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

Molecular simulation of dioleoylphosphatidylcholine lipid bilayers at differing levels of hydration

The structure and dynamics of the lipid and water components of dioleoylphosphatidylcholine bilayers at various levels of hydration were studied using molecular dynamics (MD) simulations. Equilibration of these systems proceeded by use of a hybrid MD and configurational-bias Monte Carlo technique using one atmosphere of pressure normal to the membrane and a set point for the lateral area derived from experimental Bragg spacings, combined with experimentally derived specific volumes for each of the system components. Membrane surface tensions were observed to be of the order of tens of dyn/cm. The transbilayer molecular fragment peak positions at low hydration were found to agree with experimental neutron and x-ray scattering profiles and previously published simulations. For hydration levels of 5.4, 11.4, and 16 waters/lipid, molecular fragment distributions and order parameters for the headgroup, lipid chains, and water were quantified. Spin-lattice relaxation rates and lateral self-diffusion coefficients of water agreed well with results from experimental nuclear magnetic resonance studies. Relaxation rates of the choline segments and chemical shift anisotropies for the phosphate and carbonyls were computed. Headgroup orientation, as measured by the P-N vector, showed enhanced alignment with the membrane surface at low hydration. The sign of the membrane dipole potential reversed at low hydration, with the membrane interior negative relative to the interlamellar region. Calculation of the number of water molecules in the headgroup hydration shell, as a function of hydration level, supports the hypothesis that the break point in the curve of Bragg spacing versus hydration level near 12 waters/lipid, observed experimentally by Hristova and White (1988. Biophys. J. 74:2419-2433), marks the completion of the first hydration shell.

Conventional and saturation-transfer EPR of spin-labeled mutant bacteriophage M13 coat protein in phospholipid bilayers

A mutant of bacteriophage M13 was prepared in which a cysteine residue was introduced at position 25 of the major coat protein. The mutant coat protein was spin-labeled with a nitroxide derivative of maleimide and incorporated at different lipid-to-protein (L/P) ratios in DOPC or DOPG. The rotational dynamics of the reconstituted mutant coat protein was studied using EPR and saturation transfer (ST) EPR techniques. The spectra are indicative for an anisotropic motion of the maleimide spin label with a high order parameter (S = 0.94). This is interpreted as a wobbling motion of the spin label with a correlation time of about 10(-6) to 10(-5) s within a cone, and a rotation of the spin label about its long molecular axis with a correlation time of about l0(-7) s. The wobbling motion is found to correspond generally to the overall rotational motion of a coat protein monomer about the normal to the bilayer. This motion is found to be sensitive to the temperature and L/P ratio. The high value of the order parameter implies that the spin label experiences a strong squeezing effect by its local environment, that reduces the amplitude of the wobbling motion. This squeezing effect is suggested to arise from a turn structure in the coat protein from Gly23 to Glu20.

Phospholipid headgroup dynamics in DOPG-d5-cytochrome c complexes as revealed by 2H and 31P NMR: the effects of a peripheral protein on collective lipid fluctuations

The dynamics of the glycerol headgroup of dioleoylphosphatidylglycerol (DOPG) in hydrated bilayers were studied by 2H and 31P NMR spectroscopy, and the effects of binding a peripheral protein, cytochrome c, were evaluated. The fast headgroup segmental motions (tau c, 10(-10)-(-13) s) of DOPG in fully hydrated bilayers were not affected upon binding of cytochrome c, as evaluated by the spin-lattice (T1) relaxation of deuterons in the DOPG glycerol headgroup. In contrast, the spin-spin (T2e) relaxation is strongly affected, indicating that slow cooperative bilayer motions (tau c, 10(-3)-10(-6) s) are enhanced upon the interaction with cytochrome c, 2H and 31P NMR spectral lineshape analysis reveal details of the nature of these motions. The importance of these effects are discussed in terms of a possible mechanism for modulating membrane-associated processes.

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

There is considerable uncertainty about the precise secondary structure adopted by the M13 coat protein when embedded in a phospholipid bilayer. Circular dichroism (CD) spectroscopy suggests that a major change in the structure of the coat protein occurs upon membrane insertion. It is reported that the structure of the protein in the membrane has only about 50% alpha-helix, the rest being mainly in a beta-sheet conformation, whereas the protein is almost completely alpha-helical when intact in the phage. In this study we have undertaken a spectroscopic analysis using Fourier transform infrared, Raman, and CD spectroscopy to characterize the secondary structure of M13 coat protein when present in membranes consisting of dioleoylphosphatidylglycerol and dimyristoylphosphatidylglycerol. In sharp contrast to earlier CD studies, our results indicate that the coat protein in its membrane-embedded state has a very high alpha-helical content with virtually no beta-sheet structures present. This result indicates that the structures of the coat protein when intact in the phage or when embedded in the membrane are similar. Although our results differ from earlier CD studies, they are consistent with a recent NMR study, which showed that the M13 coat protein in sodium dodecyl sulfate micelles is primarily alpha-helical with no evidence for beta-sheet structure [Henry, G. D., & Sykes, B.D. (1992) Biochemistry 31, 5284-5297]. These results lead to the conclusion that the M13 coat protein can insert from the membrane-bound state into a virus particle with a similar secondary structure, without large energy implications.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Interaction of phospholipids with proteins and peptides. New advances III

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.

Influence of staphylococcal delta-toxin on the phosphatidylcholine headgroup as observed using 2H-NMR

The interaction of the 8-toxin peptide isolated from Staphylococcus aureus with the headgroup region of lipid bilayer membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated using deuterium (2H) and phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy. At relatively low peptide/lipid ratios (P/L < 0.10), all 2H- and 31P-NMR spectral lineshapes at 25 degrees C were indicative of a single population of liquid-crystalline lipids in a bilayer arrangement. At these P/L ratios, delta-toxin had only marginal effects on the size of the quadrupole splitting measured from POPC labelled at either the alpha-methylene (POPC-alpha-d2) or the beta-methylene segment (POPC-beta-d2) of the choline headgroup and, similarly small effects on the magnitude of the chemical shift anisotropy (CSA) of the 31P-NMR spectrum. With increasing amounts of delta-toxin (0.10 < P/L < 0.15) the size of the 2H quadrupole splitting from POPC-alpha-d2, as well as the magnitude of the 31P-CSA, decreased progressively and rapidly. The quadrupole splitting from POPC-beta-d2, however, remained relatively unaffected. At yet higher levels of delta-toxin (P/L > 0.15), all 2H- and 31P-NMR spectra indicated the presence of multiple lipid populations experiencing varying degrees of increased conformational disordering. The spectral lineshapes of these apparently nonbilayer spectral components reverted to bilayer-type lineshapes upon lowering the measuring temperature to 5 degrees C. At the utmost highest level of delta-toxin measured here (P/L = 0.20), all 2H- and 31P-NMR spectra consisted of a single, broad, apparently nonbilayer-type component, indicative of hindered but virtual isotropic motional averaging of the POPC headgroups. In this case no reversion to bilayer-type spectra could be obtained by decreasing the temperature. We could obtain no evidence that the conformation of the choline headgroup of POPC was responding to any specific influence of delta-toxin on bilayer surface electrostatics.

Formation of non-bilayer structures induced by M13 coat protein depends on the conformation of the protein

A comparison is made of the interaction of the coat protein of bacteriophage M13 in a predominant alpha-helix conformation and in a predominant beta-sheet conformation. To perform a systematic study of the interaction between the protein in these two different forms of the surrounding lipid matrix, NMR spectra of 2H-nuclei of specific labelled phospholipid systems are measured. In addition 31P-NMR is employed to provide information about the morphological structure adopted by the reconstituted lipid/protein systems. From the 2H-NMR studies on specific headgroup and chain deuterium labelled phospholipids it is found that the protein in the predominant beta-sheet conformation causes a fraction of lipids to be trapped. By combining the results from the headgroup and acyl chains of the phospholipids, it is concluded that the trapped lipids are arranged in a non-bilayer structure, probably caused by a misfitting of the hydrophobic core of the protein and the membrane bilayer. The protein in the predominant alpha-helix conformation perfectly fits in the lipid bilayer and has only minor influences on the surrounding lipid matrix. A new model is proposed to explain the presence of the trapped lipids in the lipid/protein systems.