SDS induces cross beta-sheet amyloid as well as alpha-helical structure in conconavalin A

Biomimetic protein structural transitions regulate activation and inhibition of the broad-spectrum bactericidal activity of cationic nanoparticles

The development of cationic polymers as alternative materials to antibiotics necessitates addressing the challenge of balancing their antimicrobial activity and toxicity. Here we propose a precise switching strategy inspired by biomimetic voltage-gated ion channels, enabling controlled activation and inhibition of cationic antimicrobial functions through protein conformational transitions in diverse physiological environments. Following thermodynamic studies on the specific recognition between mannose end groups on polycations and concanavalin A (ConA), we synthesized a type of ConA-polycation nanoparticle. The nanoparticle was inhibited under neutral conditions, with cationic moieties shielded by ConA's β-sheet. This shielding suppresses their antimicrobial activity, thereby ensuring satisfactory biocompatibility. In mildly acidic environments, however, the transition of a portion of ConA to an α-helix conformation exposed cations at the particle periphery, activating antibacterial functionality. Compared to inhibited nanoparticles, those in the activated state exhibited a 32-256 times reduction in the minimum bactericidal concentration against bacteria and fungi (2-16 µg/mL). In a murine acute pulmonary infection model, intravenous administration of inhibited nanoparticles effectively reduced bacterial counts by 4-log within 12 h. The biomimetic design, regulating cationic antimicrobial functionality through the alteration in protein secondary structure, significantly retards bacterial resistance development, holding great promise for intelligent antimicrobial materials. STATEMENT OF SIGNIFICANCE: Cationic antimicrobial polymers exhibit advantages distinct from antibiotics due to their lower propensity for resistance development. However, the presence of cationic moieties also poses a threat to healthy cells and tissues, significantly constraining their potential for clinical applications. To address this challenge, we propose a biomimetic strategy that mimics voltage-gated ion channels to activate the antimicrobial functionality of cations selectively in bacterial environments through the conformational transitions of proteins between β-sheets and α-helices. In healthy tissues, the antimicrobial functionality is inhibited, ensuring satisfactory biocompatibility. Antimicrobial cationic materials capable of intelligent switching between an activated state and an inhibited state in response to environmental changes offer an effective strategy to prevent the development of resistance and mitigate potential side effects.

Monitoring the interactions between POPG phospholipid bilayer and amyloid-forming protein human cystatin C. Does the bilayer influence the oligomeric state and structure of the protein?

A biological membrane is a structure characteristic for various cells and organelles present in almost all living organisms. Even though, it is one of the most common structures in organisms, where it serves crucial functions, a phospholipid bilayer may also take part in pathological processes leading to severe diseases. Research indicates that biological membranes have a profound impact on the pathological processes of oligomerization of amyloid-forming proteins. These processes are a hallmark of amyloid diseases, a group of pathological states involving, e.g., Parkinson's or Alzheimer's disease. Even though amyloidogenic diseases reap the harvest in modern societies, especially in elderly patients, the mechanisms governing the amyloid deposition are not clearly described. Therefore, the presented study focuses on the description of interactions between a model biological membrane (POPG) and one of amyloid forming proteins - human cystatin C. For the purpose of the study molecular dynamics simulations were applied to confirm interactions between the protein and POPG membrane. Next the NMR techniques were used to verify how the data obtained in solution compared to MD simulations and determine fragments of the protein responsible for interactions with POPG. Finally, circular dichroism was used to monitor the changes in secondary structure of the protein and size exclusion chromatography was used to monitor its oligomerization process. Obtained data indicates that the protein interacts with POPG submerging itself into the bilayer with the AS region. However, the presence of POPG bilayer does not significantly affect the structure or oligomerization process of human cystatin C.

Bovine liver catalase turns into three conformational states after exposure to an anionic surfactant

The mechanism by which anionic surfactants promote amyloid fibril is not well understood. Here, we investigated how sodium dodecyl sulfate (SDS), a negatively charged surfactant, affects the fibrillation of the partially unfolded random-coiled bovine liver catalase (BLC) at a pH of 2.0. We used several methods, including turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM imaging, to evaluate the conformational changes of BLC in vitro in response to SDS treatment. BLC is a multimeric protein and well folded at physiological pH but forms a random coil structure at pH 2.0. Intrinsic fluorescence and far-UV CD data showed that below 0.1 mM SDS, random coiled BLC turned into a native-like structure. BLC incubated with an SDS concentration ranging from 0.1 to 2.0 mM led to the formation of aggregates. The ThT fluorescence intensity was enhanced in the aggregated BLC samples (0.1-2.0 mM SDS), and cross beta-sheeted structure was detected by the far UV CD measurements. BLC adopts a complete alpha-helical structure upon interacting with SDS at a more than 2.0 mM concentration at pH 2.0. Understanding the mechanism of surfactant- or lipid-induced fibrillation is important for therapeutic purposes.

Anionic surfactant causes dual conformational changes in insulin

Amyloid fibrillation is a process by which proteins aggregate and form insoluble fibrils that are implicated in several neurodegenerative diseases. In n this study, we aimed to investigate the impact of the negatively charged detergent sodium dodecyl sulfate (SDS) on insulin amyloid fibrillation at pH 7.4 and 2.0, as SDS has been linked to the acceleration of amyloid fibrillation in vitro, but the underlying molecular mechanism is not fully understood. Our findings show that insulin forms amyloid-like aggregates in the presence of SDS at concentrations ranging from 0.05 to 1.8 mM at pH 2.0, while no aggregates were observed at SDS concentrations greater than 1.8 mM, and insulin remained soluble. However, at pH 7.4, insulin remained soluble regardless of the concentration of SDS. Interestingly, the aggregated insulin had a cross-β sheet secondary structure, and when incubated with higher SDS concentrations, it gained more alpha-helix. The electrostatics and hydrophobic interaction of SDS and insulin may contribute to amyloid induction. Moreover, the SDS-induced aggregation was not affected by the presence of salts. Furthermore, as the concentration of SDS increased, the preformed insulin amyloid induced by SDS began to disintegrate. Overall, our study sheds light on the mechanism of surfactant-induced amyloid fibrillation in insulin protein.

SDS induces amorphous, amyloid-fibril, and alpha-helical structures in the myoglobin in a concentration-dependent manner

Amyloid fibrils have been linked to a number of diseases. Surfactants imitate plasma membrane lipids and induce amyloid fibrils. This study examined the effects of the anionic surfactant sodium dodecyl sulfate (SDS) at pH 4.5 on equine skeletal muscle myoglobin (E-Mb). To analyze the effect of SDS on aggregation and amyloid-fibril formation to E-Mb, we used various spectroscopic techniques (turbidity, light scattering, intrinsic fluorescence, ThT fluorescence, and circular dichroism (CD)), electrophoretic, and microscopic techniques. Turbidity, SDS-PAGE, and light scattering all indicated the formation of E-Mb aggregates at SDS concentrations ranging from 0.2 mM to 1.0 mM. In the presence of 0.4 mM SDS, far-UV CD and TEM data indicate that E-MB forms amorphous aggregates. ThT binding, Far-UV CD, and TEM findings indicate that E-Mb forms amyloid-like structures in the presence of 0.6-1.0 mM SDS. However, no aggregation was seen at SDS concentrations above 1 mM. In the presence of high SDS concentrations (> 1 mM), the E-Mb exhibited native-like α-helical structure. As a result, SDS exhibited three distinct behaviors: amorphous aggregates, amyloid-fibrils, and helix-inducer. These findings also shed light on how amyloid fibrils are formed when anionic surfactants are introduced, which is a significant takeaway.

Molecular mechanism of insulin aggregation in the presence of a cationic surfactant

Protein aggregation and amyloid fibrillation are connected with neurodegenerative disorders. Insulin, a small molecular weight protein related to type II diabetes, has been shown to self-assemble to form protein aggregates. In this work, we investigated the effects of cetyltrimethylammonium bromide (CTAB) of insulin on the in vitro aggregation process at pH 7.4 and 2.0. The aggregation tendency of insulin was measured using a variety of biophysical approaches, including turbidity measurements, light scattering, far UV-CD, ThT dye binding, and transmission electron microscopy. The turbidity results demonstrated that at pH 7.4, a low concentration of CTAB (30-180 μM) causes insulin aggregation but at higer concentration (>180 μM) aggregation was not seen. However, at pH 2.0, both low as well as high concentrations of CTAB were unable to promote insulin aggregation. The ThT dye binding and far-UV CD data suggest that aggregation induced by CTAB is not having an ordered structure. Insulin treated with higher concentrations (>180 μM) of CTAB, the insulin gained a secondary structure. The possible cause of inducing aggregation in insulin is electrostatic and hydrophobic interaction because insulin contains a net negative charge at pH 7.4 and no aggregation at pH 2.0 due to electrostatic repulsion.

Molecular Mechanisms of Inhibition of Protein Amyloid Fibril Formation: Evidence and Perspectives Based on Kinetic Models

Inhibition of fibril formation is considered a possible treatment strategy for amyloid-related diseases. Understanding the molecular nature of inhibitor action is crucial for the design of drug candidates. In the present review, we describe the common kinetic models of fibril formation and classify known inhibitors by the mechanism of their interactions with the aggregating protein and its oligomers. This mechanism determines the step or steps of the aggregation process that become inhibited and the observed changes in kinetics and equilibrium of fibril formation. The results of numerous studies indicate that possible approaches to antiamyloid inhibitor discovery include the search for the strong binders of protein monomers, cappers blocking the ends of the growing fibril, or the species absorbing on the surface of oligomers preventing nucleation. Strongly binding inhibitors stabilizing the native state can be promising for the structured proteins while designing the drug candidates targeting disordered proteins is challenging.

Forces involved in freeze-induced egg yolk gelation: Effects of various bond dissociation reagents on gel properties and protein structure changes

Urea, sodium dodecyl sulfate (SDS) and β-mercaptoethanol (2-ME) were used to monitor the roles of hydrogen bonds, hydrophobic interactions and disulfide bonds in frozen egg yolk. Yolk samples were prepared with a denaturant, and the textural characteristics, turbidity properties, protein patterns and structures were analysed. The results showed that SDS or 2-ME addition to egg yolk promoted its turbidity and texture properties, but urea changed the turbidity differently. SDS-PAGE results showed that yolk protein patterns with urea slightly reduced the amount of high molecular weight substances, whereas SDS and 2-ME addition increased the amount. ATR-FTIR spectroscopy revealed that the protein secondary structures changed from ordered structures to random coils. The texture properties were correlated with the protein secondary structure, especially β-sheets and β-turns. Thus, the three bond dissociation reagents induced protein denaturation. Hydrogen bonds were the critical force affecting frozen egg yolk gelation, followed by hydrophobic interactions and disulfide bonds.

SDS modulates amyloid fibril formation and conformational change in succinyl-ConA at low pH

The anionic surfactant sodium dodecyl sulfate (SDS) is homologous to the cellular membrane lipids, and is known to stimulate amyloid fibrillation in several proteins. However, the mechanism by which SDS influences aggregation and structural changes in succinylated protein has not been determined. In this study, we observed the effects of variable SDS concentrations on succinyl-ConA aggregation at pH 3.5 and proposed a possible mechanism of SDS-induced succinyl-ConA aggregation. We used several biophysical techniques to identify the changes caused by SDS. Our results suggest that SDS stimulates succinyl-ConA aggregation in a concentration-dependent manner. From turbidity measurements, it was evident that a very low concentration (<0.1 mM) of SDS did not induce succinyl-ConA aggregation and proteins remained soluble. However, aggregations were observed at 0.1-2.5 mM SDS, which then dissipated at SDS concentrations above 2.5 mM. Far-UV CD results suggest that the β-sheet secondary structure of succinyl-ConA transformed into the cross-β-sheet structure in the presence of aggregating SDS concentrations. Notably, at SDS concentrations above 2.5 mM, the succinyl-ConA β-sheet transformed into an α-helical structure. The SDS-induced succinyl-ConA amyloid-like aggregates were confirmed by transmission electron microscopy (TEM). We propose that SDS modulates amyloid fibrillation in succinyl-ConA due to electrostatic and hydrophobic interactions and succinylation affects SDS-induced succinyl-ConA aggregation.

Spontaneous Fibrillation of Bovine Serum Albumin at Physiological Temperatures Promoted by Hydrolysis-Prone Ionic Liquids

This study highlights the role of time-dependent hydrolysis of ionic liquid anion, [BF₄]^-, of ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate, [C₂mim][BF₄], which results in ever-changing pH conditions. Such pH changes along with the ionic interactions bring conformational changes in bovine serum albumin (BSA), leading to the formation of amyloid fibers at 37 °C without external control of pH or addition of electrolyte. The fibrillation of BSA occurs spontaneously with the addition of IL; however, the highest growth rate has been observed in aqueous solution of 10% IL (v/v %) among investigated systems. Thioflavin T (ThT) fluorescence emission has been employed to monitor the growth and development of β-sheet content in amyloid fibrils. The structural alterations in BSA have also been investigated using intrinsic fluorescence measurements. Circular dichroism (CD) measurements confirmed the formation of amyloid fibrils. Transmission electron microscopy (TEM) has been explored to establish the morphologies of BSA fibrils at different intervals of time, whereas atomic force microscopy (AFM) has established the helically twisted nature of grown amyloid fibrils. The docking studies have been utilized to understand the insertion of IL ions in different domains of BSA, which along with decreased pH cause the unfolding and growth of BSA into amyloid fibrils. It is expected that the results obtained from this study would help to understand the impact of IL containing [BF₄]^- anion on protein stability and aggregation along with providing a new platform to control the formation of amyloid fibrils and other biomaterials driven via ionic interactions and alterations in pH.