Modulating protein unfolding and refolding via the synergistic association of an anionic and a nonionic surfactant.

HYPOTHESIS: Nonionic surfactants can counter the deleterious effect that anionic surfactants have on proteins, where the folded states are retrieved from a previously unfolded state. However, further studies are required to refine our understanding of the underlying mechanism of the refolding process. While interactions between nonionic surfactants and tightly folded proteins are not anticipated, we hypothesized that intermediate stages of surfactant-induced unfolding could define new interaction mechanisms by which nonionic surfactants can further alter protein conformation. EXPERIMENTS: In this work, the behavior of three model proteins (human growth hormone, bovine serum albumin, and ß-lactoglobulin) was investigated in the presence of the anionic surfactant sodium dodecylsulfate, the nonionic surfactant ß-dodecylmaltoside, and mixtures of both surfactants. The transitions occurring to the proteins were determined using intrinsic fluorescence spectroscopy and far-UV circular dichroism. Based on these results, we developed a detailed interaction model for human growth hormone. Using nuclear magnetic resonance and contrast-variation small-angle neutron scattering, we studied the amino acid environment and the conformational state of the protein. FINDINGS: The results demonstrate the key role of surfactant cooperation in defining the conformational state of the proteins, which can shift away or toward the folded state depending on the nonionic-to-ionic surfactant ratio. Dodecylmaltoside, initially a non-interacting surfactant, can unexpectedly associate with sodium dodecylsulfate-unfolded proteins to further impact their conformation at low nonionic-to-ionic surfactant ratio. When this ratio increases, the protein begins to retrieve the folded state. However, the native conformation cannot be fully recovered due to remnant surfactant molecules still adsorbed to the protein. This study demonstrates that the conformational landscape of the protein depends on a delicate interplay between the surfactants, ultimately controlled by the ratio between them, resulting in unpredictable changes in the protein conformation.

Investigating thermally induced aggregation of Somatropin- new insights using orthogonal techniques.

Three orthogonal techniques were used to provide new insights into thermally induced aggregation of the therapeutic protein Somatropin at pH 5.8 and 7.0. The techniques were Dynamic Light Scattering (DLS), Asymmetric Flow-Field Flow-Fractionation (AF4), and the TEM-based analysis system MiniTEM™. In addition, Differential Scanning Calorimetry (DSC) was used to study the thermal unfolding and stability. DSC and DLS were used to explain the initial aggregation process and aggregation rate at the two pH values. The results suggest that less electrostatic stabilization seems to be the main reason for the faster initial aggregation at pH 5.8, i.e., closer to the isoelectric point of Somatropin. AF4 and MiniTEM were used to investigate the aggregation pathway further. Combining the results allowed us to demonstrate Somatropin's thermal aggregation pathway at pH 7.0. The growth of the aggregates appears to follow two steps. Smaller elongated aggregates are formed in the first step, possibly initiated by partly unfolded species. In the second step, occurring during longer heating, the smaller aggregates assemble into larger aggregates with more complex structures.

Aggregation Behavior of Structurally Similar Therapeutic Peptides Investigated by 1H NMR and All-Atom Molecular Dynamics Simulations.

Understanding of peptide aggregation propensity is an important aspect in pharmaceutical development of peptide drugs. In this work, methodologies based on all-atom molecular dynamics (AA-MD) simulations and 1H NMR (in neat H2O) were evaluated as tools for identification and investigation of peptide aggregation. A series of structurally similar, pharmaceutically relevant peptides with known differences in aggregation behavior (D-Phe6-GnRH, ozarelix, cetrorelix, and degarelix) were investigated. The 1H NMR methodology was used to systematically investigate variations in aggregation with peptide concentration and time. Results show that 1H NMR can be used to detect the presence of coexisting classes of aggregates and the inclusion or exclusion of counterions in peptide aggregates. Interestingly, results suggest that the acetate counterions are included in aggregates of ozarelix and cetrorelix but not in aggregates of degarelix. The peptides investigated in AA-MD simulations (D-Phe6-GnRH, ozarelix, and cetrorelix) showed the same rank order of aggregation propensity as in the NMR experiments. The AA-MD simulations also provided molecular-level insights into aggregation dynamics, aggregation pathways, and the influence of different structural elements on peptide aggregation propensity and intermolecular interactions within the aggregates. Taken together, the findings from this study illustrate that 1H NMR and AA-MD simulations can be useful, complementary tools in early evaluation of aggregation propensity and formulation development for peptide drugs.

An integrative toolbox to unlock the structure and dynamics of protein-surfactant complexes.

The interactions between protein and surfactants play an important role in the stability and performance of formulated products. Due to the high complexity of such interactions, multi-technique approaches are required to study these systems. Here, an integrative approach is used to investigate the various interactions in a model system composed of human growth hormone and sodium dodecyl sulfate. Contrast variation small-angle neutron scattering was used to obtain information on the structure of the protein, surfactant aggregates and surfactant-protein complexes. 1H and 1H-13C HSQC nuclear magnetic resonance spectroscopy was employed to probe the local structure and dynamics of specific amino acids upon surfactant addition. Through the combination of these advanced methods with fluorescence spectroscopy, circular dichroism and isothermal titration calorimetry, it was possible to identify the interaction mechanisms between the surfactant and the protein in the pre- and post-micellar regimes, and interconnect the results from different techniques. As such, the protein was revealed to evolve from a partially unfolded conformation at low SDS concentration to a molten globule at intermediate concentrations, where the protein conformation and local dynamics of hydrophobic amino acids are partially affected compared to the native state. At higher surfactant concentrations the local structure of the protein appears disrupted, and a decorated micelle structure is observed, where the protein is wrapped around a surfactant assembly. Importantly, this integrative approach allows for the identification of the characteristic fingerprints of complex transitions as seen by each technique, and establishes a methodology for an in-detail study of surfactant-protein systems.

Manipulating Aggregation Behavior of the Uncharged Peptide Carbetocin.

Peptides are usually administered through subcutaneous injection. For low potency drugs, this may require high concentration formulations increasing the risk of peptide aggregation, especially for compounds without any intrinsic chargeable groups. Carbetocin was used as a model to study the behavior of uncharged peptides at high concentrations. Manipulation of the aggregation behavior of 70 mg/mL carbetocin was attempted by selecting excipients which interact with hydrophobic groups in carbetocin, and cover hydrophobic surfaces and interfaces. Peptide aggregation was induced by shaking stress and followed over time. Carbetocin solutions showed significant visible particle formation already after 4 h of shaking stress. This particle formation was not due to supersaturation or phase separation but suggested a nucleated aggregation process. None of the excipients prevented carbetocin aggregation, though altered aggregation behavior was observed, such as induction of fibril formation for most, but not all, charged excipients. Sodium dodecyl sulfate was found to accelerate peptide aggregation both below and above the critical micelle concentration in half-filled vials. However, in the absence of an air headspace, sodium dodecyl sulfate above the critical micelle concentration was capable of preventing shaking-induced carbetocin aggregation. Our study highlights the complexity in rational excipient selection to stabilize uncharged peptides at high concentration.

Circulation and antigenic drift in human influenza B viruses in SE Asia and Oceania since 2000.

During annual influenza epidemics, influenza B viruses frequently co-circulate with influenza A viruses and in some years, such as 2005, large outbreaks have occurred while in other years, the virus virtually disappears. Since 1987 there have been two lineages of influenza B viruses co-circulating in various countries and causing disease in humans. The proportions of these two lineages vary from year to year and country to country. For example, in 2005, the B/Victoria/2/87 lineage was predominant in New Zealand while in Australia the B/Yamagata/16/88 lineage was more common. Antigenic and genetic analysis has revealed gradual movement in the both lineages. Careful monitoring of the two virus lineages is important, as they are antigenically distinct. This is an important consideration for influenza vaccine formulation decisions, as only one influenza B component is traditionally included in the annual trivalent influenza vaccine.

Interactions between charged polypeptides and nonionic surfactants.

The influence of molecular characteristics on the mutual interaction between peptides and nonionic surfactants has been investigated by studying the effects of surfactants on amphiphilic, random copolymers of alpha-L-amino acids containing lysine residues as the hydrophilic parts. The hydrophobic residues were either phenylalanine or tyrosine. The peptide-surfactant interactions were studied by means of circular dichroism spectroscopy and binding isotherms, as well as by 1D and 2D NMR. The binding of surfactant to the peptides was found to be a cooperative process, appearing at surfactant concentrations just below the critical micellar concentration. However, a certain degree of peptide hydrophobicity is necessary to obtain an interaction with nonionic surfactant. When this prerequisite is fulfilled, the peptide mainly interacts with self-assembled, micelle-like surfactant aggregates formed onto the peptide chain. Therefore, the peptide-surfactant complex is best described in terms of a necklace model, with the peptide interacting primarily with the palisade region of the micelles via its hydrophobic side chains. The interaction yields an increased amount of alpha-helix conformation in the peptide. Surfactants that combine small headgroups with a propensity to form small, nearly spherical micelles were shown to give the largest increase in alpha-helix content.

Comparison of the helix-coil transition of a titrating polypeptide in aqueous solutions and at the air-water interface.

The transition from alpha-helix to random coil of the titrating polyamino acid co-poly-L-(lysine, phenylalanine), (p-(Lys,Phe)), has been investigated as a function of pH and ionic strength in aqueous solution and at the air-water interface by means of circular dichroism (CD) spectroscopy and the Langmuir surface film balance technique. The results strongly suggest that the helix-coil transition for peptides at the air-water interface can be determined by using the two-dimensional Flory exponent, nu, to express the pH dependent peptide surface conformation. The helix-coil titration curve of p-(Lys,Phe) shifts approximately 2.5 pH units towards lower pH at the air-water interface, as compared with the bulk solution. This finding is of relevance for the understanding of conformation and conformational changes of membrane-transporting and membrane penetrating peptides as well as for the use of peptides in molecular devices.

Surveillance for neuraminidase inhibitor resistance in human influenza viruses from Australia.

Two hundred and forty-five human influenza A and B viruses isolated in Australia between 1996 and 2003 were tested for their sensitivity to the NA inhibitor drugs, zanamivir and oseltamivir using a fluorescence-based neuraminidase inhibition assay. Based on mean IC50 values, influenza A viruses (with neuraminidase subtypes N1 and N2) were more sensitive to both the NA inhibitors than were influenza B strains. Influenza A viruses with a N1 subtype and influenza B strains both demonstrated a greater sensitivity to zanamivir than to oseltamivir carboxylate, whereas influenza A strains with a N2 subtype were more susceptible to oseltamivir carboxylate. A comparison of IC50 values for viruses isolated before and after the release of the NA inhibitors in Australia, found there was no significant difference in the sensitivity of strains to either neuraminidase inhibitor and none of the isolates tested showed clinically significant resistance.