Protein Surfactant Research Articles

Collectins and galectins in the abomasum of goats susceptible and resistant to gastrointestinal nematode infection.

Originally described in cattle, conglutinin belongs to the collectin family and is involved in innate immune defense. It is thought that conglutinin provides the first line of defense by maintaining a symbiotic relationship with the microbes in the rumen while inhibiting inflammatory reactions caused by antibodies leaking into the bloodstream. Due to the lack of information on the similar lectins and sequence detection in goats, we characterized the goat conglutinin gene using RACE and evaluated the differences in its gene expression profile, as well as in the gene expression profiles for surfactant protein A, galectins 14 and 11, interleukin 4 and interferon-gamma in goats. We used Saanen and Anglo Nubian F2 crossbred goats monitored over a period of four months and characterized them as resistant (R) or susceptible (S) based on the average values of EPG counts. Goat conglutinin was similar to bovine conglutinin, but its gene expression varied among different tissues. However, as with bovine conglutinin, it was most highly expressed in the liver. Variation in conglutinin (R=24.3±3.9; S=23.5±2.6, p=0.059), protein surfactant A (R=23.8±5.2, S=24.4±2.3, p=0.16), galectin 14 (R=15.9±3.5, S=14.7±6.2, p=0.49) and galectin l1 gene expression (R=25.4±2.6, S=25.8±3.7, p=0.53) was not significant between groups. However, there were weak correlations between interleukin 4 and the protein surfactant A gene (r=0.459, p=0.02) and between interleukin 4 and galectin 11 (r=0.498, p=0.01). Strong correlation between interferon-gamma and galectin 14 (r=0.744, p=0.00) was observed. Galectin 14 was negatively correlated with the number of nematodes in the goat (r=-0.416, p=0.04) as well as the EPG count (r=-0.408, p=0.04). This is the first study to date that identifies the gene expression of conglutinin, surfactant protein A and galectins 14 and 11 in the goat abomasum. In conclusion, we present evidence that lectin is involved in the immune response to gastrointestinal nematodes, which suggests that collectins and galectins are involved in the molecular recognition of helminths.

Competitive adsorption of lysozyme and non-ionic surfactants (Brij-35 and pluronic P123) from a mixed solution at water-air and water-xylene interfaces

The adsorption of lysozyme in the presence of high molecular weight (pluronic P123) and low molecular weight (Brij-35) non-ionic surfactants was studied at liquid-liquid and liquid-air interfaces. Using tritium-labeled compounds and liquid scintillation spectrometry of tritium, we investigated the competitive adsorption of lysozyme-pluronic P123 and lysozyme-Brij-35 at the aqueous-xylene interface. The substitution of protein by both polymer and low molecular weight surfactant was observed, while the presence of lysozyme does not influence the behavior of non-ionic molecules. We found that the ionic strength of the aqueous phase does not influence the strength of the effect, while it has a significant influence on the rate of diffusion and penetration of the adsorption layer by free protein. The thermodynamics of the competitive adsorption was described by the model suggested by Fainerman and co-authors, and the obtained parameters were used to describe the interfacial tension isotherms of the respective mixtures at the aqueous-air interface. Thus, the adsorption of each component of the mixture (protein and non-ionic surfactant) at the aqueous-air interface was revealed.

Frog foams and natural protein surfactants

Foams and surfactants are relatively rare in biology because of their potential to harm cell membranes and other delicate tissues. However, in recent work we have identified and characterized a number of natural surfactant proteins found in the foam nests of tropical frogs and other unusual sources. These proteins, and their associated foams, are relatively stable and bio-compatible, but with intriguing molecular structures that reveal a new class of surfactant activity. Here we review the structures and functional mechanisms of some of these proteins as revealed by experiments involving a range of biophysical and biochemical techniques, with additional mechanistic support coming from more recent site-directed mutagenesis studies.

Protein-surfactant interactions between bovine lactoferrin and sophorolipids under neutral and acidic conditions.

To understand the protein-surfactant interactions between naturally derived sophorolipids (SLs) and bovine lactoferrin (bLf), we carried out spectroscopic, microscopic, and biochemical experiments under weakly acidic and neutral pH conditions. Particle size analysis, microscopy, and enzymatic digestion indicated that bLf and SLs interact with each other to form sheet-like and small aggregated structures reflecting the original self-organization of SLs at pH 5.0 and 7.0, respectively. Circular dichroism (CD) showed that SLs did not significantly affect the secondary structure of bLf.

Adsorption of the natural protein surfactant Rsn-2 onto liquid interfaces.

To stabilize foams, droplets and films at liquid interfaces a range of protein biosurfactants have evolved in nature. Compared to synthetic surfactants, these combine surface activity with biocompatibility and low solution aggregation. One recently studied example is Rsn-2, a component of the foam nest of the frog Engystomops pustulosus, which has been predicted to undergo a clamshell-like opening transition at the air-water interface. Using atomistic molecular dynamics simulations and surface tension measurements we study the adsorption of Rsn-2 onto air-water and cyclohexane-water interfaces. The protein adsorbs readily at both interfaces, with adsorption mediated by the hydrophobic N-terminus. At the cyclohexane-water interface the clamshell opens, due to the favourable interaction between hydrophobic residues and cyclohexane molecules and the penetration of cyclohexane molecules into the protein core. Simulations of deletion mutants showed that removal of the N-terminus inhibits interfacial adsorption, which is consistent with the surface tension measurements. Deletion of the hydrophilic C-terminus also affects adsorption, suggesting that this plays a role in orienting the protein at the interface. The characterisation of the interfacial behaviour gives insight into the factors that control the interfacial adsorption of proteins, which may inform new applications of this and similar proteins in areas including drug delivery and food technology and may also be used in the design of synthetic molecules showing similar changes in conformation at interfaces.

Effect of curcumin on the binding of cationic, anionic and nonionic surfactants with myoglobin

Interaction of a globular protein, myoglobin and different surfactants has been studied in the absence and presence of curcumin in phosphate buffer at pH = 7.4 by UV-VIS spectrophotometry, fluorimetry and fluorescence polarization anisotropy methods. Results show that heme environment of myoglobin is changed by cationic cetyltrimethylammonium bromide (CTAB) and sodium N-dodecanoyl sarcosinate (SDDS). In the presence of curcumin, CTAB cannot change the heme; but SDDS can make change. Nonionic surfactant N-decanoyl-N-methylglucamine (Mega 10) cannot change the heme environment. Protein is unfolded by the surfactant. Curcumin can prevent the unfolding of protein in the low concentration region of ionic surfactants such as CTAB and SDDS. In nonionic surfactant media, curcumin accelerates the denaturation process. Due to myoglobin-curcumin complex formation, rotational motion of curcumin decreases in surfactant media and so anisotropy increases.

A biocompatible surfactant, methyl ester sulphonate (MES), as a precipitating ligand for protein purification

A biocompatible surfactant, methyl ester sulphonate (MES), was evaluated in protein surfactant precipitation. The amount of lysozyme precipitated by MES was found to be a strong function of both the molar ratio of surfactant to protein (Rp), and pH. Precipitation increased proportionally with an increase in Rp up to an optimum of 16, where full precipitation was achieved, while with pH variations electrostatic interactions were found to be the main driver of precipitation. The precipitate was recoverable by solvent extraction (54–56% activity recovery by acetone, ethanol, 50% acetone/ethanol, and methanol), and counter-ionic surfactant, TOMAC (83.3% activity recovery at Rr=1.5). Importantly, the structural integrity of the lysozyme recovered, either through solvent extraction or counter-ionic surfactant, was maintained, and this was confirmed by CD spectra and deconvolution. Precipitation with MES was compared to a conventional surfactant, AOT; in contrast with AOT, MES did not resolubilise the precipitate or cause structural transformations at higher Rps. MES exhibited better selectivity than AOT since it had minimal hydrophobic interactions in the absence of electrostatic interactions between the surfactant’s anionic group, and the protein’s positively charged groups (pH>pI). Hence, along with its economic benefits, and environmental features, this work has highlighted the potential of using MES in surfactant precipitation.

Surfactant-mediated amyloidogenesis behavior of stem bromelain; a biophysical insight

Neurodegenerative disorders are mainly associated with amyloid fibril formation of different proteins. Stem bromelain (SB), a cysteine protease, is known to exist as a molten globule state at pH 10.0. It passes through the identical surrounding (pH 10.0) in the gut epithelium of intestine upon oral administration. Protein–surfactant complexes are widely employed as drug carriers, so the nature of surfactant toward protein is of great interest. The present work describes the effect of cationic surfactants (CTAB & DTAB) and their hydrophobic behavior toward amyloidogenesis behavior of SB at pH 10.0. Multiple approaches including light scattering, far UV-CD, turbidity measurements, and dye binding assay (ThT, Congo red and ANS) were performed to measure the aggregation propensity of SB. Further, we monitored the hydrodynamic radii of aggregates formed using dynamic light scattering technique. Structure of fibrils was also visualized through fluorescence microscopy as well as TEM. At pH 10.0, low concentration of CTAB (0–200 μM) induced amyloid formation in SB as evident from a prominent increase in turbidity and light scattering, gain in β-sheet content, and enhanced ThT fluorescence intensity. However, further increase in CTAB concentration suppressed the fibrillation phenomenon. In contrast, DTAB did not induce fibril formation at any concentration used (0–500 μM) due to lower hydrophobicity. Net negative charge developed on protein at high pH (10.0) might have facilitated amyloid formation at low concentration of cationic surfactant (CTAB) due to electrostatic and hydrophobic interactions.

Characterization of mucin – lipid droplet interactions: Influence on potential fate of fish oil-in-water emulsions under simulated gastrointestinal conditions

The influence of mucin upon the properties and stability of oil-in-water emulsions containing lipid droplets coated by either a protein (caseinate) or non-ionic surfactant (Tween 80) was studied. At pH values below the isoelectric point of emulsion (e.g., stomach conditions), anionic mucin molecules bound to the surfaces of cationic caseinate-coated lipid droplets, which led to extensive bridging flocculation and droplet coalescence. Conversely, at pH values above the isoelectric point (e.g., mouth conditions), there was an electrostatic repulsion between anionic mucin molecules and anionic caseinate-coated lipid droplets. At this pH, relatively high levels of mucin promoted droplet flocculation through a depletion mechanism. The extent of droplet flocculation and/or coalescence in the systems depended on both the droplet and mucin concentration. Emulsions stabilized by the non-ionic surfactant were not susceptible to bridging flocculation, and only exhibited depletion flocculation at high mucin levels, which was attributed to the strong steric repulsion between them. These results have important implications for understanding the gastrointestinal fate of lipid droplets, which is critical for the development of foods with improved nutritional attributes.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments.

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Characterization of Interfacial Rheology of Protein-Stabilized Air–Liquid Interfaces

In this review, the definition of interfacial dilatational and shear rheology is outlined and the basis of different experimental methods for their characterization is provided. The connection between interfacial rheology and structure of proteins and other macromolecules is highlighted through the application of polymer theories. Key experimental results on interfacial rheology of air–liquid interfaces stabilized by proteins and protein surfactant mixtures are then presented. This is followed by the analysis of the effect of interfacial rheology on stability of air–liquid interface.

Proteomic and glycomic analyses of a lung-specific protein surfactant protein-D.

In order to verify the protein enriched from pooled human sera to be a lung-specific protein surfactant protein-D (SP-D), we performed peptide mass fingerprinting (PMF)-based protein identification. MASCOT search results of the obtained PMF unequivocally demonstrated that it is identical to human SP-D. Meanwhile, we performed MALDI-QIT-TOF mass spectrometry-based N-glycomic analysis of the recombinant human SP-D produced in murine myeloma cells. The obtained mass spectra of N-glycans from the recombinant SP-D demonstrated that the recombinant protein is almost exclusively modified with core-fucosylated N-glycans [1].

Stabilizing and destabilizing protein surfactant-based foams in the presence of a chemical surfactant: Effect of adsorption kinetics

Stimuli-responsive protein surfactants promise alternative foaming materials that can be made from renewable sources. However, the cost of protein surfactants is still higher than their chemical counterparts. In order to reduce the required amount of protein surfactant for foaming, we investigated the foaming and adsorption properties of the protein surfactant, DAMP4, with addition of low concentrations of the chemical surfactant sodium dodecylsulfate (SDS). The results show that the small addition of SDS can enhance foaming functions of DAMP4 at a lowered protein concentration. Dynamic surface tension measurements suggest that there is a synergy between DAMP4 and SDS which enhances adsorption kinetics of DAMP4 at the initial stage of adsorption (first 60s), which in turn stabilizes protein foams. Further interfacial properties were revealed by X-ray reflectometry measurements, showing that there is a re-arrangement of adsorbed protein–surfactant layer over a long period of 1h. Importantly, the foaming switchability of DAMP4 by metal ions is not affected by the presence of SDS, and foams can be switched off by the addition of zinc ions at permissive pH. This work provides fundamental knowledge to guide formulation using a mixture of protein and chemical surfactants towards a high performance of foaming at a low cost.

Structure and dynamics of a protein-surfactant assembly studied by ion-mobility mass spectrometry and molecular dynamics simulations.

The structure and dynamics of a protein-surfactant assembly studied by ion-mobility mass spectrometry (IMS) and vacuum molecular dynamics (MD) simulations is reported. Direct evidence is provided for the ability of the surfactant dodecyl-β-D-maltoside (DDM) to prevent charge-induced unfolding of the membrane protein (PagP) in the gas-phase. Restraints obtained by IMS are used to map the surfactant positions onto the protein surface. Surfactants occupying more exposed positions at the apexes of the β-barrel structure are most in-line with the experimental observations. MD simulations provide additional evidence for this assembly organization through surfactant inversion and migration on the protein structure in the absence of solvent. Surfactant migration entails a net shift from apolar membrane spanning regions to more polar regions of the protein structure with the DDM molecule remaining attached to the protein via headgroup interactions. These data provide evidence for the role of protein-DDM headgroup interactions in stabilizing membrane protein structure from gas-phase unfolding.

Interaction of bovine serum albumin with N-acyl amino acid based anionic surfactants: Effect of head-group hydrophobicity

The function of a protein depends upon its structure and surfactant molecules are known to alter protein structure. For this reason protein–surfactant interaction is important in biological, pharmaceutical, and cosmetic industries. In the present work, interactions of a series of anionic surfactants having the same hydrocarbon chain length, but different amino acid head group, such as l-alanine, l-valine, l-leucine, and l-phenylalanine with the transport protein, bovine serum albumin (BSA), were studied at low surfactant concentrations using fluorescence and circular dichroism (CD) spectroscopy, and isothermal titration calorimetry (ITC). The results of fluorescence measurements suggest that the surfactant molecules bind simultaneously to the drug binding site I and II of the protein subdomain IIA and IIIA, respectively. The fluorescence as well as CD spectra suggest that the conformation of BSA goes to a more structured state upon surfactant binding at low concentrations. The binding constants of the surfactants were determined by the use of fluorescence as well as ITC measurements and were compared with that of the corresponding glycine-derived surfactant. The binding constant values clearly indicate a significant head-group effect on the BSA–surfactant interaction and the interaction is mainly hydrophobic in nature.

Quenching interaction of BSA with DTAB is dynamic in nature: A spectroscopic insight

The role of electrostatic interactions between the protein, Bovine Serum Albumin (BSA) and the cationic surfactant, dodecyltrimethylammonium bromide (DTAB) has been substantiated using spectroscopic approaches. The primary mechanism of fluorescence quenching of the tryptophan of BSA is most probably dynamic in nature as the complex formation resulting in a protein–surfactant assembly is not very spontaneous. The weak interaction buries the tryptophan amino acid residue inside the protein scaffolds which have been quantitatively proved by our acrylamide quenching studies. The loss in the secondary structure of the protein as a result of interaction with DTAB has been elucidated by CD spectroscopy.

Effect of silk protein surfactant on silk degumming and its properties.

The silk protein surfactant (SPS) first used as a silk degumming agent in this study is an amino acid-type anionic surfactant that was synthesized using silk fibroin amino acids and lauroyl chloride. We studied it systematically in comparison with the traditional degumming methods such as sodium carbonate (Na2CO3) and neutral soap (NS). The experimental results showed that the sericin can be completely removed from the silk fibroin fiber after boiling the fibers three times for 30 min and using a bath ratio of 1:80 (g/mL) and a concentration of 0.2% SPS in an aqueous solution. The results of the tensile properties, thermal analysis, and SEM all show that SPS is similar to the NS, far superior to Na2CO3. In short, SPS may be used as an environmentally friendly silk degumming/refining agent in the silk textile industry and in the manufacture of silk floss quilts.

Positively charged aromatic polyamide reverse osmosis membrane with high anti-fouling property prepared by polyethylenimine grafting

In this work, Polyethylenimine (PEI) with different molecular weights was used to alter the surface charge of the aromatic polyamide RO membrane, and the positively charged RO membrane was fabricated by carbodiimide-induced grafting with PEI. The effect of PEI grafting on the surface property (charge, hydrophilicity, chemical elements and morphology) and permselectivity of membrane was analyzed. The results show that the surface charge of resulting membrane was successfully reversed (isoelectric point changed from pH3.1 to pH8.0) by the PEI grafting. The membrane surface hydrophilicity was obviously improved as well, which could not only compensate the effect of the increased trans-membrane resistance resulted from the grafted PEI on water flux, but also benefit the anti-fouling property. The morphology of membrane was not obviously affected by the PEI modification. Furthermore, two kinds of representative pollutants, basic protein (lysozyme) and cationic surfactant (DTAC and CTAC) were used as the model pollutant to evaluate membrane anti-fouling property. The PEI-modified membranes show high anti-fouling property to the positively charged pollutants. The novel PEI-modified membrane complements the existing short supply of positively charged RO membranes.

Structural aspects of a protein-surfactant assembly: native and reduced States of human serum albumin.

The inherently present seventeen disulfide bonds of the circulatory protein, human serum albumin (HSA) provide the necessary structural stability. Various spectroscopic approaches were used to investigate the effect of reduction of these disulfide bonds and its binding with the anionic surfactant, sodium dodecyl sulfate (SDS). Based on several spectroscopic analyses, our investigations highlight the following interesting aspects: (1) HSA on reduction loses not only its tertiary structure but also a significant amount of secondary structure as well. However, the reduced state of the protein is not like the molten-globule, (2) this structural loss of the protein due to reduction is more prominent than that caused by higher SDS concentrations alone and can certainly be attributed to the role of disulfide bonds, (3) lower surfactant concentrations provide marginal structural rigidity to the native state of the protein, whereas, higher concentrations of SDS induces secondary structure to the reduced state of HSA, (4) the binding of SDS with both the native and reduced states of HSA, occurred in three distinct stages which was followed by a saturation stage. However, the nature of such binding is different for both the states as investigated by using the Stern-Volmer equations and estimating the thermodynamic parameters. Besides, in contrast to the native state, the reduced state of HSA shows that the lone tryptophan residue gets more buried. However, there occurs a sudden decrement in the lifetime of the tryptophan and the hydrodynamic diameter increases by twofold.

Effect of protein incorporation on the nanostructure of the bicontinuous microemulsion phase of Winsor-III systems: a small-angle neutron scattering study.

Small-angle neutron scattering (SANS) analysis using the Teubner-Strey model has been employed to evaluate the effect of protein incorporation into the middle, bicontinuous microemulsion (BμE) phase of Winsor-III (WIII) systems formed by an aerosol-OT (AOT)/alkyl ethoxylate mixed surfactant system to understand better the extraction of proteins into and out of BμEs and to study the effect of proteins on a system that serves as a biomimetic analog of cell membranes. Under conditions of high salinity, the incorporation of positively charged proteins cytochrome c, lysozyme, and α-chymotrypsin, near their solubilization limit in the BμEs promoted the release of water and oil from the BμEs, a decrease in the quasi-periodic repeat distance (d), an increase in ordering (a decrease in the amphiphilicity factor, fa) for the surfactant monolayers, and a decrease in the surface area per surfactant headgroup, suggesting that the proteins affected the self-assembly of components in the BμE phase and produced Debye shielding of AOT's sulfonate headgroup. For WIII systems possessing lower salinity, cytochrome c reduced the efficiency of surfactant in the BμE phase, noted by increases in d and fa, suggesting that the enzyme and AOT underwent ion pairing. The results of this study demonstrate the importance of ionic strength to modulate protein-surfactant interactions, which in turn will control the release of proteins encapsulated in the BμEs, relevant to WIII-based protein extraction and controlled release from BμE delivery systems, and demonstrate the utility of BμEs as a model system to understand the effect of proteins on biomembranes.