Influenza virus neuraminidase (vNEU) consists of 4 co-planar roughly spherical subunits predominantly made of β-sheets, characterized as a 6-fold β-propeller and a hydrophobic region embedded in the virus’ membrane. The active site is located near the middle of the pseudo-symmetric sphere. Influenza virus neuraminidase only cleaves terminal Neu5Ac residues. X-ray crystallography has shown a distorted half-chair arrangement of the Neu5Ac substrate in the active site. This distorted structure forms a sialosyl cation after the release of the aglycon and is then trapped in the active site by a nucleophilic attack of the tyrosine residue. The orientation of the substrate in the active site is facilitated mainly by three strain-preserved Arginine residues binding the C1 acid group with salt bridges. Furthermore, the active site consists of eight other highly conserved amino acid-residues that make direct contact to the substrate or its derivatives. Including a glutamic acid residue binding the C7 and C9 alcohol groups on the glycerol side-chain (at C6) with hydrogen bonds and several hydrophobic residues correlating with the methyl group on the C5 N-acetyl and the hydrophobic backbone of the glycerol.