Olga López - Academia.edu (original) (raw)

Papers by Olga López

Febs Letters, 1998

The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant... more The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.

Microscopy Research and Technique, 1998

The interaction of an equimolecular mixture of nonylphenol polyethoxylated [NP(EO)10] and sodium ... more The interaction of an equimolecular mixture of nonylphenol polyethoxylated [NP(EO)10] and sodium dodecyl sulfate (SDS) surfactants with phosphatidylcholine (PC) liposomes was studied by means of transmission electron microscopy (TEM) and changes in the mean particle size (quasielastic light scattering; QELS) and in the static light scattering (SLS) of the system during liposome solubilization. A good correlation was found between the TEM diameter of particles and the mean hydrodynamic diameter (HD) determined by QELS. The aggregates resulting in this interaction were dependent on the surfactant concentration in the system. Thus, an initial vesicle growth occurred when the surfactant concentration was 15.98 mol%, together with the formation of a very small percentage of smaller particles. Additional surfactant amounts (28.32 mol%) led first to the formation of largest vesicles (HD 418 nm) and second to a fall in the vesicle diameter and in the SLS of the system. Thus, for 38.27 mol%, the TEM picture still showed the presence of vesicles, albeit with signs of disintegration. When additional amounts of surfactant were added to the system, the size curve started to show a bimodal distribution. Thus, for 51.81 mol% surfactant concentration, a sharp curve appeared at 51 nm, corresponding to the formation of small particles and TEM pictures clearly showed vesicle disintegration with formation of tubular structures. It is noteworthy that additional surfactant amounts (from 52 to 60 mol%) led to the formation of unclosed multilayered structures together with smaller aggregates. The gradual increase in the proportion of these smaller aggregates (mixed micelles) led to the complete solubilization of liposomes.

Biochemistry, 2007

The eosinophil cationic protein (ECP) is an antipathogen protein involved in the host defense sys... more The eosinophil cationic protein (ECP) is an antipathogen protein involved in the host defense system. ECP displays bactericidal and membrane lytic capacities [Carreras et al. (2003) Biochemistry 42, 6636-6644]. We have now characterized in detail the protein-membrane interaction process. All observed fluorescent parameters of the wild type and single-tryptophan-containing mutants, as well as the results of decomposition analysis of protein fluorescence, suggest that W10 and W35 belong to two distinct spectral classes I and III, respectively. Tryptophan residues were classified and assigned to distinct structural classes using statistical approaches based on the analysis of tryptophan microenvironment structural properties. W10 belongs to class I and is buried in a relative nonpolar, nonflexible protein environment, while W35 (class III) is fully exposed to free water molecules. Tryptophan solvent exposure and the depth of the protein insertion in the lipid bilayer were monitored by the degree of protein fluorescence quenching by KI and brominated phospholipids, respectively. Results indicate that W35 partially inserts into the lipid bilayer, whereas W10 does not. Further analysis by electron microscopy and dynamic light scattering indicates that ECP can destabilize and trigger lipid vesicle aggregation at a nanomolar concentration range, corresponding to about 1:1000 protein/lipid ratio. No significant leakage of the vesicle aqueous content takes place below that protein concentration threshold. The data are consistent with a membrane destabilization "carpet-like" mechanism. FIGURE 1: ECP surface molecular representation. The figure was drawn according to the ECP crystal structure coordinates, PDB entry code 1QMT (34). In this representation, hydrophobic, basic, acidic, and cysteine residues are colored in yellow, blue, red, and green, respectively. W10 and W35 locations are indicated. The figure was created with Pymol DeLano Scientific LLC.

Archives of Biochemistry and Biophysics, 1999

The vesicle-to-micelle structural transitions that occurred in the interaction of sodium dodecyl ... more The vesicle-to-micelle structural transitions that occurred in the interaction of sodium dodecyl sulfate with phosphatidylcholine vesicles were studied at the equilibrium by means of dynamic light scattering (at different scattering angles) and freeze-fracture electron microscopy techniques. The incorporation of surfactant monomers in the bilayers resulted in an initial contraction of the mixed vesicles formed up to their saturation (size reduction of about 10%). Then, a progressive relaxation of these structures (growth from 170 to 225 nm) and a simultaneous formation of mixed micelles (particles of about 6 nm) occurred. Hence, in this interval "relaxed mixed vesicles" and mixed micelles coexisted in different proportions without formation of intermediate complex aggregates (bimodal size distribution curves). Freeze-fracture electron microscopy showed a direct formation of mixed micelles within the bilayer and their subsequent separation from the vesicle surface without formation of complex intermediate aggregates. This simple process progressed up to the complete vesicle solubilization.

Langmuir, 1999

The ability of sodium dodecyl sulfate (SDS) to traverse phosphatidylcholine bilayers was examined... more The ability of sodium dodecyl sulfate (SDS) to traverse phosphatidylcholine bilayers was examined by fluorescence spectroscopy. To this end, we measured the interaction of the anionic fluorescent probe 2-(ptoluidinyl)naphthalene-6-sodium sulfonate present in the outer vesicle leaflet with the SDS monomers incorporated in this structure. The surfactant transbilayer movement, or "flip-flop", was measured from the fluorescence intensity changes due to the interaction of the liposome/probe with SDS versus incubation time. This effect was quantified as the resulting variations in the surface potential (ψo) of liposomes. When the SDS concentration increased, ψo rose due to the electronegative contribution of the sulfate group incorporated in the bilayer surface. Increased periods of incubation resulted in a decreased ψo and, consequently, in a fall in the number of surfactant molecules in the outer vesicle leaflet. This variation was associated to the SDS "flip-flop". The maximum "flip-flop" (of about 50%) was always detected at a very low surfactant concentration, and the effective molar ratio of surfactant to PC for this maximum was always a constant value (0.02 mol/mol). Although the incorporation of SDS monomers to the bilayer surface was a very rapid process, the "flip-flop" rate of these monomers across lipid bilayer was very slow and time dependent with an enhanced kinetics between 10 and 90 min after mixing.

Chemistry and Physics of Lipids, 1998

The role played by the ceramides in the sublytic interactions of sodium dodecyl sulfate (SDS) wit... more The role played by the ceramides in the sublytic interactions of sodium dodecyl sulfate (SDS) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (k) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The presence in liposomes of higher and lower ceramide proportions than that existing in the SC lipids led to a fall and to a rise in the sublytic activity of SDS on these structures. However, the SDS partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to achieve almost a constant value for a Cer proportion similar to that in the SC lipids (about 40%). Thus, at low Cer proportions the ability of SDS molecules to alter these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies. The fact that the free surfactant concentration needed to achieve the two interaction levels investigated was lower than the surfactant critical micellar concentration (CMC) indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of the liposome lipid composition.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 1997

The composition and structure of pig stratum corneum (SC) tissue were investigated using differen... more The composition and structure of pig stratum corneum (SC) tissue were investigated using different solubilization methods. Whereas chloroform-methanol mixtures resulted in an almost complete removal of the intercellular lipids of the SC tissue and a small amount of proteins, the action of the nonionic surfactant octyl glucoside (OG) at concentrations lower and higher than its critical micelle concentration (CMC) led to the disaggregation of the SC tissue due to the solubilization of the corneocyte envelope. From a structural viewpoint, the intercellular lipids were bound one to another by means of hydrophobic interactions and the amino acids building the keratinocyte envelopes were linked covalently to these lipids (predominantly ceralnides). The material extracted by organic solvents was able to form liposomes (proteoliposomes), whereas that solubilized using OG surfactant (richer in proteins) did not form these structures. Two different approaches may be envisaged in the interaction of the OG and organic solvents with the SC tissue. On the one hand, the OG can be considered as a preferential and selective agent with respect to the use of organic solvents to obtain more specific information on the assembly properties of the lipids and amino acids building the corneocyte lipid envelope. On the other hand, the organic solvents appear to be specifically suitable for studying the lipids building the intercellular SC matrix. In addition to the generally accepted assumption that organic solvents exert a protein denaturing influence, it was demonstrated that the action of chloroform-methanol mixtures does not affect the architecture of the SC tissue, whereas the OG leads to its disaggregation. . neocyte consists of closely packed arrays of keratin filaments inside a very insoluble cross-linked protein envelope. On the outer surface of the envelope, long-chain ceramides are chemically bound to the protein and interact with the intercellular lipid lamellae . The main function of this complex structure is to provide a protection against transepidermal water loss and chemical insult. The analytical composition of proteins forming the SC and the specific lipids responsible for its barrier have been the subject of numerous studies .

Journal of The American Oil Chemists Society, 1997

The alterations caused by different surfactants in the permeability of liposomes formed by a lipi... more The alterations caused by different surfactants in the permeability of liposomes formed by a lipid mixture that models the stratum corneum (SC) composition (40% ceramides, 25% cholesterol, 25% palmitic acid, and 10% cholesteryl sulfate) were investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase surfactant partition coefficients (K) were determined at two sublytic levels. The selected surfactant were sodium dodecyl sulfate (SDS); sodium dodecyl ether sulfate (SDES) to assess the influence of the ethylene oxide groups on the anionic surfactant’s behavior; Triton X-100 (OP-10EO) and dodecyl betaine (D-Bet) as representatives of nonionic and amphoteric surfactants. Permeability alterations were determined by monitoring the increase in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The SC liposomes/surfactant sublytic interactions were mainly ruled by the action of surfactant monomers. OP-10EO showed the highest ability to alter the permeability of bilayers and the highest affinity with these structures, whereas D-Bet showed the lowest tendencies. Although SDS and SDES exhibited similar activity at 50% CF release (similar Re values), SDES appeared to be more active at 100% CF release, its affinity with bilayers being also increased. The different ability exhibited by SDS, SDES, and D-Bet (same alkyl chainlength) to alter the permeability of SC liposomes emphasizes the role played by the polar part of these surfactants in this interaction. Different trends in the evolution of Re and K were observed when comparing the results with those reported for phosphatidylcholine (PC) liposomes. Thus, whereas SC liposomes appeared to be more resistant to the action of surfactants, the surfactant affinity with SC bilayers was always greater than that reported for PC bilayers.

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Certificación: procedimiento mediante el cual una autoridad legalmente facultada da testimonio, p... more Certificación: procedimiento mediante el cual una autoridad legalmente facultada da testimonio, por medio de un documento oficial, que se acreditó total o parcialmente un grado, curso, nivel educativo u otra unidad de aprendizaje, según lo establezca la regulación respectiva.