1.
Membrane Activity and Channel Formation of the Adenylate Cyclase Toxin (CyaA) of Bordetella pertussis in Lipid Bilayer Membranes.
Knapp, O, Benz, R
Toxins. 2020;(3)
Abstract
The Gram-negative bacterium Bordetella pertussis is the cause of whooping cough. One of its pathogenicity factors is the adenylate cyclase toxin (CyaA) secreted by a Type I export system. The 1706 amino acid long CyaA (177 kDa) belongs to the continuously increasing family of repeat in toxin (RTX) toxins because it contains in its C-terminal half a high number of nine-residue tandem repeats. The protein exhibits cytotoxic and hemolytic activities that target primarily myeloid phagocytic cells expressing the αMβ2 integrin receptor (CD11b/CD18). CyaA represents an exception among RTX cytolysins because the first 400 amino acids from its N-terminal end possess a calmodulin-activated adenylate cyclase (AC) activity. The entry of the AC into target cells is not dependent on the receptor-mediated endocytosis pathway and penetrates directly across the cytoplasmic membrane of a variety of epithelial and immune effector cells. The hemolytic activity of CyaA is rather low, which may have to do with its rather low induced permeability change of target cells and its low conductance in lipid bilayer membranes. CyaA forms highly cation-selective channels in lipid bilayers that show a strong dependence on aqueous pH. The pore-forming activity of CyaA but not its single channel conductance is highly dependent on Ca2+ concentration with a half saturation constant of about 2 to 4 mM.
2.
Cholesterol level affects surface charge of lipid membranes in saline solution.
Magarkar, A, Dhawan, V, Kallinteri, P, Viitala, T, Elmowafy, M, Róg, T, Bunker, A
Scientific reports. 2014;:5005
Abstract
Cholesterol is an important component of all biological membranes as well as drug delivery liposomes. We show here that increasing the level of cholesterol in a phospholipid membrane decreases surface charge in the physiological environment. Through molecular dynamics simulation we have shown that increasing the level of cholesterol decreases Na+ ion binding. Complementary experimental ζ--potential measurements have shown a decreased ζ--potential with increasing cholesterol content, indicative of reduced surface charge. Both experiments and simulations have been carried out on both saturated 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and monounsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. This result is particularly important because membrane surface charge plays an important role in the interactions of biomembranes with peripheral membrane proteins and drug delivery liposomes with the immune system.
3.
Interaction of endocannabinoid receptors with biological membranes.
Dainese, E, Oddi, S, Maccarrone, M
Current medicinal chemistry. 2010;(14):1487-99
Abstract
Cellular signaling is regulated by several biochemical reactions, whose dynamics depends on changes in the fluxes of specific ligands through the containment barriers that are the biological membranes. The regulation of this complex dynamic equilibrium is mainly due to the activity of border proteins, that must be able to interact simultaneously with the lipid bilayer and the extracellular milieu. Endocannabinoid receptors, that include type-1 and type-2 cannabinoid receptors, the transient vanilloid potential receptors and the peroxisome proliferator-activated receptors, represent one of the most intriguing examples of "border" proteins. They have also been identified as important drug discovery targets with potential therapeutic applications, from antiemesis, appetite enhancement, analgesia, glaucoma treatment, and immune suppression. However, as yet the molecular details of endocannabinoid receptor regulation remain elusive. In this review we summarize the most relevant aspects of the structural/functional characterization of these receptors, with a focus on the active role played by biological membranes (in particular lipid rafts) in the modulation of their accessibility and mode of ligand binding. Based on available evidence, we propose that endocannabinoid receptors can be regulated by the rate of interlayer exchange and lateral diffusion of endocannabinoid/cholesterol complexes within lipid bilayers, thus suggesting innovative approaches for the therapeutic exploitation of the membrane component of endocannabinoid signaling.
4.
Effects of ceramide on liquid-ordered domains investigated by simultaneous AFM and FCS.
Chiantia, S, Kahya, N, Ries, J, Schwille, P
Biophysical journal. 2006;(12):4500-8
Abstract
The sphingolipid ceramides are known to influence lipid lateral organization in biological membranes. In particular, ceramide-induced alterations of microdomains can be involved in several cell functions, ranging from apoptosis to immune response. We used a combined approach of atomic force microscopy, fluorescence correlation spectroscopy, and confocal fluorescence imaging to investigate the effects of ceramides in model membranes of biological relevance. Our results show that physiological quantities of ceramide in sphingomyelin/dioleoylphosphatidylcholine/cholesterol supported bilayers lead to a significant rearrangement of lipid lateral organization. Our experimental setup allowed a simultaneous characterization of both structural and dynamic modification of membrane microdomains, induced by the presence of ceramide. Formation of similar ceramide-enriched domains and, more general, alterations of lipid-lipid interactions can be of crucial importance for the biological function of cell membranes.