The changing face of SDS denaturation: Complexes of Thermomyces lanuginosus lipase with SDS at pH 4.0, 6.0 and 8.0.

Hypothesis: Lipases are widely used in the detergent industry and must withstand harsh conditions involving both anionic and zwitterionic surfactants at alkaline pH. Thermomyces lanuginosus lipase (TlL) is often used and stays active at high concentrations of the anionic surfactant sodium dodecyl sulfate (SDS) at pH 8.0, but is sensitive to SDS at pH 6.

Pseudomonas aeruginosa rhamnolipid induces fibrillation of human α-synuclein and modulates its effect on biofilm formation.

The Parkinson's disease-associated protein α-synuclein (αSN) is natively unfolded but its structure can be modulated by membranes and surfactants. The opportunistic pathogen Pseudomonas aeruginosa (PA) produces and secretes the biosurfactant rhamnolipid (RL) which modulates bacterial biofilm. Here, we show that monomeric RL enhances the ability of αSN to permeabilize membranes, while micellar RL rapidly induces protein β-sheet structure with a worm-like fibrillary appearance, which cannot seed RL-free fibrillation but transforms into linear fibrils faster than αSN fibrillating on its own.

Myoglobin and α-Lactalbumin Form Smaller Complexes with the Biosurfactant Rhamnolipid Than with SDS.

Biosurfactants (BSs) attract increasing attention as sustainable alternatives to petroleum-derived surfactants. This necessitates structural insight into how BSs interact with proteins encountered by current chemical surfactants. Thus, small-angle x-ray scattering (SAXS) has been used for studying the structures of complexes made of the proteins α-Lactalbumin (αLA) and myoglobin (Mb) with the biosurfactant rhamnolipid (RL).

Glycolipid Biosurfactants Activate, Dimerize, and Stabilize Thermomyces lanuginosus Lipase in a pH-Dependent Fashion.

We present a study of the interactions between the lipase from Thermomyces lanuginosus (TlL) and the two microbially produced biosurfactants (BSs), rhamnolipid (RL) and sophorolipid (SL). Both RL and SL are glycolipids; however, RL is anionic, while SL is a mixture of anionic and non-ionic species. We investigate the interactions of RL and SL with TlL at pH 6 and 8 and observe different effects at the two pH values.

Concatemers of Outer Membrane Protein A Take Detours in the Folding Landscape.

Outer membrane protein A (OmpA) is the most abundant protein in the outer membrane of Escherichia coli. The N-terminal domain forms an eight-stranded membrane-embedded β-barrel that is widely used as a model protein for in vitro folding into the membrane and into surfactant micelles. Under conditions that include a low surfactant concentration, OmpA can form stable higher-order structures by intermolecular association.

Human Lysozyme Peptidase Resistance Is Perturbed by the Anionic Glycolipid Biosurfactant Rhamnolipid Produced by the Opportunistic Pathogen Pseudomonas aeruginosa.

Infection by the opportunistic pathogen Pseudomonas aeruginosa (PA) is accompanied by the secretion of virulence factors such as the secondary metabolite rhamnolipid (RL) as well as an array of bacterial enzymes, including the peptidase elastase. The human immune system tries to counter this via defensive proteins such as lysozyme (HLZ). HLZ targets the bacterial cell wall but may also have other antimicrobial activities.

Weak and Saturable Protein-Surfactant Interactions in the Denaturation of Apo-α-Lactalbumin by Acidic and Lactonic Sophorolipid.

Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited.

The anionic biosurfactant rhamnolipid does not denature industrial enzymes.

Biosurfactants (BS) are surface-active molecules produced by microorganisms. Their combination of useful properties and sustainable production make them promising industrial alternatives to petrochemical and oleochemical surfactants. Here we compare the impact of the anionic BS rhamnolipid (RL) and the conventional/synthetic anionic surfactant sodium dodecyl sulfate (SDS) on the structure and stability of three different commercially used enzymes, namely the cellulase Carezyme® (CZ), the phospholipase Lecitase Ultra® (LT) and the α-amylase Stainzyme® (SZ).

Denaturation of α-lactalbumin and myoglobin by the anionic biosurfactant rhamnolipid.

Glycolipid biosurfactants (GBS) are promising environmentally friendly alternatives to chemical surfactants. Surfactants interact with proteins in many applications, often leading to significant changes in protein properties. Given GBS' marked difference in structure compared to traditional chemical surfactants, it is of interest to investigate their impact on protein structure and stability.

Folding of outer membrane protein A in the anionic biosurfactant rhamnolipid.

Folding and stability of bacterial outer membrane proteins (OMPs) are typically studied in vitro using model systems such as phospholipid vesicles or surfactant. OMP folding requires surfactant concentrations above the critical micelle concentration (cmc) and usually only occurs in neutral or zwitterionic surfactants, but not in anionic or cationic surfactants. Various Gram-negative bacteria produce the anionic biosurfactant rhamnolipid.

Folding of outer membrane proteins.

Outer membrane proteins (OMPs) represent a large group of β-barrel proteins found both in the membranes of both bacteria and eukaryotes. Their general ease of expression and refolding and straightforward methods to monitor their degree of folding conspire to make OMPs excellent model systems to investigate how the membrane environment and other biological factors modulating the membrane insertion and folding of OMPs influence the folding pathway. This review attempts to provide an overview of how these proteins are studied in vitro and what kind of information can reliably be extracted.

A kinetic analysis of the folding and unfolding of OmpA in urea and guanidinium chloride: single and parallel pathways.

The outer membrane protein OmpA from Escherichia coli can fold into lipid vesicles and surfactant micelles from the urea-denatured state. However, a complete kinetic description of the folding and unfolding of OmpA, which can provide the basis for subsequent protein engineering studies of the protein's folding pathway, is lacking. Here we use two different denaturants to probe the unfolding mechanism of OmpA in the presence of the surfactant octyl maltoside (OM).

How chain length and charge affect surfactant denaturation of acyl coenzyme A binding protein (ACBP).

Using intrinsic tryptophan fluorescence, equilibria and kinetics of unfolding of acyl coenzyme A binding protein (ACBP) have been investigated in sodium alkyl sulfate surfactants of different chain length (8-16 carbon atoms) and with different proportions of the nonionic surfactant dodecyl maltoside (DDM). The aim has been to determine how surfactant chain length and micellar charge affect the denaturation mechanism. ACBP denatures in two steps irrespective of surfactant chain length, but with increasing chain length, the potency of the denaturant rises more rapidly than the critical micelle concentration (cmc) declines.

The role of decorated SDS micelles in sub-CMC protein denaturation and association.

We have combined spectroscopy, chromatography, calorimetry, and small-angle X-ray scattering (SAXS) to provide a comprehensive structural and stoichiometric description of the sodium dodecyl sulfate (SDS)-induced denaturation of the 86-residue alpha-helical bovine acyl-coenzyme-A-binding protein (ACBP). Denaturation is a multistep process. Initial weak binding of 1-3 SDS molecules per protein molecule below 1.

Stable intermediates determine proteins' primary unfolding sites in the presence of surfactants.

Despite detailed knowledge of the overall structural changes and stoichiometries of surfactant binding, little is known about which protein regions constitute the preferred sites of attack for initial unfolding. Here we have exposed three proteins to limited proteolysis at anionic (SDS) and cationic (DTAC) surfactant concentrations corresponding to specific conformational transitions, using the surfactant-robust broad-specificity proteases Savinase and Alcalase. Cleavage sites are identified by SDS-PAGE and N-terminal sequencing.

Aggregation of S6 in a quasi-native state by sub-micellar SDS.

Anionic surfaces promote protein fibrillation in vitro and in vivo. Monomeric SDS has also been shown to stimulate this process. We describe the dynamics of conformational changes and aggregative properties of the model protein S6 at sub-micellar SDS concentrations.

Global study of myoglobin-surfactant interactions.

Surfactants interact with proteins in multifarious ways which depend on surfactant concentration and structure. To obtain a global overview of this process, we have analyzed the interaction of horse myoglobin (Mb) with an anionic (SDS) and cationic (CTAC) surfactant, using both equilibrium titration techniques and stopped-flow kinetics. Binding and kinetics of conformational changes can be divided into a number of different regions (five below the cmc and one above) with very distinct features (broadly similar between the two surfactants, despite their difference in head group and chain length), which nuance the classical view of biphasic binding prior to micellization.

Unfolding of beta-sheet proteins in SDS.

Beta-sheet proteins are particularly resistant to denaturation by sodium dodecyl sulfate (SDS). Here we compare unfolding of two beta-sandwich proteins TNfn3 and TII27 in SDS. The two proteins show different surface electrostatic potential.

Versatile interactions of the antimicrobial peptide novispirin with detergents and lipids.

Novispirin G-10 is an 18-residue designed cationic peptide derived from the N-terminal part of an antimicrobial peptide from sheep. This derivative is more specific for bacteria than the parent peptide. We have analyzed Novispirin's interactions with various amphipathic molecules and find that a remarkably wide variety of conditions induce alpha-helical structure.