title: Protein design provides lead(II) ion biosensors for imaging molecular fluxes around red blood cells.
abstract: Metalloprotein design and semiconductor nanoparticles have been combined to generate a reagent for selective fluorescence imaging of Pb(2+) ions in the presence red blood cells. A biosensor system based on semiconductor nanoparticles provides the photonic properties for small molecule measurement in and around red blood cells. Metalloprotein design was used to generate a Pb(2+) ion selective receptor from a protein that is structurally homologous to a protein used previously in this biosensing system. Parameters for the Pb(2+) ion binding site were derived from crystallographic structures of low molecular weight Pb(2+) ion complexes that contain a stereoactive lone pair. When the designed protein was produced and attached to ZnS-coated CdSe nanoparticles, two Pb(NO(3))(2)-associated binding events were observed (2-fold emission decrease; K(A1) = 1 x 10(9) M(-1); K(A2) = 3.5 x 10(6) M(-1)). The fluorescence response had a 100 pM Pb(NO(3))(2) detection limit, while no response was observed with Ca(2+) ions (10 mM), Zn(2+) ions (100 muM), or Cd(2+) ions (100 muM). Metal ion selectivity presumably comes from the coordination geometry selected to favor lone pair formation on Pb(2+) ions and electrostatically disfavor tetrahedral coordination. Replacement of ZnS-coated CdSe with ZnS-coated InGaP nanoparticles provided similar biosensors (100 pM limit of detection; K(A1) = 1 x 10(9) M(-1); K(A2) = 1 x 10(7) M(-1)) but with excitation/emission wavelengths longer than the major absorbance of red blood cell hemoglobin (>620 nm). The InGaP nanoparticle-based biosensors provided a 5 nM Pb(NO(3))(2) detection limit in the presence of red blood cells. The modularity of the biosensor system provides exchangeable Pb(2+) ion detection around red blood cells.
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
authors.forename: Vivekanand S
authors.initials: VS
authors.lastname: Shete
authors.forename: David E
authors.initials: DE
authors.lastname: Benson
mesh_terms: D001665:Binding Sites; D015374:Biosensing Techniques / Q000379:methods*; D002413:Cations, Divalent / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods; D004912:Erythrocytes / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D007854:Lead / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D000073718:Pancreatitis-Associated Proteins; D010316:Particle Size; D055585:Physical Phenomena; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D045663:Quantum Dots; D015203:Reproducibility of Results
chemical_list: D002413:Cations, Divalent; D000073718:Pancreatitis-Associated Proteins; D011506:Proteins; C000612141:REG3A protein, human; D007854:Lead