Self-interaction of native and denatured lysozyme in the presence of osmolytes, l-arginine and guanidine hydrochloride

Changing relations between proteins and osmolytes: a choice of nature

The stabilization and destabilization of the protein in the presence of any additive is mainly attributed to its preferential exclusion from protein surface and its preferential binding to the protein surface, respectively.

The accurate measurement of second virial coefficients using self-interaction chromatography: experimental considerations

Measurement of B22, the second virial coefficient, is an important technique for describing the solution behaviour of proteins, especially as it relates to precipitation, aggregation and crystallisation phenomena. This paper describes the best practise for calculating B22 values from self-interaction chromatograms (SIC) for aqueous protein solutions. Detailed analysis of SIC peak shapes for lysozyme shows that non-Gaussian peaks are commonly encountered for SIC, with typical peak asymmetries of 10%. This asymmetry reflects a non-linear chromatographic retention process, in this case heterogeneity of the protein-protein interactions. Therefore, it is important to use the centre of mass calculations for determining accurate retention volumes and thus B22 values. Empirical peak maximum chromatogram analysis, often reported in the literature, can result in errors of up to 50% in B22 values. A methodology is reported here for determining both the mean and the variance in B22 from SIC experiments, includes a correction for normal longitudinal peak broadening. The variance in B22 due to chemical effects is quantified statistically and is a measure of the heterogeneity of protein-protein interactions in solution. In the case of lysozyme, a wide range of B22 values are measured which can vary significantly from the average B22 values.

Protein-associated cation clusters in aqueous arginine solutions and their effects on protein stability and size

Arginine is one of the most prominent residues in protein interactions, and arginine hydrochloride is widely used as an additive in protein solutions because of its exceptional effects on protein association and folding. The molecular origins of arginine effects on protein processes remain, however, controversial, and little is known about the molecular interactions between arginine cations and protein surfaces in aqueous arginine solutions. In this study, we report a unique biochemical phenomenon whereby clusters of arginine cations (Arg(+)) are associated with a protein surface. The formation of protein-associated Arg(+) clusters is initiated by Arg(+) ions that associate with specific protein surface loci through cooperative interactions with protein guanidinium and carboxyl groups. Molecular dynamics simulations indicate that protein-associated Arg(+) ions subsequently attract other Arg(+) ions and form dynamic cation clusters that extend further than 10 Å from the protein surface. The effects of arginine on the thermal stability and size of lysozyme and ovalbumin are measured over a wide concentration range (0 to 2 M), and we find that the formation of protein-associated Arg(+) clusters consistently explains the complex effects of arginine on protein stability and size. This study elucidates the molecular mechanisms and implications of cluster formation of Arg(+) ions at a protein surface, and the findings of this study may be used to manipulate synthetic and biological systems through arginine-derived groups.

The effect of osmolytes on protein fibrillation

Osmolytes are small molecules that are exploited by cells as a protective system against stress conditions. They favour compact protein states which makes them stabilize globular proteins in vitro and promote folding. Conversely, this preference for compact states promotes aggregation of unstructured proteins. Here we combine a brief review of the effect of osmolytes on protein fibrillation with a report of the effect of osmolytes on the unstructured peptide hormone glucagon. Our results show that osmolytes either accelerate the fibrillation kinetics or leave them unaffected, with the exception of the osmolyte taurine. Furthermore, the osmolytes that affected the shape of the fibrillation time profile led to fibrils with different structure as revealed by CD. The structural changes induced by Pro, Ser and choline-O-sulfate could be due to specific osmolytes binding to the peptides, stabilizing an otherwise labile fibrillation intermediate.

Self-interaction chromatography of proteins on a microfluidic monolith

A novel miniaturized system has been developed for measuring protein-protein interactions in solution with high efficiency and speed, and minimal use of protein. A chromatographic monolith synthesized in a capillary is used in the method to make interaction measurements by self-interaction chromatography (SIC) in a manner that, compared to column methods, is more efficient as well as more readily practicable even if only small amounts of protein are available. The microfluidic monolith requires much less protein for both column synthesis and the chromatographic measurements than a conventional SIC system, and in addition offers improved mass transfer and hence higher chromatographic efficiency than for previous SIC miniaturization systems. Protein self-interactions for catalase as a model protein, quantified by measurement of second virial coefficients, B(22), were determined by SIC and follow trends that are consistent with previously reported values. Different column derivatization conditions were studied in order to optimize the chromatographic behavior of the microfluidic system for SIC measurements. Chromatographic sensitivity can be further increased by using different column synthesis conditions.