INHIBITION BY PRODUCT. A DIFFERENTIAL MODE OF REGULATION BETWEEN FERREDOXIN-NADP+ REDUCTASES

CECCARELLI, EDUARDO A.; CATALANO DUPUY, DANIELA L.; MONCHIETTI, PAULA

Buenos Aires

Congreso; REUNIÓN CONJUNTA DE SOCIEDADES DE BIOCIENCIAS; 2017

SOCIEDAD ARGENTINA DE INVESTIGACIÓN BIOQUÍMICA Y BIOLOGÍA MOLECULAR (SAIB) y otras

Ferredoxin-NADP+ reductases (FNR) are flavoenzymes involved in biologically relevant processes. FNR catalyzes the reversible electron transfer between NADP(H) and ferredoxin or flavodoxin. The reaction involves a hydride exchange with the pyridine nucleotide and then an electron transfer to or from the other substrate. We have previously identified that Escherichia coli FNR is purified with the substrate/product NADP+ tightly bound. The nucleotide binding produces an inhibition of the enzyme activity which is lost when NADP+ is released. Our findings suggest that this inhibition may have a regulatory function on this bacterial FNR and would implicate a different catalytic mechanism than the one reported for the plastidic enzymes. E. coli FNR belongs to one of the three plant-type FNR groups in which these enzymes can be classified. These groups have well-identified structural differences. One of the most relevant is located in the carboxyl terminus of FNR, where NADP+ binding and catalysis occur. We have comparatively studied the catalytic properties of FNR from different pathogenic bacteria: E. coli, Pectobacterium carotovorum, Brucella abortus and Leptospira interrogans, in order to determine if the phenomenon observed in E. coli reductase is a unique process of bacterial FNR. We found that all the aforementioned reductases, except L. interrogans FNR, contain NADP+ bound. Moreover, kinetic analyses of these enzymes allowed establishing a direct correlation between the ability of high-affinity binding of NADP+ and a decrease of their catalytic efficiences. It is important to note that L. interrogans possesses a plastidic FNR. We propose that this regulation would be an important aspect of the functionality of the enzymes and, therefore, in the regulation of redox homeostasis in bacteria. From these results, we propose using this high-affinity binding as a differential target for the inactivation of metabolic pathways in which FNR participate in pathogenic bacteria.