title: Microcystin-LR Binds Iron, and Iron Promotes Self-Assembly.
abstract: The microcystin-producing Microcystis aeruginosa PCC 7806 and its close strain, the nonproducing Microcystis aeruginosa PCC 7005, grow similarly in the presence of 17 μM iron. Under severe iron deficient conditions (0.05 μM), the toxigenic strain grows slightly less than in iron-replete conditions, while the nonproducing microcystin strain is not able to grow. Isothermal titration calorimetry performed at cyanobacterial cytosol or meaningful environmental pHs values shows a microcystin-LR dissociaton constant for Fe2+and Fe3+of 2.4 μM. Using atomic force microscopy, 40% of microcystin-LR dimers were observed, and the presence of iron promoted its oligomerization up to six units. Microcystin-LR binds also Mo6+, Cu2+, and Mn2+. Polymeric microcystin binding iron may be related with a toxic cell colony advantage, providing enhanced iron bioavailability and perhaps affecting the structure of the gelatinous sheath. Inside cells, with microcystin implicated in the fitness of the photosynthetic machinery under stress conditions, the toxin would be involved in avoiding metal-dependent Fenton reactions when photooxidation causes disassembly of the iron-rich photosystems. Additionally, it could be hypothesized that polymerization-depolymerization dynamics may be an additional signal that could trigger changes (for example, in the binding of microcystin to proteins).
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Ceballos-Laita
authors.forename: Carlos
authors.initials: C
authors.lastname: Marcuello
authors.forename: Anabel
authors.identifier: http://orcid.org/0000-0001-7460-5916
authors.initials: A
authors.lastname: Lostao
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Calvo-Begueria
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: Adrián
authors.initials: A
authors.lastname: Velazquez-Campoy
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Bes
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: María F
authors.initials: MF
authors.lastname: Fillat
authors.affiliation: Institute for Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC) , Aragón 50018, Spain.
authors.forename: María-Luisa
authors.initials: ML
authors.lastname: Peleato
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D052998:Microcystins / Q000378:metabolism*; D046931:Microcystis / Q000378:metabolism; D010456:Peptides, Cyclic; D010788:Photosynthesis
chemical_list: D052998:Microcystins; D010456:Peptides, Cyclic; D007501:Iron