Deglycation activity of the Escherichia coli glycolytic enzyme phosphoglucose isomerase

Glycation is a spontaneous chemical reaction, which affects the structure and function of proteins under normal physiological conditions. Therefore, organisms have evolved diverse mechanisms to combat glycation. In this study, we show that the Escherichia coli glycolytic enzyme phosphoglucose isomerase (Pgi) exhibits deglycation activity. We found that E. coli Pgi catalyzes the breakdown of glucose 6-phosphate (G6P)-derived Amadori products (APs) in chicken lysozyme. The affinity of Pgi to the glycated lysozyme (K_m, 1.1 mM) was ten times lower than the affinity to its native substrate, fructose 6-phosphate (K_m, 0.1 mM). However, the high kinetic constants of the enzyme with the glycated lysozyme (k_cat, 396 s^-1 and k_cat/K_m, 3.6 × 10⁵ M^-1 s^-1) indicated that the Pgi amadoriase activity may have physiological implications. Indeed, when using total E. coli protein (20 mg/mL) as a substrate in the deglycation reaction, we observed a release of G6P from the bacterial protein at a Pgi specific activity of 33 μmol/min/mg. Further, we detected 11.4 % lower APs concentration in protein extracts from Pgi-proficient vs. deficient cells (p = 0.0006) under conditions where the G6P concentration in Pgi-proficient cells was four times higher than in Pgi-deficient cells (p = 0.0001). Altogether, these data point to physiological relevance of the Pgi deglycation activity.