Check out our New Publishers' Select for Free Articles

BBA - Biomembranes (v.1716, #2)

Editorial Board (pp. ii).

Lysolipid incorporation in dipalmitoylphosphatidylcholine bilayer membranes enhances the ion permeability and drug release rates at the membrane phase transition by Jeffrey K. Mills; David Needham (pp. 77-96).

The enhanced permeability of lipid bilayer membranes at their gel-to-liquid phase transition has been explained using a “bilayer lipid heterogeneity�? model, postulating leaky interfacial regions between still solid and melting liquid phases. The addition of lysolipid to dipalmitoylphosphatidylcholine bilayers dramatically enhances the amount of, and speed at which, encapsulated markers or drugs are released at this, already leaky, phase transition through these interfacial regions. To characterize and attempt to determine the mechanism behind lysolipid-generated permeability enhancement, dithionite permeability and doxorubicin release were measured for lysolipid and non-lysolipid, containing membranes. Rapid release of contents from lysolipid-containing membranes appears to occur through lysolipid-stabilized pores rather than a simple enhancement due to increased drug solubility in the bilayer. A dramatic enhancement in the permeability rate constant begins about two degrees below the calorimetric peak of the thermal transition, and extends several degrees past it. The maximum permeability rate constant coincides exactly with this calorimetric peak. Although some lysolipid desorption from liquid state membranes cannot be dismissed, dialyzation above T_m and mass spectrometry analysis indicate lysolipid must, and can, remain in the membrane for the permeability enhancement, presumably as lysolipid stabilized pores in the grain boundary regions of the partially melted solid phase.

Keywords: Liposome; Drug delivery; Vesicle; Thermal-sensitive; Interface; Triggered

Organization of protochlorophyllide oxidoreductase in prolamellar bodies isolated from etiolated carotenoid-deficient wheat leaves as revealed by fluorescence probes by Iliya D. Denev; Galina T. Yahubyan; Ivan N. Minkov; Christer Sundqvist (pp. 97-103).

Carotenoid importance for membrane organization of NADPH protochlorophyllide oxidoreductase (POR) was studied by comparing interaction of two membrane fluorescent probes with proteins in prolamellar bodies isolated from norflurazon-treated wheat plants (cdPLBs) to those isolated form plants with normal carotenoid amount (oPLBs). The tryptophan fluorescence quenching by 1-anilino-8-naphthalene sulfonate (attached to the surface of membrane lipid phase) and pyrene (situated deep into the fatty acid region of membrane lipids) was used to locate the position of POR molecules toward lipid phase, to analyze their supramolecular organization and the light-induced structural transitions. Our results showed that the pigment–protein complexes of cdPLBs were larger than those of oPLBs. Upon flash irradiation the aggregates of both types of PLB dissociated into smaller units but in cdPLBs this process was accompanied by reorientation of the POR molecules closer to the lipid surface and/or dissociation from the lipids. These results revealed that carotenoid deficiency led to a looser attachment of POR to the lipid phase and its early (in comparison with oPLBs) dissociation from the membranes during the light-induced transformation of cdPLBs. This might be one of the reasons for the inability of carotenoid-deficient plants to form functional plastids.

Keywords: Carotenoid; Fluorescence probe; NADPH-protochlorophyllide oxidoreductase; Norflurazon; Prolamellar body

The novel chelator lipid 3(nitrilotriacetic acid)-ditetradecylamine (NTA₃-DTDA) promotes stable binding of His-tagged proteins to liposomal membranes: Potent anti-tumor responses induced by simultaneously targeting antigen, cytokine and costimulatory signals to T cells by Christina L. van Broekhoven; Joseph G. Altin (pp. 104-116).

Recent studies indicate that the chelator lipid nitrilotriacetic acid ditetradecylamine (NTA-DTDA) can be used to engraft T cell costimulatory molecules onto tumor cell membranes, potentially circumventing the need for genetic manipulation of the cells for development of cell- or membrane-based tumor vaccines. Here, we show that a related lipid 3(nitrilotriacetic acid)-ditetradecylamine (NTA₃-DTDA, which has three NTA moieties in its headgroup instead of one) is several-fold more effective than NTA-DTDA at promoting stable His-tagged protein engraftment. IAsys biosensor studies show that binding of His-tagged B7.1 (B7.1-6H) to NTA₃-DTDA-containing membranes, exhibit a faster on-rate and a slower off-rate, compared to membranes containing NTA-DTDA. Also, NTA₃-DTDA-containing liposomes and plasma membrane vesicles (PMV) engrafted with B7.1-6H and CD40-6H exhibit greater binding to T cells, in vitro and in vivo. Engrafted NTA₃-DTDA-containing PMV encapsulated cytokines such as IL-2, IL-12, GM-CSF and IFN-γ, allowing targeted delivery of both antigen and cytokine to T cells, and stimulation of antigen-specific T cell proliferation and cytotoxicity. Importantly, use of B7.1-CD40-engrafted PMV containing IL-2 and IL-12 as a vaccine in DBA/2J mice induced protection against challenge with syngeneic tumor cells (P815 mammary mastocytoma), and regression of established tumors. The results show that stable protein engraftment onto liposomal membranes using NTA₃-DTDA can be used to simultaneously target associated antigen, costimulatory molecules and cytokines to T cells in vivo, inducing strong anti-tumor responses and immunotherapeutic effect.

Keywords: Abbreviations; PMV; Plasma membrane vesicles; Streptavidin-FITC; Fluorescein isothiocyanate-conjugated streptavidin; POPC; Palmitoyl-oleoyl-phosphatidylcholine; DMPC; Dimyristoyl-phosphatidylcholine; NTA-DTDA; nitrilotriacetic acid ditetradecylamine; PEG; ₄₀₀; Polyethyleneglycol-400; FITC-DHPE; N; -(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-; sn; -glycero-3-phospho-ethanolamine, triethylammonium salt; PE-PEG; ₂₀₀₀; 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-polyethylene-glycol-2000Chelator lipid; T cell; Costimulatory molecule; Cytokine; Tumor vaccine; Liposome; Plasma membrane vesicle

Porous membranes for reconstitution of ion channels by M.A. Dhoke; P.J. Ladha; F.J. Boerio; L.B. Lessard; D.H. Malinowska; J. Cuppoletti; D.S. Wieczorek (pp. 117-125).

Functional biological synthetic composite (BSC) membranes were made using phospholipids, biological membrane proteins and permeable synthetic supports or membranes. Lipid bilayers were formed on porous polycarbonate (PC), polyethylene terephthalate (PETE) and poly (l-lactic acid) (PLLA) membranes and in 10–100 μm laser-drilled pores in a 96-well plastic plate as measured by increased resistance or decreased currents. Bilayers in 50 μm and smaller pores were stable for up to 4 h as measured by resistance changes or a current after gramicidin D reconstitution. Biological membrane transport reconstitution was then carried out. Using vesicles containing Kv1.5 K⁺ channels, K⁺ currents and decreased resistance were measured across bilayers in 50 μm pores in the plastic plate and PLLA membranes, respectively, which were inhibited by compound B, a Kv1.5 K⁺ channel inhibitor. Functional reconstitution of Kv1.5 K⁺ channels was successful. Incorporation of membrane proteins in functional form in stable permeable membrane-supported lipid bilayers is a simple technology to create BSC membranes that mimic biological function which is readily adaptable for high throughput screening.

Keywords: Polycarbonate; PETE; PLLA membrane; Lipid bilayer

Membrane perturbation effects of peptides derived from the N-termini of unprocessed prion proteins by Mazin Magzoub; Kamila Oglęcka; Aladdin Pramanik; L.E. Göran Eriksson; Astrid Gräslund (pp. 126-136).

Peptides derived from the unprocessed N-termini of mouse and bovine prion proteins (mPrPp and bPrPp, respectively), comprising hydrophobic signal sequences followed by charged domains (KKRPKP), function as cell-penetrating peptides (CPPs) with live cells, concomitantly causing toxicity. Using steady-state fluorescence techniques, including calcein leakage and polarization of a membrane probe (diphenylhexatriene, DPH), as well as circular dichroism, we studied the membrane interactions of the peptides with large unilamellar phospholipid vesicles (LUVs), generally with a 30% negative surface charged density, comparing the effects with those of the CPP penetratin (pAntp) and the pore-forming peptide melittin. The prion peptides caused significant calcein leakage from LUVs concomitant with increased membrane ordering. Fluorescence correlation spectroscopy (FCS) studies of either rhodamine-entrapping (REVs) or rhodamine-labeled (RLVs) vesicles, showed that addition of the prion peptides resulted in significant release of rhodamine from the REVs without affecting the overall integrity of the RLVs. The membrane leakage effects due to the peptides had the following order of potency: melittin>mPrPp>bPrPp>pAntp. The membrane perturbation effects of the N-terminal prion peptides suggest that they form transient pores (similar to melittin) causing toxicity in parallel with their cellular trafficking.

Keywords: Abbreviations; PrP; prion protein; PrP; ^C; cellular isoform of PrP; PrP; ^Sc; scrapie isoform of PrP; mPrPp; peptide with sequence corresponding to the N-terminus of the mouse prion protein, residues 1–28; bPrPp; peptide with sequence corresponding to the N-terminus of the bovine prion protein, residues 1–30; NLS; nuclear localization sequence; CPP; cell-penetrating peptide; pAntp; penetratin, Antennapedia homeodomain-derived CPP; ER; endoplasmic reticulum; DHPC; 1,2-dihexanoyl-; sn; -glycero-3-phosphatidylcholine; POPC; 1-palmitoyl-2-oleoyl-; sn; -glycero-3-phosphocholine; POPG; 1-palmitoyl-2-oleoyl-; sn; -glycero-3-phosphoglycerol; POPG/POPC; [30/70] notation refers to vesicles with 30 mol% POPG content; SUVs; small unilamellar vesicles; LUVs; large unilamellar vesicles; Rh; rhodamine; REVs; Rh-entrapping LUVs; RLVs; Rh-labeled LUVs; FCS; fluorescence correlation spectroscopy; CD; circular dichroism; DPH; diphenylhexatriene, membrane bound fluorescence probe; P/L; total peptide-to-phospholipid molar ratioPrion protein; Phospholipid vesicle; Membrane perturbation; Fluorescence; FCS; CD

Membrane-bound peptides mimicking transmembrane Vph1p helix 7 of yeast V-ATPase: A spectroscopic and polarity mismatch study by Renske W. Hesselink; Rob B.M. Koehorst; Petr V. Nazarov; Marcus A. Hemminga (pp. 137-145).

The V-ATPases are a family of ATP-dependent proton pumps, involved in a variety of cellular processes, including bone breakdown. V-ATPase enzymes that are too active in the latter process can result in osteoporosis, and inhibitors of the enzyme could be used to treat this disease. As a first step in studying the structure and function of the membrane-embedded interface at which proton translocation takes place, and its role in V-ATPase inhibition, synthetic peptides P1 and P2 consisting of 25 amino acid residues are presented here that mimic Vph1p helix 7 of yeast V-ATPase. A single mutation R10A between peptide P1 and P2 makes it possible to focus on the role of the essential arginine residue R735 in proton translocation. In the present work, we use a novel combination of spectroscopic techniques, such as CD spectroscopy, tryptophan emission spectra, acrylamide quenching and parallax analysis, and polarity mismatch modeling to characterize the peptides P1 and P2 in lipid bilayer systems. Based on both the spectroscopic experiments and the polarity mismatch modeling, P1 and P2 adopt a similar transmembrane conformation, with a mainly α-helical structure in the central part, placing the tryptophan residue at position 12 at a location 4±2 Å from the centre of the lipid bilayer. Furthermore, the arginine at position 10 in P1 does not have an effect on the bilayer topology of the peptide, showing that the long, flexible side chain of this residue is able to snorkel towards the lipid headgroup region. This large flexibility of R735 might be important for its function in proton translocation in the V-ATPase enzyme.

Keywords: Abbreviations; 5-DOX-PC; 1-Palmitoyl-2-stearoyl(5-DOXYL)-; sn; -glycero-3-phosphocholine; 12-DOX-PC; 1-Palmitoyl-2-stearoyl(12-DOXYL)-; sn; -glycero-3-phosphocholine; CD; Circular dichroism; DOPC; 1,2-Dioleoyl-; sn; -glycero-3-phosphocholine; DOPG; 1,2-Dioleoyl-; sn; -glycero-3-[phospho-rac-(1-glycerol)]; K; _SV; Stern–Volmer constant; L; /; P; Lipid to peptide molar ratio; LUV; Large unilamellar vesicle; TEMPO-PC; 1,2-Dioleoyl-; sn; -glycero-3-TEMPO-phosphocholine; TFE; Trifluoroethanol; V-ATPase; Vacuolar H; ⁺; -ATPase enzymeV-ATPase; Transmembrane peptide; Protein–lipid interaction; Arginine snorkeling; Tryptophan location; Polarity mismatch simulation

Biomembranes Cumulative Contents (pp. 146-146).

Sections

Personal tools

BBA - Biomembranes (v.1716, #2)

Sections

Personal tools

Local resources

BBA - Biomembranes (v.1716, #2)