Secondary structure of M13 coat protein in phospholipids studied by circular dichroism, Raman, and Fourier transform infrared spectroscopy

Probing the Role of Ion-Pair Strategy in Controlling Dexmedetomidine Penetrate Through Drug-in-Adhesive Patch: Mechanistic Insights Based on Release and Percutaneous Absorption Process

The purpose of present study was to develop a controlled release drug-in-adhesive patch for transdermal delivery of dexmedetomidine (Dex) using ion-pair technique. Based on the in vitro transdermal experiment, the role of ion-pair on the Dex release behavior and percutaneous absorption process was also investigated. Fourier transform infrared spectroscopy (FTIR), molecular modeling, differential scanning calorimetry (DSC), and rheological test were conducted to probe the effect of ion-pair on the Dex release from patch. Besides, the tape stripping test, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and molecular simulation were carried out to elaborate the action of ion-pair on the Dex percutaneous permeation process. Results showed that the optimized patch prepared with Dex-salicylic acid (SA) showed zero-order skin permeation profile within 24 h; Dex-SA had greater hydrogen bonding formation potential with pressure sensitive adhesive (PSA) than Dex, which resulted in the decrease in the formation ability of free volume of PSA and the increase with the improvement of mechanical strength and chain stiffness of PSA and thus controlled the release rate of Dex from transdermal patch. Besides, the physicochemical properties of Dex such as molecular weight and octanol/water partition coefficient were changed after forming ion-pair with SA, which decreased the permeation ability of Dex. In conclusion, a controlled release drug-adhesive patch for Dex was developed and the mechanism study of ion-pair on the Dex release and percutaneous permeation process was proposed at molecular level.

RGD peptide and graphene oxide co-functionalized PLGA nanofiber scaffolds for vascular tissue engineering

In recent years, much research has been suggested and examined for the development of tissue engineering scaffolds to promote cellular behaviors. In our study, RGD peptide and graphene oxide (GO) co-functionalized poly(lactide-co-glycolide, PLGA) (RGD-GO-PLGA) nanofiber mats were fabricated via electrospinning, and their physicochemical and thermal properties were characterized to explore their potential as biofunctional scaffolds for vascular tissue engineering. Scanning electron microscopy images revealed that the RGD-GO-PLGA nanofiber mats were readily fabricated and composed of random-oriented electrospun nanofibers with average diameter of 558 nm. The successful co-functionalization of RGD peptide and GO into the PLGA nanofibers was confirmed by Fourier-transform infrared spectroscopic analysis. Moreover, the surface hydrophilicity of the nanofiber mats was markedly increased by co-functionalizing with RGD peptide and GO. It was found that the mats were thermally stable under the cell culture condition. Furthermore, the initial attachment and proliferation of primarily cultured vascular smooth muscle cells (VSMCs) on the RGD-GO-PLGA nanofiber mats were evaluated. It was revealed that the RGD-GO-PLGA nanofiber mats can effectively promote the growth of VSMCs. In conclusion, our findings suggest that the RGD-GO-PLGA nanofiber mats can be promising candidates for tissue engineering scaffolds effective for the regeneration of vascular smooth muscle.

Reconstitution of the M13 Major Coat Protein and Its Transmembrane Peptide Segment on a DNA Template

The major coat protein (pVIII) of M13 phage is of particular interest to structure biologists since it functions in two different environments: during assembly and infection, it interacts with the bacterial lipid bilayer, but in the phage particle, it exists as a protein capsid to protect a closed circular, single-stranded DNA (ssDNA) genome. We synthesized pVIII and a 32mer peptide consisting of the transmembrane and DNA binding domains of pVIII. The 32mer peptide displays typically an alpha-helical structure in trifluroethanol or 0.2 M octylglucoside solutions similar to pVIII. Attachment of polyethylene glycol (PEG) onto the N-terminal of 32mer increased the alpha-helical content and the peptide thermal stability. The peptides were reconstituted with DNA from a detergent solution into a discrete (<200 nm diameter) nanoparticle on both linear double-stranded DNA (dsDNA) and linear ssDNA, where the linear dsDNA is used to mimic the closed circular, ssDNA in M13 phage, upon removal of the detergent. The peptide/DNA particle was an irregular and not a rod-shaped aggregate when imaged by atomic force microscopy. All three peptides underwent a structural transition from alpha-helix to beta-sheet within approximately 1 h of DNA addition to the detergent solution. There was a further decrease in alpha-helical content when the detergent was removed. The presence of anionic (such as octanoic acid) or cationic (such as 1,5-diaminopentane) molecules in the detergent mixture resulted in the retention of the peptide alpha-helical structure. Thus the interaction between the peptide and DNA in octylglucoside is driven by electrostatic forces, and peptide-peptide interactions are responsible for the transition from alpha-helix to beta-sheet conformation in pVIII and its analogues. These results suggest that the assembly process to form a rod-shaped phage is a delicate balance to maintain pVIII in an alpha-helical conformation that requires either an oriented bilayer to solubilize pVIII prior to interaction with the DNA or other phage proteins to nucleate pVIII in the alpha-helical conformation on the DNA.

Secondary structure analysis of HIV-1-gp41 in solution and adsorbed to aluminum hydroxide by Fourier transform infrared spectroscopy

The formulation of human vaccines often includes adjuvants such as aluminum hydroxide that are added to enhance the immune responses to vaccine antigens. However, these adjuvants may also affect the conformation of antigenic proteins. Such structural modifications could lead to changes in antigenicity such that suboptimal protective immune responses could be generated relative to those induced by the vaccine antigens alone. Here, we used attenuated total reflectance infrared spectroscopy (ATR-FTIR) to compare the secondary structures of recombinant HIV-1-gp41 (gp41) in solution or adsorbed to aluminum hydroxide. The gp41 secondary structure content was 72% alpha-helices and 28% beta-sheets in 5 mM formate buffer p(2)H 2.5, while it was 66% beta-sheets and 34% random coil in acetonitril/(2)H(2)O (95/5:v/v). A fully reversible conformational change of gp41 in acetonitril/(2)H(2)O (95/5:v/v) was observed upon addition of either 35 mM formate p(2)H 2.5 or 0.1% (w/v) detergent (Tween 20, Hecameg, Brij 35 or beta-d-octyl-glucopyranoside). When gp41 was adsorbed to aluminum hydroxide in the presence of 0.1% (w/v) detergent, in either formate or in acetonitril/(2)H(2)O (95/5:v/v) its secondary structure remained stable and was identical to that of gp41 in 5 mM formate buffer p(2)H 2.5. The method described here could be applied for the characterization of gp41 conformers for use in immunological screening of antigens, and more generally to all antigenic proteins adsorbed to aluminum hydroxide.

Membrane assembly of M13 major coat protein: evidence for a structural adaptation in the hinge region and a tilted transmembrane domain

New insights into the low-resolution structure of the hinge region and the transmembrane domain of the membrane-bound major coat protein of the bacteriophage M13 are deduced from a single cysteine-scanning approach using fluorescence spectroscopy. New mutant coat proteins are labeled and reconstituted into phospholipid bilayers with varying headgroup compositions (PC, PE, and PG) and thicknesses (14:1PC, 18:1PC, and 22:1PC). Information about the polarity of the local environment around the labeled sites is deduced from the wavelength of maximum emission using AEDANS attached to the SH groups of the cysteines as a fluorescent probe. It is found that the protein is almost entirely embedded in the membrane, whereas the phospholipid headgroup composition of the membrane hardly affects the overall embedment of the protein in the membrane. From the assessment of a hydrophobic and hydrophilic face of the transmembrane helix, it is concluded that the helix is tilted with respect to the membrane normal. As compared to the thicker 18:1PC and 22:1PC membranes, reconstitution of the protein in the thin 14:1PC membranes results in a loss of helical structure and in the formation of a stretched conformation of the hinge region. It is suggested that the hinge region acts as a flexible spring between the N-terminal amphipathic arm and transmembrane hydrophobic helix. On average, the membrane-bound state of the coat protein can be seen as a gently curved and tilted, "banana-shaped" molecule, which is strongly anchored in the membrane-water interface at the C-terminus. From our experiments, we propose a rather small conformational adaptation of the major coat protein as the most likely reversible mechanism for responding to environmental changes during the bacteriophage disassembly and assembly process.

The core of the tetrameric mycobacterial porin MspA is an extremely stable beta-sheet domain

MspA is the major porin of Mycobacterium smegmatis mediating the exchange of hydrophilic solutes across the cell wall and is the prototype of a new family of tetrameric porins with a single central pore of 10 nm in length. Infrared and circular dichroism spectroscopy revealed that MspA consists mainly of antiparallel beta-strands organized in a coherent domain. Heating to 92 and 112 degrees C was required to dissociate the MspA tetramer and to unfold the beta-sheet domain in the monomer, respectively. The stability of the MspA tetramer exceeded the remarkable stability of the porins of Gram-negative bacteria for every condition tested and was not reduced in the presence of 2% SDS and at any pH from 2 to 14. These results indicated that the interactions between the MspA subunits are different from those in the porins of Gram-negative bacteria and are discussed in the light of a channel-forming beta-barrel as a core structure of MspA. Surprisingly, the channel activity of MspA in 2% SDS and 7.6 m urea at 50 degrees C was reduced 13- and 30-fold, respectively, although the MspA tetramer and the beta-sheet domain were stable under those conditions. Channel closure by conformational changes of extracellular loops under those conditions is discussed to explain these observations. This study presents the first experimental evidence that outer membrane proteins not only from Gram-negative bacteria but also from mycobacteria are beta-sheet proteins and demonstrates that MspA constitutes the most stable transmembrane channel protein known so far. Thus, MspA may be of special interest for biotechnological applications.

Passive and iontophoretic transport enhancement of insulin through porcine epidermis by depilatories: permeability and fourier transform infrared spectroscopy studies

The effect of thioglycolate-based depilatory lotions was studied on the in vitro passive and iontophoretic permeability of insulin through porcine epidermis and biophysical changes in the stratum corneum (SC) lipids and proteins. The porcine epidermis and Franz diffusion cells modified for iontophoresis were used for the in vitro transport studies. Cathodal iontophoresis was performed at 0.2 mA/cm2 current density. Resistance of the control- and depilatory-lotion-treated epidermis was determined according to Ohm's law. Biophysical changes were studied on porcine SC before (control) and after treatment with the depilatory lotions using Fourier transform infrared (FT-IR) spectroscopy. Asymmetric (approximately 2915 cm(-1)) and symmetric approximately 2848 cm(-1)) Carbon-Hydrogen (C-H) stretching absorbances were studied to estimate the extent of lipid extraction. Fourier self-deconvolution and second derivative procedures were applied to amide I band (1700-1600 cm(-1)) in order to estimate quantitatively the changes in the secondary structure of the SC protein. The passive permeability of insulin was significantly (P <.05) increased through depilatory-lotion-treated (ie, Better Off, Marzena, and Sally Hansen) epidermis in comparison to control. Iontophoresis significantly enhanced (P <.05) the permeability of insulin through depilatory-pretreated epidermis in comparison with the control epidermis. Further, we were able to achieve the desired flux of insulin (5.25 U/cm2/d) through Better Off-treated epidermis using 0.2 mA/cm2 current density and 100 U/mL donor concentration of insulin. The SC treated with depilatory lotions showed a decrease in peak areas of C-H stretching absorbances in comparison with untreated SC. Depilatory lotion treatment also decreased (P <.05) the epidermal resistance in comparison with the control epidermis. The decrease in the alpha-helix conformation and the increase in the random and turn structures were observed in the SC proteins due to depilatory lotion treatment. The changes in the secondary structure of proteins and lipid extraction from the SC are suggested as the cause of the decrease in the epidermal resistance and the increase in the passive and iontophoretic permeability of insulin through depilatory-pretreated epidermis in comparison with the control epidermis.

Structural and orientational information of the membrane embedded M13 coat protein by (13)C-MAS NMR spectroscopy

Oriented and unoriented M13 coat protein, incorporated into dimyristoyl phosphatidylcholine bilayers, has been studied by (13)C-magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Rotational resonance experiments provided two distance constraints between Calpha and C&z.dbnd6;O positions of the labelled residues Val-29/Val-30 (0.4+/-0.5nm) and Val-29/Val-31 (0.45+/-0. 5nm) in its hydrophobic domain. The derived dihedral angles (Phi, Psi) for Val-30 revealed a local alpha-helical conformation. (13)C-CP-MAS experiments on uniformly aligned samples (MAOSS experiments) using the (13)C&z.dbnd6;O labelled site of Val-30 allowed the determination of the helix tilt (20 degrees +/-10 degrees ) in the membrane. It is shown that one uniform MAS high-resolution solid state NMR approach can be used to obtain structural and orientational data.

Secondary structure analysis of the putative membrane-associated domains of the inward rectifier K+ channel ROMK1

The inward rectifier K+ channels contain two putative membrane-spanning domains per subunit (M1, M2) and a 'pore' (P) region, which is similar to the H5 domain of voltage-gated K+ channels. Here we have used Fourier transform infrared (FTIR) and CD spectroscopy to analyse the secondary structures of synthetic peptides corresponding to the M1, M2 and P regions of ROMK1 in aqueous solution, in organic solvents and in phospholipid membranes. A previous CD study was unable to provide any structural data on a similar P peptide [Ben-Efraim and Shai (1997) Biophys. J. 72, 85-96]. However, our FTIR and CD spectroscopic analyses indicate that this peptide adopts an alpha-helical structure when reconstituted into dimyristoyl phosphatidylcholine vesicles and lysophosphatidyl choline (LPC) micelles as well as in trifluoroethanol (TFE) solvent. This result is in good agreement with a previous study on a peptide corresponding to the pore domain of a voltage-gated K+ channel [Haris, Ramesh, Sansom, Kerr, Srai and Chapman (1994) Protein Eng. 7, 255-262]. FTIR spectra of the M1 peptide in LPC micelles displayed a strong absorbance characteristic of an intermolecular beta-sheet structure, suggesting aggregation of the M1 peptide. Sucrose gradient centrifugation was used to separate aggregated peptide from peptide incorporated into micelles in an unaggregated manner; subsequent analysis by FTIR suggested that the M1 peptide adopted an alpha-helical structure when incorporated into phospholipid membranes. FTIR and CD spectra of the M2 peptide in phospholipids and high concentrations of TFE suggest that this peptide adopts an alpha-helical structure. The structural data obtained in these experiments have been used to propose a model for the structure of the membrane-associated core (M1-P-M2) of the inward rectifier K+ channel protein.

Filamentous phage structure, infection and assembly

The structural model of filamentous phage derived by X-ray fibre diffraction is supported by spectroscopic and genetic experiments. The structure of the receptor-binding domain at the end of the phage and the structure of the phage-coded intracellular DNA-binding protein have been determined at high resolution. The recent dissection of the virus life cycle by genetic and biochemical analyses, combined with structural information, suggests models for virus infection and assembly.

Magic angle-oriented sample spinning (MAOSS): A new approach toward biomembrane studies

The application of magic angle sample spinning (MAS) NMR to uniformly aligned biomembrane samples is demonstrated as a new general approach toward structural studies of membrane proteins, peptides, and lipids. The spectral linewidth from a multilamellar lipid dispersion is dominated, in the case of protons, by the dipolar coupling. For low-gamma or dilute spins, however, the chemical shift anisotropy dominates the spectral linewidth, which is reduced by the two-dimensional order in a uniformly aligned lipid membrane. The remaining line broadening, which is due to orientational defects ("mosaic spread") can be easily removed at low spinning speeds. This orientational order in the sample also allows the anisotropic intermolecular motions of membrane components (such as rotational diffusion, tauc = 10(-10) s) for averaging dipolar interactions to be utilized, e.g., by placing the membrane normal parallel to the rotor axis. The dramatic resolution improvement for protons which are achieved in a lipid sample at only 220 Hz spinning speed in a 9.4 T field is slightly better than any data published to date using ultra-high fields (up to 17.6 T) and high-speed spinning (14 kHz). Additionally, the analysis of spinning sidebands provides valuable orientational information. We present the first 1H, 31P, and 13C MAS spectra of uniformly aligned dimyristoylphosphatidylcholine (DMPC) bilayers. Also, 1H resolution enhancement for the aromatic region of the M13 coat protein reconstituted into DMPC bilayers is presented. This new method combines the high resolution usually achieved by MAS with the advantages of orientational constraints obtained by working with macroscopically oriented samples. We describe the general potential and possible perspectives of this technique.

In situ aggregational state of M13 bacteriophage major coat protein in sodium cholate and lipid bilayers

The in situ aggregational behavior of the bacteriophage M13 major coat protein was determined for the protein isolated in sodium cholate and reconstituted into DOPC lipid bilayers. For this purpose, the cysteine mutants A49C and T36C of the major coat protein were labeled with either a maleimido spin-label or a fluorescence label (IAEDANS). The steric restrictions sensed by the spin-label were used to evaluate the local protein conformation and the extent of protein-protein interactions at the position of the labeled residue. In addition, fluorescent labels covalently attached to the protein were used to determine the polarity of the local environment. The labeled coat protein mutants were examined under different conditions of protein association (amphiphile environment, ionic strength, temperature, and pH). The aggregational state of the major coat protein solubilized from the phage particle in sodium cholate was not dependent on the ionic strength, but was strongly dependent on cholate concentration and pH during sample preparation. At pH 7.0 and high sodium cholate concentration, the protein was in a dimeric form. The unusually strong association properties of the protein dimer in sodium cholate at pH 7.0 were attributed to the inability of sodium cholate to disrupt the strong hydrophobic forces between neighboring protein subunits in the phage particle. Such a "structural protein dimer" was, however, completely and irreversibly disrupted at pH 10.0. Qualitatively the same aggregational tendency was found upon changing the pH for the coat protein reconstituted in DOPC lipid bilayers. This reveals that the dimer disruption process is primarily a protein property, because there are no titratable groups on DOPC in the experimental pH range. The results are interpreted in terms of a model relating the protein aggregational state in the assembled phage to the protein aggregational behavior in sodium cholate and lipid bilayers.

Synthetic putative transmembrane region of minimal potassium channel protein (minK) adopts an alpha-helical conformation in phospholipid membranes

Minimal potassium channel protein (minK) is a potassium channel protein consisting of 130 amino acids, possessing just one putative transmembrane domain. In this study we have synthesized a peptide with the amino acid sequence RDDSKLEALYILMVLGFFGFFTLGIMLSYI, containing the putative transmembrane region of minK, and analysed its secondary structure by using Fourier-transform IR and CD spectroscopy. The peptide was virtually insoluble in aqueous buffer, forming intermolecular beta-sheet aggregates. On attempted incorporation of the peptide into phospholipid membranes with a method involving dialysis, the peptide adopted a predominantly intermolecular beta-sheet conformation identical with that of the peptide in aqueous buffer, in agreement with a previous report [Horvàth, Heimburg, Kovachev, Findlay, Hideg and Marsh, (1995) Biochemistry 34, 3893-3898]. However, by using an alternative method of incorporating the peptide into phospholipid membranes we found that the peptide adopted a predominantly alpha-helical conformation, a finding consistent with various proposed structural models. These observed differences in secondary structure are due to artifacts of aggregation of the peptide before incorporation into lipid.

Local dynamics of the M13 major coat protein in different membrane-mimicking systems

The local environment of the transmembrane and C-terminal domain of M13 major coat protein was probed by site-directed ESR spin labeling when the protein was introduced into three membrane-mimicking systems, DOPC vesicles, sodium cholate micelles, and SDS micelles. For this purpose, we have inserted unique cysteine residues at specific positions in the transmembrane and C-terminal region, using site-directed mutagenesis. Seven viable mutants with reasonable yield were harvested: A25C, V31C, T36C, G38C, T46C, A49C, and S50C. The mutant coat proteins were indistinguishable from wild type M13 coat protein with respect to their conformational and aggregational properties. The ESR data suggest that the amino acid positions 25 and 46 of the coat protein in DOPC vesicles are located close to the membrane-water interface. In this way the lysines at positions 40, 43, and 44 and the phenylalanines at positions 42 and 45 act as hydrophilic and hydrophobic anchors, respectively. The ESR spectra of site specific maleimido spin-labeled mutant coat proteins reconstituted into DOPC vesicles and solubilized in sodium cholate or SDS indicate that the local dynamics of the major coat protein is significantly affected by its structural environment (micellar vs bilayer), location (aqueous vs hydrophobic), and lipid/protein ratio. The detergents SDS and sodium cholate sufficiently well solubilize the major coat protein and largely retain its secondary structure elements. However, the results indicate that they have a poorly defined protein-amphiphilic structure and lipid-water interface as compared to bilayers and thus are not a good substitute for lipid bilayers in biophysical studies.

Effects of pH and KCl on the conformations of creatine kinase from rabbit muscle. Infrared, circular dichroic and fluorescence studies

The activity loss of creatine kinase (CK), observed at low pH (midpoint was 4.8) corresponded to the monomerization of the dimeric protein and was correlated with structural changes. The acid-induced unfolding was not complete at this pH, as probed by circular dichroic (CD) and fluorescence methods. Further decrease of pH, led to a second transition (midpoint was pH 3.5). The loss of activity was irreversible at pH 4.8 (< 20% native activity was recovered) while it was almost fully reversible (> 90% of native activity was recovered) for the enzyme incubated at pH 0.9-2.5. The amount of intermolecular beta-sheets (monitored with the 1620 cm-1 infrared component band) was maximal when the enzyme was incubated at pH 4.8, as a consequence of protein aggregation, while it was minimal at extremes of pH and at low ionic strength. Acid-induced and alkaline-induced denaturations promoted different structural changes, leading to distinct partially unfolded conformational states. The addition of KCl (from 0.05 M to 0.5 M) to an acidic solution of monomeric creatine kinase (pH 1.6) resulted in a highly cooperative transition from the partially unfolded conformation (UA) to the more compact conformation (A) with the properties of a molten globule, as probed by CD spectra and by fluorescence. The formation of intermolecular beta-sheets in the compact conformation was observed by infrared spectroscopy, indicating formation of unstable aggregates.

FT-IR spectroscopy of the major coat protein of M13 and Pf1 in the phage and reconstituted into phospholipid systems

FT-IR spectroscopy has been applied to study the secondary structure of the major coat protein of Pf1 and M13 as present in the phage and reconstituted in DOPG and mixed DOPC/DOPG (4/1) bilayers. Infrared absorbance spectra of the samples were examined in dehydrated films and in suspensions of D2O and H2O. The secondary structure of the coat protein is investigated by second-derivative analysis, Fourier self-deconvolution, and curve fitting of the infrared bands in the amide I region (1600-1700 cm-1). It is found that, in dehydrated films of Pf1 and M13 phage, the amide I region contains three bands located at about 1633, 1657, and 1683 cm-1, that are assigned to hydrogen-bonded turn, alpha-helix/random coil, and non-hydrogen-bonded turn, respectively. From a comparison of the infrared spectra in dehydrated film with those in aqueous suspension, the percentages of secondary structure were found with an accuracy of about +/- 5%. For the coat protein of Pf1 phage, the FT-IR quantification gives 69% alpha-helix conformation, 19% turn structure, and 12% random coil structure. For Pf1 coat protein in the membrane-embedded state, the amount of alpha-helix is 57%, whereas 42% is in a turn structure and 1% in a random coil structure. The same assignment strategy was used for the analysis of the data obtained for M13 coat protein reconstitution into phospholipid systems. For M13 coat protein in the phage, this gives 75% alpha-helix conformation, 21% turn structure, and 4% random coil structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermal and pH stabilities of alkaline phosphatase from bovine intestinal mucosa: a FTIR study

The inactivation of alkaline phosphatase (AP) from bovine intestinal mucosa caused by lowering the p2H from 10.4 to 5.4 or by increasing the temperature from 25 degrees C to 70 degrees C were not followed by significant FTIR changes, indicating that the native conformation of AP was preserved under these conditions. Further decrease of p2H from 5.4 to 3.4 leaded to small infrared spectral changes of AP in the amide I' and amide II regions that were similar to the infrared spectral changes of AP induced by raising the temperature from 70 degrees C to 80 degrees C. The increase of temperature from 70 degrees C to 80 degrees C promoted the formation of intermolecular beta-sheets at the expense of some alpha-helix structures as evidenced by the appearance of the 1684 cm-1 and 1620 cm-1 component bands and the disappearance of the 1651-1657 cm-1 component band. This conformational change was followed by a sharp increase of the 2H/H exchange rate. CD spectra confirmed the FTIR results and were very sensitive to the variation of alpha-helix content while FTIR spectra were more receptive to the changes of beta-sheet structures.

The macroscopic organization of reconstituted M13 coat protein-phospholipid systems. An EPR spectroscopy and polarizing microscope study

The coat protein of the bacteriophage M13 in the alpha-helical state is reconstituted in macroscopically oriented systems of dioleoylphosphatidylcholine that are prepared by squeezing the reconstituted material between glass plates. The coat protein dramatically influences the macroscopic orientation of the multibilayers, as is investigated by polarizing microscopy and EPR spectroscopy of the cholestane spin label embedded in the bilayers. It is found that with increasing amounts of protein the spontaneous macroscopic orientation of the reconstituted system decreases. This effect is proposed to be due to an increase of the apparent viscosity of the lipid-protein systems with increasing amounts of protein. This is assumed to arise from a sticky effect of the C- and N-terminal protein parts that extend into the aqueous phase between the bilayers.