Conformational alteration of bradykinin in presence of GM1 micelle

Comprehensive Analysis of Coupled Proline Cis-Trans States in Bradykinin Using ωBP-REMD Simulations

It is well-known that proline (Pro) cis-trans isomerization plays a decisive role in the folding and stabilization of proteins. The conformational coupling between isomerization states of different Pro residues in proteins during conformational adaptation processes is not well understood. In the present work, we investigate the coupled cis-trans isomerization of three Pro residues using bradykinin (BK), a partially unstructured nonapeptide hormone, as a model system. We use a recently developed enhanced-sampling molecular dynamics method (ω-bias potential replica exchange molecular dynamics; ωBP-REMD) that allows us to exhaustively sample all combinations of Pro isomer states and obtain converged probability densities of all eight state combinations within 885 ns ωBP-REMD simulations. In agreement with experiment, the all-trans state is seen to be the preferred isomer of zwitterionic aqueous BK. In about a third of its structures, this state presents the characteristic C-terminal β-turn conformation; however, other isomer combinations also contribute significantly to the structural ensemble. Unbiased probabilities can be projected onto the peptide bond dihedral angles of the three Pro residues. This unveils the interdependence of the individual Pro isomerization states, i.e., a possible coupling of the different Pro isomers. The cis/trans equilibrium of a Pro residue can change by up to 2.5 kcal·mol-1, depending on the isomerization state of other Pro residues. For example, for Pro7, the simulations indicate that its cis state becomes favored compared to its trans state when Pro2 is switched from the trans state to the cis state. Our findings demonstrate the efficiency of the ωBP-REMD methodology and suggest that the coupling of Pro isomerization states may play an even more decisive role in larger folded proteins subject to more conformational restraints.

Interaction Between Luteinizing Hormone-Releasing Hormone and GM1-Doped Cholesterol/Sphingomyelin Vesicles: A Spectroscopic Study

Understanding the role of neural membrane in translocation and action of neurohormone is of great importance. Luteinizing hormone-releasing hormone (LHRH) is a neuropeptide hormone and it acts as a final signaling molecule by stimulating the synthesis of LH and FSH to maintain reproduction in all vertebrates. The receptors of LHRH are found in breast tumors and pituitary gland in the brain. Moreover, neural plasma membrane is also found to contain specific binding site for LHRH. The mechanism by which LHRH binds to membrane before it binds to the receptors is a very critical step and can have a profound impact upon the translation of peptide across the membrane. A complex form of glycosphingolipids known as Ganglioside is an important component of plasma membrane of nerve cells and breast tumor tissues. They play an important role in various physiological membrane processes. Therefore, the interaction of ganglioside-containing membrane with LHRH might be crucial in aiding the LHRH to translate through the neural membrane and reach its receptor for binding and activation. Using CD, UV-Absorbance, and fluorescence spectroscopy, the effect of Ganglioside Monosialo 1(GM1)-induced conformational changes of LHRH in the presence of Cholesterol (CHOL)/Sphingomyelin (SM) and GM1/CHOL/SM vesicles was studied. The aforesaid spectroscopic studies show that LHRH is able to bind with both the vesicles, but GM1-containing vesicles interact more effectively than vesicles without GM1. CHOL/SM vesicles partially disturb the conformation of the peptide. Moreover, binding of LHRH to GM1/CHOL/SM vesicles induces loss of conformational rigidity and attainment of a random coil.

Surface- and tip-enhanced Raman scattering of bradykinin onto the colloidal suspended Ag surface

In this paper, surface- (SERS) and tip-enhanced Raman scattering (TERS) techniques were used to determine the adsorption mode of bradykinin (BK), a small peptide implicated in, for example, carcinoma growth, onto colloidal suspended Ag surfaces under various environmental conditions, including: peptide concentrations (10(-5)-10(-7) M), excitation wavelengths (514.5 and 785.0 nm), and pH of aqueous sol solutions (from pH = 3 to pH = 11). The metal surface plasmon and rheology of the colloidal suspended Ag surface were explored by ultraviolet-visible (UV-Vis) spectroscopy and atomic force/scanning electron microscopy (AFM/SEM). The SERS results indicated that the peptide concentration of 10(-5) M was the optimal peptide concentration for monolayer colloidal coverage. The Phe(5/8) and Arg(9) residues of BK generally participated in the interactions with colloidal suspended Ag surfaces. The amide group appeared to be arranged in the same manner to the Ag surface in the pH range of 3 to 11. At acidic pH of the solution (pH = 3 to 5), the BK -COO(-) terminal group binds to the Ag surface as a bidentate (at pH = 3) or monodentate (at pH = 5) chelating ligand. At pH = 11, the imino group of Arg(9), probably due to its -C[double bond, length as m-dash]N(⊕)H2 protonation state, was not involved in the interaction with Ag. The reduction in the solution alkalinity (pH = 9) produced the deprotonation of the -C=N(⊕)H2 group followed by group rearrangement in a way favoring the interaction between the lone electron pair on N and Ag. The TERS studies confirmed the proposed, on the basis of SERS, behavior of BK onto the colloidal suspended Ag at pH = 7 and showed that in different points of the colloidal suspended Ag surface the same peptide fragments approximately having the same orientations with respect to this surface interact with it.

Photo-Fries rearrangement of aryl acetamides: regioselectivity induced by the aqueous micellar green environment

NMR spectroscopy shows the location of acetanilides within the shells and hydrophobic cores in micellar solutions. Irradiation of acetanilides in aqueous micellar solutions involves C–N homolytic cleavage to yield singlet radical pairs that selectively provide 2-aminoacetophenone derivatives.

Multivalency amplifies the selection and affinity of bradykinin-derived peptides for lipid nanovesicles

The trimer of a bradykinin derivative displayed a more than five-fold increase in binding affinity for phosphatidylserine-enriched nanovesicles as compared to its monomeric precursor. The nanovesicle selection is directly correlated with multivalency, which amplifies the electrostatic attraction. This strategy may lead to the development of novel molecular probes for detecting highly curved membrane bilayers.

Cis-trans isomerizations of proline residues are key to bradykinin conformations

A recent ion mobility-mass spectrometry (IM-MS) study of the nonapeptide bradykinin (BK, amino acid sequence Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) found evidence for 10 populations of conformations that depend upon the solution composition [J. Am. Chem. Soc. 2011, 133, 13810]. Here, the role of the three proline residues (Pro(2), Pro(3), and Pro(7)) in establishing these conformations is investigated using a series of seven analogue peptides in which combinations of alanine residues are substituted for prolines. IM-MS distributions of the analogue peptides, when compared to the distribution for BK, indicate the multiple structures are associated with different combinations of cis and trans forms of the three proline residues. These data are used to assign the structures to different peptide populations that are observed under various solution conditions. The assignments also show the connectivity between structures when collisional activation is used to convert one state into another.

Molecular dynamics simulations of the interactions of kinin peptides with an anionic POPG bilayer

We have performed molecular dynamics simulations of peptide hormone bradykinin (BK) and its fragment des-Arg9-BK in the presence of an anionic lipid bilayer, with an aim toward delineating the mechanism of action related to their bioactivity. Starting from the initial aqueous environment, both of the peptides are quickly adsorbed and stabilized on the cell surface. Whereas BK exhibits a stronger interaction with the membrane and prefers to stay on the interface, des-Arg9-BK, with the loss of C-terminal Arg, penetrates further. The heterogeneous lipid-water interface induces β-turn-like structure in the otherwise inherently flexible peptides. In the membrane-bound state, we observed C-terminal β-turn formation in BK, whereas for des-Arg9-BK, with the deletion of Arg9, turn formation occurred in the middle of the peptide. The basic Arg residues anchor the peptide to the bilayer by strong electrostatic interactions with charged lipid headgroups. Simulations with different starting orientations of the peptides with respect to the bilayer surface lead to the same observations, namely, the relative positioning of the peptides on the membrane surface, deeper penetration of the des-Arg9-BK, and the formation of turn structures. The lipid headgroups adjacent to the bound peptides become substantially tilted, causing bilayer thinning near the peptide contact region and increase the degree of disorder in nearby lipids. Again, because of hydrogen bonding with the peptide, the neighboring lipid's polar heads exhibit considerably reduced flexibility. Corroborating findings from earlier experiments, our results provide important information about how the lipid environment promotes peptide orientation/conformation and how the peptide adapts to the environment.

Structural transition of a 15 amino acid residue peptide induced by GM1

The ganglioside GM1-binding peptide, p3, with a sequence of VWRLLAPPFSNRLLP, displayed a clear structural alteration depending on the presence or absence of GM1 micelles. The three-dimensional structures of the p3 peptide in the free and GM1 bound states were analyzed using two-dimensional NMR spectroscopic experiments with distance-restrained simulated annealing calculations. The NMR experiments for the p3 peptide alone indicated that the peptide has two conformers derived from the exchange of cis and trans forms at Pro(7)-Pro(8). Further study with theoretical modeling revealed that the p3 peptide has a curb conformation without regular secondary structure. On the other hand, the NMR studies for the p3 peptide with the GM1 micelles elucidated a trans conformer and gave a structure stabilized by hydrophobic interactions of beta- and helical turns. Based on these structural investigations, tryptophan, a core residue of the hydrophobic cluster, might be an essential residue for the recognition of the GM1 saccharides. The dynamic transition of the p3 peptide may play an important role in the function of GM1 as a multiple receptor as in the traditional pathway of the infection by cholera toxin.

Interaction and structural study of kinin peptide bradykinin and ganglioside monosialylated 1 micelle

Partitioning of small proteins and peptides from the aqueous to membrane phase is often coupled with folding. In this work we examine the binding and folding of the kinin peptide, bradykinin (BK), in the presence of the ganglioside monosialylated 1 (GM1) micelle. Using two-dimensional NMR techniques, we have shown that at low concentration, GM1 micelle is able to induce a turn conformation to BK. A pulsed-field gradient diffusion NMR study indicated that the peptide partitions into the GM1 micelle with a DeltaG(part) of -3.14 +/- 0.03 kcal/mol. A saturation transfer difference (STD) NMR study indicated that the binding is mostly through hydrophobic residues.