Engineering protein-based machines to emulate key steps of metabolism (biological energy conversion)

Dynamic Structural Changes and Thermodynamics in Phase Separation Processes of an Intrinsically Disordered-Ordered Protein Model

Elastin-like proteins (ELPs) are biologically important proteins and models for intrinsically disordered proteins (IDPs) and dynamic structural transitions associated with coacervates and liquid-liquid phase transitions. However, the conformational status below and above coacervation temperature and its role in the phase separation process is still elusive. Employing matrix least-squares global Boltzmann fitting of the circular dichroism spectra of the ELPs (VPGVG)20 , (VPGVG)40 , and (VPGVG)60 , we found that coacervation occurs sharply when a certain number of repeat units has acquired β-turn conformation (in our sequence setting a threshold of approx. 20 repeat units). The character of the differential scattering of the coacervate suspensions indicated that this fraction of β-turn structure is still retained after polypeptide assembly. Such conformational thresholds may also have a role in other protein assembly processes with implications for the design of protein-based smart materials.

Elastin-Like Protein, with Statherin Derived Peptide, Controls Fluorapatite Formation and Morphology

The process of enamel biomineralization is multi-step, complex and mediated by organic molecules. The lack of cells in mature enamel leaves it unable to regenerate and hence novel ways of growing enamel-like structures are currently being investigated. Recently, elastin-like protein (ELP) with the analog N-terminal sequence of statherin (STNA15-ELP) has been used to regenerate mineralized tissue. Here, the STNA15-ELP has been mineralized in constrained and unconstrained conditions in a fluoridated solution. We demonstrate that the control of STNA15-ELP delivery to the mineralizing solution can form layered ordered fluorapatite mineral, via a brushite precursor. We propose that the use of a constrained STNA15-ELP system can lead to the development of novel, bioinspired enamel therapeutics.

Batch production of a silk-elastin-like protein in E. coli BL21(DE3): key parameters for optimisation

Background

Silk-elastin-like proteins (SELPs) combining the physicochemical and biological properties of silk and elastin have a high potential for use in the pharmaceutical, regenerative medicine and materials fields. Their development for use is however restrained by their production levels. Here we describe the batch production optimisation for a novel recently described SELP in the pET-E. coli BL21(DE3) expression system. Both a comprehensive empirical approach examining all process variables (media, induction time and period, temperature, pH, aeration and agitation) and a detailed characterisation of the bioprocess were carried out in an attempt to maximise production with this system.

Results

This study shows that maximum SELP volumetric production is achieved at 37°C using terrific broth at pH 6–7.5, a shake flask volume to medium volume ratio of 10:1 and an agitation speed of 200 rpm. Maximum induction is attained at the beginning of the stationary phase with 0.5 mM IPTG and an induction period of at least 4 hours. We show that the selection agents ampicillin and carbenicillin are rapidly degraded early in the cultivation and that plasmid stability decreases dramatically on induction. Furthermore, acetate accumulates during the bioprocess to levels which are shown to be inhibitory to the host cells. Using our optimised conditions, 500 mg/L of purified SELP was obtained.

Conclusions

We have identified the optimal conditions for the shake flask production of a novel SELP with the final production levels obtained being the highest reported to date. While this study is focused on SELPs, we believe that it could also be of general interest to any study where the pET (ampicillin selective marker)-E. coli BL21(DE3) expression system is used. In particular, we show that induction time is critical in this system with, in contrast to that which is generally believed, optimal production being obtained by induction at the beginning of the stationary phase. Furthermore, we believe that we are at or near the maximum productivity for the system used, with rapid degradation of the selective agent by plasmid encoded β-lactamase, plasmid instability on induction and high acetate production levels being the principal limiting factors for further improved production.

Elastic-contractile model proteins: Physical chemistry, protein function and drug design and delivery

This review presents the structure and physico-chemical properties of ECMPs, elastic-contractile model proteins using sparse design modifications of elastic (GVGVP)(n); it describes the capacity of ECMP to perform the energy conversions that sustain living organisms; it arrives at the hydration thermodynamics of ECMP in terms of the change in Gibbs free energy of hydrophobic association, ΔG(HA), and the apolar-polar repulsive free energy of hydration, ΔG(ap); it applies ΔG(HA), ΔG(ap), and the nature of elasticity to describe the function of basic diverse proteins, namely - the F₁-motor of ATP synthase, Complex III of mitochondria, the KscA potassium-channel, and the molecular chaperonin, GroEL/ES; it applies ΔG(HA) and ΔG(ap) to describe the function of ABC exporter proteins that confer multi-drug resistance (MDR) on micro-organisms and human carcinomas and suggests drug modifications with which to overcome MDR. Using ECMP, means are demonstrated, for quantifying drug hydrophobicity with which to combat MDR and for preparing ECMP drug delivery nanoparticles, ECMPddnp, decorated with synthetic antigen-binding fragments, Fab1 and Fab2, with which to target specific up-regulated receptors, characteristic of human carcinoma cells, for binding and localized drug release.

Sodium sulphate reactivates a protein A minidomain with a short elastin beta-turn

Elastin polymer sequences derived from muscle exhibit temperature and salt-induced reversible contractions and expansions. A folded and contracted beta-turn helical elastin structure is stabilised by increased intramolecular hydrophobic interactions. We have generated a switchable binding protein by inserting a typical elastin turn sequence, GVPGVG, between the two IgG-binding helices of an engineered globular minidomain from Protein A. This mutant showed increased binding of IgG-molecules compared to the wild-type sequence in the presence of sodium sulphate, as measured by surface plasmon resonance spectroscopy. Analysis by circular dichroism revealed a salt-induced folding of the mutant minidomain to a native type I beta-turn, likely stabilised as a result of the two interacting dehydrated valines across the beta-turn. Since sodium sulphate can be successfully used to regulate the folding/unfolding or binding/dissociation of this minidomain, this suggests an alternative protein purification method.