Expression and purification of a recombinant amyloidogenic peptide from transthyretin for solid-state NMR spectroscopy

Strategies for Optimizing the Production of Proteins and Peptides with Multiple Disulfide Bonds

Bacteria can produce recombinant proteins quickly and cost effectively. However, their physiological properties limit their use for the production of proteins in their native form, especially polypeptides that are subjected to major post-translational modifications. Proteins that rely on disulfide bridges for their stability are difficult to produce in Escherichia coli. The bacterium offers the least costly, simplest, and fastest method for protein production. However, it is difficult to produce proteins with a very large size. Saccharomyces cerevisiae and Pichia pastoris are the most commonly used yeast species for protein production. At a low expense, yeasts can offer high protein yields, generate proteins with a molecular weight greater than 50 kDa, extract signal sequences, and glycosylate proteins. Both eukaryotic and prokaryotic species maintain reducing conditions in the cytoplasm. Hence, the formation of disulfide bonds is inhibited. These bonds are formed in eukaryotic cells during the export cycle, under the oxidizing conditions of the endoplasmic reticulum. Bacteria do not have an advanced subcellular space, but in the oxidizing periplasm, they exhibit both export systems and enzymatic activities directed at the formation and quality of disulfide bonds. Here, we discuss current techniques used to target eukaryotic and prokaryotic species for the generation of correctly folded proteins with disulfide bonds.

Self-assembling nanomaterials: monitoring the formation of amyloid fibrils, with a focus on small-angle X-ray scattering

Amyloid fibrils are attractive targets for applications in biotechnology. These thin, nanoscale protein fibers are highly ordered structures that self-assemble from their component proteins or peptides. This chapter describes the use of several biophysical techniques to monitor the formation of amyloid fibrils including a common dye-binding assay, turbidity assay, and small-angle X-ray scattering. These techniques provide information about the assembly mechanism, the rate and reproducibility of assembly, as well as the size of species along the assembly pathway.

More than just bare scaffolds: towards multi-component and decorated fibrous biomaterials

We are entering a new phase in biomaterials research in which rational design is being used to produce functionalised materials tailored to specific applications. As is evident from this Themed Issue, there are now a number of distinct types of designed, self-assembling, fibrous biomaterials. Many of these are ripe for development and application for example as scaffolds for 3D cell culture and tissue engineering, and in templating inorganic materials. Whilst a number of groups are making headway towards such applications, there is a general challenge to translate a wealth of excellent basic research into materials with a genuine future in real-life applications. Amongst other contemporary aspects of this evolving research area, a key issue is that of decorating or functionalising what are mostly bare scaffolds. There are a number of hurdles to overcome to achieve effective and controlled labelling of the scaffolds, for instance: maintaining biocompatibility, i.e., by minimising covalent chemistry, or using milder bioconjugation methods; attaining specified levels of decoration, and, in particular, high and stoichiometric labelling; introducing orthogonality, such that two or more functions can be appended to the same scaffold; and, in relevant cases, maintaining the possibility for recombinant peptide/protein production. In this critical review, we present an overview of the different approaches to tackling these challenges largely for self-assembled, peptide-based fibrous systems. We review the field as it stands by placing work within general routes to fibre functionalisation; give worked examples on our own specific system, the SAFs; and explore the potential for future developments in the area. Our feeling is that by tackling the challenges of designing multi-component and functional biomaterials, as a community we stand to learn a great deal about self-assembling biomolecular systems more broadly, as well as, hopefully, delivering new materials that will be truly useful in biotechnology and biomedical applications (107 references).

Conformational flexibility of Y145Stop human prion protein amyloid fibrils probed by solid-state nuclear magnetic resonance spectroscopy

Amyloid aggregates of a C-truncated Y145Stop mutant of human prion protein, huPrP23-144, associated with a heritable amyloid angiopathy, have previously been shown to contain a compact, relatively rigid, and beta-sheet-rich approximately 30-residue amyloid core near the C-terminus under physiologically relevant conditions. In contrast, the remaining huPrP23-144 residues display considerable conformational dynamics, as evidenced by the absence of corresponding signals in cross-polarization (CP)-based solid-state NMR (SSNMR) spectra under ambient conditions and their emergence in analogous spectra recorded at low temperature on frozen fibril samples. Here, we present the direct observation of residues comprising the flexible N-terminal domain of huPrP23-144 amyloid by using 2D J-coupling-based magic-angle spinning (MAS) SSNMR techniques. Chemical shifts for these residues indicate that the N-terminal domain is effectively an ensemble of protein chains with random-coil-like conformations. Interestingly, a detailed analysis of signal intensities in CP-based 3D SSNMR spectra suggests that non-negligible molecular motions may also be occurring on the NMR time scale within the relatively rigid core of huPrP23-144 amyloid. To further investigate this hypothesis, quantitative measurements of backbone dipolar order parameters and transverse spin relaxation rates were performed for the core residues. The observed order parameters indicate that, on the submicrosecond time scale, these residues are effectively rigid and experience only highly restricted and relatively uniform motions similar to those characteristic for well-structured regions of microcrystalline proteins. On the other hand, significant variations in magnitude of transverse spin relaxation rates were noted for residues present at different locations within the core region and correlated with observed differences in spectral intensities. While interpreted only qualitatively at the present time, the extent of the observed variations in transverse relaxation rates is consistent with the presence of relatively slow, microsecond-millisecond time scale chemical exchange type phenomena within the huPrP23-144 amyloid core.