 influenza A virus) (HA)

H5N1 influenza A virus hemagglutinin (HA) is a critical surface glycoprotein that mediates the initial stages of viral infection [UniProt, Wikipedia]. It functions as a homotrimeric protein consisting of two subunits, HA1 and HA2, which are responsible for receptor binding and membrane fusion, respectively [UniProt, PubMed]. HA binds to sialic acid-containing receptors on the host cell surface, triggering viral internalization via endocytosis [UniProt, NIH]. Upon exposure to the acidic environment of the endosome, HA undergoes a dramatic conformational change that facilitates the fusion of the viral envelope with the host membrane, releasing the viral genome into the cytoplasm [Wikipedia, PubMed]. In the context of H5N1, HA is a primary determinant of the virus's high pathogenicity and its ability to cross species barriers [NIH, PubMed]. It is the principal target for neutralizing antibodies and the primary component of influenza vaccines, such as Audenz, making it a central focus for therapeutic and prophylactic interventions against potential pandemics [FDA, PubMed]. Drugs targeting HA typically work by blocking the receptor-binding site or preventing the conformational change required for fusion [NIH, PubMed]. The protein's high rate of mutation, known as antigenic drift, poses a significant challenge for long-term vaccine efficacy and drug development [UniProt, NIH].

Other names

H5H5 HAH5N1 HAHemagglutinin antigenInfluenza A virus H5N1 hemagglutinin

Neutralization of viral attachment by binding to the receptor-binding site; inhibition of membrane fusion by stabilizing the prefusion conformation of the HA stem.