Fluorescent and photoactivable probes in depth-dependent analysis of membranes

Role of Phenothiazines and Structurally Similar Compounds of Plant Origin in the Fight against Infections by Drug Resistant Bacteria

Phenothiazines have their primary effects on the plasma membranes of prokaryotes and eukaryotes. Among the components of the prokaryotic plasma membrane affected are efflux pumps, their energy sources and energy providing enzymes, such as ATPase, and genes that regulate and code for the permeability aspect of a bacterium. The response of multidrug and extensively drug resistant tuberculosis to phenothiazines shows an alternative therapy for the treatment of these dreaded diseases, which are claiming more and more lives every year throughout the world. Many phenothiazines have shown synergistic activity with several antibiotics thereby lowering the doses of antibiotics administered to patients suffering from specific bacterial infections. Trimeprazine is synergistic with trimethoprim. Flupenthixol (Fp) has been found to be synergistic with penicillin and chlorpromazine (CPZ); in addition, some antibiotics are also synergistic. Along with the antibacterial action described in this review, many phenothiazines possess plasmid curing activities, which render the bacterial carrier of the plasmid sensitive to antibiotics. Thus, simultaneous applications of a phenothiazine like TZ would not only act as an additional antibacterial agent but also would help to eliminate drug resistant plasmid from the infectious bacterial cells.

Benzophenone-containing fatty acids and their related photosensitive fluorescent new probes: design, physico-chemical properties and preliminary functional investigations

Hydrophobic photoaffinity labeling is a powerful strategy to identify hydrophobic segments within molecules, in particular membrane proteins. Here we report the design and synthesis of a novel family of fluorescent and photosensitive lipid tools, which have a common amino acid scaffold functionalized by three groups: (i) a first fatty acid chain grafted with a photoactivatable benzophenone moiety (Fatty Acid BenzoPhenone, FABP), (ii) a second fatty acid chain to ensure anchoring into a half-bilayer or hydrophobic environment, and (iii) a fluorescent carboxytetramethylrhodamine headgroup (CTMR) to detect the photolabeled compound. We present data of the synthesis and characterization of three lipid tools whose benzophenone ring is situated at various distances from the central scaffold. We could therefore establish structure/properties relationships dependent upon the depth of insertion of benzophenone into the membrane. Our lipid tools were extensively characterized both physico- and bio-chemically, and we assessed their functionality in vitro using bacterioRhodopsin (bR). We thus provide the scientific community with novel and reliable tools for the identification and study of hydrophobic regions in proteins.

Distribution and favorable binding sites of pyrroloquinoline and its analogues in a lipid bilayer studied by molecular dynamics simulations

The distribution of 1H-pyrrolo[3,2-h]quinoline (PQ), 11H-dipyrido[2,3-a]carbazole (PC) and 7-azaindole (7AI) at a water/membrane interface has been investigated by molecular dynamics (MD) simulations. The MD study focused on favorable binding sites of the azaaromatic probes across a dipalmitoylphosphatidylcholine (DPPC) bilayer. Our simulations show that PQ and PC are preferably accommodated at the hydrocarbon core of the bilayer below the glycerol moiety. In addition, it is found that the hydrophobic aromatic parts of the probes are located inside a more ordered region of DPPC, consisting of hydrophobic lipid chains. In contrast to PQ and PC, 7AI is characterized by a broad distribution between a DPPC interface and water, so that the three preferable binding sites are found across a water/membrane interface. It is found that in the sequence 7AI-PQ-PC, due to the increase of the number of aromatic rings and, hence, the hydrophobic character of the probes, the depth of the probe localization is gradually shifted deeper inside the hydrocarbon core of the bilayer. We found that the probe-lipid hydrogen-bonding contributes weakly to the favorable localizations of the azaaromatic probes inside the DPPC bilayer, so that the probe localization is mainly driven by electrostatic dipole-dipole and van der Waals interactions.

Enhanced fluorescence of epicocconone in surfactant assemblies as a consequence of depth-dependent microviscosity

The extents of fluorescence enhancement of epicocconone are found to be different in the micelles of the surfactants sodium dodecyl sulfate (SDS) and Triton X100 (TX 100). A decrease in fluorescence, observed in the cationic cetyltrimethylammonium bromide (CTAB) micelles, is rationalized by the formation of anions of the fluorophore at the Stern layer. To understand the difference in the effects of SDS and TX 100, the nature of the excited-state process in the fluorophore has been investigated by fluorescence spectroscopy, supported by complementary quantum chemical calculations. The excited-state dynamics of epicocconone is found to depend on polarity and viscosity of the medium, with a more pronounced dependence on viscosity. An inspection of the molecular orbitals involved in the electronic absorption of the molecule reveals the possibility of photoisomerization, which conforms to the observed solvent dependence of the fluorescence spectral properties. An apparent mismatch between trends observed in steady-state spectra and those in temporal decays indicates a significant contribution of an ultrafast component, which cannot be detected in the time resolution of our instrument. The viscosity dependence of the fluorescence quantum yields provides an explanation for the difference in the extents of fluorescence enhancement in the two micelles, in the light of location of the fluorophore at different depths of the micelle. The enhancement of fluorescence, with an unchanged fluorescence maximum, opens up the possibility that the fluorophore could be a useful dual emitting marker for fluorescence microscopy of heterogeneous systems, as the fluorescence of protein-bound epicocconone has been previously reported to be significantly red-shifted.

Synthesis of photoactivatable analogues of lysophosphatidic acid and covalent labeling of plasma proteins

[reaction: see text] Lysophosphatidic acids bearing a benzophenone group in either the sn-1 or sn-2 chain of an oleoyl-type ester or oleyl-type ether chain and (32)P in the phosphate group were synthesized. The benzophenone moiety was introduced by selective hydroboration of the double bond of enyne 11 at low temperature, followed by a Suzuki reaction with 4-bromobenzophenone. The key intermediates for the preparation of ester-linked lysophosphatidic acid (LPA) 1 and 3 were obtained in one pot by a modified DIBAL-H reduction of orthoformate intermediate 22. These probes were shown to covalently modify a single protein target in rat plasma containing albumin and several protein targets in rat plasma containing a low level of albumin.