title: Borate binding to siderophores: structure and stability.
abstract: Well-known as specific iron chelating agents produced by bacteria, it is shown that some, but not all, siderophore classes have an unexpected binding affinity for boron. The relevant criterium is the availability of a vicinal dianionic oxygen containing binding group (i.e., citrate or catecholate). The resulting boron complexes have been characterized by ESI-MS, multinuclear NMR, and DFT calculations. Detailed boron binding constants have been measured for vibrioferrin, rhizoferrin, and petrobactin. The observed affinity of certain siderophores for borate, a common chemical species in the marine but not the terrestrial environment, allows for small, but potentially significant, concentrations of B-siderophores to exist at oceanic pH. We hypothesize that these concentrations could be sufficient for them to function as cell signaling molecules or as mediators of biological boron uptake. In addition, binding of the tetrahedral boron to these siderophores results in a conformation that is different from either the free siderophore or its iron complex and would thus allow a distinction to be made between its iron uptake and any putative cell signaling roles.
authors.affiliation: Department of Chemistry and Biochemistry, San Diego State University, San Diego, California 92182-1030, USA.
authors.forename: Wesley R
authors.initials: WR
authors.lastname: Harris
authors.forename: Shady A
authors.initials: SA
authors.lastname: Amin
authors.forename: Frithjof C
authors.initials: FC
authors.lastname: Küpper
authors.forename: David H
authors.initials: DH
authors.lastname: Green
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Carrano
mesh_terms: D001549:Benzamides / Q000737:chemistry / Q000378:metabolism; D001667:Binding, Competitive; D001881:Borates / Q000737:chemistry / Q000378:metabolism; D001895:Boron / Q000737:chemistry* / Q000378:metabolism; D002951:Citrates / Q000737:chemistry / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D006877:Hydroxamic Acids / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D053520:Marinobacter / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D019906:Nuclear Magnetic Resonance, Biomolecular; D011199:Potentiometry; D011760:Pyrrolidinones / Q000737:chemistry / Q000378:metabolism; D017262:Siderophores / Q000737:chemistry* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship
chemical_list: D001549:Benzamides; D001881:Borates; D002951:Citrates; D005290:Ferric Compounds; D006877:Hydroxamic Acids; D011760:Pyrrolidinones; D017262:Siderophores; C450699:petrobactin; C087496:rhizoferrin; C090126:vibrioferrin; C031819:aerobactin; D001895:Boron