Deactivation by S-Glutathionylation overrules activation by PRMT1-dependent asymmetrical di-methylation in PFKFB3

To understand PFKFB3 control by covalent modifications, the structure/function effect of protein arginine methyl transferase 1-dependent asymmetric di-methylations at Arg131 and Arg134 (N-CH3) and its relationship to S-glutathionylation at Cys206 (S-Gsh) was investigated. Distinctly from the report that N-CH3 is for protection of PFKFB3 from the APC/C-Cdh-mediated polyubiquitination and proteolysis, an increase in the activity for Fru-2,6-P₂ production was shown from a molecular simulation and in-vitro tests. The simulation suggested that N-CH3 would uncouple the Fru-6-P entry turn (-¹³⁰TRERRH-) from its coupling to the p-helix (-²⁰⁴DKCDRD-) by disabling the interaction between Arg131/134 and Asp207. The uncoupling consequently is likely to facilitate the Fru-6-P binding by enhancing the conformational flexibility.

Confirming the simulation, N-CH3 was shown to cause a 5-fold increase in the specific activity (k_cat/K_m) mostly through a 4-fold decrease in K_ms for Fru-6-P. A similar extent of activation was induced by Asp207àA mutagenesis, which disables the coupling, while the activation by N-CH3 was almost abolished by Arg131àA mutagenesis. More interestingly, PFKFB3 with N-CH3 could be additionally S-glutathionylated at Cys206, when oxidative stress is elevated. When modified by both N-CH3 and S-Gsh, the activity was decreased, as if there was no N-CH3 at all, suggesting that the deactivation completely overrules the activation.

When HeLa cells were treated for the dual modifications of PFKFB3, the overruling deactivation effect of S-Gsh was prevalent, causing decreases in Fru-2,6-P₂ levels and increases in glycolytic flux redirected to the pentose phosphate pathway. As a result, the levels of NADPH and reduced glutathione were markedly elevated, enhancing cell viability under the conditions of elevated oxidative stress. Altogether, it is suggested that the functional effect of S-Gsh, which represents a mechanism for survival under detrimental oxidative stress, dominates over the effect of N-CH3, which has been suggested as a mechanism for growth.