A single evolutionarily divergent mutation determines the different FAD-binding affinities of human and rat NQO1 due to site-specific phosphorylation

Phenotypic Modulation of Cancer-Associated Antioxidant NQO1 Activity by Post-Translational Modifications and the Natural Diversity of the Human Genome

Human NAD(P)H:quinone oxidoreductase 1 (hNQO1) is a multifunctional and antioxidant stress protein whose expression is controlled by the Nrf2 signaling pathway. hNQO1 dysregulation is associated with cancer and neurological disorders. Recent works have shown that its activity is also modulated by different post-translational modifications (PTMs), such as phosphorylation, acetylation and ubiquitination, and these may synergize with naturally-occurring and inactivating polymorphisms and mutations. Herein, I describe recent advances in the study of the effect of PTMs and genetic variations on the structure and function of hNQO1 and their relationship with disease development in different genetic backgrounds, as well as the physiological roles of these modifications. I pay particular attention to the long-range allosteric effects exerted by PTMs and natural variation on the multiple functions of hNQO1.

Different phenotypic outcome due to site-specific phosphorylation in the cancer-associated NQO1 enzyme studied by phosphomimetic mutations

Protein phosphorylation is a common phenomenon in human flavoproteins although the functional consequences of this site-specific modification are largely unknown. Here, we evaluated the effects of site-specific phosphorylation (using phosphomimetic mutations at sites S40, S82 and T128) on multiple functional aspects as well as in the structural stability of the antioxidant and disease-associated human flavoprotein NQO1 using biophysical and biochemical methods. In vitro biophysical studies revealed effects of phosphorylation at different sites such as decreased binding affinity for FAD and structural stability of its binding site (S82), conformational stability (S40 and S82) and reduced catalytic efficiency and functional cooperativity (T128). Local stability measurements by H/D exchange in different ligation states provided structural insight into these effects. Transfection of eukaryotic cells showed that phosphorylation at sites S40 and S82 may reduce steady-levels of NQO1 protein by enhanced proteasome-induced degradation. We show that site-specific phosphorylation of human NQO1 may cause pleiotropic and counterintuitive effects on this multifunctional protein with potential implications for its relationships with human disease. Our approach allows to establish relationships between site-specific phosphorylation, functional and structural stability effects in vitro and inside cells paving the way for more detailed analyses of phosphorylation at the flavoproteome scale.