Structural dynamics at the active site of the cancer-associated flavoenzyme NQO1 probed by chemical modification with PMSF

A large conformational heterogeneity of human NAD(P)H:quinone oxidoreductase 1 (NQO1), a flavoprotein associated with various human diseases, has been observed to occur in the catalytic site of the enzyme. Here, we report the X-ray structure of NQO1 with phenylmethylsulfonyl fluoride (PMSF) at 1.6 angstrom resolution. Activity assays confirmed that, despite being covalently bound to the Tyr128 residue at the catalytic site, PMSF did not abolish NQO1 activity. This may indicate that the PMSF molecule does not reduce the high flexibility of Tyr128, thus allowing NADH and DCPIP substrates to bind to the enzyme. Our results show that targeting Tyr128, a key residue in NQO1 function, with small covalently bound molecules could possibly not be a good drug discovery strategy to inhibit this enzyme. Human NAD(P)H:quinone oxidoreductase 1 (NQO1), a flavoenzyme associated with a variety of human diseases, possesses high plasticity in the catalytic site. We report the crystal structure of NQO1 with phenylmethylsulfonyl fluoride (PMSF) covalently bound to the Tyr128 residue. We show that, unexpectedly, the catalytic activity of the enzyme was not abolished, indicating that the PMSF molecule does not limit the dynamics of this residue.image

Automated summary

This study reports the crystal structure of human NQO1 enzyme in covalent complex with PMSF, which unexpectedly does not abolish the enzyme's catalytic activity, indicating that the flexibility of the key residue Tyr128 may not be reduced by the PMSF molecule.