Interactions between charged polypeptides and nonionic surfactants

Conjugated Nonionic Detergent Micelles: An Efficient Purification Platform for Dimeric Human Immunoglobulin A

The SARS-COV-2 virus is a deadly agent of inflammatory respiratory disease. Since 2020, studies have focused on developing new therapies based on galactose-rich IgA antibodies. Clinical surveys have also revealed that galactose-deficient IgA1 polymerizes in serum, producing IgA nephropathy, which is a common cause of kidney failure in young adults. Here we show that IgA1-IgA2 dimers are efficiently and economically purified in solution via conjugated nonionic surfactant micellar aggregates. Quantitative capture at pH 7 and extraction at pH 6.5 can avoid antibody exposure to acidic, potentially denaturing conditions. Brij-O20 aggregates lead to the highest process yields (88-91%) and purity (94%). Recovered IgA dimers preserve their native secondary structure and do not self-associate. Increasing the reaction volume has little impact on yield or purity. By introducing an efficient, inexpensive IgA purification protocol, we assist pharmaceutical firms and research laboratories in developing new IgA-based therapies as well as in increasing our understanding of IgA1 polymerization.

Development of a novel purification method for AAV vectors using tangential flow filtration

Adeno-associated virus (AAV) vector can efficiently transduce therapeutic genes in various tissue types with less side effects; however, owing to complex multistep processes during manufacture, there have been surges in the pricing of recently approved AAV vector-based gene therapy products. This study aimed to develop a simple and efficient method for high-quality purification of AAV vector via tangential flow filtration (TFF), which is commonly used for concentration and diafiltration of solutions during AAV vector purification. We established a novel purification method using TFF and surfactants. Treatment with two classes of surfactants (anionic and zwitterionic) successfully inhibited the aggregation of residual proteins separated from the AAV vector in the crude product by TFF, obtaining a clearance of 99.5% residual proteins. Infectivity of the AAV vector purified using the new method was confirmed both in vitro and in vivo, and no remarkable inflammation or tissue damage was observed in mouse skeletal muscle after local administration. Overall, our proposed method could be used to establish a platform for the purification of AAV vector.

Efficient separation of IgG from IgM antibodies via conjugated surfactant micelles

Immunoglobulin-G (IgG) (∼150 kDa) antibodies confer longer term immunity against bacterial or viral infections than the heavier IgM's (∼900 kDa), which are generally detectable in blood circulation in response to more recently acquired infections. There may be, however, a time overlap, which is problematic for diagnostic purposes, in the interests of which it is essential to separate IgM's from IgG's. We describe a purification platform, functioning at pH 6.5, containing Tween-20, or Brij-O20, non-ionic detergent micelles, mixed with the sugar-rich detergent dodecyl maltoside (DDM), amino acid monomer tyrosine (Tyr), and conjugated by the amphiphilic complex [(bathophenanthroline)₃: Fe²⁺]. Using conjugated Brij-O20 micelles, with input molar ratio IgG: IgM 9:1, IgG is recovered at 10 °C with 85-90% yield, (by SDS-PAGE densitometry) and ≥95% purity (also by SDS-PAGE), while IgM's are recovered at lower yields (28-34%) and contain small amounts of co-extracted IgG's. Addition of E. coli lysate as an artificial contamination background does not reduce the yield or purity of the recovered IgG. Tween-20/DDM/Tyr micelles lead to IgG purity ≥95% similar to that of Brij-O20, but with lower process yields (64-70%, by densitometry). Chromatographic separation with Protein A or Protein G resins leads to yields comparable to those obtained with Brij-O20 micelles, but with lower purity.

Insights into the Stabilization of Interferon Alpha by Two Surfactants Revealed by STD-NMR Spectroscopy

Surfactants are commonly used in biopharmaceutical formulations to stabilize proteins against aggregation. However, the choice of a suitable surfactant for a particular protein is decided mostly empirically, and their mechanism of action on molecular level is largely unknown. Here we show that a straightforward label-free method, saturation transfer difference (STD) nuclear magnetic resonance (NMR) spectroscopy, can be used to detect protein-surfactant interactions in formulations of a model protein, interferon alpha. We find that polysorbate 20 binds with its fatty acid to interferon, and that the binding is stronger at pH closer to the isoelectric point of the protein. In contrast, we did not detect interactions between poloxamer 407 and interferon alpha. Neither of the two surfactants affected the tertiary structure and the thermal stability of the protein as evident from circular dichroism and nanoDSF measurements. Interestingly, both surfactants inhibited the formation of subvisible particles during long-term storage, but only polysorbate 20 reduced the amount of small soluble aggregates detected by size-exclusion chromatography. This proof-of-principle study demonstrates how STD-NMR can be employed to quickly assess surfactant-protein interactions and support the choice of surfactant in protein formulation.

Detergent micelle conjugates containing amino acid monomers allow purification of human IgG near neutral pH

Industrial scale production of therapeutic monoclonal antibodies (mAbs) is commonly achieved with Protein A chromatography, a process that requires exposure of the antibody to strongly acidic conditions during the eluting step. Exposure to acid inactivates virus contaminants but may, in parallel, lead to antibody aggregation that must be eliminated or kept at acceptably low levels. This report seeks to provide a practical method for overcoming a long-standing problem. We show how Brij-O20 detergent micelles, conjugated by the amphiphilic [(bathophenanthroline)₃:Fe²⁺] complex in the presence of amino acid monomers: phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), isoleucine (Ile) or valine (Val), efficiently capture polyclonal human IgG (hIgG) at neutral pH and allow its recovery by extraction either at pH 4 (85-97% yield) or at pH 6.3 (72-84% yield). Of the five amino acid monomers surveyed, Phe or Tyr produced the highest overall process yield at both pH 4 and 6.3. The monomeric state of the purified hIgG's was confirmed by dynamic light scattering (DLS). Potential advantages of the purification method are discussed.

(De)stabilization of Alpha-Synuclein Fibrillary Aggregation by Charged and Uncharged Surfactants

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. An important hallmark of PD involves the pathological aggregation of proteins in structures known as Lewy bodies. The major component of these proteinaceous inclusions is alpha (α)-synuclein. In different conditions, α-synuclein can assume conformations rich in either α-helix or β-sheets. The mechanisms of α-synuclein misfolding, aggregation, and fibrillation remain unknown, but it is thought that β-sheet conformation of α-synuclein is responsible for its associated toxic mechanisms. To gain fundamental insights into the process of α-synuclein misfolding and aggregation, the secondary structure of this protein in the presence of charged and non-charged surfactant solutions was characterized. The selected surfactants were (anionic) sodium dodecyl sulphate (SDS), (cationic) cetyltrimethylammonium chloride (CTAC), and (uncharged) octyl β-D-glucopyranoside (OG). The effect of surfactants in α-synuclein misfolding was assessed by ultra-structural analyses, in vitro aggregation assays, and secondary structure analyses. The α-synuclein aggregation in the presence of negatively charged SDS suggests that SDS-monomer complexes stimulate the aggregation process. A reduction in the electrostatic repulsion between N- and C-terminal and in the hydrophobic interactions between the NAC (non-amyloid beta component) region and the C-terminal seems to be important to undergo aggregation. Fourier transform infrared spectroscopy (FTIR) measurements show that β-sheet structures comprise the assembly of the fibrils.

Kinetic and thermodynamic of lactoferrin - Ethoxylated-nonionic surfactants supramolecular complex formation

Understanding nonionic surfactant-protein interactions is fundamental from both technological and scientific points of view. However, there is a complete absence of kinetic data for such interactions. We employed surface plasmon resonance (SPR) to determine the kinetic and thermodynamic parameters of bovine lactoferrin-Brij58 interactions at various temperatures under physiological conditions (pH 7.4). The adsorption process was accelerated with increasing temperature, while the desorption rate decreased, resulting in a more thermodynamically stable complex. The kinetic energetic parameters obtained for the formation of the activated complex, [bLF-Brij58]^‡, indicated that the potential energy barrier for [bLF-Brij58]^‡ formation arises primarily from the reduction in system entropy. [bLF-Brij58]^○ formation was entropically driven, indicating that hydrophobic interactions play a fundamental role in bLF interactions with Brij58.

Hydrophobic H-bond pairing: A novel approach to improve membrane permeability

The aim of the present study was to develop hydrophobic H-bond pairs (HHPs) of leuprolide (LEU) with non-ionic surfactants to improve its membrane permeability. LEU was lipidized via hydrophobic H-bond pairing (HHP) with the sucrose esters (SEs) sucrose laurate HLB 15 (SLA-15), sucrose palmitate HLB 16 (SPA-16), sucrose stearate HLB 11 (SST-11) and sucrose stearate HLB 15 (SST-15). HHPs were evaluated regarding precipitation efficiency in water, zeta potential, log Pn-octanol/water and dissociation behavior at various pH over time. Cytotoxic potential of HHPs of LEU with SST-11 was investigated on Caco-2 cells. Subsequently, ex vivo permeation studies were carried out across freshly excised Sprague-Dawley rat intestinal mucosa. At a molar ratio of LEU to SEs of 1:≥1 a precipitation efficiency of above 50% was achieved. Zeta potential of complexes was neither influenced by the type nor the amount of added surfactants. Log Pn-octanol/water of LEU was up to 250-fold increased due to HHP utilizing SST-11. Dissociation studies showed that HHPs of LEU with SST-11 dissociate up to 20% in gastrointestinal (GI) pH conditions within 4 h. Moreover, HHPs of LEU with SST-11 exhibited no cytotoxicity. Ex vivo permeation studies revealed 2-fold improved membrane permeation of HHPs of LEU with SST-11 compared to free LEU. Findings of this study show that HHP can be considered as a promising strategy to improve membrane permeation.

Toward Milder Personal Care Cleansing Products: Fast ex vivo Screening of Irritating Effects of Surfactants on Skin Using Raman Microscopy

We report a novel Raman technique that allows fast and reliable ex vivo assessment of the irritability of personal care cleansing products to the skin in terms of the molecular-level effects such as retention of water by corneocytes, change in the packing order and content of intercellular lipids, and the structure of keratin. We test this technique for the single surfactants (dodecyl glucoside, sodium dodecyl sulfate, sodium cocoyl glycinate, lauramidopropyl betaine) that are typically used in personal care, as well as on three types of commercial soap bars (“superfat”, “syndet”, and “combar”). We find that soaking of the skin for prolonged time in pure water can cause unfolding of keratin, which is commonly considered as a signature of “harshness” when dealing with the surfactant formulations. Moreover, molecular-level signatures of irritability of the test surfactants and soaps at brief (10 min) exposure times do not follow the trend expected from their critical micelle concentrations (CMC) and collagen swelling. In particular, dodecyl glucoside has positive impact on the barrier properties of the stratum corneum (SC) and apparent detergency properties (solubilizes lipids without affecting their packing order). We also find that two qualitatively different soap bars (“superfat” and “syndet”) are similarly mild under the conditions studied, while the “combar” soap has detergency properties. These results demonstrate that to improve methodology of predicting irritability of a surfactant-based formulation, we need to study more systematically the molecular-level responses of the SC to exposure.

Structural insights into the combinatorial effects of antimicrobial peptides reveal a role of aromatic-aromatic interactions in antibacterial synergism

The recent development of plants that overexpress antimicrobial peptides (AMPs) provides opportunities for controlling plant diseases. Because plants employ a broad-spectrum antimicrobial defense, including those based on AMPs, transgenic modification for AMP overexpression represents a potential way to utilize a defense system already present in plants. Herein, using an array of techniques and approaches, we report on VG16KRKP and KYE28, two antimicrobial peptides, which in combination exhibit synergistic antimicrobial effects against plant pathogens and are resistant against plant proteases. Investigating the structural origin of these synergistic antimicrobial effects with NMR spectroscopy of the complex formed between these two peptides and their mutated analogs, we demonstrate the formation of an unusual peptide complex, characterized by the formation of a bulky hydrophobic hub, stabilized by aromatic zippers. Using three-dimensional structure analyses of the complex in bacterial outer and inner membrane components and when bound to lipopolysaccharide (LPS) or bacterial membrane mimics, we found that this structure is key for elevating antimicrobial potency of the peptide combination. We conclude that the synergistic antimicrobial effects of VG16KRKP and KYE28 arise from the formation of a well-defined amphiphilic dimer in the presence of LPS and also in the cytoplasmic bacterial membrane environment. Together, these findings highlight a new application of solution NMR spectroscopy to solve complex structures to study peptide-peptide interactions, and they underscore the importance of structural insights for elucidating the antimicrobial effects of AMP mixtures.

Influence of Conventional Surfactants on the Self-Assembly of a Bola Type Amphiphilic Peptide

Structural and morphological regulation is a distinctly important topic in peptide self-assembly, and is also regarded as the fundamental point in peptide-based biomaterials development. In this paper, we showed that adding anionic surfactant SDS to a bola amphiphilic peptide KI₄K could result in the reconstruction of β-sheet secondary structure besides the changes in self-assembly morphologies from nanotubes to helical ribbons, nanofibers, or straight nanotapes according to the negatively stained transmission electron microscopy, atomic force microscopy, circular dichroism spectroscopy, and Fourier transform infrared spectroscopy results. The inducing effect of SDS was observed at both above and below its CMC but with different transformation rates. Through comparison to other surfactants, including CTAB, C₁₂EO₄, and AOT, we proposed that the transitions of KI₄K self-assemblies induced by anionic surfactants could be mainly attributed to the effect of hydrophobic interaction and electrostatic attraction between surfactants and peptide molecules. Rheological property measurement and dye adsorption experiments were also carried out to evaluate the properties of hydrogels formed by the peptide/surfactant hybrids. The samples formed self-supporting hydrogels at proper SDS or AOT concentrations, and the charges of hydrogel could be regulated by peptide to surfactant ratio.

Transformation of Cellulose into Nonionic Surfactants Using a One-Pot Catalytic Process

Alkyl glucosides surfactants are synthesized by a cascade process that involves the methanolysis of cellulose into methyl glucosides followed by the transacetalization with n-octanol. The first step was performed using methanol as solvent and acid catalysts (such as, inorganic acids, heteropolyacids, ionexchange resins, or modified carbon materials). Subsequently, long-chain alkyl glucosides are obtained in the second step by transacetalization, which involves the reaction of methyl glucosides with a fatty alcohol using the same acid catalyst. The overall process was performed under mild conditions. Amorphous sulfonated carbon catalyst achieved the best results for the complete conversion of cellulose in methanol at 200 °C with methyl α,β-glucopyranosides yields higher than 80 %. Moreover, this material containing -SO₃ H groups is ideal to perform the second step to obtain octyl and decyl glucosides in yields higher than 73 % at 120 °C. In addition, the sulfonated carbon catalyst (C-SO₃ H) can be reused with only a slightly decrease of its activity after four consecutive cycles.

Top-down mass spectrometry of hybrid materials with hydrophobic peptide and hydrophilic or hydrophobic polymer blocks

A multidimensional mass spectrometry (MS) methodology is introduced for the molecular level characterization of polymer-peptide (or polymer-protein) copolymers that cannot be crystallized or chromatographically purified. It encompasses electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) coupled with mass analysis, tandem mass spectrometry (MS(2)) and gas-phase separation by ion mobility mass spectrometry (IM-MS). The entire analysis is performed in the mass spectrometer ("top-down" approach) within milliseconds and with high sensitivity, as demonstrated for hybrid materials composed of hydrophobic poly(tert-butyl acrylate) (PtBA) or hydrophilic poly(acrylic acid) (PAA) blocks tethered to the hydrophobic decapeptide VPGVGVPGVG (VG2) via triazole linkages. The composition of the major products can be rapidly surveyed by MALDI-MS and MS(2). For a more comprehensive characterization, the ESI-IM-MS (and MS(2)) combination is more suitable, as it separates the hybrid materials based on their unique charges and shapes from unconjugated polymer and partially hydrolyzed products. Such separation is essential for reducing spectral congestion, deconvoluting overlapping compositions and enabling straightforward structural assignments, both for the hybrid copolymers as well as the polymer and peptide reactants. The IM dimension also permits the measurement of collision cross-sections (CCSs), which reveal molecular architecture. The MS and MS(2) spectra of the mobility separated ions conclusively showed that [PtBA-VG2]m and [PAA-VG2]m chains with the expected compositions and sequences were formed. Single and double copolymer blocks (m = 1-2) could be detected. Further, the CCSs of the hybrids, which were prepared via azide/alkyne cycloadditions, confirmed the formation of macrocyclic structures. The top-down methodology described would be particularly useful for the detection and identification of peptide/protein-polymer conjugates which are increasingly used in biomedical and pharmaceutical applications.

Synthesis of octyl-β-D-glucopyranoside catalyzed by Thai rosewood β-glucosidase-displaying Pichia pastoris in an aqueous/organic two-phase system

We explored the ability of a Thai rosewood β-glucosidase-displaying P. pastoris whole-cell biocatalyst (Pp-DCBGL) system to synthesize alkyl β-D-glucosides. The primary investigation centered on the synthesis of octyl-β-D-glucopyranoside (octyl-glu, OG). OG could be synthesized through reverse hydrolysis reaction with very low efficiency. Then, OG was synthesized between BG and octanol by a transglycosylation reaction. In a 2-ml reaction system, OG was synthesized with a conversion rate of 51.1% in 3h when 5 mg/ml BG was utilized as the glucosyl donor under optimized conditions. And, even after being reused four times, the Pp-DCBGL was relatively stable. Additionally, a 500-ml-scale reaction system was conducted in a 2-L stirred reactor with a conversion rate of 47.5% in 1.5 h. Moreover, the conversion rate did not decrease after the whole-cell catalyst was reused two times. In conclusion, Pp-DCBGL has high reaction efficiency and operational stability, which is a powerful biocatalyst available for industrial synthesis.

Surfactant-Amino Acid and Surfactant-Surfactant Interactions in Aqueous Medium: a Review

An overview of surfactant-amino acid interactions mainly in aqueous medium has been discussed. Main emphasis has been on the solution thermodynamics and solute-solvent interactions. Almost all available data on the topic has been presented in a lucid and simple way. Conventional surfactants have been discussed as amphiphiles forming micelles and amino acids as additives and their effect on the various physicochemical properties of these conventional surfactants. Surfactant-surfactant interactions in aqueous medium, various mixed surfactant models, are also highlighted to assess their interactions in aqueous medium. Finally, their applied part has been taken into consideration to interpret their possible uses.

Exploring the affinity binding of alkylmaltoside surfactants to bovine serum albumin and their effect on the protein stability: A spectroscopic approach

Steady-state and time-resolved fluorescence together with circular dichroism (CD) spectroscopic studies was performed to examine the interactions between bovine serum albumin (BSA) and two alkylmaltoside surfactants, i.e. n-decyl-β-D-maltoside (β-C10G2) and n-dodecyl-β-D-maltoside (β-C12G2), having identical structures but different tail lengths. Changes in the intrinsic fluorescence of BSA from static as well as dynamic measurements revealed a weak protein-surfactant interaction and gave the corresponding binding curves, suggesting that the binding mechanism of surfactants to protein is essentially cooperative in nature. The behavior of both surfactants is similar, so that the differences detected were attributed to the more hydrophobic nature of β-C12G2, which favors the adsorption of micelle-like aggregates onto the protein surface. These observations were substantially demonstrated by data derived from synchronous, three-dimensional and anisotropy fluorescence experiments. Changes in the secondary structure of the protein induced by the interaction with surfactants were analyzed by CD to determine the contents of α-helix and β-strand. It was noted that whereas the addition of β-C10G2 appears to stabilize the secondary structure of the protein, β-C12G2 causes a marginal denaturation of BSA for a protein:surfactant molar ratio as high as 1 to 100.

The nature of fatty acid interaction with a polyelectrolyte-surfactant pair revealed by NMR spectroscopy

The interaction mechanisms of an oppositely charged polyelectrolyte-surfactant pair and dodecanoic (lauric) acid (LA) were experimentally investigated using a combination of nuclear magnetic resonance (NMR) techniques. It is observed that LA significantly affects the interaction between the anionic surfactant sodium dodecylethersulfate (SDES) and the cationic polymer guar modified with grafted hydroxypropyl trimethylammonium chloride (Jaguar C13 BF). Typically, oppositely charged polymers and surfactants interact electrostatically at a certain surfactant concentration known as the critical aggregation concentration (CAC). Once the polymer is neutralized by the surfactant, an insoluble complex (precipitate) is observed (phase separation), and, at concentrations beyond the surfactant critical micellar concentration (CMC'), the system returns to a one phase entity. In a system in which a mixture of SDES-LA is added to the polymer, NMR data show that below the neutralization onset, some of the polymer interacts with SDES, while some of the polymer is adsorbed at the surface of LA solid aggregates present in the system. Furthermore, SDES is found to aggregate in a lamellar-like structure at the polymer side chain prior to the SDES CMC'. Above the SDES (CMC'), LA is solubilized and incorporated at the palisade region of SDES micelles. Analysis of (1)H resonances provided estimated concentrations of all species in the system phases at all stages of interaction.

Development and biological evaluation of Gymnema sylvestre extract-loaded nonionic surfactant-based niosomes

Aim: To develop and characterize Gymnema sylvestre extract-loaded niosomes using nonionic surfactants, and to evaluate their antihyperglycemic efficacy in comparison with the parent extract. Materials & methods: Nonionic surfactant-based G. sylvestre extract-loaded niosomes were prepared using the thin-film hydration method. The optimized formulation was screened for entrapment efficiency of the constituents, as well as other parameters such as release kinetics, vesicle size, zeta-potential and stability studies. The parent extract and optimized niosomal formulation were evaluated for their antihyperglycemic potential in an alloxan-induced diabetic animal model. Results: Niosomes prepared using Span™ 40 (SD Fine Chemicals Ltd, Mumbai, India) provided sterically stable vesicles 229.5 nm in size with zeta-potential and entrapment efficiency of 150.86 mV and 85.3 ± 4.5%, respectively. The surface morphology of vesicles was confirmed to be spherical by scanning electron microscopy studies. An in vitro release study demonstrated 77.4% of phytoconstituents release within 24 h. The niosome formulation demonstrated significant blood glucose level reduction in an oral glucose tolerance test, and increased antihyperglycemic activity compared with the parent extract in an alloxan-induced diabetic model. Conclusion: This study reveals the merits of G. sylvestre extract-loaded niosomes, and justifies the potential of niosomes for improving the efficacy of G. sylvestre extract as antidiabetic.

Original submitted 30 March 2012; Revised submitted 29 August 2012; Published online 24 December 2012

Signal intensities in ¹H-¹³C CP and INEPT MAS NMR of liquid crystals

Spectral editing with CP and INEPT in (13)C MAS NMR enables identification of rigid and mobile molecular segments in concentrated assemblies of surfactants, lipids, and/or proteins. In order to get stricter definitions of the terms "rigid" and "mobile", as well as resolving some ambiguities in the interpretation of CP and INEPT data, we have developed a theoretical model for calculating the CP and INEPT intensities as a function of rotational correlation time τc and C-H bond order parameter SCH, taking the effects of MAS into account. According to the model, the range of τc can at typical experimental settings (5kHz MAS, 1ms ramped CP at 80-100kHz B1 fields) be divided into four regimes: fast (τc<1ns), fast-intermediate (τc≈0.1μs), intermediate (τc≈1μs), and slow (τc>0.1ms). In the fast regime, the CP and INEPT intensities are independent of τc, but strongly dependent on |SCH|, with a cross-over from dominating INEPT to dominating CP at |SCH|>0.1. In the intermediate regime, neither CP nor INEPT yield signal on account of fast T1ρ and T2 relaxation. In both the fast-intermediate and slow regimes, there is exclusively CP signal. The theoretical predictions are tested by experiments on the glass-forming surfactant n-octyl-β-d-maltoside, for which τc can be varied continuously in the nano- to millisecond range by changing the temperature and the hydration level. The atomistic details of the surfactant dynamics are investigated with MD simulations. Based on the theoretical model, we propose a procedure for calculating CP and INEPT intensities directly from MD simulation trajectories. While MD shows that there is a continuous gradient of τc from the surfactant polar headgroup towards the methyl group at the end of the hydrocarbon chain, analysis of the experimental CP and INEPT data indicates that this gradient gets steeper with decreasing temperature and hydration level, eventually spanning four orders of magnitude at completely dry conditions.

A study of interaction of cationic dyes with anionic polyelectrolytes

The interactions of Acridine Orange with Sodium Alginate and Pinacyanol Chloride with Heparin have been investigated by spectrophotometric method. The polymers induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the corresponding dyes. The interaction constant and thermodynamic parameters of polymer-dye interactions have been determined. The effect of additives such as alcohols, and urea on the reversal of metachromasy has been studied. The data has been used to determine the stability of the metachromatic complex and the nature of binding. The thermodynamic parameters of interaction revealed that binding between Acridine Orange and Sodium Alginate involved only electrostatic forces while that between Pinacyanol Chloride involved both electrostatic and hydrophobic forces. The reversal studies using surfactants indicated the involvement of both electrostatic and hydrophobic forces in binding. Based on the results it can be concluded that Pinacyanol Chloride is more effective inducing metachromasy than Acridine Orange.

Comparative analyses of different surfactants on matrix-assisted laser desorption/ionization mass spectrometry peptide analysis

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been extensively used for proteomics and peptidomics analysis. Nevertheless, these analyses, when focused on low molecular mass proteins, show some limitation due to background interference from surfactant ions. Surfactants are routinely used as a solubilizing or denaturing agents for proteins and peptides. In this report, an evaluation and further comparison of the effects of an ionic surfactant, sodium dodecyl sulfate (SDS), and a non-ionic surfactant, tergitol, on MALDI-MS analyses of the amphipathic peptides, angiotensin and bradykinin, were carried out. At concentrations > or = 10 mmol L(-1), SDS deteriorates the MALDI spectral quality by reducing the signal and intensity of the analyte ions. In particular, it affects the hydrophobic peptide where the signal of surfactant-interfering ions suppresses the analyte ion signal. Whereas, the non-ionic surfactant, tergitol, improves the MALDI-MS analysis of peptide mixtures or hydrophobic peptides by reducing interference from the surfactant itself in positive ion mode analysis. Three-dimensional molecular modeling of two different peptides in complex to tergitol NP-40 and SDS were conducted in order to explain the molecular effects of both agents. In summary, while SDS must be removed from the sample solution to avoid interference of ions from SDS and suppression of analyte ion signal, tergitol at low concentrations may be used as an additive with sample solution for MALDI-MS analysis of peptides. Finally, molecular modeling analyses associated with docking were used in order to explain experimental biochemical data.

Efficient synthesis of a long carbohydrate chain alkyl glycoside catalyzed by cyclodextrin glycosyltransferase (CGTase)

Alkyl glycosides with long carbohydrate groups are surfactants with attractive properties but they are very difficult to synthesize. Here, a method for extension of the carbohydrate group of commercially available dodecyl-beta-d-maltoside (DDM) is presented. DDM was converted to dodecyl-beta-d-maltooctaoside (DDMO) in a single step by using a CGTase as catalyst and alpha-cyclodextrin (alpha-CD) as glycosyl donor. The coupling reaction is under kinetic control and the maximum yield depends on the selectivity of the enzyme. The Bacillus macerans CGTase favored the coupling reaction while the Thermoanaerobacter enzyme also catalyzed disproportionation reactions leading to a broader product range. A high ratio alpha-CD/DDM favored a high yield of DDMO and yields up to 80% were obtained using the B. macerans enzyme as catalyst.

A comparative study of polyelectrolyte-dye interactions

The interaction of Azure B with sodium alginate and heparin in aqueous solution has been studied by spectrophotometric method. Absorbance of Azure B at 645 nm decreases and a new band appeared at 545 nm and at 556 nm respectively which indicated that a new metachromatic complex formed. A linear decrease in absorbance is noted. It was found that sodium alginate is more effective than heparin in decreasing the absorbance of Azure B at 645 nm. The stoichiometry of sodium alginate or heparin with Azure B was determined by spectrophotometry. The results suggested that the interaction between Azure B with sodium alginate or heparin was a result of electrostatic forces and the difference between heparin and sodium alginate were attributed to the different negative charge number on repetitive disaccharides unit. Studies on the effect of alcohol or urea indicated that sodium alginate and heparin interacted with the aggregates of Azure B. Thermodynamic parameters of interaction has been evaluated to determine the stability of the metachromatic complex. The effect of surfactants on reversal of metachromasy has also been studied.

Structural and dynamic properties of juxta-membrane segments of caveolin-1 and caveolin-2 at the membrane interface

Caveolins (cav1-3) are essential membrane proteins found in caveolae. The caveolin scaffolding domain of cav-1 includes a short sequence containing a CRAC motif (V94TKYWFYR101) at its C-terminal end. To investigate the role of this motif in the caveolin-membrane interaction at the atomic level, we performed a detailed structural and dynamics characterization of a cav-1(V94-L102) nonapeptide encompassing this motif and including the first residue of cav-1 hydrophobic domain (L102), in dodecylmaltoside (DM) or dodecylphosphocholine (DPC) micelles, as membrane mimics. Cav-1(V94-L102) partitioned better in DPC and in DM/anionic lipid micelles than in DM micelles, as shown by fluorescence titration and CD. NMR data revealed that this peptide folded as an amphipathic helix located in the polar head group region of DPC micelles. The two tyrosine side-chains, flanked by arginine and lysine residues, are situated on one face of this helix, whereas the phenylalanine and tryptophan side-chains are located on the opposite face. Fluorescence studies showed significant Trp subnanosecond rotations, the presence of several rotamers, and a heterogeneous location within the water/micelle interface. NMR studies of the shorter cav-1(V94-R101) peptide and of the homologous sequence of cav-2(I79SKYVMYKF87) allowed the description of the effect of L102 and of the amino acid variations occurring in cav-2 on the structure and localization in DPC micelles. Based on the topological model of caveolins, our results suggest that the cav-1 and cav-2 nonapeptides studied form interfacial alpha-helix membrane anchors in which the K/RhhhYK/Rh motif, also found in cav-3, may play a significant role.

Shape variation of bilayer membrane daughter vesicles induced by anisotropic membrane inclusions

A theoretical model of a two-component bilayer membrane was used in order to describe the influence of anisotropic membrane inclusions on shapes of membrane daughter micro and nano vesicles. It was shown that for weakly anisotropic inclusions the stable vesicle shapes are only slightly out-of-round. In contrast, for strongly anisotropic inclusions the stable vesicle shapes may significantly differ from spheres, i.e. they have a flattened oblate shape at small numbers of inclusions in the membrane, and an elongated cigar-like prolate shape at high numbers of inclusions in the vesicle membrane.

The conformation of fusogenic B18 peptide in surfactant solutions

The interaction of B18 peptide with surfactants has been studied by circular dichroism spectroscopy and fluorescence measurements. B18 is the fusogenic motif of the fertilization sea urchin protein. The peptide forms an alpha-helix structure when interacting with positively or negatively charged surfactants below and above the critical micellar concentration (CMC). The alpha-helix formation is due to binding of surfactant monomers rather than the formation of surfactant micelles on the peptide. Fluorescence measurements show that the CMC of the negatively charged surfactant increases in the presence of B18, supporting the fact that there is a strong interaction between the peptide and monomers. Nonionic surfactant monomers have no effect on the peptide structure, whereas the micelles induce an alpha-helical conformation. In this case the helix stabilization results from the formation of surfactant micelles on the peptide.