Conformational analysis of the natural iron chelator myo-inositol 1,2,3-trisphosphate using a pyrene-based fluorescent mimic.
myo-Inositol phosphates possessing the 1,2,3-trisphosphate motif share the remarkable ability to completely inhibit iron-catalysed hydroxyl radical formation. The simplest derivative, myo-inositol 1,2,3-trisphosphate [Ins(1,2,3)P(3)], has been proposed as an intracellular iron chelator involved in iron transport. The binding conformation of Ins(1,2,3)P(3) is considered to be important to complex Fe(3+) in a 'safe' manner. Here, a pyrene-based fluorescent probe, 4,6-bispyrenoyl-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-bispyrenoyl Ins(1,2,3,5)P(4)], has been synthesised and used to monitor the conformation of the 1,2,3-trisphosphate motif using excimer fluorescence emission. Ring-flip of the cyclohexane chair to the penta-axial conformation occurs upon association with Fe(3+), evident from excimer fluorescence induced by pi-pi stacking of the pyrene reporter groups, accompanied by excimer formation by excitation at 351 nm. This effect is unique amongst biologically relevant metal cations, except for Ca(2+) cations exceeding a 1 : 1 molar ratio. In addition, the thermodynamic constants for the interaction of the fluorescent probe with Fe(3+) have been determined. The complexes formed between Fe(3+) and 4,6-bispyrenoyl Ins(1,2,3,5)P(4) display similar stability to those formed with Ins(1,2,3)P(3), indicating that the fluorescent probe acts as a good model for the 1,2,3-trisphosphate motif. This is further supported by the antioxidant properties of 4,6-bispyrenoyl Ins(1,2,3,5)P(4), which closely resemble those obtained for Ins(1,2,3)P(3). The data presented confirms that Fe(3+) binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif.
Mansell
David
D
School of Pharmacy & Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester, UK M13 9PT.
Rattray
Nicholas
N
Etchells
Laura L
LL
Schwalbe
Carl H
CH
Blake
Alexander J
AJ
Torres
Julia
J
Kremer
Carlos
C
Bichenkova
Elena V
EV
Barker
Christopher J
CJ
Freeman
Sally
S
D005456:Fluorescent Dyes / Q000737:chemistry*; D015544:Inositol 1,4,5-Trisphosphate / Q000737:chemistry; D007295:Inositol Phosphates / Q000737:chemistry*; D007502:Iron Chelating Agents / Q000737:chemistry*; D011721:Pyrenes / Q000737:chemistry*; D013329:Structure-Activity Relationship
D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D007502:Iron Chelating Agents; D011721:Pyrenes; C092449:inositol 1,2,3-trisphosphate; D015544:Inositol 1,4,5-Trisphosphate