Fluorescence methods to study lipid-protein association: The interaction of protein kinase C with lipid-loaded mixed micelles

Global analysis of fluorescence fluctuation data

Over the last decade the number of applications of fluorescence correlation spectroscopy (FCS) has grown rapidly. Here we describe the development and application of a software package, FCS Data Processor, to analyse the acquired correlation curves. The algorithms combine strong analytical power with flexibility in use. It is possible to generate initial guesses, link and constrain fit parameters to improve the accuracy and speed of analysis. A global analysis approach, which is most effective in analysing autocorrelation curves determined from fluorescence fluctuations of complex biophysical systems, can also be implemented. The software contains a library of frequently used models that can be easily extended to include user-defined models. The use of the software is illustrated by analysis of different experimental fluorescence fluctuation data sets obtained with Rhodamine Green in aqueous solution and enhanced green fluorescent protein in vitro and in vivo.

Light Scattering, Atomic Force Microscopy and Fluorescence Correlation Spectroscopy Studies of Polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) Micelles

Polymeric nanoparticles formed by triblock copolymer polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide), PS-PVP-PEO, in aqueous media were studied by a combination of fluorescence correlation spectroscopy with other fluorescence techniques, light scattering and atomic force microscopy. The studied polymeric nanoparticles exist in the form of (i) core/shell micelles in acid solution at pH lower than 4.8 and (ii) three-layer onion micelles at higher pH. Since water is a very strong precipitant for PS, both types of micelles have kinetically frozen spherical PS cores. The cores of micelles in acid media are surrounded by soluble shells formed by partly protonated PVP and PEO, while the cores of micelles in alkaline media are surrounded by compact insoluble layers of deprotonated PVP and soluble PEO shells. The micellization behavior of PS-PVP-PEO micelles is accompanied by secondary aggregation of micelles, which is provoked by stirring, shaking and also by filtration of micellar solutions. Therefore fluorescence correlation spectroscopy (FCS), which, in contrast to light scattering techniques, does not require filtration, was used as the main experimental technique for the characterization of non-aggregated micelles. The binding of a fluorescence probe, octadecylrhodamine B (ORB), to polymeric micelles, was studied before the FCS study of micelles.

Coumarin 6, Hypericin, Resorufins, and Flavins: Suitable Chromophores for Fluorescence Correlation Spectroscopy of Biological Molecules

In this work we show that the dyes coumarin 6, hypericin, 7-O-ethylresorufin and resorufin are suitable for fluorescence correlation spectroscopy (FCS) and demonstrate the use of these dyes in physiologically relevant protein studies. Since coumarins are metabolised by cytochromes P450, the binding of coumarin 6 to cytochrome P450 3A4 was investigated by FCS. Coumarin 6 appears to be a very bright non-covalent cytochrome P450 label. When titrating cytochrome P450 3A4 with coumarin 6, the diffusion time of the coumarin 6/ cytochrome P450 3A4 complex increases roughly two-fold at protein concentrations higher than 1 μmol l-1, indicating the formation of cytochrome aggregates. FCS of the flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) shows that both endogenous dyes undergo photobleaching. Moreover, FAD appears to be present to great extent, as a non-fluorescent intramolecular complex. Analysis of the FCS data of the flavoprotein NADPH-cytochrome P450 oxidoreductase (molecular weight 76 500) yielded two components. While the slow component corresponds to a globular protein with the molecular weight about 75 000, the fast component appears to be due to free diffusing FMN and FAD molecules. The amount of free FMN and FAD increases with increasing laser power. At high laser power a complete photodissociation of FMN and FAD occurs.

Reorientational properties of fluorescent analogues of the protein kinase C cofactors diacylglycerol and phorbol ester

The reorientational properties of the fluorescently labelled protein kinase C (PKC) cofactors diacylglycerol (DG) and phorbol ester (PMA) in vesicles and mixed micelles have been investigated using time-resolved polarised fluorescence. The sn-2 acyl chain of DG was replaced by diphenylhexatriene- (DPH) propionic acid, while a dansyl labelled analogue of phorbol ester was used. The extent of ordering of DPH-DG in vesicles turned out to be slightly different from that of the control choline lipid DPH-PC. Addition of PKC to vesicles containing 30 mole% brain PS considerably slowed down the DPH-DG anisotropy decay. This was not observed when DPH-DG was replaced by DPH-PC. Analysis of the fluorescence anisotropy decays of these DPH-lipids in micelles polyoxyethylene-9-laurylether mixed with 10 mole% of the essential phosphatidylserine allowed estimation of their lateral diffusion, orientation distribution and reorientational dynamics within the micelles. Addition of PKC resulted in a significantly slower decay of the fluorescence anisotropy of both DPH-DG and DPH-PC even in the absence of calcium, indicating a calcium independent complexation of PKC with the PS containing micelles. Addition of calcium resulted in a further reduction of the decay of anisotropy of DPH-DG but not of DPH-PC indicating that the Ca2+ dependent immobilisation is cofactor-specific. Similar specific interactions with PKC resulted in a slower decay of dansylated PMA when calcium and PS were present.