Biomedical subjects

Raz Jelinek

Publications and source records attributed to Raz Jelinek.

22 records · Page 2Linked to original sources

PubMed2003

Quantitative interactions between cryptdin-4 amino terminal variants and membranes.

Paneth cells secrete alpha-defensins into the lumen from the base of small intestinal crypts, and cryptdin-4 (Crp4) is the most potent mouse alpha-defensin in vitro. Purified recombinant Crp4 and Crp4 variants with (des-Gly)-, (Gly1Val)-, (Gly1Asp)-, and (Gly1Arg)-substitutions were all bactericidal with Crp4 and (Gly1Arg)-Crp4 being slightly more active than other variants. Bactericidal activities correlated directly with permeabilization of live Escherichia coli, with equilibrium binding to E. coli membrane phospholipid bilayers and vesicles, and with induced graded fluorophore leakage from phospholipid vesicles. The Crp4 peptide N-terminus affects bactericidal activity modestly, apparently by influencing peptide binding to phospholipid bilayers and subsequent permeabilization of target cell membranes.

Acetylene↗

PubMed2003

Bilayer localization of membrane-active peptides studied in biomimetic vesicles by visible and fluorescence spectroscopies.

Depth of bilayer penetration and effects on lipid mobility conferred by the membrane-active peptides magainin, melittin, and a hydrophobic helical sequence KKA(LA)7KK (denoted KAL), were investigated by colorimetric and time-resolved fluorescence techniques in biomimetic phospholipid/poly(diacetylene) vesicles. The experiments demonstrated that the extent of bilayer permeation and peptide localization within the membrane was dependent upon the bilayer composition, and that distinct dynamic modifications were induced by each peptide within the head-group environment of the phospholipids. Solvent relaxation, fluorescence correlation spectroscopy and fluorescence quenching analyses, employing probes at different locations within the bilayer, showed that magainin and melittin inserted close to the glycerol residues in bilayers incorporating negatively charged phospholipids, but predominant association at the lipid-water interface occurred in bilayers containing zwitterionic phospholipids. The fluorescence and colorimetric analyses also exposed the different permeation properties and distinct dynamic influence of the peptides: magainin exhibited the most pronounced interfacial attachment onto the vesicles, melittin penetrated more into the bilayers, while the KAL peptide inserted deepest into the hydrophobic core of the lipid assemblies. The solvent relaxation results suggest that decreasing the lipid fluidity might be an important initial factor contributing to the membrane activity of antimicrobial peptides.

Antimicrobial Cationic Peptides↗

PubMed2003

Biomimetic lipid/polymer colorimetric membranes: molecular and cooperative properties.

Characterization of membranes and of biological processes occurring within membranes is essential for understanding fundamental cellular behavior. Here we present a detailed biophysical study of a recently developed colorimetric biomimetic membrane assembly constructed from physiological lipid molecules and conjugated polydiacetylene. Various analytical techniques have been applied to characterize the organization of the lipid components in the chromatic vesicles and their contributions to the observed blue-to-red color transitions. Experiments reveal that both the polymerized units as well as the lipids exhibit microscopic phases and form domains whose properties and bilayer organization are interdependent. These domains are interspersed within mixed lipid/polymer vesicles that have a size distribution different from those of aggregates of the individual molecular constituents. The finding that fluidity changes induced within the lipid domains are correlated with the chromatic transitions demonstrates that the colorimetric platform can be used to evaluate the effects of individual molecular components, such as negatively charged lipids and cholesterol, upon membrane fluidity and thermal stability.

Acetylene↗

PubMed2002

Structures and mode of membrane interaction of a short alpha helical lytic peptide and its diastereomer determined by NMR, FTIR, and fluorescence spectroscopy.

The interaction of many lytic cationic antimicrobial peptides with their target cells involves electrostatic interactions, hydrophobic effects, and the formation of amphipathic secondary structures, such as alpha helices or beta sheets. We have shown in previous studies that incorporating approximately 30%d-amino acids into a short alpha helical lytic peptide composed of leucine and lysine preserved the antimicrobial activity of the parent peptide, while the hemolytic activity was abolished. However, the mechanisms underlying the unique structural features induced by incorporating d-amino acids that enable short diastereomeric antimicrobial peptides to preserve membrane binding and lytic capabilities remain unknown. In this study, we analyze in detail the structures of a model amphipathic alpha helical cytolytic peptide KLLLKWLL KLLK-NH2 and its diastereomeric analog and their interactions with zwitterionic and negatively charged membranes. Calculations based on high-resolution NMR experiments in dodecylphosphocholine (DPCho) and sodium dodecyl sulfate (SDS) micelles yield three-dimensional structures of both peptides. Structural analysis reveals that the peptides have an amphipathic organization within both membranes. Specifically, the alpha helical structure of the L-type peptide causes orientation of the hydrophobic and polar amino acids onto separate surfaces, allowing interactions with both the hydrophobic core of the membrane and the polar head group region. Significantly, despite the absence of helical structures, the diastereomer peptide analog exhibits similar segregation between the polar and hydrophobic surfaces. Further insight into the membrane-binding properties of the peptides and their depth of penetration into the lipid bilayer has been obtained through tryptophan quenching experiments using brominated phospholipids and the recently developed lipid/polydiacetylene (PDA) colorimetric assay. The combined NMR, FTIR, fluorescence, and colorimetric studies shed light on the importance of segregation between the positive charges and the hydrophobic moieties on opposite surfaces within the peptides for facilitating membrane binding and disruption, compared to the formation of alpha helical or beta sheet structures.

Amino Acid Sequence↗