sodium-dodecyl-sulfate and 1-palmitoyl-2-oleoylglycero-3-phosphoglycerol

Human dermcidin (DCD) is an antimicrobial peptide secreted constitutively by sweat glands. The anionic derivative, DCD-1L, comprises of the N-terminal 47 residues of DCD and one additional leucine residue. A previous NMR structure of DCD-1L in 50% TFE showed a partial helical conformation, and its crystal structure in the presence of Zn

Topics: Amino Acid Sequence; Bacteria; Cell Membrane; Humans; Models, Molecular; Mutagenesis, Site-Directed; Peptides; Phosphatidylglycerols; Protein Aggregates; Protein Conformation, alpha-Helical; Sodium Dodecyl Sulfate; Zinc

Human beta defensin-3 (HBD-3) is a unique potent antimicrobial peptide. To explore the importance of the three-dimensional structure of HBD-3 in its activity and selectivity, we have mutated all six cysteine residues of HBD-3 to other amino acids, expressed the mutant (named as Def-A) in Escherichia coli, and analyzed the mutant's activity, structure, and dynamics. Def-A is active against several bacterial strains, but the activity is influenced by the ionic strength of the environment. When subjected to vesicles like POPG or to micelles like SDS, Def-A is changed from a random coil structure to an ordered helical form. We have determined the structure of Def-A in SDS micelle and found that it is folded into two distinct helices separated by a proline kink. We propose that the long N-terminal helix with many hydrophobic residues is inserted inside the micelle while the C-terminal helix with one large positive charge patch is located outside the micelle and interacts with the charged head groups of the micelle. The model is supported by NMR relaxation and H-D exchange data. Our results indicate that in addition to the number of positively charged residues and hydrophobic residues, the arrangement of these residues in the three-dimensional space is important to the antimicrobial selectivity and salt-dependent activity of human beta defensins.

Topics: Amino Acid Sequence; Amino Acid Substitution; Bacteria; beta-Defensins; Calorimetry; Cell Proliferation; Cysteine; Humans; Hydrophobic and Hydrophilic Interactions; Liposomes; Membranes, Artificial; Micelles; Microbial Sensitivity Tests; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Osmolar Concentration; Phosphatidylglycerols; Protein Conformation; Protein Structure, Secondary; Recombinant Proteins; Sodium Dodecyl Sulfate; Surface Properties; Thermodynamics

We have studied the thermodynamic, surface, and structural properties of alphaM1 transmembrane sequence of the nicotinic acetylcholine receptor (nAChR) by using Langmuir monolayer, FT-IR spectroscopy and molecular dynamics simulation techniques in membrane-mimicking environments. M1 spontaneously incorporates into a lipid-free air-water interface, showing a favourable adsorption free energy of -7.2 kcal/mol. A cross-sectional molecular area of 210 A(2)/molecule, a surface potential of 4.2 fV/molecule and a high stability of the film were deducted from pure M1 monolayers. FT-IR experiments and molecular dynamics simulations in membrane-mimicking environments (sodium-dodecyl-sulfate and CCl(4), respectively) indicate coexistence between helical and non-helical structures. Furthermore, mixed peptide-lipid monolayers and monolayer penetration experiments were performed in order to study the peptide-lipid interaction. Mixed with condensed lipids (dipalmitoyl-phosphocholine, and dipalmitoyl-phosphoglycerol), M1 shows immiscible/miscible behaviour at low/high peptide concentration, respectively. Conversely, a complete miscible peptide-lipid interface is observed with liquid-expanded lipids (palmitoyl-oleoyl-phosphocholine, and palmitoyl-oleoyl-phosphoglycerol). Peptide penetration experiments demonstrate that the M1 peptide preferentially interacts with zwitterionic phosphocholine interfaces.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Adsorption; Amino Acid Sequence; Cell Membrane; Computer Simulation; Micelles; Models, Molecular; Molecular Sequence Data; Peptide Fragments; Phosphatidylcholines; Phosphatidylglycerols; Protein Conformation; Protein Subunits; Receptors, Nicotinic; Sodium Dodecyl Sulfate; Spectroscopy, Fourier Transform Infrared; Surface Properties; Thermodynamics; Water