Direct Covalent Biomolecule Immobilization on Plasma-Nanotextured Chemically Stable Substrates

A new method for direct covalent immobilization of protein molecules (including antibodies) on organic polymers with plasma-induced random micronanoscale topography and stable-in-time chemical functionality is presented. This is achieved using a short (1-5 min) plasma etching and simultaneous micronanotexturing process, followed by a fast thermal annealing step, which induces accelerated hydrophobic recovery while preserving important chemical functionality created by the plasma. Surface-bound biomolecules resist harsh washing with sodium dodecyl sulfate and other detergents even at elevated temperatures, losing less than 40% of the biomolecules bound even at the harshest washing conditions. X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, and electron paramagnetic resonance are used to unveil the chemical modification of the plasma-treated and stabilized surfaces. The nanotextured and chemically stabilized surfaces are used as substrates for the development of immunochemical assays for the sensitive detection of C-reactive protein and salmonella lipopolysaccharides through immobilization of the respective analyte-specific antibodies onto them. Such substrates are stable for a period of 1 year with ambient storage.

Isolation and spectroscopic characterization of a recombinant bell pepper hydroperoxide lyase

Fatty acid hydroperoxide (HPO) lyase is a component of the oxylipin pathway and holds a central role in elicited plant defense. HPO lyase from bell pepper has been identified as a heme protein which shares 40% homology with allene oxide synthase, a cytochrome P450 (CYP74A). HPO lyase of immature bell pepper fruits was expressed in Escherichia coli and the enzyme was purified and characterized by spectroscopic techniques. The electronic structure and ligand coordination properties of the heme were investigated by using a series of exogenous ligands. The various complexes were characterized by using UV-visible absorption and electron paramagnetic resonance spectroscopy. The spectroscopic data demonstrated that the isolated recombinant HPO lyase has a pentacoordinate, high-spin heme with thiolate ligation. Addition of the neutral ligand imidazole or the anionic ligand cyanide results in the formation of hexacoordinate adducts that retain thiolate ligation. The striking similarities between both the ferric and ferrous HPO lyase-NO complexes with the analogous P450 complexes, suggest that the active sites of HPO lyase and P450 share common structural features.

Orientation of the Mn(II)-Mn(III) dimer which results from the reduction of the oxygen-evolving complex of photosystem II by NO: an electron paramagnetic resonance study

The central part of the oxygen-evolving complex of photosystem II is a cluster of four manganese atoms. The known EPR spectra in the various oxidation states of the cluster are complicated by the magnetic interactions of the four Mn ions and accordingly are difficult to analyze. It has been shown recently that NO at -30 degrees C slowly reduces the cluster to a Mn(II)-Mn(III) state [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581-3587). We study herein the orientation dependence of the Mn(II)-Mn(III) EPR spectrum with respect to the thylakoid membrane plane. Both the powder and the oriented spectra are satisfactorily simulated with the same set of fine and hyperfine parameters assuming axial symmetry and collinear g and A tensors. The axial component of the tensors is found to be oriented at an angle of 20 degrees +/- 10 degrees to the membrane plane normal (mosaic spread Omega = 40 degrees ). We make the reasonable assumption that the Mn(II)-Mn(III) dimer is one of the di-mu-oxo units that has been suggested to comprise the Mn tetramer. On the basis of the sign of the hyperfine tensor anisotropy, the axial direction is assigned to the d(z(2)) orbital of Mn(III), which by comparison with synthetic model complexes is assumed to be oriented perpendicular to the Mn-(mu-oxo)-Mn plane. The present results complement earlier orientation studies by EXAFS and suggest that the Mn-(mu-oxo)-Mn plane makes a small angle (approximately 20 degrees) with the membrane plane and the axis connecting the bridging oxygens is approximately parallel to the plane.

Interaction of nitric oxide with the oxygen evolving complex of photosystem II and manganese catalase: a comparative study

We compare the interaction of nitric oxide with the S states of the oxygen evolving complex (OEC) of photosystem II and the dinuclear Mn cluster of Thermus thermophilus catalase. Flash fluorescence studies indicate that the S3 state of the OEC in the presence of ca. 0.6 mM NO is reduced to the S1 with an apparent halftime of ca. 0.4 s at about 18 degrees C, compared with a biphasic decay, with approximate halftimes of 28 s for S3 to S2 and 140 s for S2 to S1 in the absence of NO. Under similar conditions the S2 state is reduced by NO to the S1 state with an approximate halftime of 2 s. These results extend a recent study indicating a slow reduction of the S1 state at -30 degrees C, via the S0 and S(-1) states, to a Mn(II)-Mn(III) state resembling the corresponding state in catalase. The reductive mode of action of NO is repeated with the di-Mn cluster of catalase: the Mn(III)-Mn(III) redox state is reduced to the Mn(II)-Mn(II) state via the intermediate Mn(II)-Mn(III) state. The kinetics of this reduction suggest a decreasing reduction potential with decreasing oxidation state, similar to what is observed with the active states of the OEC. What is unique about the OEC is the rapid interaction of NO with the S3 state of the OEC, which is compatible with a metalloradical character of this state.

Electron paramagnetic resonance signals from the S(3) state of the oxygen-evolving complex. A broadened radical signal induced by low-temperature near-infrared light illumination

The tetranuclear manganese cluster responsible for the oxidation of water in photosystem II cycles through five redox states denoted S(i)() (i = 0, 1, 2, 3, 4). Progress has been made recently in the detection of weak low-field EPR absorptions in both the perpendicular and parallel modes, associated with the integer spin state S(3) [Matsukawa, T., Mino, H., Yoneda, D., and Kawamori, A. (1999) Biochemistry 38, 4072-4077]. We confirm observation of these signals and have obtained them in high yield by illumination of photosystem II membranes, in which the non-heme iron was chemically preoxidized. It is shown that a split g = 4 signal accompanies the S(3) state signals. The signals diminish in the presence of ethanol and vanish in the presence of methanol. This effect is similar to that exerted by these alcohols to the high-spin component (g = 4.1) of the S(2) state and suggests that the latter spin configuration is the precursor of the S(3) state low-field signals. The S(3) state shows similar sensitivity to infrared illumination as has been observed previously in the S(2) state [Boussac, A., Un, S., Horner, O., and Rutherford, A. W. (1998) Biochemistry 37, 4001-4007]. Illumination of the S(3) state with near-infrared light (700-900 nm), at temperatures around 50 K, results in the modification of the low-field signals and most notably to the appearance of a broad (DeltaH approximately 200 G) radical-type signal centered at g = 2. The signal is tentatively assigned to the interaction of the Mn cluster in a modified S(2) state with a radical.

NO reversibly reduces the water-oxidizing complex of photosystem II through S0 and S-1 to the state characterized by the Mn(II)-Mn(III) multiline EPR signal

Incubation of photosystem II preparations with NO at -30 degreesC results in the slow formation of a unique state of the water-oxidizing complex (WOC), which was recently identified as a Mn(II)-Mn(III) dimer [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581-3587]. Evolution of the Mn(II)-Mn(III) EPR signal proceeds through one or more intermediates [Goussias, C., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261-9266]. In an effort to identify these intermediates, we have examined the time course of the signal evolution in the presence and absence of methanol. An early step of the interaction of NO with the WOC is the reduction of S1 to the S0 state, characterized by the weak Mn-hyperfine structure recently reported for that state. At longer times S0 is further reduced to a state which has the properties of the S-1 state, in that single-turnover illumination restores the S0 signal. The Mn(II)-Mn(III) state forms after the S-1 state and is tentatively assigned to an (iso)S-2 state, although lower states or a modified S-1 state cannot be excluded at present. Following removal of NO 60-65% of the initial S2 multiline signal size or the O2-evolving activity can be restored. The data provide for the first time EPR information on a state lower than S0. Furthermore, the low-temperature NO treatment provides a simple means for the selective population of the S0, S-1 and the Mn(II)-Mn(III) states.

A Mn(II)-Mn(III) EPR signal arises from the interaction of NO with the S1 state of the water-oxidizing complex of photosystem II

It was shown recently [Goussias, C., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261-9266] that incubation of photosystem II preparations with NO at -30 degrees C in the dark results in the formation of a new intermediate of the water-oxidizing complex. This is characterized by an EPR signal centered at g = 2 with prominent manganese hyperfine structure. We have examined the detailed structure of the signal using difference EPR spectroscopy. This is facilitated by the observations that NO can be completely removed without decrease or modification of the signal, and illumination at 0 degree C eliminates the signal. The signal spans 1600 G and is characterized by sharp hyperfine structure. 14NO and 15NO cw EPR combined with pulsed ENDOR and ESEEM studies show no detectable contributions of the nitrogen nucleus to the spectrum. The spectrum bears similarities to the experimental spectrum of the Mn(II)-Mn(III) catalase [Zheng, M., Khangulov, S. V., Dismukes, G. C., and Barynin, V. V. (1994) Inorg. Chem. 33, 382-387]. Simulations allowing small variations in the catalase-tensor values result in an almost accurate reproduction of the NO-induced signal. This presents strong evidence for the assignment of the latter to a magnetically isolated Mn(II)-Mn(III) dimer. Since the starting oxidation states of Mn are higher than II, we deduce that NO acts effectively as a reductant, e.g., Mn(III)-Mn(III) + NO--> Mn(II)-Mn(III) + NO+. The temperature dependence of the nonsaturated EPR-signal intensity in the range 2-20 K indicates that the signal results from a ground state. The cw microwave power saturation data in the range 4-8 K can be interpreted assuming an Orbach relaxation mechanism with an excited state at delta = 42 K. Assuming antiferromagnetic coupling, -2JS1.S2, between the two manganese ions, J is estimated to be 10 cm-1. The finding that an EPR signal from the Mn cluster of PSII can be clearly assigned to a magnetically isolated Mn(II)-Mn(III) dimer bears important consequences in interpreting the structure of the Mn cluster. Although the signal is not currently assigned to a particular S state, it arises from a state lower than S1, possibly lower than S0, too.

Low-temperature interactions of NO with the S1 and S2 states of the water-oxidizing complex of photosystem II. A novel Mn-multiline EPR signal derived from the S1 state

The spin-1/2-carrying NO molecule interacts with both the S1 and S2 states of the water oxidizing complex. The intermediates of the interaction can be resolved and trapped by NO treatment at subzero temperatures. At -30 degrees C and in the presence of approx. 500-700 microM NO, S1 loses the ability to yield by illumination an EPR active S2-state with an approximate half-time of 40-60 min. At longer incubation times (t1/2 = 4-5 h), an intense new multiline signal develops. The new signal has a hyperfine splitting similar to the S2 multiline [Dismukes, G. C., & Siderer, Y. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 274-278], but a modified shape with intense lines on the high field side. The NO modified S1 state can act as a low-temperature electron donor yielding an EPR silent state upon illumination at 200 K. NO interacts also with the S2 state of the water oxidizing complex rapidly at temperatures as low as -75 degrees C, to yield an EPR silent state. The rates of the latter interaction show analogies to the ammonia binding to the S2 state. It is possible, however, that NO, unlike ammonia, destabilizes the S2 state. On the basis of preliminary experiments with varying chloride concentrations in the range 0.1-50 mM, the S1 multiline state is attributed to binding of NO at a chloride sensitive site on the Mn cluster. The rapid interactions with the S2 state as well as the intermediate binding to the S1 state are less well understood at present, but they are tentatively assigned to the chloride-insensitive site of ammonia binding in the Mn cluster.

NO interacts with the tyrosine radical Y(D). of photosystem II to form an iminoxyl radical

Incubation of photosystem II, PSII, membranes with NO for a few minutes results in the reversible elimination of the electron paramagnetic resonance (EPR) signal II from the oxidized Tyr Y(D)., presumably due to the formation of a weak Tyr Y(D).-NO complex [Petrouleas, V., & Diner, B. A. (1990) Biochim. Biophys. Acta 1015, 131-140]. Illumination of such a sample at ambient or cryogenic temperatures produces no new EPR signals. If, however, the incubation with NO is extended to the hours time range, illumination induces an EPR signal with resolved hyperfine structure in the g = 2 region. The signal shows the typical features of an immobilized iminoxyl radical (> C=NO.) with hyperfine values A(parallel) = 44 G, A(perpendicular) = 22 G, and A(iso) = 29.3 G. The following observations suggest that the iminoxyl signal is associated with PSII: (a) the signal results from an immobilized species at room temperature probably associated with a membrane-bound component, (b) the abundance of the signal is (sub)stoichiometric to PSII, (c) the signal is light-induced, (d) some of the treatments that affect PSII (Tris, Ca2+ depletion, high-salt wash) severely diminish the size of the signal, and (e) the development of the signal correlates with the release of Mn. In addition, the following observations suggest that the iminoxyl signal results from an interaction of Y(D). with NO: (a) the evolution of the signal correlates with the loss in reversibility of the Tyr Y(D).-NO interaction and (b) the size of the signal correlates with the initial amount of oxidized Tyr Y(D). It is accordingly proposed that during the incubation with NO, a weak Tyr Y(D).-NO complex is rapidly formed and is then slowly converted to a tyrosine-nitroso adduct. Light-induced oxidation of the latter produces the iminoxyl radical. The nitrosotyrosine is expected to have an oxidation potential significantly lower than the parent tyrosine and can act as an efficient electron donor in PSII even at cryogenic temperatures. It is probably this lowered redox potential of the tyrosine Y(D) that explains the release of Mn concomitant with the formation of the nitroso species.

UV-B-induced inhibition of photosystem II electron transport studied by EPR and chlorophyll fluorescence. Impairment of donor and acceptor side components

Inhibition of photosystem II electron transport by UV-B radiation has been studied in isolated spinach photosystem II membrane particles using low-temperature EPR spectroscopy and chlorophyll fluorescence measurements. UV-B irradiation results in the rapid inhibition of oxygen evolution and the decline of variable chlorophyll fluorescence. These effects are accompanied by the loss of the multiline EPR signal arising from the S2 state of the water-oxidizing complex and the induction of Signal IIfast originating from stabilized Try-Z+. The EPR signals from the QA-Fe2+ acceptor complex, Tyr-D+, and the oxidized non-heme iron (Fe3+) are also decreased during the course of UV-B irradiation, but at a significantly slower rate than oxygen evolution and the multiline signal. The decrease of the Fe3+ signal at high g values (g = 8.06, g = 5.6) is accompanied by the induction of another EPR signal at g = 4.26 that arises most likely from the same Fe3+ ion in a modified ligand environment. UV-B irradiation also affects cytochrome b-559. The g = 2.94 EPR signal that arises from the dark- oxidized form is enhanced, whereas the light inducible g = 3.04 signal that arises from the photo-oxidizable population of cytochrome b-559 is diminished. UV-B irradiation also induces the degradation of the D1 reaction center protein. The rate of the D1 protein loss is slower than the inhibition of oxygen evolution and of the multiline signal but follows closely the loss of Signal IIslow, the QA-Fe2+ and the Fe3+ EPR signals, as well as the release of protein-bound manganese. It is concluded from the results that UV-B radiation affects photosystem II redox components at both the donor and acceptor side. The primary damage occurs at the water-oxidizing complex. Modification and/or inactivation of tyrosine-D, cytochrome b-559, and the QAFe2+ acceptor complex are subsequent events that coincide more closely with the UV-B-induced damage to the protein structure of the photosystem II reaction center.

Effects of photoinhibition on the QA-Fe2+ complex of photosystem II studied by EPR and Mössbauer spectroscopy

Effects of photoinhibition on the iron-quinone electron acceptor complex of oxygen-evolving photosystem II have been studied using low-temperature EPR and Mössbauer spectroscopy. Photoinhibition of spinach photosystem II membrane particles at 4 degrees C decreases the EPR signal arising from the interaction of QA- with Fe2+ to 30% in 90 min under our conditions. The free radical EPR signal from QA- induced by cyanide treatment of the iron [Sanakis, Y., et al. (1994) Biochemistry 33, 9922-9928] declines with the same kinetics as the QA-Fe2+ EPR signal. In contrast, Fe2+ is present in about 70% of the centers after 90 min of photoinhibition, as shown by its EPR-detected interaction with NO and by its Mössbauer absorption. Complete oxidation of this Fe2+ population to Fe3+ by ferricyanide is possible only in the presence of glycolate, which lowers the redox potential of the Fe3+/Fe2+ couple. In a fraction of PSII centers, which reach 30% after 90 min of photoinhibition, the iron cannot be detected. It is concluded that photoinhibition of oxygen-evolving photosystem II affects both QA and Fe2+. However, the photoinhibitory impairment of the QA redox functioning precedes the modification of the non-heme iron. In a considerable portion of the photoinhibited centers, which do not have functional QA, the non-heme iron is still present and redox active, but its redox potential is increased relative to that in the normal centers. This is probably due to a minor modification of the bicarbonate ligation site.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyanide binding at the non-heme Fe2+ of the iron-quinone complex of photosystem II: at high concentrations, cyanide converts the Fe2+ from high (S = 2) to low (S = 0) spin

The primary electron acceptor complex of photosystem II, QAFe2+, can bind a number of small molecules at the iron site, including cyanide [Koulougliotis, D., Kostopoulos, T., Petrouleas, V., & Diner, B. A. (1993) Biochim. Biophys. Acta 1141, 275-282)]. In the presence of NaCN (30-300 mM) at pH 6.5, the reduced state, QA-Fe2+, produced either by illumination at < or = 200 K or by reduction in the dark with sodium dithionite, is characterized by a g = 1.98 EPR signal. The light- or dithionite-induced g = 1.98 signal decays with increasing pH above 6.5 and is almost totally absent at pH 8.1 and NaCN concentrations above 300 mM. However, at high pH (8.1), the g = 1.98 signal still forms transiently before it decays with a t1/2 of approximately 30 min in spinach BBY preparations treated with 100 mM NaCN. Complementary to the disappearance of the g = 1.98 signal with increasing pH or incubation time, a new EPR signal develops at g = 2.0045. This signal has the characteristics of the semiquinone, QA-, uncoupled from its magnetic interaction with the iron. Prolonged incubation of a high pH, high cyanide treated sample in a cyanide-free medium at pH 6 restores the ability of the sample to develop the cyanide-induced g = 1.98 signal at pH 6.5. This indicates that the iron is not physically dissociated during the high pH cyanide treatment. The high pH, high cyanide effects are accompanied by the conversion of the characteristic Fe2+ (S = 2) Mössbauer doublet [isomer shift (Fe) = 1.19 mm/s, quadrupole splitting = 2.95 mm/s] to a new one with parameters (isomer shift = 0.26 mm/s, quadrupole splitting = 0.36 mm/s) characteristic of an Fe2+(S = 0) state.(ABSTRACT TRUNCATED AT 250 WORDS)

Participation of the g = 1.9 and g = 1.82 EPR forms of the semiquinone-iron complex, QA-.Fe2+ of photosystem II in the generation of the Q and C thermoluminescence bands, respectively

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about 0 degree C (Q band) and +50 degrees C (C band) in the glow curve were investigated by comparative TL and EPR measurements in DCMU-treated photosystem II particles. Decay half-time measurements carried out at -25 degrees C and +25 degrees C, respectively, suggest that the S2 state (multi-line signal) undergoes charge recombination with the g = 1.9 form of the semiquinone-iron complex, QA-.Fe2+, resulting in the appearance of the Q band, and that the g = 1.82 form of QA-.Fe2+ back-reacts with the oxidized tyrosine, YD+ (Signal IIs), accounting for the generation of the C band.

A new mechanism-based inhibitor of photosynthetic water oxidation: acetone hydrazone. 1. Equilibrium reactions

The process of photosynthetic water oxidation has been investigated by using a new type of water oxidation inhibitor, the alkyl hydrazones. Acetone hydrazone (AceH), (CH3)2CNNH2, inhibits water oxidation by a mechanism that is analogous to that of NH2OH. This involves binding to the water-oxidizing complex (WOC), followed by photoreversible reduction of manganese (loss of the S1----S2 reaction). At higher AceH concentrations the S1 state is reduced in the dark and Mn is released, albeit to a lesser extent than with NH2OH. Following extraction of Mn, AceH is able to donate electrons rapidly to the reaction center tyrosine radical Z+ (161Tyr-D1 protein), more slowly to a reaction center radical C+, and not at all to the dark-stable tyrosine radical D+ (160Tyr-D2 protein) which must be sequestered in an inaccessible site. Manganese, Z+, and C+ thus appear to be located in a common protein domain, with Mn being the first accessible donor, followed by Z+ and then C+. Photooxidation of Cyt b-559 is suppressed by AceH, indicating either reduction or competition for donation to P680+. Unexpectedly, Cl- was found not to interfere or compete with AceH for binding to the WOC in the S1 state, in contrast to the reported rate of binding of N,N-dimethylhydroxylamine, (CH3)2NOH [Beck, W., & Brudvig, G. (1988) J. Am. Chem. Soc. 110, 1517-1523]. We interpret the latter behavior as due to ionic screening of the thylakoid membrane, rather than a specific Cl- site involved in water oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

A Mössbauer analysis of the low-potential iron-sulfur center in photosystem I: spectroscopic evidence that FX is a [4Fe-4S] cluster

We report the results of a Mössbauer study of the low-potential iron-sulfur cluster FX in the Photosystem I core protein of Synechococcus 6301. The Mössbauer spectrum of FX in the oxidized state shows an isomer shift of 0.42 mm/s, which is in good agreement with the 0.43 mm/s isomer shift found in [4Fe-4S] proteins but not with the isomer shift of 0.26 mm/s found in [2Fe-2S] proteins. In the reduced state the spectrum is asymmetrically broadened at 80 K, indicating the presence of two very closely spaced doublets with an average isomer shift of 0.55 mm/s, which is also in agreement with [4Fe-4S] proteins. At 4.2 K, the spectrum exhibits broadening and magnetic splitting similar to what is observed for [4Fe-4S] proteins and quite unlike [2Fe-2S] proteins. Given the assumption that the iron atoms of FX are tetrahedrally coordinated with sulfur ligands, the data strongly support the assignment of FX as a [4Fe-4S] cluster.