title: Protoporphyrin (PPIX) efflux by the MacAB-TolC pump in Escherichia coli.
abstract: In most organisms, heme biosynthesis is strictly controlled so as to avoid heme and heme precursor accumulation, which is toxic. Escherichia coli regulates heme biosynthesis by a feedback loop involving heme-induced proteolytic cleavage of HemA, glutamyl-tRNA reductase, which is the first enzyme in the heme biosynthetic pathway. We show here that heme homeostasis can be disrupted by overproduction of YfeX, a cytoplasmic protein that captures iron from heme that we named deferrochelatase. We also show that it is disrupted by iron chelation, which reduces the intracellular iron concentration necessary for loading iron into protoporphyrin IX (PPIX, the immediate heme precursor). In both cases, we established that there is an increased PPIX concentration and we demonstrate that this compound is expelled by the MacAB-TolC pump, an efflux pump involved in E. coli and Salmonella for macrolide efflux. The E. coli macAB and tolC mutants accumulate PPIX and are sensitive to photo-inactivation. The MacAB-TolC pump is required for Salmonella typhimurium survival in macrophages. We propose that PPIX is an endogenous substrate of the MacAB-TolC pump in E. coli and S. typhimurium and that this compound is produced inside bacteria when natural heme homeostasis is disrupted by iron shortage, as happens when bacteria invade the mammalian host.
authors.affiliation: Unité des Membranes Bactériennes, Département de Microbiologie, Institut Pasteur, 75724, Paris Cedex 15, France.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Turlin
authors.forename: Gesine
authors.initials: G
authors.lastname: Heuck
authors.forename: Maria Inês
authors.initials: MI
authors.lastname: Simões Brandão
authors.forename: Noémie
authors.initials: N
authors.lastname: Szili
authors.forename: J R
authors.initials: JR
authors.lastname: Mellin
authors.forename: Norbert
authors.initials: N
authors.lastname: Lange
authors.forename: Cécile
authors.initials: C
authors.lastname: Wandersman
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011524:Protoporphyrins / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C436312:MacA protein, E coli; C436313:MacB protein, E coli; D026901:Membrane Transport Proteins; D011524:Protoporphyrins; C073126:tolC protein, E coli; C028025:protoporphyrin IX
keywords: Heme homeostasy; MacAB-TolC pump; iron chelation; photosensitivity; protoporphyrin IX