A Fe2+ ion on the acceptor side of plant photosystem II has been substituted by Zn2+ and an anion radical of the primary acceptor quinone, Q−A, has been studied by electron spin echo method. The electron spin echo modulation shows the interaction of the unpaired electron of Q−A with nitrogen nuclei of the histidine and, probably, alanine residues situated nearby. The comparison of the modulation spectra of Q−A with those of the anion radical of plastoquinone-9 stabilized in protonated and deuterated isopropanol matrices allows one to distinguish between the spectrum lines due to the quinone protons and due to the protons of other molecules that form hydrogen bonds with the oxygen atoms of the quinones.

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Influenza virus, through cell invasion and propagation with the interaction between hemagglutinin (HA) present on its surface and glycans on the host cell, causes a rapidly spreading infection throughout the world. In the present investigation, we succeeded for the first time in the attomolar-level sensing and discrimination of influenza A viral HA molecules H1 and H5 by using a glycan-immobilized field effect transistor (FET) biosensor. The small ligand glycans immobilized on the FET device, which make effective use of the charge-detectable region for FET-based detection in terms of Debye length, gave an advantage in the highly sensitive detection of the proteins. Two kinds of trisaccharides receptors terminating in sialic acid-α2,6-galactose (6'-sialyllactose) and in sialic acid-α2,3-galactose (3'-sialyllactose) were conjugated directly with the SiO2 surface of FET devices by a simple glycoblotting method using the self-assembled monolayer (SAM) of aminooxy terminated silane-coupling reagent, 3-aminooxypropyltriethoxysilane. Furthermore, it was demonstrated that the FETs with densely immobilized glycans, which possess the high capture ability by achieving the glycoside cluster effect, clearly distinguish HA molecules between their subtypes H1 (human) and H5 (avian) at the attomolar level, while the conventional method based on HA antibodies achieves only picomolar-level detection. Our findings indicate that the glycan-immobilized FET is a promising device to detect various pathogenic bacteria and viruses through glycan-protein interaction found ubiquitously in many infectious diseases.

Articles you may be interested inRestricted orientational motion of nitroxides in molecular glasses: Direct estimation of the motional time scale basing on the comparative study of primary and stimulated electron spin echo decays J. Chem. Phys. 122, 094702 (2005); 10.1063/1.1856926Electron spin echo envelope modulation theory for high electron spin systems in weak crystal fieldThe electron spin echo envelope modulation spectra of the reduced primary acceptor quinone, Q A , in two preparations of plant photosystem II, have been studied. In one of these preparations the Fe 2ϩ ion in the quinone-iron complex has been substituted by diamagnetic Zn 2ϩ . In the other preparation this iron ion has been converted into the diamagnetic state using a potassium cyanide treatment. A comparative analysis of two-dimensional three-pulse electron spin echo envelope modulation spectra has shown similar structure of the binding site of Q A in both preparations. Two nitrogen nuclei have been found to contribute to the spectra in both preparations. One of these nitrogens is, most probably, an amino nitrogen in the imidazole ring of histidine 215 of the D2 protein. The other nitrogen has been assigned to the peptide group of alanine 261 of the D2 protein. The numerical simulations of the electron spin echo envelope modulation spectra have shown that both nitrogens are simultaneously bound to Q A .

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