Séminaire de l'IFR Institut de Microbiologie de la Méditerranée

Cécile WANDERSMAN : « Les systèmes bactériens d'acquisition et de métabolisme de l'hème : vieilles protéines avec de nouvelles fonctions »

Résumé :

Since heme is the major iron-containing molecule in vertebrates, the ability to use heme-bound iron is a determining factor in successful infection by bacterial pathogens. Heme is extracted from hemoproteins either in the extra cellular medium by hemophores or directly at the cell surface by heme or hemoprotein receptors. In Gram-negative bacteria, heme docked to the cell surface is transported through the outer membrane by an energy dependent process. In Gram-positive bacteria, docked heme is transferred to membrane-anchored heme binding lipoproteins. In all the so far described systems, heme is actively transported through the plasma membrane by an ATP hydrolysis-powered ABC transporter. In the cytoplasm, heme is degraded and iron is recovered. Until today, all known enzymes performing iron extraction from heme did so through the rupture of the tetrapyrrol skeleton. We have identified two Escherichia coli paralogs, highly conserved in bacteria, without any previously known physiological functions, that promote iron extraction from heme preserving the tetrapyrrol ring intact. This novel enzymatic reaction corresponds to a reverse ferrochelatase activity, termed as deferrochelatase activity. They are the sole proteins able to provide iron from exogenous heme to E. coli.