Molecule of the Month: Influenza Neuraminidase

Drug Resistance in Neuraminidase (PDB entries 2bat, 2hu4 and 3cl0)

When designing a drug, we walk a fine line. Drugs need to be different from the natural substrate of the enzyme so that the enzyme can't catalyze a reaction to destroy it. However, drugs must also be very similar to the natural substrate of the enzyme, so that they bind tightly and block the enzyme. It is also important to make drugs similar to the natural substrates in order to avoid drug resistance. An example of this problem is shown in these three structures. The first structure shows neuraminidase with sialic acid in the active site (PDB entry 2bat ). This structure shows us how the enzyme interacts with polysaccharides during its normal reaction. The second structure shows the binding of oseltamivir, one of the drugs used to fight influenza infection (PDB entry 2hu4 ). Notice that it is similar but not identical to sialic acid: it is slightly larger and it forces a glutamate (shown in pink) to swing upwards a bit towards a neighboring histidine (also shown in pink). The third structure is a drug resistant strain of the enzyme (PDB entry 3cl0 ). The histidine has mutated to a larger tyrosine, forcing the glutamate down against the drug. The drug still binds, but not nearly as tightly, so the polysaccharide substrates can easily displace it and the drug is no longer effective against the mutant virus. However, there is still plenty of room for the sialic acid to bind, so the enzyme still works for its normal function of viral release.