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Influenza neuraminidase is a glycoprotein in the influenza virus membrane. Before an infected cell can release the virus into its surroundings to infect new cells, neuraminidase must cleave sialic acid from both virus and cellular glycoproteins. Neuraminidase is a homotetramer -- here we will examine only one monomer.

Exploring the Structure

Because of its important role in virus infectivity, several anti-viral drugs have been designed to target neuraminidase, including oseltamivir (Tamiflu) and zanamivir (Relenza). Oseltamavir binding to neuraminidase moves glutamate 276 towards histidine 274, making more room for oseltamavir to bind tightly (PDB entry 2hu4). But, in a common mutant (H274Y), a larger tyrosine replaces the smaller histidine 274, preventing glutamate 276 from moving to make room for oseltamavir binding, resulting in weaker drug binding and thus resistance (PDB entry 3cl0). Luckily the H274Y neuraminidase mutant is still susceptible to zanamivir, which is smaller than oseltamavir.