Long-lifetime Ru(II) complexes as labeling reagents for sulfhydryl groups

Activating the delivery of a model drug to lipid membrane by encapsulation of cyclodextrin: Combined experimental and molecular docking studies

Drug delivery science is always an important topic as it studies the delivery of therapeutic payloads to the desired target cells without affecting the healthy tissues/cells, thus minimizing drug-induced toxicity. Aiming towards the targeted drug delivery, the present project deals with the delivery of a polarity-sensitive solvatochromic model drug, namely, salt of 8-anilinonaphthalene-1-sulphonic acid (ANSA) to the model bio-membrane (which mimic several aspects of the real cell membrane), more precisely at the lipid-water interface of L-α-Dipalmitoylphosphatidylcholine (DPPC) phospholipid. The drug delivery process has been activated through the binding of dye with cyclodextrin, acting as a drug transporter. Detailed steady-state and time-resolved spectroscopic studies including molecular docking analysis imply the targeted drug delivery of dye, ANSA, towards the lipid-water interface region of lipid bilayers through encapsulation within the cyclodextrin void. Stronger binding interaction of the dye with the lipid bilayers relative to β-cyclodextrin (β-CD) is the foremost reason for the targeted delivery. The present biophysical interaction studies of drug-lipid interaction, thus, may provide a cordial approach for drug formulation and drug delivery.

Multi-target antibacterial mechanism of ruthenium polypyridine complexes with anthraquinone groups against Staphylococcus aureus

Three new Ru(ii) complexes, [Ru(dtb)2PPAD](PF6)2 (Ru-1), [Ru(dmob)2PPAD](PF6)2 (Ru-2) and [Ru(bpy)2PPAD](PF6)2 (Ru-3) (dtb = 4,4'-di-tert-butyl-2,2'-bipyridine, dmob = 4,4'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine and PPAD = 2-(pyridine-3-yl)-1H-imidazo[4,5f][1.10]phenanthracene-9,10-dione), were synthesized and characterized by 1H NMR and 13C NMR spectroscopy, HRMS and HPLC. Among them, Ru-1 showed excellent antimicrobial activity against Gram-positive bacteria Staphylococcus aureus (minimum inhibitory concentration (MIC) = 1 μg mL-1) and low hemolytic and cytotoxic activity. In addition, Ru-1 showed obviously rapid bactericidal activity, low resistance rate, bacterial biofilm destroying activity and high biosafety in vivo. Moreover, skin infection models and a mouse model of sepsis indicated that the anti-infective efficacy of Ru-1 was comparable to that of vancomycin. Mechanism exploration results showed that the antibacterial behavior is probably related with targeting of the bacterial cell membrane and inhibiting topoisomerase I.

Ruthenium polypyridine complexes with triphenylamine groups as antibacterial agents against Staphylococcus aureus with membrane-disruptive mechanism

Due to the emergence and wide spread of methicillin-resistant Staphylococcus aureus, the treatment of this kind of infection becomes more and more difficult. To solve the problem of drug resistance, it is urgent to develop new antibiotics to avoid the most serious situation of no drug available. Three new Ru complexes [Ru (dmob)₂PMA] (PF6)₂ (Ru-1) [Ru (bpy)₂PMA] (PF6)₂ (Ru-2) and [Ru (dmb)₂PMA] (PF6)₂ (Ru-3) (dmob = 4,4′-dimethoxy-2,2′-bipyridine, bpy = 2,2′-bipyridine, dmb = 4,4′-dimethyl-2,2′-bipyridine and PMA = N-(4-(1H-imidazo [4,5-f] [1,10] phenanthrolin-2-yl) -4-methyl-N-(p-tolyl) aniline) were synthesized and characterized by 1H NMR, 13C NMR and HRMS. The detailed molecular structure of Ru-3 was determined by single crystal X-ray diffraction. Their antibacterial activities against Staphylococcus aureus (Staphylococcus aureus) were obvious and Ru-3 showed the best antibacterial effect with the minimum inhibitory concentration value of 4 μg ml⁻¹. Therefore, further study on its biological activity showed that Ru-3 can effectively inhibit the formation of biofilm and destroy cell membrane. In vitro hemolysis test showed that Ru-3 has almost negligible cytotoxicity to mammalian red blood cells. In the toxicity test of wax moth insect model, Ru-3 exhibited low toxicity in vivo. These results, combined with histopathological studies, strongly suggest that Ru-3 was almost non-toxic. In addition, the synergistic effect of Ru-3 with common antibiotics such as ampicillin, chloramphenicol, tetracycline, kanamycin and gentamicin on Staphylococcus aureus was detected by chessboard method. Finally, in vivo results revealed that Ru-3 could obviously promote the wound healing of Staphylococcus aureus infected mice.

Promoting P450 BM3 heme domain dimerization with a tris(5-iodoacetamido-1,10-phenanthroline)Ru(II) complex

Protein dimerization often occurs in many biological systems as to provide structural and functional advantages. A tris(5-iodoacetamido-1,10-phenanthroline)Ruthenium(II) complex was shown to promote the covalent dimerization of a P450 BM3 heme domain mutant containing a surface exposed non-native single cysteine residue. The formation of homodimeric species was confirmed by protein gel electrophoresis, mass spectrometry and UV-Vis spectroscopy. The dimeric species could be separated from the monomer and aggregates by size-exclusion chromatography. Docking simulation reveals a plausible structure with two proteins covalently conjugated to the inorganic compound.

Tuning the Photo-electrochemical Performance of RuII -Sensitized Two-Dimensional MoS2

Covalently tethering photosensitizers to catalytically active 1T-MoS₂ surfaces holds great promise for the solar-driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new Ru^II -complex-functionalized MoS₂ hybrids [Ru^II (bpy)₂ (phen)]-MoS₂ and [Ru^II (bpy)₂ (py)Cl]-MoS₂ . The influence of covalent functionalization of chemically exfoliated 1T-MoS₂ with coordinating ligands and Ru^II complexes on the HER activity and photo-electrochemical performance of this dye-sensitized system was studied systematically. We find that the photo-electrochemical performance of this Ru^II -complex-sensitized MoS₂ system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS₂ . The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye-sensitized MoS₂ system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye-sensitized MoS₂ hydrogen production devices towards improved the photofuel conversion efficiency.

Modelling Förster resonance energy transfer (FRET) using anisotropy resolved multi-dimensional emission spectroscopy (ARMES)

BACKGROUND

Förster Resonance Energy Transfer (FRET) is widely used to study the structure and dynamics of biomolecular systems and also causes the non-linear fluorescence response observed in multi-fluorophore proteins. Accurate FRET analysis, in terms of measuring changes in donor and acceptor spectra and energy transfer efficiency is therefore critical.

METHODS

We demonstrate a novel quantitative FRET analysis using anisotropy resolved multidimensional emission spectroscopy (ARMES) in a Human Serum Albumin (HSA) and 1,8-anilinonaphathalene sulfonate (ANS) model. ARMES combines 4D measurement of polarized excitation emission matrices (pEEM) with multivariate data analysis to spectrally resolve contributing fluorophores. Multivariate analysis (Parallel Factor, PARAFAC and restricted Tucker3) was used to resolve fluorophore contributions and for modelling the quenching of HSA emission and the HSA-ANS interactions.

RESULTS

pEEM spectra were modelled using Tucker3 which accommodates non-linearities introduced by FRET and a priori chemical knowledge was used to optimise the solution, thus resolving three components: HSA emission, ANS emission from indirect FRET excitation, and ANS emission from direct excitation. Perpendicular emission measurements were more sensitive to indirectly excited acceptor emission. PARAFAC modelling of HSA, donor emission, separated ANS FRET interacting (Tryptophan) and non-interacting (Tyrosine) components. This enabled a new way of calculating quenching constants using the multi-dimensional emission of individual donor fluorophores.

CONCLUSIONS

FRET efficiency could be calculated using the multi-dimensional, resolved emission of the interacting donor fluorophores only which yielded higher ET efficiencies compared to conventional methods.

GENERAL SIGNIFICANCE

Shows the potential of multidimensional fluorescence measurements and data analysis for more accurate FRET modelling in proteins.

Nanodisc self-assembly is thermodynamically reversible and controllable

Many highly ordered complex systems form by the spontaneous self-assembly of simpler subunits. An important biophysical tool that relies on self-assembly is the Nanodisc system, which finds extensive use as native-like environments for studying membrane proteins. Nanodiscs are self-assembled from detergent-solubilized mixtures of phospholipids and engineered helical proteins called membrane scaffold proteins (MSPs). Detergent removal results in the formation of nanoscale bilayers stabilized by two MSP "belts." Despite their numerous applications in biology, and contributions from many laboratories world-wide, little is known about the self-assembly process such as when the bilayer forms or when the MSP associates with lipids. We use fluorescence and optical spectroscopy to probe self-assembly at various equilibria defined by the detergent concentration. We show that the bilayer begins forming below the critical micellar concentration of the detergent (10 mM), and the association of MSP and lipids begins at lower detergent levels, showing a dependence on the concentrations of MSP and lipids. Following the dissolution process by adding detergent to purified Nanodiscs demonstrates that the self-assembly is reversible. Our data demonstrate that Nanodisc self-assembly is experimentally accessible, and that controlling the detergent concentration allows exquisite control over the self-assembly reaction. This improved understanding of self-assembly could lead to better functional incorporation of hitherto intractable membrane target proteins.

Hole Hopping through Cytochrome P450

High-potential iron-oxo species are intermediates in the catalytic cycles of oxygenase enzymes. They can cause heme degradation and irreversible oxidation of nearby amino acids. We have proposed that there are protective mechanisms in which hole hopping from oxidized hemes through tryptophan/tyrosine chains generates a surface-exposed amino-acid oxidant that could be rapidly disarmed by reaction with cellular reductants. In investigations of cytochrome P450_BM3, we identified Trp96 as a critical residue that could play such a protective role. This Trp is cation-π paired with Arg398 in 81% of mammalian P450s. Here we report on the effect of the Trp/Arg cation-π interaction on Trp96 formal potentials as well as on electronic coupling strengths between Trp96 and the heme both for wild type cytochrome P450 and selected mutants. Mutation of Arg398 to His, which decreases the Trp96 formal potential, increases Trp-heme electronic coupling; however, surprisingly, the rate of phototriggered electron transfer from a Ru-sensitizer (through Trp96) to the P450_BM3 heme was unaffected by the Arg398His mutation. We conclude that Trp96 has moved away from Arg398, suggesting that the protective mechanism for P450s with this Trp-Arg pair is conformationally gated.

Versatile Impact of Serum Proteins on Ruthenium(II) Polypyridyl Complexes Properties - Opportunities and Obstacles

Ruthenium(II) polypyridyl complexes have been extensively studied for the past few decades as promising anticancer agents. Despite the expected intravenous route of administration, the interaction between Ru(II) polypyridyl compounds and serum proteins is not well characterized and vast majority of the available literature data concerns determination of the binding constant. Ru-protein adducts can modify the biological effects of the Ru complexes influencing their cytotoxic and antimicrobial activity as well as introduce significant changes in their photophysical properties. More extensive research on the interaction between serum proteins and Ru(II) polypyridyl complexes is important for further development of Ru(II) polypyridyl compounds towards their application in anticancer therapy and diagnostics and can open new opportunities for already developed complexes.

The hydrodynamic motion of Nanodiscs

We present a fluorescence-based methodology for monitoring the rotational dynamics of Nanodiscs. Nanodiscs are nano-scale lipid bilayers surrounded by a helical membrane scaffold protein (MSP) that have found considerable use in studying the interactions between membrane proteins and their lipid bilayer environment. Using a long-lifetime Ruthenium label covalently attached to the Nanodiscs, we find that Nanodiscs of increasing diameter, made by varying the number of helical repeats in the MSP, display increasing rotational correlation times. We also model our system using both analytical equations that describe rotating spheroids and numerical calculations performed on atomic models of Nanodiscs. Using these methods, we observe a linear relationship between the experimentally determined rotational correlation times and those calculated from both analytical equations and numerical solutions. This work sets the stage for accurate, label-free quantification of protein-lipid interactions at the membrane surface.

Nanodiscs: A Controlled Bilayer Surface for the Study of Membrane Proteins

The study of membrane proteins and receptors presents many challenges to researchers wishing to perform biophysical measurements to determine the structure, function, and mechanism of action of such components. In most cases, to be fully functional, proteins and receptors require the presence of a native phospholipid bilayer. In addition, many complex multiprotein assemblies involved in cellular communication require an integral membrane protein as well as a membrane surface for assembly and information transfer to soluble partners in a signaling cascade. Incorporation of membrane proteins into Nanodiscs renders the target soluble and provides a native bilayer environment with precisely controlled composition of lipids, cholesterol, and other components. Likewise, Nanodiscs provide a surface of defined area useful in revealing lipid specificity and affinities for the assembly of signaling complexes. In this review, we highlight several biophysical techniques made possible through the use of Nanodiscs.

Hole Hopping through Tryptophan in Cytochrome P450

Electron-transfer kinetics have been measured in four conjugates of cytochrome P450 with surface-bound Ru-photosensitizers. The conjugates are constructed with enzymes from Bacillus megaterium (CYP102A1) and Sulfolobus acidocaldarius (CYP119). A W96 residue lies in the path between Ru and the heme in CYP102A1, whereas H76 is present at the analogous location in CYP119. Two additional conjugates have been prepared with (CYP102A1)W96H and (CYP119)H76W mutant enzymes. Heme oxidation by photochemically generated Ru³⁺ leads to P450 compound II formation when a tryptophan residue is in the path between Ru and the heme; no heme oxidation is observed when histidine occupies this position. The data indicate that heme oxidation proceeds via two-step tunneling through a tryptophan radical intermediate. In contrast, heme reduction by photochemically generated Ru⁺ proceeds in a single electron tunneling step with closely similar rate constants for all four conjugates.

Ru(II)-diimine functionalized metalloproteins: From electron transfer studies to light-driven biocatalysis

The unique photochemical properties of Ru(II)-diimine complexes have helped initiate a series of seminal electron transfer studies in metalloenzymes. It has thus been possible to experimentally determine rate constants for long-range electron transfers. These studies have laid the foundation for the investigation of reactive intermediates in heme proteins and for the design of light-activated biocatalysts. Various metalloenzymes such as hydrogenase, carbon monoxide dehydrogenase, nitrogenase, laccase and cytochrome P450 BM3 have been functionalized with Ru(II)-diimine complexes. Upon visible light-excitation, these photosensitized metalloproteins are capable of sustaining photocatalytic activity to reduce small molecules such as protons, acetylene, hydrogen cyanide and carbon monoxide or activate molecular dioxygen to produce hydroxylated products. The Ru(II)-diimine photosensitizers are hence able to deliver multiple electrons to metalloenzymes buried active sites, circumventing the need for the natural redox partners. In this review, we will highlight the key achievements of the light-driven biocatalysts, which stem from the extensive electron transfer investigations. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

Binding interaction of differently charged fluorescent probes with egg yolk phosphatidylcholine and the effect of β-cyclodextrin on the lipid-probe complexes: a fluorometric investigation

Interaction of cationic phenosafranin (PSF), anionic 8-anilino-1-naphthalene sulfonate (ANS) and non-ionic nile red (NR) have been studied with the zwitterionic phospholipid, egg yolk L-α-phosphatidylcholine (EYPC). The study reveals discernible binding interactions of the three fluorescent probes with the EYPC lipid vesicle. Once the binding of the probes with the lipid is established, the effect of cyclic oligosaccharide, β-cyclodextrin (β-CD), on these lipid bound probes has been investigated. Different fluorometric techniques suggest that addition of β-CD to the probe-lipid complexes leads to the release of the probes from the lipid medium through the formation of probe-β-CD inclusion complexes. A competitive binding of the probes between β-cyclodextrin and the lipid is ascribed to be responsible for the effect. This provides an easy avenue for the removal of the probe molecules from the lipid environment. Extension of this work with drug molecules in cell membranes is expected to give rise to a strategy for the removal of adsorbed drugs from the cell membranes by the use of non-toxic β-cyclodextrin.

A facile and versatile methodology for cysteine specific labeling of proteins with octahedral polypyridyl d⁶ metal complexes

We have synthesized and characterized four octahedral polypyridyl d(6) metal complexes bearing the 5,6-epoxy-5,6-dihydro-[1,10]phenanthroline ligand (L1) as cysteine specific labeling reagents. The proposed synthetic pathways allow the preparation of the metal complexes containing Re(I), Ru(II), Os(II) and Ir(III) while preserving the epoxide functionality. The complexes were characterized by (1)H and (13)C NMR, mass spectrometry, UV-visible and luminescence spectroscopies as well as cyclic voltammetry. As proof of concept, a set of non-native single cysteine P450 BM3 heme domain mutants previously developed in our laboratory was used to study the labeling reaction. We demonstrate that the proposed labels can selectively react, often in high yield, with cysteine residues of the protein via the nucleophilic thiol ring opening of the epoxide moiety. In addition, under basic conditions, subsequent loss of a water molecule led to the aromatization of the phenanthroline ring on the protein-bound label compounds, as observed by mass spectrometry and luminescence measurements.

2-Nitroimidazole-ruthenium polypyridyl complex as a new conjugate for cancer treatment and visualization

A novel long-lifetime highly luminescent ruthenium polypyridyl complex containing 2-nitroimidazole moiety [Ru(dip)2(bpy-2-nitroIm)]Cl2 (dip=4,7-diphenyl-1,10-phenanthroline, bpy-2-nitroIm=4-[3-(2-nitro-1H-imidazol-1-yl)propyl]-2,2'-bipyridine) has been designed cancer treatment and imaging. The luminescence properties of the synthesized compound strongly depend on the oxygen concentration. Under oxygen-free conditions quantum yield of luminescence and the average lifetime of emission were found to be 0.034 and 1.9 μs, respectively, which is ca. three times higher in comparison to values obtained in air-equilibrated solution. The binding properties of the investigated ruthenium complex to human serum albumin have been studied and the apparent binding constant for the formation of the protein-ruthenium adduct was determined to be 1.1×10(5)M(-1). The quantum yield and the average lifetime of emission are greatly enhanced upon binding of ruthenium compound to the protein. The DNA binding studies revealed two distinguished binding modes which lead to a decrease in luminescence intensity of ruthenium complex up to 60% for [DNA]/[Ru]<2, and enhancement of emission for [DNA]/[Ru]>80. Preliminary biological studies confirmed fast and efficient accumulation of the ruthenium complex inside cells. Furthermore, the ruthenium complex was found to be relatively cytotoxic with LD50 of 12 and 13 μM for A549 and CT26 cell lines, respectively, under normoxic conditions. The retention and cellular uptake of ruthenium complex is enhanced under hypoxic conditions and its LD50 decreases to 8 μM for A549 cell line.

A series of hybrid P450 BM3 enzymes with different catalytic activity in the light-initiated hydroxylation of lauric acid

We have developed a series of hybrid P450 BM3 enzymes to perform the light-activated hydroxylation of lauric acid. These enzymes contain a Ru(II)-diimine photosensitizer covalently attached to single cysteine residues of mutant P450 BM3 heme domains. The library of hybrid enzymes includes four non-native single cysteine mutants (K97C, Q397C, Q109C and L407C). In addition, mutations around the heme active site, F87A and I401P, were inserted in the Q397C mutant. Two heteroleptic Ru(II) complexes, Ru(bpy)(2)phenA (1) and Ru(phen)(2)phenA (2) (bpy=bipyridine, phen=1,10-phenanthroline, and phenA=5-acetamido-1,10-phenanthroline), are used as photosensitizers. Upon visible light irradiation, the hybrid enzymes display various total turnover numbers in the hydroxylation of lauric acid, up to 140 for the L407C-1 mutant, a 16-fold increase compared to the F87A/Q397C-1 mutant. CO binding studies confirm the ability of the photogenerated Ru(I) compound to reduce the fraction of ferric high spin species present in the mutants upon substrate binding.

ATP-uncoupled, six-electron photoreduction of hydrogen cyanide to methane by the molybdenum-iron protein

A detailed study of the eight-electron/eight-proton catalytic reaction of nitrogenase has been hampered by the fact that electron and proton flow in this system is controlled by ATP-dependent protein-protein interactions. Recent studies have shown that it is possible to circumvent the dependence on ATP through the use of potent small-molecule reductants or light-driven electron injection, but success has been limited to two-electron reductions of hydrazine, acetylene, or protons. Here we show that a variant of the molybdenum-iron protein labeled with a Ru-photosensitizer can support the light-driven, six-electron catalytic reduction of hydrogen cyanide into methane and likely also ammonia. Our findings suggest that the efficiency of this light-driven system is limited by the initial one- or two-electron reduction of the catalytic cofactor (FeMoco) to enable substrate binding, but the subsequent electron-transfer steps into the FeMoco-bound substrate proceed efficiently.

Light-initiated hydroxylation of lauric acid using hybrid P450 BM3 enzymes

We have developed hybrid P450 BM3 enzymes consisting of a Ru(II)-diimine photosensitizer covalently attached to non-native single cysteine residues of P450 BM3 heme domain mutants. These enzymes are capable, upon light activation, of selectively hydroxylating lauric acid with 40 times higher total turnover numbers compared to the peroxide shunt.

Probing deuterium isotope effect on structure and solvation dynamics of human serum albumin

The deuterium isotopic effect on the structure and solvation dynamics of the protein, human serum albumin (HSA), has been studied by using circular dichroism (CD), femtosecond up-conversion, FRET, and single-molecule spectroscopy. The CD spectra suggest that D(2)O affects the structure of HSA, leading to a 20% decrease in the helical structure. The FRET study indicates that the distance of C153 from the lone tryptophan residue of HSA is quite similar (≈21 Å) in H(2)O and D(2)O, and hence, the location of the probe in the protein remains the same in the two solvents. The single-molecule study suggests that coumarin 153 (C153) binds almost exclusively (>96%) to one site of HSA. Solvation dynamics of C153 in HSA is found to be markedly retarded in D(2)O compared with H(2)O. In H(2)O, the solvation of C153 bound to HSA is found to be biexponential with one component of 7 ps (30%) and a long component of 350 ps (70%). In D(2)O, we detected a short component of 4 ps (41%) and a long component of 950 ps (59%). Thus, the ultraslow component of the solvation dynamics of C153 bound to HSA in D(2)O (950 ps) is 2.5-fold slower than that in H(2)O (350 ps). The marked deuterium isotope effect has been ascribed to water molecules confined in the protein environment and to a lesser extent to the structural modification of protein by D(2)O.

Photooxidation of cytochrome P450-BM3

High-valent iron-oxo species are thought to be intermediates in the catalytic cycles of oxygenases and peroxidases. An attractive route to these iron-oxo intermediates involves laser flash-quench oxidation of ferric hemes, as demonstrated by our work on the ferryl (compound II) and ferryl porphyrin radical cation (compound I) intermediates of horseradish peroxidase. Extension of this work to include cytochrome P450-BM3 (CYP102A1) has required covalent attachment of a Ru(II) photosensitizer to a nonnative cysteine near the heme (RuIIK97C-FeIIIP450), in order to promote electron transfer from the Fe(III) porphyrin to photogenerated Ru(III). The conjugate was structurally characterized by X-ray crystallography (2.4 Å resolution; Ru-Fe distance, 24 Å). Flash-quench oxidation of the ferric-aquo heme produces an Fe(IV)-hydroxide species (compound II) within 2 ms. Difference spectra for three singly oxidized P450-BM3 intermediates were obtained from kinetics modeling of the transient absorption data in combination with generalized singular value decomposition analysis and multiexponential fitting.

Modular and versatile hybrid coordination motifs on alpha-helical protein surfaces

We report here the construction of phenanthroline (Phen) and terpyridine (Terpy)-based hybrid coordination motifs (HCMs), which were installed on the surface of the four-helical bundle hemeprotein cytochrome cb(562). The resulting constructs, termed HPhen1, HPhen2, HPhen3, and HTerpy1, feature HCMs that are composed of a histidine ligand and a Phen or Terpy functionality located two helix turns away, yielding stable tri- or tetradentate coordination platforms. Our characterization of the tridentate HCMs indicates that they accommodate many divalent metal ions (Co(2+), Ni(2+), Cu(2+), Zn(2+)) with nanomolar to femtomolar affinities, lead to significant stabilization of the alpha-helical protein scaffold through metal-mediated cross-linking, assert tight control over protein dimerization, and provide stable and high-affinity binding sites for substitution-inert metal probes. Our analyses suggest that such tridentate HCMs may be used modularly on any alpha-helical protein surface in a sequence-independent fashion.

Dynamics of bacteriophage R17 probed with a long-lifetime Ru(II) metal-ligand complex

The metal-ligand complex, [Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc), was used as a spectroscopic probe for studying macromolecular dynamics. RuBDc is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. To further show the usefulness of this luminophore for probing macromolecular dynamics, we examined the intensity and anisotropy decays of RuBDc when conjugated to R17 bacteriophage using frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. The intensity decays were best fit by a sum of two exponentials, and we obtained a longer mean lifetime at 4 degrees C (<tau> = 491.8 ns) as compared to that at 25 degrees C (<tau> = 435.1 ns). The anisotropy decay data showed a single rotational correlation time, which is typical for a spherical molecule, and the results showed a longer rotational correlation time at 4 degrees C (2,574.9 ns) than at 25 degrees C (2,070.1 ns). The use of RuBDc enabled us to measure the rotational correlation time up to several microseconds. These results indicate that RuBDc has significant potential for studying hydrodynamics of biological macromolecules.

Translational and rotational motions of albumin sensed by a non-covalent associated porphyrin under physiological and acidic conditions: a fluorescence correlation spectroscopy and time resolved anisotropy study

The interaction between a free-base, anionic water-soluble porphyrin, TSPP, and the drug carrier protein, bovine serum albumin (BSA) has been studied by time-resolved fluorescence anisotropy (TRFA) and fluorescence correlation spectroscopy (FCS) at two different pH-values. Both rotational correlation times and translational diffusion times of the fluorescent species indicate that TSPP binding to albumin induces very little conformational changes in the protein under physiological conditions. By contrast, at low pH, a bi-exponential decay is obtained where a short rotational correlation time (phi (int) = 1.2 ns) is obtained, which is likely associated to wobbling movement of the porphyrin in the protein binding site. These physical changes are corroborated by circular dichroism (CD) data which show a 37% loss in the protein helicity upon acidification of the medium. In the presence of excess porphyrin formation of porphyrin J-aggregates is induced, which can be detected by time-resolved fluorescence with short characteristic times. This is also reflected in FCS data by an increase in molecular brightness together with a decrease in the number of fluorescent molecules passing through the detection volume of the sample.

Targeting and photodynamic killing of a microbial pathogen using protein cage architectures functionalized with a photosensitizer

The selectivity of antimicrobial photodynamic therapy (PDT) can be enhanced by coupling the photosensitizer (PS) to a targeting ligand. Nanoplatforms provide a medium for designing delivery vehicles that incorporate both functional attributes. We report here the photodynamic inactivation of a pathogenic bacterium, Staphylococcus aureus, using targeted nanoplatforms conjugated to a photosensitizer (PS). Both electrostatic and complementary biological interactions were used to mediate targeting. Genetic constructs of a protein cage architecture allowed site-specific chemical functionalization with the PS and facilitated dual functionalization with the PS and the targeting ligand. These results demonstrate that protein cage architectures can serve as versatile templates for engineering nanoplatforms for targeted antimicrobial PDT.

Luminescent property and catalytic activity of Ru(II) carbonyl complexes containing N, O donor of 2-hydroxy-1-naphthylideneimines

The reaction of the chelating ligands (obtained by the condensation of 2-hydroxy-1-naphthaldehyde with various primary amines) with [RuHCl(CO)(EPh(3))(2)(B)] (where E=P; B=PPh(3), py or pip: E=As; B=AsPh(3)) in benzene afforded new stable ruthenium(II) carbonyl complexes of the general formula [Ru(Cl)(CO)(EPh(3))(B)(L)] (L=anion of bidentate Schiff bases). The structure of the new complexes was investigated using elemental analyses, spectral (FT-IR, UV-vis and (1)H NMR) and electrochemical studies and is found to be octahedral. All the metal complexes exhibit characteristic MLCT absorption and luminescence bands in the visible region. The luminescence efficiency of the ruthenium(II) complexes was explained based on the ligand environment around the metal ion. These complexes catalyze oxidation of primary and secondary alcohols into their corresponding carbonyl compounds in the presence of N-methylmorpholine-N-oxide (NMO) as the source of oxygen. The formation of high valent Ru(IV)=O species as a catalytic intermediate is proposed for the catalytic process.

Peptide beacons: a new design for polypeptide-based optical biosensors

Both epitope mapping and other in vitro selection techniques produce short polypeptides that tightly and specifically bind to any of a wide range of macromolecular targets. Here, we demonstrate a potentially general means of converting such polypeptides into optical biosensors. The sensing architecture we have developed, termed peptide beacons, is based on the observation that, whereas short peptides are almost invariably unfolded and highly dynamic, they become rigid when complexed to a macromolecular target. Using this effect to segregate a long-lived fluorophore from an electron transfer based, contact quencher (both covalently attached to the peptide), we have produced a robust optical sensor for anti-HIV antibodies. The binding-induced segregation of the fluorophore-quencher pair produces a 6-fold increase in sensor emission, thus allowing us to readily detect as low as approximately 250 pM of the target antibody. Because the sensor is based on binding-induced folding and a visible-light fluorophore, it is sufficiently selective to work directly in complex, contaminant-ridden samples such as saliva and blood.

Luminescent property and catalytic activity of Ru(II) carbonyl complexes containing N, O donor of 2-hydroxy-1-naphthylideneimines

The reaction of the chelating ligands (obtained by the condensation of 2-hydroxy-1-naphthaldehyde with various primary amines) with [RuHCl(CO)(EPh3)2(B)] (where E=P; B=PPh3, py or pip: E=As; B=AsPh3) in benzene afforded new stable ruthenium(II) carbonyl complexes of the general formula [Ru(Cl)(CO)(EPh3)(B)(L)] (L=anion of bidentate Schiff bases). The structure of the new complexes was investigated using elemental analyses, spectral (FT-IR, UV-vis and 1H NMR) and electrochemical studies and is found to be octahedral. All the metal complexes exhibit characteristic MLCT absorption and luminescence bands in the visible region. The luminescence efficiency of the ruthenium(II) complexes was explained based on the ligand environment around the metal ion. These complexes catalyze oxidation of primary and secondary alcohols into their corresponding carbonyl compounds in the presence of N-methylmorpholine-N-oxide (NMO) as the source of oxygen. The formation of high valent Ru(IV)=O species as a catalytic intermediate is proposed for the catalytic process.