Raman spectroscopy of membrane constituents and related molecules

Raman scattering in protonated and deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC): Indicators of conformational and lateral orders

The use of deuterocarbons is an effective method in the Raman spectroscopy of multicomponent lipid materials and biological samples. Here, Raman spectra of hydrated multilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), its deuterated analog 1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (DPPC_d62), and DPPC-DPPC_d62 mixtures were studied in a wide temperature range to specify the Raman indicators of conformational and lateral orders. The temperature dependence of the 985 cm^-1 line in the deuterated phospholipid unequivocally indicates that this line corresponds to the CC stretching vibrations of deuterated hydrocarbon chains in the all-trans conformation. It was also concluded that the ratio of Raman intensities at the maximum of the peak of the symmetric CD₂ stretching and at a maximum near 2168 cm^-1 reflects the conformational order of the hydrocarbon chain and can be used for an evaluation of the fraction of the all-trans sequences. The frequency of the symmetric CD₂ stretching peak is sensitive to the phase state (gel or fluid) but has a low sensitivity to the partial conformational disordering within the gel phase. The Raman study of DPPC-DPPC_d62 mixtures reveals that the lateral order contributes to the ratio of intensities of the antisymmetric and symmetric CH₂ stretching peaks as a prefactor enhancing the effect of conformational ordering.

A new in vivo Raman probe for enhanced applicability to the body

This paper describes a new in vivo Raman probe that allows investigation of areas of the body that are otherwise difficult to access. It is coupled to a previously described commercially available in vivo Raman spectrometer that samples the skin through an optical flat. In the work presented here, the laser light emerges from a smaller pen-shaped probe. It thus works on the same principles as the original spectrometer, while its relative performance in terms of signal-to-noise ratio of the spectra and obtained spatial resolution is only slightly diminished. It allows the window to be placed against the subject in more curved and recessed areas of subject's body and also for them to be more comfortable while the measurements take place. Results from three areas of the body that have previously been very difficult to study are described, the mouth, axilla, and scalp. Results from the scalp and axilla strata cornea (SC) show significant differences from the "normal" SC of the volar forearm. For instance, the scalp is observed to have lower amounts of natural moisturizing factors (NMF) compared to the volar forearm within the same subjects. Also for both the axilla and scalp the lipids show a change in order as compared to the lipids in the volar forearm and also differences from each other. The potential significance of these observations is discussed. Further, we show how we can probe the mouth, in this case observing the presence of the astringent tea polyphenol epigallocatechin gallate within the oral mucosa.

The use of exogenous fluorescent probes for temperature measurements in single living cells

The fluorescent membrane probes 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) and 6-dodecanoyl-2-dimethylamino-naphthalene (laurdan) have been studied for use as optical thermometers in living cells. The thermal sensitivity of NBD is primarily a consequence of rapid, heat-induced electronic changes, which increase the observed fluorescence decay rate. As a result, fluorescence intensity and lifetime variations of membrane-bound NBD-conjugated phospholipids and fatty acids can be directly correlated with cellular temperature. In contrast, laurdan fluorescence undergoes a dramatic temperature-dependent Stokes shift as the membrane undergoes a gel-to-liquid-crystalline phase transition. This facilitates the use of fluorescence spectra to record the indirect effect of microenvironmental changes, which occur during bilayer heating. Microscope and suspension measurements of cells and phospholipid vesicles are compared for both probes using steady-state and fluorescence lifetime (suspension only) data. Our results show that NBD fluorescence lifetime recordings can provide reasonable temperature resolution (approximately 2 degrees C) over a broad temperature range. Laurdan's microenvironmental sensitivity permits better temperature resolution (0.1-1 degree C) at the expense of a more limited dynamic range that is determined solely by bilayer properties. The temperature sensitivity of NBD is based on rapid intramolecular rotations and vibrations, while laurdan relies on a slower, multistep mechanism involving bilayer rearrangement, water penetration and intermolecular processes. Because of these differences in time scale, NBD appears to be more suitable for monitoring ultrafast phenomena, such as the impact of short-pulse microirradiation on single cells.

Protein conformational transitions in sarcoplasmic reticulum membranes

Fourier-transform infrared spectroscopic studies of sarcoplasmic reticulum proteins, in H2O and D2O, suggest that 10 mM ATP induces a conformational change in those proteins, increasing their contents in alpha-helical and beta-antiparallel structures. Ca2+ on the contrary, is seen to reduce the proportion of alpha-helix and increase the contribution of random coil.

Fourier transform infrared spectroscopic studies of lipid-protein interaction in native and reconstituted sarcoplasmic reticulum

Fourier transform infrared spectroscopy has been used to monitor lipid-protein interaction and protein secondary structure in native and reconstituted sarcoplasmic reticulum vesicles. Studies of the temperature dependence of the CH2 symmetric stretching frequency reveal no cooperative phase transitions in purified sarcoplasmic reticulum or in vesicles reconstituted with dioleoylphosphatidylcholine, although a continuous introduction of disorder into the lipid acyl chains is observed as the temperature is raised. In addition, temperature-dependent changes are observed in the Amide I and Amide II vibrations arising from protein peptide bonds. A comparison of lipid order in native sarcoplasmic reticulum and its lipid extract showed that the introduction of protein is accompanied by a slight increase in lipid order. Reconstitution of Ca2+-ATPase from sarcoplasmic reticulum with dipalmitoylphosphatidylcholine (lipid/protein ratio 30:1), reveals a perturbed lipid melting event broadened and reduced in midpoint temperature from multilamellar lipid vesicles. The onset of melting (27-28 degrees C) correlates well with the onset of ATPase activity and confirms a suggestion (Hesketh, T.R., Smith, G.A., Houslay, M.D., McGill, K.A., Birdsall, N.J.M., Metcalfe, J.C. and Warren, G.B. (1976) Biochemistry 15, 4145-4151) that a liquid crystalline environment is a requirement for optimal protein function. Finally, Ca2+-ATPase has been reconstituted into binary lipid mixtures of DOPC and acyl-chain perdeuterated DPPC. The effect of protein on the structure and melting behavior of each lipid component was monitored. The protein appears to preferentially interact with the DOPC component.

Interaction of glycophorin with phosphatidylserine: a Fourier transform infrared investigation

Glycophorin, from the human erythrocyte membrane, has been isolated in pure form and reconstituted into unilamellar vesicles with bovine brain phosphatidylserine (PS). Fourier transform infrared spectroscopy has been used to monitor the protein conformation as well as the effect of protein on lipid order and melting. Glycophorin, at levels of 1 mol %, nearly abolishes the gel to liquid-crystal phase transition seen in pure PS vesicles between 8 and 16 degrees C by inducing significant disorder into the lipid gel phase. A transition of reduced magnitude remains between 14 and 22 degrees C in the lipid/protein complexes. Evidence is presented for specific interaction of glycophorin with the interfacial region of PS. In general, the effects on lipid melting produced by protein at the 1 mol % level are more pronounced than those noted in a previous study of glycophorin/phosphatidylcholine interactions [ Mendelsohn , R., Dluhy , R. A., Taraschi , T., Cameron, D., & Mantsch , H.H. (1981) Biochemistry 20, 6699-6706]. Two bands are observed for the protein amide I (C = O stretching) mode. A main feature at 1653 cm-1 indicates that the bulk of the secondary structure is random coil or alpha-helical. A weaker shoulder at 1675 cm-1 suggests the occurrence of a small proportion of the beta-sheet form. The results confirm circular dichroism studies of Schulte & Marchesi (1979) [ Schulte , T.H., & Marchesi , V.T. (1979) Biochemistry 18, 275-280]. Fourier transform infrared (FT-IR) studies of a ternary complex of PS/dipalmitoyl-phosphatidylcholine- d62 (DPPC- d62 )/glycophorin indicate that the glycophorin preferentially interacts with the PS component.(ABSTRACT TRUNCATED AT 250 WORDS)