Search results for "pore formation"
showing 6 items of 6 documents
Stability of Asymmetric Lipid Bilayers Assessed by Molecular Dynamics Simulations
2009
The asymmetric insertion of amphiphiles into biological membranes compromises the balance between the inner and outer monolayers. As a result, area expansion of the receiving leaflet and curvature strain may lead to membrane permeation, shape changes, or membrane fusion events. We have conducted both atomistic and coarse-grained molecular dynamics simulations of dipalmitoyl-phosphatidylcholine (DPPC) bilayers to study the effect of an asymmetric distribution of lipids between the two monolayers on membrane stability. Highly asymmetric lipid bilayers were found to be surprisingly stable within the submicrosecond time span of the simulations. Even the limiting case of a monolayer immersed in …
Mutations in the Bacillus thuringiensis Cry1Ca toxin demonstrate the role of domains II and III in specificity towards Spodoptera exigua larvae
2004
Several mutants of the Bacillus thuringiensis Cry1Ca toxin affected with regard to specific activity towards Spodoptera exigua were studied. Alanine was used to replace single residues in loops 2 and 3 of domain II (mutant pPB19) and to replace residues 541– 544 in domain III (mutant pPB20). Additionally, a Cry1Ca mutant combining all mutations was constructed (mutant pPB21). Toxicity assays showed a marked decrease in toxicity against S. exigua for all mutants, while they retained their activity against Manduca sexta, confirming the importance of these residues in determining insect specificity. Parameters for binding to the specific receptors in BBMV (brush border membrane vesicles) of S.…
Correct oligomerization is a prerequisite for insertion of the central molecular domain of staphylococcal α-toxin into the lipid bilayer
1995
Staphylococcal alpha-toxin is a primarily hydrophilic molecule that binds as a monomer to target membranes and then aggregates to form amphiphilic oligomers that represent water-filled transmembrane channels. Current evidence indicates that a region located in the center of the molecule inserts deeply into the bilayer. In the present study, we sought to determine whether membrane insertion was triggered by the oligomerization process, and whether insertion correlated with pore formation. Double mutants of alpha-toxin were prepared in which His-35 was replaced by Arg, and cysteine residues were introduced at positions 69, 130 and 186. Substitution of His-35 with Arg rendered the toxin molecu…
A membrane associated metalloprotease cleaves Cry3Aa Bacillus thuringiensis toxin reducing pore formation in Colorado potato beetle brush border memb…
2007
AbstractInsect proteases are implicated in Bacillus thuringiensis insecticidal proteins mode of action determining toxin specificity and sensitivity. Few data are available on the involvement of proteases in the later steps of toxicity such as protease interaction with toxin–receptor complexes and the pore formation process. In this study, a Colorado potato beetle (CPB) midgut membrane metalloprotease was found to be involved in the proteolytic processing of Cry3Aa. Interaction of Cry3Aa with BBMV membrane proteases resulted in a distinct pattern of proteolysis. Cleavage was demonstrated to occur in protease accessible regions of domain III and was specifically inhibited by the metalloprote…
Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles
2011
Mesoporous silicon is a biocompatible, biodegradable material that is receiving increased attention for pharmaceutical applications due to its extensive specific surface. This feature enables to load a variety of drugs in mesoporous silicon devices by simple adsorption-based procedures. In this work, we have addressed the fabrication and characterization of two new mesoporous silicon devices prepared by electrochemistry and intended for protein delivery, namely: (i) mesoporous silicon microparticles and (ii) chitosan-coated mesoporous silicon microparticles. Both carriers were investigated for their capacity to load a therapeutic protein (insulin) and a model antigen (bovine serum albumin) …
Lipid and phase specificity of α-toxin from S. aureus
2013
AbstractThe pore forming toxin Hla (α-toxin) from Staphylococcus aureus is an important pathogenic factor of the bacterium S. aureus and also a model system for the process of membrane-induced protein oligomerisation and pore formation. It has been shown that binding to lipid membranes at neutral or basic pH requires the presence of a phosphocholine-headgroup. Thus, sphingomyelin and phosphatidylcholine may serve as interaction partners in cellular membranes. Based on earlier studies it has been suggested that rafts of sphingomyelin are particularly efficient in toxin binding. In this study we compared the oligomerisation of Hla on liposomes of various lipid compositions in order to identif…