The association of defensin HNP-2 with negatively charged membranes: A combined fluorescence and linear dichroism study.

The association of defensin HNP-2 with negatively charged membranes has been studied using a new approach that combines fluorescence and linear dichroism (LD) spectroscopies with simulated LD spectra in order to characterise the binding kinetics and bound configurations of the peptide. Binding to membranes composed of mixtures of diacylglycerophosphocholines (PC) with either diacylglycerophosphoglycerol (PG) or diacylglycerophosphoserine (PS) was conducted at lipid:peptide ratios that yielded binding, but not membrane fusion. HNP-2 association with membranes under these conditions was a 2 stage-process, with both stages exhibiting first order kinetics.

The reproducibility of phospholipid analyses by MALDI-MSMS.

The identification of phosphocholine and phosphoethanolamine lipids by MALDI TOF/TOF, including characterisation of the headgroup and delineation of the acyl chain at each position of the glycerol backbone, has been explored using lipids representative of each type. The relative intensities of fragments involving the neutral loss of one or other of the acyl chains from ion adducts of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) were compared. For POPC and POPE, a statistical preference for the loss of the chain from the sn-1 position was observed in the presence of lithium.

Acyl transfer from phosphocholine lipids to melittin.

Transfer of fatty acyl groups from membrane phospholipids to melittin, a commonly studied membrane-active peptide, has been observed to occur over extended time periods. Transfer can be detected after 1-2 days and selectively targets amino groups at the N-terminal end of the peptide.

The synergistic action of melittin and phospholipase A2 with lipid membranes: development of linear dichroism for membrane-insertion kinetics.

Here we present data on the kinetics of insertion of melittin, a peptide from bee venom, into lipid membranes of different composition. Another component of bee venom is the enzyme phospholipase A2 (PLA₂). We have examined the interaction of melittin and PLA₂ with liposomes both separately and combined and demonstrate that they work synergistically to disrupt the membranes.

Peptide adsorption to lipid bilayers: slow processes revealed by linear dichroism spectroscopy.

The adsorption and insertion kinetics for the association of two 34-residue cyclic peptides with phosphocholine membranes have been studied using circular and linear dichroism approaches. The two peptides studied are identical with the exception of two residues, which are both tyrosine in one of the peptides and tryptophan in the other. Both peptides adopt random coil conformations in solution in the absence of membranes and do not aggregate at concentrations below 20 microM.