Effect of the C-terminal proline repeats on ordered packing of squid rhodopsin and its mobility in membranes

Negative stain electron microscopy and saturation transfer electron spin resonance spectroscopy have been used to compare the lattice ordering and in-plane membrane mobility of full-length and C-terminally cleaved squid rhodopsin. The C-terminus of squid rhodopsin contains a negatively charged region followed by 9-10 repeats of a proline-rich sequence, not found in rhodopsins other than those of cephalopod invertebrates, but similar proline repeats are found in other, unrelated membrane proteins. We find that the proline repeats cluster the rhodopsins into small groups, interfering with two-dimensional crystallization and maintaining their mobility in the membrane.

Report on the Annual Conference of the British Association of Teachers of Conservative Dentistry

The Annual Conference of the British Association of Teachers of Conservative Dentistry (BATCD) was held in Sheffield on 16 and 17 September 1993. The main programme addressed educational issues in three areas: the undergraduate/vocational-trainee interface, the teaching of implants in the undergraduate curriculum, and the changing role of dental instructors in restorative dentistry. The programme also included a number of research papers and poster demonstrations, which were submitted for the Association's new QED/Maillefer prizes in Restorative Dentistry. This paper presents reports of the four principal lectures, and abstracts of the research papers and poster demonstrations, with details of the prize winners.

Pulp response to a novel adhesive calcium hydroxide based cement

This study compares pulp responses to 3 formulations of calcium hydroxide, namely: a) An experimental adhesive calcium hydroxide cement containing polyacrylic acid, b) Dycal (L.D> Caulk Co, Milford, Delaware) Batch Nos 176970/176990, c) "Analar" calcium hydroxide mixed with sterile distilled water. After 28 days dentine bridges were present in 77% of teeth capped with the test material, 64% of teeth treated with Dycal and in 62% of teeth capped with calcium hydroxide and water. Inflammatory infiltrates were observed in a number of teeth remote from the bridges. Bacteria were detected in these specimens. Exposed rat molar pulp responses to an experimental adhesive calcium hydroxide cement were similar to to those observed with 2 other calcium hydroxide formulations.

High-resolution, non-crystallographic structural studies of large integral membrane proteins

The work described here clearly demonstrates that n.m.r. is a viable method with which to resolve molecular details about membrane proteins and can give information at a resolution comparable with that gained from crystallographic studies, where, in the limited number of cases studied so far, such information is available. Sensitivity is not a major problem although other difficulties may prevent particular kinds of information being resolved. However, because bond orientational details are obtained ab initio, the method is quite model independent and interpretationally unique. The requirements for solid-state n.m.r. methods to be applied to a large membrane protein are that: a sufficient amount of functionally active protein is available; the protein should be located in bilayers; and suitable specific isotopic enrichment is achieved, in ideal cases, either by chemical or biosynthetic means. Achieving these requirements will need to draw on a range of skills, possibly genetic or chemical or both, and a full understanding of the biochemistry is essential to ensure that any structural information gained is functionally relevant. The structural information potentially available includes: (a) conformation details about specific parts of a protein or its binding sites; (b) distance measurements between specific labels introduced into the protein; (c) dynamics of particular parts of the protein; (d) chain folding and residue orientation; and (e) the mechanistic changes that can occur during a functional cycle. Much developmental work still needs to be done both on the sample handling instrumental side and with the theoretical aspect of the method.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of two new lining/base materials based upon calcium hydroxide/polyacrylic acid

Two experimental adhesive calcium hydroxide cements containing polyacrylic acid were formulated and tested. These experimental materials were stronger than a proprietary calcium hydroxide formulation and were capable of adhesion to dentine. The properties of these new formulations indicated that preliminary biological testing is warranted.

Incorporation of fatty acids by concanavalin A-stimulated lymphocytes and the effect on fatty acid composition and membrane fluidity

The fatty acid compositions of the neutral lipid and phospholipid fractions of rat lymph node lymphocytes were characterized. Stimulation of rat lymphocytes with the T-cell mitogen concanavalin A resulted in significant changes in the fatty acid composition of both neutral lipids and phospholipids (a decrease in the proportions of stearic, linoleic and arachidonic acids and an increase in the proportion of oleic acid). Membrane fluidity was measured using nitroxide spin-label e.s.r., and increased during culture with concanavalin A. Culturing the lymphocytes in the absence of mitogen did not affect fatty acid composition or membrane fluidity. The uptake and fate of palmitic, oleic, linoleic and arachidonic acids were studied in detail; there was a time-dependent incorporation of each fatty acid into all lipid classes but each fatty acid had a characteristic fate. Palmitic and arachidonic acids were incorporated principally into phospholipids whereas oleic and linoleic acids were incorporated in similar proportions into phospholipids and triacylglycerols. Oleic acid was incorporated mainly into phosphatidylcholine, palmitic and linoleic acids were incorporated equally into phosphatidylcholine and phosphatidylethanolamine, and arachidonic acid was incorporated mainly into phosphatidylethanolamine. Supplementation of the culture medium with particular fatty acids (myristic, palmitic, stearic, oleic, linoleic, alpha-linolenic, arachidonic, eicosapentaenoic or docosahexaenoic acid) led to enrichment of that fatty acid in both neutral lipids and phospholipids. This generated lymphocytes with phospholipids differing in saturated/unsaturated fatty acid ratio, degree of polyunsaturation, index of unsaturation and n - 6/n - 3 ratio. This method allowed the introduction into lymphocyte phospholipids of fatty acids not normally present (e.g. alpha-linolenic) or usually present in low proportions (eicosapentaenoic and docosahexaenoic). These three n - 3 polyunsaturated fatty acids replaced arachidonic acid in lymphocyte phospholipids. Fatty acid incorporation led to an alteration in lymphocyte membrane fluidity: palmitic and stearic acids decreased fluidity whereas the unsaturated fatty acids increased fluidity. It is proposed that the changes in lymphocyte phospholipid fatty acid composition and membrane fluidity brought about by culture in the presence of polyunsaturated fatty acids are responsible for the inhibition of lymphocyte functions caused by these fatty acids.

Morphological and biochemical characterization of influenza vaccines commercially available in the United Kingdom

Four vaccines are available in the United Kingdom against influenza virus. All are subunit vaccines, defined as either split-virion or purified surface antigen vaccine; there are two of each distinct type available. Both vaccine types are less reactogenic than whole inactivated virus, with antigenicity induced by viral surface glycoproteins. Here, each of the four vaccines has been characterized by electron microscopy and SDS-PAGE analysis, giving a unique vaccine profile. Three vaccines contain internal viral nucleoprotein which, in the presence of residual haemagglutinin, may induce an influenza A virus cross-reactive cytotoxic T-cell response and thus be of value to vaccine efficacy. Residual lipid was present in three vaccines and recent evidence suggests that pyrogenicity is correlated with the presence of viral lipid with clusters of surface glycoproteins. By a combination of electron microscopic evidence and biochemical characterization, it has been possible to resolve compositional differences, not only between vaccine type, but also between each individual currently available vaccine. Hence, there is the possibility that the morphological differences characterized here may be contributory to potential reactogenic effects subsequent to vaccination.

Distorted structure of the retinal chromophore in bacteriorhodopsin resolved by 2H-NMR

Structural details about the geometry of the retinal chromophore in the binding pocket of bacteriorhodopsin are revealed by measuring the orientations of its individual methyl groups. Solid-state 2H-NMR measurements were performed on macroscopically oriented samples of purple membrane patches, containing retinal specifically deuterium-labeled at one of the three methyl groups along the polyene chain (C18, C19, C20). The deuterium quadrupole splitting of each "zero-tilt" spectrum is used to calculate the orientation of the corresponding C-CD3 bond vector with respect to the membrane normal; however, two possible solutions may arise. These ambiguities in angle could be resolved by recording a tilt series of spectra at different sample inclinations to the magnetic field and analyzing the resulting complex line shapes with the aid of computer simulations. The angles for the C18, C19, and C20 group are found to be 37 +/- 1 degree, 40 +/- 1 degree, and 32 +/- 1 degree, respectively. These highly accurate values imply that the polyene chain of the retinal chromophore is not straight but rather has an in-plane curvature and possibly an out-of-plane twist. Together with the angles of the remaining methyl groups on the cyclohexene ring that have been measured previously, an overall picture has thus emerged of the intramolecular conformation and the three-dimensional orientation of retinal within bacteriorhodopsin. The deduced geometry confirms and refines the known structural information on the chromophore, suggesting that this 2H-NMR strategy may serve as a valuable tool for other membrane proteins.

Molecular response of the lipid headgroup to bilayer hydration monitored by 2H-NMR

The effect of hydration on the conformation and dynamics of the phosphatidylcholine headgroup has been investigated by 2H-NMR measurements of liquid crystalline dioleoylphosphatidylcholine in multilamellar liposomes. Deuterium quadrupole splittings (delta nu Q) and spin-lattice relaxation rates (1/T1) were recorded for three selectively labeled headgroup segments (alpha, beta, and gamma) over the range of water/lipid mole ratios from 4 to 100. The smooth changes in delta nu Q and 1/T1 are found to essentially parallel each other and can be described by a single exponential decay function. Progressive hydration thus induces a concerted change in headgroup conformation together with an increase in its rate of motion (detected by delta nu Q and 1/T1, respectively). The enhanced mobility is partially due to a shift in the lipid phase transition temperature (as monitored by differential scanning calorimetry) and is furthermore attributed to an entropic contribution. It is concluded that the choline dipole becomes slightly raised in its average orientation into the aqueous layer and that the rate is increased at which the headgroup is fluctuating and protruding. The observed molecular changes can thus be accommodated within a model where the effective accessible headgroup volume expands with increasing hydration.

Phospholipid headgroup-headgroup electrostatic interactions in mixed bilayers of cardiolipin with phosphatidylcholines studied by 2H NMR

The headgroup-headgroup interactions in binary mixed bilayers of diacylphosphatidylcholines (PC) and cardiolipin were analyzed by 2H NMR. Specific changes in the quadrupole splittings of the choline headgroup deuterated PC at alpha,beta-methylenes, and gamma-methyls are observed upon the insertion of the negatively charged tetraacylphospholipid, cardiolipin. The effects are consistent with an electrostatic interaction between PC and cardiolipin headgroups, in which a concerted conformational reorientation of the entire phosphocholine moiety toward the membrane surface is involved. On the basis of the "choline-tilt" model by Macdonald and co-workers (1991) the variations in the quadrupole splittings are consistent with a change in orientation of the choline P-N vector up to 23 degrees for the highest cardiolipin concentrations. Additional information on headgroup conformational changes was obtained through the analysis of the dependence on temperature of the quadrupole splittings for the various deuterium-labeled segments. Evaluation of the deuterium spin-lattice (T1) relaxation times for the deuterons in the various positions of the choline headgroup in mixed bilayers of PC and cardiolipin showed that the internal fast segmental motions were not affected on addition of cardiolipin to PC membranes.

NMR observation of substrate in the binding site of an active sugar-H+ symport protein in native membranes

NMR methods have been adopted to observe directly the characteristics of substrate binding to the galactose-H+ symport protein GalP, in its native environment, the inner membranes of Escherichia coli. Sedimented inner-membrane vesicles containing the GalP protein, overexpressed to levels above 50% of total protein, were analyzed by 13C magic-angle spinning NMR, when in their normal "fluid" state and with incorporated D-[1-13C]glucose. Using conditions of cross-polarization intended to discriminate bound substrate alone, it was possible to detect as little as 250 nmol of substrate added to the membranes containing about 0.5 mumol (approximately 26 mg) of GalP protein. Such high measuring sensitivity was possible from the fluid membranes by virtue of their motional contributions to rapid relaxation recovery of the observed nuclei and due to a high-resolution response that approached the static field inhomogeneity in these experiments. This good spectral resolution showed that the native state of the membranes presents a substrate binding environment with high structural homogeneity. Inhibitors of the GalP protein, cytochalasin B and forskolin, which are specific, and D-galactose, but not L-galactose, prevent or suppress detection of the 13C-labeled glucose substrate, confirming that the observed signal was due to specific interactions with the GalP protein. This specific substrate binding exhibits a preference for the beta-anomer of D-glucose and substrate translocation is determined to be slow, on the 10(-2) s time scale. The work describes a straightforward NMR approach, which achieves high sensitivity, selectivity, and resolution for nuclei associated with complex membrane proteins and which may be combined with other NMR methodologies to yield additional structural information on the binding site for the current transport system without isolating it from its native membrane environment.

Hydration of DOPC bilayers by differential scanning calorimetry

The phase diagram of the unsaturated lipid dioleoylphosphatidylcholine (DOPC) in aqueous multibilayer dispersions has been constructed from a series of differential scanning calorimetry (DSC) thermograms over the temperature range from -40 to +10 degrees C, covering a range of hydration levels from the monohydrate to excess free water. Both the lipid chain melting transition and the ice melting point are found to be hydration dependent. From their respective variations it is found that the bilayer in the gel phase binds approximately 9 H2O per lipid, while the liquid-crystalline state has a saturation limit near 20 H2O. The water transition exhibits a hydration-dependent melting point depression, which can be explained in terms of newly incorporated water between the bilayer surfaces upon melting of the acyl chains, and which is reminiscent of the events that occur at the pre-transition for saturated lipids. From the melting point depression, the thermodynamic activity of the interbilayer water can be calculated and thus the repulsive hydration force characterized quantitatively. We evaluate a (non-isothermal) hydration force decay constant around 2.8 H20, which demonstrates that this DSC approach is well-suited for quantitatively characterizing the hydration properties of unsaturated lipid dispersions at low temperature.

A combined X-ray and neutron diffraction study of selectively deuterated melittin in phospholipid bilayers: effect of pH

In order to study consequences of protonation of the N-terminus upon the interaction of the bee venom melittin with phospholipid bilayers, analogues of melittin, some of which were specifically deuterated at either Ala-12 or 15, were synthesized. These peptides were incorporated into bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine at either low pH (N-terminus protonated) or high pH (N-terminus unprotonated). X-ray and neutron diffraction data were collected from ordered stacks of these bilayers and from peptide-free controls. Phase determination was carried out using the swelling series (X-ray) and isomorphous derivative (neutron) methods. The water distribution between adjacent bilayers in the stacks may be described by a pair of Gaussians whose position and width change with the protonation state of the melittin. Difference Fourier profiles reveal that the melittin largely incorporates into the phospholipid bilayers. Changes in the water, melittin and deuterium label distributions fit a model in which the melittin lies both at the surface and close to the centre of the bilayer, the distribution of peptide between these locations being pH-dependent, with a larger population of surface melittin when the N-terminus is unprotonated.

Resolution of individual lipids in mixed phospholipid membranes and specific lipid-cytochrome c interactions by magic-angle spinning solid-state phosphorus-31 NMR

A model of the inner mitochondrial membrane was constructed with dioleoyphosphatidylcholine (PC), dioleoylphosphatidylethanolamine (PE), and cardiolipin (CL) at a PC:PE:CL molar ratio of 2:2:1, and the interaction of the peripheral membrane protein cytochrome c with this mixed membrane has been investigated by static and magic-angle spinning (MAS) solid-state 31P NMR. The static 31P NMR spectrum of the three-component membrane is a typical broad powder pattern for phospholipids in a bilayer structure, and is a result of three overlapping spectra of each individual phospholipid component in the mixed membrane, with an average effective chemical shift anisotropy of approximately 41 ppm. Using magic-angle spinning NMR methods, three resolved resonances are observed in the narrowed MAS 31P NMR spectrum, each of which has been assigned to each lipid component in the mixed membrane. This allows the investigation of individual phospholipid-protein interactions in multicomponent lipid bilayers. The interaction of cytochrome c with each lipid in a model mitochondrial membrane could now be evaluated. Phosphorus-31 spin-lattice (T1) relaxation times for each lipid phosphate were measured as a function of temperature, in the absence and presence of bound cytochrome c. T1 was not affected for any lipid upon binding of cytochrome c over the temperature range analyzed. However, averaging of the phosphorus-31 chemical shift anisotropy for the cardiolipin component in mixed PC/PE/CL bilayers at lower temperatures ceases to be axially symmetric on binding of cytochrome c, while for PC and PE components the axial symmetry is retained over the temperature interval studied here.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid specificity in the interaction of cytochrome c with anionic phospholipid bilayers revealed by solid-state 31P NMR

Phosphorus-31 NMR has been used to investigate the interaction of cytochrome c with bilayers of the anionic lipids dioleoylphosphatidylglycerol (DOPG), dioleoylphosphatidylserine (DOPS), and diacylphosphatidylinositol (diacylPI). All 31P NMR spectra revealed the typical line shapes characteristics of phospholipids in liquid-crystalline bilayers. The effects on the 31P chemical shift anisotropy (CSA) for each system reflect particular modes of phospholipid headgroup interaction with cytochrome c. A distinct increase in the CSA for DOPS bilayers was observed upon binding of cytochrome c, which is likely to arise from a partial restriction of the amplitude of motion on this phospholipid headgroup. 31P NMR spin-lattice (T1) relaxation times of the various phospholipid-cytochrome c complexes show that conformational changes occur in the protein on binding to anionic phospholipids. These protein conformational changes are observed through paramagnetic enhancement of the measured 31P spin-lattice relaxation times for lipid phosphates. However, the 31P T1 values for the various complexes with cytochrome c show a different temperature dependence for each lipid, revealing different modes of protein interaction for each of the different lipid headgroups. The phosphate of DOPS was most efficiently relaxed by cytochrome c, while the relaxation of the phosphate in the PI headgroup was not affected. The relaxation profile for DOPG-bound cytochrome c shows a more complex behavior, where the lipid phosphorus relaxation is strongly enhanced above 15 degrees C, but not significantly affected at lower temperatures. It was found that the enhancement of lipid phosphorus relaxation is a result of the conformational changes in the protein, in which the heme becomes accessible to lipid phosphate upon binding to charged bilayer surfaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Development and harmonisation of the norms and parameters in biological testing protocols designed for root canal sealing materials within the European Community

The EC has mounted the BIOMED 1 as a specific programme to facilitate cooperative research programmes in identified areas of interest throughout Europe. They have recently announced support under this programme for a joint initiative designed to evaluate in vitro and in vivo methods of biological testing of root canal sealing materials. This proposal was prepared by a group of research workers in the field. It provides a summary of the current suggested protocols for the biological testing of dental materials and then provides a detailed protocol of the studies to be carried out in the joint programme which commenced in January 1993. The authors are publishing the proposal to invite comments from colleagues and interested parties.

The antiviral peptide carbobenzoxy-D-phenylalanyl-L-phenylalanylglycine changes the average conformation of phospholipids in membranes

The influence of the antiviral peptide, carbobenzoxy-D-phenylalanyl-L-phenylalanylglycine (ZfFG), on the average conformation of phosphatidylcholine in hydrated bilayers was investigated with multinuclear solid state magnetic resonance (NMR). Phosphatidylcholine was specifically deuterated (separately) in the choline N-methyls, the alpha and beta positions of the choline, the C2 carbon of the acyl chains, and at all the carbons of the acyl chains of the phosphatidylcholine. Phosphatidylcholine was also synthesized with the carbonyl carbons of the ester bonds between the glycerol and the hydrocarbon chains enriched in 13C. 2H NMR of the phosphatidylcholine perdeuterated in the acyl chains showed a loss of intensity from the deuteriums with the largest quadrupole splitting in the presence of ZfFG, while the remainder of the powder pattern was largely unaffected. The phosphatidylcholine specifically deuterated at the C2 carbon (representative of the C-D bonds giving rise to the largest quadrupole splittings) showed the same loss of intensity suggesting changes in the phospholipid conformation and conformational dynamics near the glycerol. Analysis of the powder patterns in the 13C NMR spectrum of phosphatidylcholine labeled with 13C in the carbonyl carbons revealed a significant change in the average orientation of the sn-1 carbonyl due to the presence of the ZfFG and no change in the sn-2 carbonyl orientation. Changes in the headgroup conformation, as detected by 2H NMR of the deuteriums in the alpha and beta methylenes of the choline headgroup and 31P NMR of the phosphate segment, reflected the electrostatic nature of the interaction of the carboxyl of ZfFG with phosphatidylcholine bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

A role for band 4.2 in human erythrocyte band 3 mediated anion transport

Human erythrocyte band 3 was purified essentially free of peripheral proteins, in particular band 4.2, using affinity chromatography. Band 3 protein was then reconstituted into liposomes of lipid type and ratio approximating that of erythrocyte membranes. Stilbenedisulfonate inhibition of band 3 mediated efflux of radiolabeled sulfate from preloaded liposomes was used to test the functionality and correct orientation of the protein. When sulfate efflux, mediated by purified band 3, was compared with partially purified band 3, which contained detectable amounts of bands 4.1 and 4.2, a clear difference in efflux was measured. Sulfate efflux was approximately 30% faster from liposomes containing purified band 3 compared with those containing partially purified protein. In order to investigate further any specific effect of band 4.2 protein on band 3 mediated anion transport, band 4.2 was purified. Increasing amounts of band 4.2 were complexed with purified band 3 and then reconstituted into liposomes. Increasing amounts of band 4.2 complexed with band 3 caused a decrease in band 3 mediated anion transport. The effect of band 4.2 on band 3 mediated anion transport appears to be specific since increasing concentrations of band 4.2 added exogenously to band 3 in reconstituted vesicles (rather than complexed with band 3 before reconstitution) produced no significant changes in sulfate efflux. Further, when increasing amounts of band 4.2 were added to the functionally active transmembrane domain of band 3 and then reconstituted into vesicles, there was also no significant change in sulfate efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of two complementary fragments of the bovine spinal cord myelin basic protein with phosphatidylglycerol bilayers, studied by 2H and 31P NMR spectroscopy

The interaction of two complementary fragments of myelin basic protein from bovine spinal cord with bilayers of dimyristoylphosphatidylglycerol has been studied by broad line 2H and 31P NMR. The fragments, produced by cleavage at the single tryptophan, consist of an N-terminal portion of molecular mass 12.6 kDa and a C-terminal portion of molecular mass 5.8 kDa. The phosphatidylglycerol lipid was deuterated at all three segments of the glycerol headgroup. The approximately linear dependence of the 2H quadrupole splittings and 31P chemical shift anisotropy on protein/lipid ratio in the complexes indicates that the lipids interacting with the protein fragments were in fast exchange on the NMR time scale (approximately 10(-4)-10(-5) s). The relative gradients of the dependence on protein/lipid ratio of both these parameters decrease with the size of the protein fragment and correlate reasonably well with both the net charge on the protein and the lipid binding stoichiometries in the absence of salt. The results are therefore consistent with a model in which the perturbation of the quadrupole splittings either is determined by the net surface potential or is constant for the different protein fragments. Either possibility is consistent with the reduced activity of the fragments relative to the whole protein.

Dynamics in a protein-lipid complex: nuclear magnetic resonance measurements on the headgroup of cardiolipin when bound to cytochrome c

Deuterium and phosphorus nuclear magnetic resonance (NMR) has been used to investigate the dynamics of slow motional processes induced in bilayer cardiolipin upon binding with cytochrome c. 31P NMR line shapes suggest that protein binding induces less restricted, isotropic-like motions in the lipid phosphates within the ms time scale of this measurement. However, these motions impart rapid transverse relaxation to methylene deuterons adjacent to the phosphate in the lipid headgroup and so did not feature strongly in the NMR line shapes recorded from these nuclei by using the quadrupolar echo. Nonetheless, motional characteristics of the headgroup deuterons were accessible to a dynamic NMR approach using the Carr-Purcell-Meiboom-Gill multiple-pulse experiment. Compared to the well-studied case of deuterons in fatty acyl chains of bilayer phosphatidylcholine, the motions determining the 2H spin transverse relaxation in the headgroup of bilayer cardiolipin were much faster, having a lower limit in the 5-10 kHz range. On binding with cytochrome c, the T2 effecting motions in the cardiolipin headgroup became faster still, with rates comparable to the residual quadrupolar coupling frequency of the headgroup deuterons (approximately 25 kHz) and so coincided with the time scale for recording the quadrupolar echo (approximately 40 microseconds). It is concluded that the headgroup of cardiolipin does not exclusively report localized dynamic information but is particularly sensitive to collective motions occurring throughout the bilayer molecules. Although the rates of collective modes of motion may be dependent on the lipid type in pure lipid bilayers, these low-frequency fluctuations appear to occupy a similar dynamic range in a variety of lipid-protein systems, including the natural membranes.

The effect of general anesthetics on the dynamics of phosphatidylcholine-acetylcholine receptor interactions in reconstituted vesicles

The interaction of general anesthetics at the lipid/protein interface of the nicotinic acetylcholine receptor reconstituted in dioleoylphosphatidylcholine bilayers at various lipid/protein ratios has been studied using the electron spin resonance spectra of phosphatidylcholine spin-labeled at the fourteenth acyl carbon (14-PCSL). In addition to the bilayer spectrum, the spin label reported a more motionally restricted environment whose contribution increased with increasing protein/lipid ratio. Exchange between these two environments occurred at a rate of approx. 6 x 10(7) s-1. The motionally restricted, protein-associated 14-PCSL had a rotational correlation time of about 10-20 ns, an order of magnitude slower than when in the bilayer. Addition of 1-hexanol (up to 16 mM) to the reconstituted receptor perturbed the acyl chains of the bulk lipid phase, but the motional properties of the lipid acyl chains at the protein/lipid interface near the membrane center were not significantly perturbed on the EPR motional time-scale. Similarly, anesthetics that were less effective at perturbing the bilayer, such as pentobarbital (up to 2 mM) and isoflurane (7 mM), did not perturb the lipid/protein interface on the conventional EPR motional time scale.

2H NMR lineshapes of immobilized uniaxially oriented membrane proteins

As a method for the structure determination of integral membrane proteins or other large macromolecular complexes, a solid state 2H NMR approach is presented, capable of measuring the orientations of individual chemical bond vectors. In an immobilized uniaxially oriented sample, the bond angle of a deuterium-labelled methyl group relative to the axis of ordering can be calculated from the quadrupole splitting in the "zero-tilt" spectrum where the sample normal is aligned parallel to the spectrometer field direction. However, since positive and negative values of this splitting cannot be distinguished, there may appear to be two solutions, of which only one describes the correct molecular geometry. We show that it is possible to determine the bond angle uniquely between 0 degree and 90 degrees, by analysing the lineshapes of a tilt series of spectra acquired over different sample inclinations. The lineshape equation describing such oriented 2H NMR spectra will be derived (for asymmetry parameter eta = 0) and discussed, with an illustration of the various linebroadening effects from which the orientational distribution function in the macroscopically ordered system can be determined. This strategy is then applied to specifically deuterium-labelled retinal in dark-adapted bacteriorhodopsin, prepared in a uniaxially oriented sample from purple membrane fragments. From the quadrupole splitting in the zero-tilt spectrum and by lineshape simulations, the deuteromethyl group at C20 on retinal is found to make an angle of 32 degrees +/- 1 degree with the membrane normal, and the sample mosaic spread to be around +/- 8 degrees. The resulting orientation of retinal is in excellent agreement with its known structure in bacteriorhodopsin, and together with the results on other methyl groups it will be possible to construct a detailed picture of the chromophore in the protein binding pocket.

Therapeutic agents utilized in urban/rural prehospital care

INTRODUCTION

Objectives of this study were to determine the number of prehospital emergency patients who were given advanced life support (ALS) drugs and to compare utilization rates for ALS drugs in urban and rural environments. Certified ALS emergency medical technicians (Arizona) have 29 therapeutic agents authorized for prehospital administration. These agents may be administered only under direction of a medical control authority or by following standing orders.

METHODS

A retrospective review was made of prehospital emergency encounter records. They were acquired by the Arizona Office of Emergency Medical Services (OEMS) from rural EMS providers who used optically scannable forms and from a metropolitan fire department's medical emergency response records.

RESULTS

In 1989 and 1990, 273,611 emergency patient encounter records were entered into the EMS database; 197,260 were urban responses and 76,351 were rural responses. Drugs (ALS) were administered to 16,730 (8.5%) urban emergency patients and to 5,359 (7%) rural emergency patients at the incident site or during transport to a medical care facility. Nitrostat, 0.4 mg sublingual tablet, was the drug most frequently administered to emergency patients in the prehospital setting. Utilization rates found in the urban and the rural data sets were consistent for the individual agents. Variations in use frequency between urban and rural setting were noted for some drugs. Of the 29 approved ALS drugs, seven (24%) were administered to 10% or more urban patients who received drugs. In the rural areas, eight (27.6%) were administered to 10% or more patients who received drugs. There were nine (31%) agents administered to less than 1% of all patients who received drugs. A majority of the approved drugs, 17 (59%) were administered at a rate below 5% of all patients receiving medications.

CONCLUSION

Severity of illness or injury prompted administration of ALS drugs to 8.1% of patients receiving prehospital emergency care. The most frequently utilized medication in the urban/rural areas was for treatment of cardiac symptoms. Variations between urban/rural drug utilization reflected the drugs of choice which are compatible with long transport times to a medical facility.

The bony crescent sign--a new sign of facial nerve schwannoma

Schwannomas of the facial nerve are rare slowly growing lesions that have a predilection for the geniculate ganglion. Radiological evaluation is important in their diagnosis and in the assessment of their extent. In our series of 4 cases the facial nerve schwannoma was seen on high resolution CT as a soft tissue mass bounded anteriorly by a thin rim of bone. This bony crescent sign is a previously undescribed sign of facial nerve schwannoma which appears on the basis of this small series to be strongly indicative of the presence of this tumour. Schwannomas are relatively uncommon intracranial tumours. They most commonly involve the acoustic nerve followed in frequency by the trigeminal nerve. Other cranial nerves are rarely involved. Facial nerve schwannomas occurring within the petrous temporal bone are very rare. Their diagnosis may be missed prospectively even when appropriate CT scans are performed. Even in retrospect the site of abnormality may be difficult to identify, especially if there is an associated middle ear mass such as a cholesteatoma. Lesions occurring in the petrous area are all rare. The differential diagnosis includes cholesterol granuloma, epidermoid, carotid aneurysm and, very rarely, primary and secondary bone tumours. We describe a new sign associated with facial nerve schwannoma on CT, that of a bony crescent. Recognition of this sign makes those tumours arising in the region of the geniculate ganglion easy to diagnose prospectively.

Structure determination of the cyclohexene ring of retinal in bacteriorhodopsin by solid-state deuterium NMR

The orientation and conformation of retinal within bacteriorhodopsin of the purple membrane of Halobacterium halobium was established by solid-state deuterium NMR spectroscopy, through the determination of individual chemical bond vectors. The chromophore ([2,4,4,16,16,17,17,17,18,18-2H11]retinal) was specifically deuterium-labeled on the cyclohexene ring and incorporated into the protein. A uniaxially oriented sample of purple membrane patches was prepared and measured at a series of inclinations relative to the spectrometer field. 31P NMR was used to characterize the mosaic spread of the oriented sample, and computer simulations were applied in the analysis of the 2H NMR and 31P NMR spectral line shapes. From the deuterium quadrupole splittings, the specific orientations of the three labeled methyl groups on the cyclohexene ring could be calculated. The two adjacent methyl groups (on C1) of the retinal were found to lie approximately horizontal in the membrane and make respective angles of 94 degrees +/- 2 degrees and 75 degrees +/- 2 degrees with the membrane normal. The third group (on C5) points toward the cytoplasmic side with an angle of 46 degrees +/- 3 degrees. These intramolecular constraints indicate that the cyclohexene ring lies approximately perpendicular to the membrane surface and that it has a (6S)-trans conformation. From the estimated angle of the tilt of the chomophore long axis, it is concluded that the polyene chain is slightly curved downward to the extracellular side of the membrane.

Cytochrome c interactions with cardiolipin in bilayers: a multinuclear magic-angle spinning NMR study

The influence of cytochrome c binding to cardiolipin bilayers on the motional characteristics of each component has been analyzed by magic-angle spinning (MAS) NMR. Observations were made by NMR of natural abundance 31P, 13C, and 1H nuclei in the lipid as well as sites enriched with 13C in the protein. Analysis of methyl carbons enriched in ([epsilon-13CH3]methionine)cytochrome c at residues 65 and 80 reveal quite different behavior for these sites when the protein was bound at a 1:15 molar ratio with hydrated cardiolipin. Cross-polarization (CP) shows a single broad resonance downfield in the methyl region which corresponds to the spectral characteristics of methionine 65 in the solution protein when subjected to moderate thermal perturbations. These observations suggest that although methionine 65 remains motionally restricted when the protein binds to the lipid bilayers, this residue becomes less shielded and exposed to more chemically distinct environments than in the native state of the protein. In contrast to its behavior in native oxidized protein, the methionine 80 methyl could be detected following direct pi/2 pulse excitation, and this residue is assumed to be released from the axial ligand site on the heme iron to become more exposed and highly mobile in the protein-lipid complex. An analysis of the CP response for natural abundance 13C nuclei in the lipid reveals a general increase in motions with slower rates (tens of kilohertz) on binding with cytochrome c, except for sites within the region of fatty acyl chain unsaturation which appear to be selectively mobilized in the complex with protein. It is concluded that, aside from effects on the unsaturated segments, the bound protein induces new modes of slow motions in the lipid assemblies rather than restricting the overall reorientation freedom of the lipid. The strong paramagnetic effects observed previously on the relaxation of phosphorus in protein-bound lipid [Spooner, P.J.R., & Watts, A. (1991) Biochemistry 30, 3880-3885] were not extended to any carbon and proton sites observable by MAS NMR in the lipid, and this infers a specific interaction of lipid phosphate groups with the heme. However, when protein was bound to cardiolipin mixed at a 1:4 mole ratio with dioleoylphosphatidylcholine in bilayers, no direct interaction with the heme was apparent from the phosphorus NMR relaxation behavior in this component, resolved by MAS. Instead, the spectral anisotropy of cardiolipin phosphorus was determined to be reduced, indicating that, on binding with cytochrome c, the headgroup organization was perturbed in this component.(ABSTRACT TRUNCATED AT 400 WORDS)

'Usage' testing of root canal sealing materials--a personal view

A number of systems for the biological testing of dental materials have been suggested. This paper reviews the protocols suggested in the ISO standards for the in-use or 'usage' tests for root canal sealing materials.

Initial biological testing of root canal sealing materials--a critical review

A number of systems for the biological testing of dental materials have been suggested. This paper presents a critical review of the protocols suggested in the ISO standards for the initial and secondary biological testing of root canal sealing materials.

The essential role of specific Halobacterium halobium polar lipids in 2D-array formation of bacteriorhodopsin

The mechanism whereby bacteriorhodopsin (BR), the light driven proton pump from the purple membrane of Halobacterium halobium, arranges in a 2D-hexagonal array, has been studied in bilayers containing the protein, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and various fractions of H. halobium membrane lipids, by freeze fracture electron microscopy and examination of optical diffractograms of the micrographs obtained. Electron micrographs of BR/DMPC complexes containing the entire polar lipid component of H. halobium cell membranes or the total lipid component of the purple membrane, with a protein-to-total lipid molar ratio of less than 1:50 and to which 4 M NaCl had been added, revealed that trimers of BR formed into an hexagonal 2D-array similar to that found in the native purple membrane, suggesting that one or more types of the purple membrane polar lipids are required for array formation. To support this suggestion, bacteriorhodopsin was purified free of endogenous purple membrane lipids and reconstituted into lipid bilayer complexes by detergent dialysis. The lipids used to form these complexes are 1,2-dimyristoyl-sn-glycerol-phosphocholine (DMPC) as the major lipid and, separately, each of the individual lipid types from the H. halobium cell membranes, namely 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol 1'-phosphate (DPhPGP), 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol 1'-sulphate (DPhPGS), 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol (DPhPG) and 2,3-di-O-phytanyl-1-O-[beta-D-Galp-3-sulphate-(1----6)-alpha-D- Manp-(1----2)-alpha-D-Glcp]-sn-glycerol (DPhGLS). When examined by freeze-fracture electron microscopy, only the complexes containing 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol- 1'-phosphate or 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol-1'-sulphate, at high protein density (less than 1:50, bacteriorhodopsin/phospholipid, molar ratio) and to which 4 M NaCl had been added, showed well defined 2D hexagonal arrays of bacteriorhodopsin trimers similar to those observed in the purple membrane of H. halobium.

Effect of bacteriorhodopsin on the orientation of the headgroup of 1,2-dimyristoyl-sn-glycero-3-phosphocholine in bilayers: a 31P- and 2H-NMR study

Bacteriorhodopsin (BR), purified from the halophilic bacterium, Halobacterium halobium, has been separated from the endogenous purple membrane lipids and reconstituted by detergent dialysis into bilayers of the zwitterionic phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), which was selectively deuterated at the headgroup in the choline alpha- and beta-methylene segments and the choline gamma-methyl groups. Complexes of DMPC/BR contents from 67:1 to 222:1 (mol/mol) were produced under conditions to promote formation of large vesicles (mean diameters 600-700 nm). The magnitudes of the 2H-NMR quadrupole splittings recorded from the deuterium-labelled headgroup segments, and the 31P-NMR chemical shift anisotropy (CSA) of the phosphate group appeared to vary linearly with the BR content in the complexes over the range of DMPC/BR ratios studied. On increasing the proportion of BR in the DMPC-BR complexes, the 2H-NMR quadrupole splittings measured from the choline gamma-methyl groups and the beta-methylene segments and the 31P-NMR CSA increased in magnitude, while the 2H-NMR quadrupole splitting from the alpha-methylene segment decreased. Such opposing changes in the choline alpha- and beta-methylene segment quadrupole splittings are similar to those reported on increasing the proportion of positively charged amphiphile at the bilayer surface (Seelig et al. (1987) Biochemistry 26, 7535-7541). It is suggested that BR presents a net positive charge to the phosphocholine headgroups at the protein/lipid interface.

Pulp responses to two strains of bacteria isolated from human carious dentine (L. plantarum) (NCTC 1406) and S. mutans (NCTC 10919)

A series of studies has been conducted in which monoinfected gnotobiotic rats were used to study the responses of the dental pulp to micro-organisms isolated from carious lesions in dentine. In this study pulp responses to L. plantarum (formerly odontolyticus) (NCTC 1406) in pure culture and in combination with S. mutans (NCTC 10919) are reported. The incidence of inflammation/necrosis/dentine bridge formation observed in animals monoinfected with L. plantarum was similar to that reported in previous germ-free studies. There was a greater incidence of dentine bridge formation in rats monoinfected with L. plantarum compared with those monoinfected with S. mutans. When the two organisms were combined, periapical inflammation was observed in 14% of the teeth examined after 28 days, but there was no significant difference in the incidence of dentine bridge formation. Considerable variation in the density of staining of the two microorganisms in histological sections was observed.

Pulp response to, and cariogenicity of, a further strain of Streptococcus mutans (NCTC 10832)

The pulpal response to and cariogenicity of a third strain of Streptococcus mutans, namely S. mutans (NCTC 10832), was studied in monoinfected gnotobiotic rats of the Fischer strain using the techniques described previously by the present authors. Unlike S. mutans (NCTC 10449 and 10919), S. mutans (NCTC 10832) was associated with the presence of inflammatory cell infiltrates in the coronal pulp of a small number of teeth and extensive periapical inflammation 28 days after the creation of untreated pulpal exposures. S. mutans (NCTC 10832) was associated with the presence of extensive pulpal necrosis and reduced dentine bridge formation. These changes were similar to those noted with the other two strains of S. mutans. S. mutans (NCTC 10832) was non-cariogenic in monoinfected gnotobiotic rats of the Fischer strain.

Saturation transfer, continuous wave saturation, and saturation recovery electron spin resonance studies of chain-spin labeled phosphatidylcholines in the low temperature phases of dipalmitoyl phosphatidylcholine bilayers. Effects of rotational dynamics and spin-spin interactions

The saturation transfer electron spin resonance (STESR) spectra of 10 different positional isomers of phosphatidylcholine spin-labeled in the sn-2 chain have been investigated in the low temperature phases of dipalmitoyl phosphatidylcholine (DPPC) bilayers. The results of continuous wave saturation and of saturation recovery measurements on the conventional ESR spectra were used to define the saturation properties necessary for interpreting the STESR results in terms of the chain dynamics. Spin labels with the nitroxide group located in the center of the chain tended to segregate preferentially from the DPPC host lipids in the more ordered phases, causing spin-spin interactions which produced spectral broadening and had a very pronounced effect on the saturation characteristics of the labels. This was accompanied by a large decrease in the STESR spectral intensities and diagnostic line height ratios relative to those of spin labels that exhibited a higher degree of saturation at the same microwave power. The temperature dependence of the STESR spectra of the different spin label isomers revealed a sharp increase in the rate of rotation about the long axis of the lipid chains at approximately 25 degrees C, correlating with the pretransition of gel phase DPPC bilayers, and a progressive increase in the segmental motion towards the terminal methyl end of the chains in all phases. Prolonged incubation at low temperatures led to an increase in the diagnostic STESR line height ratios in all regions of the spectrum, reflecting the decrease in chain mobility accompanying formation of the subgel phase. Continuous recording of the central diagnostic peak height of the STESR spectra while scanning the temperature revealed a discontinuity at approximately 14-17 degrees C, corresponding to the DPPC subtransition which occurred only on the initial upward temperature scan, in addition to the discontinuity at 29-31 degrees C corresponding to the pretransition which displayed hysteresis on the downward temperature scan.

Structural stability of the erythrocyte anion transporter, band 3, in native membranes and in detergent micelles

The exothermic thermal denaturation transition of band 3, the anion transporter of the human erythrocyte membranes, has been studied by differential scanning calorimetry, in ghost membranes and in nonionic detergent micelles. In detergent micelles the transmembrane domain of band 3 gave an irreversible denaturation transition (C transition). However, no thermal transition was observed for the N-terminal cytoplasmic domain when band 3 was solubilised in detergent micelles. A reduction in enthalpy (190-300 kcal mol-1) with an accompanying decrease in thermal denaturation temperatures (48-60 degrees C) for the C transition was observed in detergent solubilised band 3 when compared with ghost membranes. Unlike ghost membranes, two thermal transitions for band 3 in detergent micelles were observed for the C transition when in the presence of excess covalent inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS), which derive from the thermal unfolding of a single protein with two different thermal stabilities; DIDS-stabilised (75 degrees C) and DIDS-insensitive (62 degrees C). A reduction in the denaturation temperature for the transmembrane domain of band 3 was observed when compared with intact band 3 although no significant differences was observed in the corresponding enthalpy values. This indicates some cooperativity of the two domains of band 3 in maintaining the transmembrane conformation. The results presented in this study show that detergents of intermediate micelle size (e.g. Triton X-100 and C12E8) are required for optimal thermal stability of band 3.

Characterization of phospholipid compositions and physical properties of DMPC/bacteriorhodopsin vesicles produced by a detergent-free method

Homogeneous complexes of bacteriorhodopsin (BR) from Halobacterium halobium purple membrane (PM) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) have been produced by a detergent-free process in which bovine liver non-specific phospholipid transfer protein (nsTP) promotes net transfer of DMPC from small unilamellar vesicles directly into PM. The number of DMPC molecules incorporated per BR monomer follows a close to linear dependence with the relative proportions of DMPC and PM added to the initial mixture over the ranges studied. The resulting complexes, with total lipid phosphate/BR contents of between 31:1 and 152:1 (mole/mole), were purified free from any remaining unincorporated DMPC by sucrose density gradient centrifugation. Broad line 31P-NMR spectra and partitioning studies with the nitroxide spin label, Tempo, confirm that the BR and DMPC coexist in bilayer complexes. Quantitative analysis of high resolution 31P-NMR spectra from complexes after solubilization in 4% SDS revealed 74-84% of the major PM phospholipid to be retained in the complexes.

Partitioning behaviour of 1-hexanol into lipid membranes as studied by deuterium NMR spectroscopy

Deuterium nuclear magnetic resonance (NMR) spectroscopy was used to study the partitioning behaviour of 1-hexanol specifically deuterated in the alpha-position into model lipid bilayers. In all systems studied, the observed deuterium NMR lineshapes were time-dependent. Initially, 1-hexanol-d2 gave rise to an isotropic deuterium resonance with a different chemical shift from that of aqueous 1-hexanol-d2. After equilibration over a period of days, a broader spectral component characteristic of a spherically-averaged powder-pattern was observed. The quadrupole anisotropy of the 1-hexanol-d2 giving rise to the broad spectrum depended upon the cholesterol content of the membrane. From quantitation of the anisotropic to isotropic deuterium NMR spectra, the partition coefficients of 1-hexanol-d2 in a number of bilayer systems (asolectin and phosphatidylcholine bilayers (the latter with and without cholesterol] were determined. The partitioning of 1-hexanol-d2 into red blood cell membranes, and a suspension of lipids extracted from red blood cell membranes, was also examined. It is suggested that 1-hexanol, and probably other lipophiles, can partition to either the bilayer surface or the bilayer interior in a time-dependent manner.

A review of current proprietary bonding systems

This is the third of a series of articles reviewing the current knowledge on bonding systems. In the two previous papers the nature of the dentine smear layer and the preparation of the dentine surface for bonding were considered. This article reviews the current knowledge of the mechanisms of dentine bonding and presents a summary of the composition and mode of action of some of the more recent proprietary bonding systems.

A NMR investigation on the interactions of the alpha-oligomeric form of the M13 coat protein with lipids, which mimic the Escherichia coli inner membrane

The interaction of the M13 bacteriophage major coat protein in the alpha-oligomeric form with specifically deuterated phospholipid headgroups which mimic the Escherichia coli inner membrane, has been studied using NMR methods. As can be seen from the deuterium NMR spectra obtained with headgroup trimethyl deuterated DOPC, the coat protein in the alpha-oligomeric form does not give rise to trapped lipids as observed with M13 coat protein in the beta-polymeric form (Van Gorkom et al. (1990) Biochemistry 29, 3828-3834). The quadrupolar splittings of the alpha headgroup methylene deuterons of deuterated phosphatidylcholine and phosphatidylethanolamine decrease, whereas the quadrupolar splittings of the beta headgroup methylene deuterons of the two lipids increase with increasing protein content. All deuterated segments in the phosphatidylglycerol headgroup show the same relative decrease of the NMR quadrupolar splittings. These results are interpreted in terms of a change in torsion angles of the methylene groups, induced by positive charges, probably lysine residues of the protein at the membrane surface. For all lipid bilayer compositions studied the head-group perturbations are similar. It is concluded that there is no strong specific interaction between one of the lipid types examined and the M13 coat protein. From the spin-spin (T2e) relaxation time and spin-lattice (T1z) relaxation time of all deuterated lipids it is concluded that at the bilayer surface only slow motions are affected by the M13 coat protein.

Reversible unfolding of cytochrome c upon interaction with cardiolipin bilayers. 2. Evidence from phosphorus-31 NMR measurements

31P NMR measurements were conducted to determine the structural and chemical environment of beef heart cardiolipin when bound to cytochrome c. 31P NMR line shapes infer that the majority of lipid remains in the bilayer state and that the average conformation of the lipid phosphate is not greatly affected by binding to the protein. An analysis of the spin-lattice (T1) relaxation times of hydrated cardiolipin as a function of temperature describes a T1 minimum at around 25 degrees C which leads to a correlation time for the phosphates in the lipid headgroup of 0.71 ns. The relaxation behavior of the protein-lipid complex was markedly different, showing a pronounced enhancement in the phosphorus spin-lattice relaxation rate. This effect of the protein increased progressively with increasing temperature, giving no indication of a minimum in T1 up to 75 degrees C. The enhancement in lipid phosphorus T1 relaxation was observed with protein in both oxidation states, being somewhat less marked for the reduced form. The characteristics of the T1 effects and the influence of the protein on other relaxation processes determined for the lipid phosphorus (spin-spin relaxation and longitudinal relaxation in the rotating frame) point to a strong paramagnetic interaction from the protein. A comparison with the relaxation behavior of samples spinning at the "magic angle" was also consistent with this mechanism. The results suggest that cytochrome c reversibly denatures on complexation with cardiolipin bilayers, such that the electronic ground state prevailing in the native structure of both oxidized and reduced protein can convert to high-spin states with greater magnetic susceptibility.

Reversible unfolding of cytochrome c upon interaction with cardiolipin bilayers. 1. Evidence from deuterium NMR measurements

Deuterium NMR has been used to investigate the structure and dynamic state of cytochrome c complexed with bilayers of cardiolipin. Reductive methylation was employed to prepare [N epsilon, N epsilon-C2H3]lysyl cytochrome c, and deuterium exchange provided labeling of backbone sites to give [amide-2H]cytochrome c or more selective labeling of just histidine residues in [epsilon-2H]histidine cytochrome c. Deuterium NMR measurements on [N epsilon, N epsilon-C2H3]lysyl cytochrome c in the solid state showed restricted motions, fairly typical of the behavior of aliphatic side-chain sites in proteins. The [amide-2H]cytochrome c provided "immobile" amide spectra showing that only the most stable backbone sites remained labeled in this derivative. Relaxation measurements on the aqueous solution of [amide-2H]cytochrome c yielded a rotational correlation time of 7.9 ns for the protein, equivalent to a hydrodynamic diameter of 4.0 nm, just 0.6 nm greater than its largest crystallographic dimension. Similar measurements on [epsilon-2H]histidine cytochrome c in solution showed that all labeled histidine residues were also "immobile" compared with the overall reorientational motion of the protein. The interaction with cardiolipin bilayers appeared to create a high degree of mobility for the side-chain sites of [N epsilon, N epsilon-C2H3]lysyl cytochrome c and perturbed backbone structure to instantaneously release all deuterons in [amide-2H]cytochrome c. The [epsilon-2H]histidine cytochrome c derivative, when complexed with cardiolipin, failed to produce any detectable wide-line 2H NMR spectrum, demonstrating that the overall reorientational motion of bound protein was not isotropic on the NMR time scale, i.e., tau c greater than 10(-7)s.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipid phase transitions as revealed by NMR

Aqueous dispersions of phospholipids can adopt a range of polymorphic phases which include bilayer and non-bilayer forms. Within the bilayer form, laterally separated phases may be induced as a result of surface electrostatic associations, thermotropic behaviour, lipid-protein interactions or because of molecular mismatch between chemically distinct phospholipids. Nuclear magnetic resonance (NMR) methods, designed to exploit the properties of either indigenous nuclei or isotopic labels introduced specifically into a phospholipid, can be used in some cases to describe the molecular properties and behaviour of phospholipids in both macroscopically distinct phases and in molecularly distinct phases within the same polymorphic state. If the molecular motion of phospholipids in co-existing phases is sufficiently different, NMR methods can, in principle, give estimates of the life-time of the phases and the rate of molecular exchange between the phases.

Identification of trapped and boundary lipid binding sites in M13 coat protein/lipid complexes by deuterium NMR spectroscopy

The major coat protein of M13 bacteriophage has been incorporated into bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, deuterated in the trimethyl segments of the choline headgroup (DMPC-d9). Two-component deuterium and phosphorus-31 NMR spectra have been observed from bilayer complexes containing the coat protein, indicating slow exchange (on the deuterium quadrupole anisotropy and phosphorus-31 chemical shift averaging time scales) of lipid molecules of less than 10(3) Hz between two motionally distinct environments in the complexes. The fraction of the isotropic spectral component increases with increasing M13 protein concentration, and this component is attributed to lipid headgroups, which are disordered relative to their order in protein-free bilayers. The activation energy of the fast local motions of the trimethyl groups of the choline residue in the headgroup decreases from 23 kJ mol-1 in the pure lipid bilayers to 20 kJ mol-1 for the protein-associated lipid headgroups. The chemical exchange rate of lipid molecules between the two motionally distinct environments has been estimated to be 20-50 Hz by steady-state line-shape simulations of the deuterium spectra of DMPC-d9/M13 coat protein complexes using exchange-coupled modified Bloch equations. The off-rate was, as expected from one-to-one exchange, independent of the L/P ratio; tau off -1 = 0.23 kHz. It is suggested that the protein-associated lipid may be trapped between closely packed parallel aggregates of M13 coat protein and that the high local concentration of protein in a one-dimensional arrangement in lipid bilayers may be required for the fast reassembly of phage particles before release from an infected cell.

A study of the effect of general anesthetics on lipid-protein interactions in acetylcholine receptor enriched membranes from Torpedo nobiliana using nitroxide spin-labels

Stearic acid, phosphatidylcholine, and phosphatidylglycerol nitroxide spin-labels were used to probe the effect of 1-hexanol, urethane, diethyl ether, and ethanol on lipid-protein interactions in nicotinic acetylcholine receptor (nAcChoR) rich membranes from Torpedo nobiliana. For stearic acid spin-labeled at the C-14 position of the sn-1 acyl chain, 1-hexanol induced little change (over a wide concentration range, 0-16.7 mM) in either the ESR line shape or the proportion of motionally restricted spectral component from labels probing the protein interface. The main effect of 1-hexanol was limited to an increase in the mobility of stearic acid spin-labels probing the non-protein-associated environment. In contrast, for C-14 phosphatidylcholine spin-label, 1-hexanol decreased the fraction of spin-labels motionally restricted at the protein interface from 0.33 without 1-hexanol to 0.20 with 16.7 mM 1-hexanol, with no change in the line shape of the spectral component of these labels. The ESR spectral line shape of the fluid component due to phosphatidylcholine labels in sites away from the protein interface displayed a gradual decrease in spectral anisotropy on addition of increasing amounts of 1-hexanol. At a concentration of 1-hexanol that desensitizes half the receptors, the fraction of motionally restricted phosphatidylcholine spin-label is reduced by approximately 15%. The effect of 1-hexanol on phosphatidylglycerol spin-labels was intermediate between these two cases. Similar effects were measured with other general anesthetics, including urethane, diethyl ether, and ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)