Cratylia mollis lectin at the air–aqueous solution interface: adsorption and lectin–lipid interactions

Ferromagnetic levan composite: an affinity matrix to purify lectin

A simple and inexpensive procedure used magnetite and levan to synthesize a composite recovered by a magnetic field. Lectins from Canavalia ensiformis (Con A) and Cratylia mollis (Cramoll 1 and Cramoll 1, 4) did bind specifically to composite. The magnetic property of derivative favored washing out contaminating proteins and recovery of pure lectins with glucose elution. Cramoll 1 was purified by this affinity binding procedure in two steps instead of a previous three-step protocol with ammonium sulfate fractionation, affinity chromatography on Sephadex G-75, and ion exchange chromatography through a CM-cellulose column.

Interaction between puroindolines and the major polar lipids of wheat seed endosperm at the air–water interface

To understand the role of the puroindolines (PIN-a and PIN-b) in the defense mechanism and stabilization of lipid films in the gas cell of bread dough, we have isolated the proteins and lipids from wheat seed endosperm and studied their interaction at the air/water interface using a Langmuir trough. The nature and shape of the pressure-area compression isotherms of the lipid monolayer in the presence of puroindolines in the subphase depended on the concentration of protein. A distinct phase separation occurred, when the concentration of protein in the subphase increased. The interfacial elasticity of the lipid monolayer in the presence of puroindolines in the subphase was higher than the pure lipid. Injection of protein beneath the preexisting lipid monolayer resulted in the increase of surface pressure due to the penetration of proteins. The extent of penetration depended on the nature of lipid head groups as well as on the initial surface pressure. The penetration of puroindolines to lipid monolayer was observed to be zero after crossing a critical initial surface pressure. The magnitude of the critical initial surface pressure for anionic lipids was significantly higher than the zwitterionic and nonionic lipids. The experimental results showed that both PIN-a and PIN-b had more affinity for anionic polar lipids than the neutral polar lipids and stabilized the lipid monolayer.

Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid

The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.

Ultrastructural analysis and immunocytochemical localization of isolectins in Cratylia mollis seeds

Cratylia mollis is a native forage from the semi-arid region of Northeast, State of Pernambuco, Brazil, whose seeds have been considered an important lectin source. Multiple molecular forms of lectins, carbohydrate-binding proteins, have been purified from C. mollis seeds (Cra Iso) allowing several applications of these purified proteins. In this work seeds were processed for ultrastructural analysis and immunocytochemical localization of the two most abundant isolectins, Cra Iso 1 and Cra Iso 3, with glucose/mannose and galactose specificities, respectively. The ultrastructural analysis revealed a typical plant cell: organelles, nucleus and cellular wall were visualized. The localization of isolectins occurred mainly in the amorphous matrix of protein bodies, and in the cellular walls of the embryonic axis. The results showed that the isolectins, which differ in relation to carbohydrate specificity and glycosylation are located in the same cellular compartment suggesting different functions inside the same subcellular organelle. Cra Iso 1 and Cra Iso 3 distribution in the C. mollis seeds was consistent with the subcellular localization of several legume lectins.

Effects of lipid chain length on molecular interactions between paclitaxel and phospholipid within model biomembranes

Molecular interactions between an anticancer drug, paclitaxel, and phosphatidylcholine (PC) of various chain lengths were investigated in the present work by the Langmuir film balance technique and differential scanning calorimetry (DSC). Both the lipid monolayer at the air-water interface and lipid bilayer vesicles (liposomes) were employed as model biological cell membranes. Measurement and analysis of the surface pressure versus molecular area curves of the mixed monolayers of phospholipids and paclitaxel under various molar ratio showed that phospholipids and paclitaxel formed a nonideal miscible system at the interface. Paclitaxel exerted an area-condensing effect on the lipid monolayer at small molecular surface areas and an area-expanding effect at large molecular areas, which could be explained by the intermolecular forces and geometric accommodation between the two components. Paclitaxel and phospholipids could form thermodynamically stable monolayer systems: the stability increased with the chain length in the order DMPC (C14:0)>DPPC (C16:0)>DSPC (C18:0). Investigation of paclitaxel penetration into the pure lipid monolayer showed that DMPC had a higher ability to incorporate paclitaxel and the critical surface pressure for paclitaxel penetration also increased with the chain length in the order DMPC>DPPC>DSPC. A similar trend was testified by DSC studies on vesicles of the mixed paclitaxel/phospholipids bilayer. Paclitaxel showed the greatest interaction with DMPC while little interaction could be measured in the paclitaxel/DSPC liposomes. Paclitaxel caused broadening of the main phase transition without significant change at the peak melting temperature of the phospholipid bilayers, which demonstrated that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer. The interaction between paclitaxel and phospholipid was nonspecific and the dominant factor in this interaction was the van der Waals force or hydrophobic force. As the result of the lower net van der Waals interaction between hydrocarbon chains for the shorter acyl chains, paclitaxel interacted more readily with phospholipids of shorter chain length, which also increased the bilayer intermolecular spacing.

Antitumor activity of Cratylia mollis lectin encapsulated into liposomes

The hemagglutinating (HA) activity of Cratylia mollis lectin (Cra) was evaluated and the influence of ultrasound and mechanical agitation on its activity examined. The antitumor activity of Cra-loaded liposomes was also investigated. Liposomes were obtained by the lipid thin film method. Physicochemical characterization was carried out and long-term stability of Cra-loaded liposomes assessed. Antitumor activity of Cra-loaded liposomes was investigated against Sarcoma 180 in Swiss mice. The treatment was performed intraperitoneally (7 mg/kg body weight per day) for 7 days. Histopathological analyses of tumor, liver, spleen and kidneys were carried out after treatment of the animals. The results showed that Cra-HA activity is affected under ultrasound exposure. However, Cra was successfully encapsulated into liposomes and the activity of the lectin was preserved despite the use of ultrasound in the liposome preparation. Cra-loaded liposomes were produced with an 84% encapsulation ratio (700 microg/ml) and a tumor inhibition of 71% was achieved. The encapsulation of Cra produced a decrease in its tissue toxicity and improved its antitumor activity. In particular, histopathological analysis revealed that treatment with Cra-loaded liposomes prevented Cra cytotoxicity in the liver and kidney of animals.

Electrochemical potential of free and immobilized Cratylia mollis seed lectin

The electrochemical potentials for free or immobilized Cratylia mollis seed lectin (Cra) were obtained through potentiostatic techniques. A saline solution was used as support to control the charge distribution between saturated calomel electrode and platinum electrode (working electrode). The electrochemical potential to free Cra was determined at the following concentrations: 0.6, 0.9 and 1.0 mg/ml in an aerated environment under different temperatures (5, 10 and 20 degrees C). The best electrochemical potential was obtained with 1.0 mg/ml, at 5 and 10 degrees C, 87 and 102 mV, respectively. Electrochemical potential to Cra immobilized on glass beads activated with 3-aminopropyltriethoxysilane described a linear behavior in relation to the increase in glucose concentration. The development of techniques to define interface electrical parameters will be able to give information about charged groups adsorbed to electrode surface revealing interactions particularly in biological systems.

Native and Hydrophobically Modified Human Immunoglobulin G at the Air/Water Interface

The adsorption of human immunoglobulin G (IgG) at the air/water interface was monitored both by the in situ radiotracer technique using [(14)C] labeled IgG and by surface tension measurements. The results reveal that adsorption of IgG from single protein systems displays bimodality due to molecular rearrangements at the interface. Above the threshold value of 1.5x10(-2) mg/ml solution concentration, adsorbed IgG molecules reoriented from the side-on to the end-on configuration. The existence of a lag time which did not appear in Gamma=f(t) curves, was observed in Pi=f(t) relationships at low protein concentrations and was due to the limits of the surface pressure technique to detect protein adsorption. The adsorption of native IgG was also carried out in the presence of a hydrophobized IgG obtained by grafting capryloyl residues to its lysine groups by reaction with N-hydroxysuccinimide ester of caprylic acid, which yielded 19 covalently bound alkyl chains to the IgG molecule (19C(8)-IgG). This modified IgG exhibited enhanced adsorption at the air/water interface, as manifested by its increased adsorption efficiency relative to the native protein. Sequential and competitive adsorption experiments from binary mixtures of native IgG and 19C(8)-IgG clearly demonstrate that the displacement of the native protein from the air/water interface strongly depended on the manner of how 19C(8)-IgG and native IgG competed with each other. When the two proteins competed simultaneously, 19C(8)-IgG predominantly occupied the available area but when native IgG was adsorbed first, for 2 h, the sequentially adsorbed 19C(8)-IgG was incapable of substantially displacing it from the interface. Copyright 2001 Academic Press.