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Hydrophobic Face (hydrophobic + face)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Capillary electrophoresis of amphipathic ,-helical peptide diastereomers

ELECTROPHORESIS, Issue 1 2004
Traian V. Popa
Abstract We have made a rigorous assessment of the ability of capillary electrophoresis to resolve peptide diastereomers through its application to the separation of a series of synthetic 18-residue, amphipathic ,-helical monomeric peptide analogues, where a single site in the centre of the hydrophobic face of the ,-helix is substituted by 19 L - or D -amino acids. Such L - and D -peptide pairs have the same mass-to-charge ratio, amino acid sequence and intrinsic hydrophobicity, varying only in the stereochemistry of one residue. CE approaches assessed in their ability to separate diastereomeric peptide pairs included capillary zone electrophoresis (uncoated capillary), micellar electrokinetic chromatography (uncoated capillary in the presence of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, CHAPS), open-tubular capillary electrochromatography (C8 -coated capillary in the presence of 25% 2,2,2-trifluoroethanol (TFE) or 25% ethanol). Overall, the OT-CEC methods were the most effective at separating the most peptide pairs, particularly for those containing hydrophilic side chains. However, the MEKC approach proved most effective for separation of peptide pairs containing hydrophobic or aromatic side chains. [source]

4-Fluorophenylglycine as a Label for 19F NMR Structure Analysis of Membrane-Associated Peptides

CHEMBIOCHEM, Issue 11 2003
Sergii Afonin
Abstract The non-natural amino acid 4-fluorophenylglycine (4F-Phg) was incorporated into several representative membrane-associated peptides for dual purpose. The 19F-substituted ring is directly attached to the peptide backbone, so it not only provides a well-defined label for highly sensitive 19F NMR studies but, in addition, the D and L enantiomers of the stiff side chain may serve as reporter groups on the transient peptide conformation during the biological function. Besides peptide synthesis, which is accompanied by racemisation of 4F-Phg, we also describe separation of the epimers by HPLC and removal of trifluoroacetic acid. As a first example, 18 different analogues of the fusogenic peptide "B18" were prepared and tested for induction of vesicle fusion; the results confirmed that hydrophobic sites tolerated 4F-Phg labelling. Similar fusion activities within each pair of epimers suggest that the peptide is less structured in the fusogenic transition state than in the helical ground state. In a second example, five doubly labelled analogues of the antimicrobial peptide gramicidin S were compared by using bacterial growth inhibition assays. This cyclic ,-sheet peptide could accommodate both L and D substituents on its hydrophobic face. As a third example, we tested six analogues of the antimicrobial peptide PGLa. The presence of d- 4F-Phg reduced the biological activity of the peptide by interfering with its amphiphilic ,-helical fold. Finally, to illustrate the numerous uses of l- 4F-Phg in 19F NMR spectroscopy, we characterised the interaction of labelled PGLa with uncharged and negatively charged membranes. Observing the signal of the free peptide in an aqueous suspension of unilamellar vesicles, we found a linear saturation behaviour that was dominated by electrostatic attraction of the cationic PGLa. Once the peptide is bound to the membrane, however, solid-state 19F NMR spectroscopy of macroscopically oriented samples revealed that the charge density has virtually no further influence on the structure, alignment or mobility of the peptide. [source]

Structural studies and model membrane interactions of two peptides derived from bovine lactoferricin

JOURNAL OF PEPTIDE SCIENCE, Issue 7 2005
Leonard T. Nguyen
Abstract The powerful antimicrobial properties of bovine lactoferricin (LfcinB) make it attractive for the development of new antimicrobial agents. An 11-residue linear peptide portion of LfcinB has been reported to have similar antimicrobial activity to lactoferricin itself, but with lower hemolytic activity. The membrane-binding and membrane-perturbing properties of this peptide were studied together with an amidated synthetic version with an added disulfide bond, which was designed to confer increased stability and possibly activity. The antimicrobial and cytotoxic properties of the peptides were measured against Staphylococcus aureus and Escherichia coli and by hemolysis assays. The peptides were also tested in an anti-cancer assay against neuroblastoma cell lines. Vesicle disruption caused by these LfcinB derivatives was studied using the fluorescent reporter molecule calcein. The extent of burial of the two Trp residues in membrane mimetic environments were quantitated by fluorescence. Finally, the solution NMR structures of the peptides bound to SDS micelles were determined to provide insight into their membrane bound state. The cyclic peptide was found to have greater antimicrobial potency than its linear counterpart. Consistent with this property, the two Trp residues of the modified peptide were suggested to be embedded deeper into the membrane. Although both peptides adopt an amphipathic structure without any regular ,-helical or ß-sheet conformation, the 3D-structures revealed a clearer partitioning of the cationic and hydrophobic faces for the cyclic peptide. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source]

Open-and-shut cases in coiled-coil assembly: ,-sheets and ,-cylinders

PROTEIN SCIENCE, Issue 3 2001
John Walshaw
Abstract The coiled coil is a ubiquitous protein-folding motif. It generally is accepted that coiled coils are characterized by sequence patterns known as heptad repeats. Such patterns direct the formation and assembly of amphipathic ,-helices, the hydrophobic faces of which interface in a specific manner first proposed by Crick and termed "knobs-into-holes packing". We developed software, socket, to recognize this packing in protein structures. As expected, in a trawl of the protein data bank, we found examples of canonical coiled coils with a single contiguous heptad repeat. In addition, we identified structures with multiple, overlapping heptad repeats. This observation extends Crick's original postulate: Multiple, offset heptad repeats help explain assemblies with more than two helices. Indeed, we have found that the sequence offset of the multiple heptad repeats is related to the coiled-coil oligomer state. Here we focus on one particular sequence motif in which two heptad repeats are offset by two residues. This offset sets up two hydrophobic faces separated by ,150°,160° around the ,-helix. In turn, two different combinations of these faces are possible. Either similar or opposite faces can interface, which leads to open or closed multihelix assemblies. Accordingly, we refer to these two forms as ,-sheets and ,-cylinders. We illustrate these structures with our own predictions and by reference to natural variants on these designs that have recently come to light. [source]