Engineering of an E. coli outer membrane protein FhuA with increased channel diameter

<p>Abstract</p> <p>Background</p> <p>Channel proteins like FhuA can be an alternative to artificial chemically synthesized nanopores. To reach such goals, channel proteins must be flexible enough to be modified in their geometry, <it>i.e</it>. length and diameter. As continuation of a previous study in which we addressed the lengthening of the channel, here we report the increasing of the channel diameter by genetic engineering.</p> <p>Results</p> <p>The FhuA Δ1-159 diameter increase has been obtained by doubling the amino acid sequence of the first two N-terminal β-strands, resulting in variant FhuA Δ1-159 Exp. The total number of β-strands increased from 22 to 24 and the channel surface area is expected to increase by ~16%. The secondary structure analysis by circular dichroism (CD) spectroscopy shows a high β-sheet content, suggesting the correct folding of FhuA Δ1-159 Exp. To further prove the FhuA Δ1-159 Exp channel functionality, kinetic measurement using the HRP-TMB assay (HRP = Horse Radish Peroxidase, TMB = 3,3',5,5'-tetramethylbenzidine) were conducted. The results indicated a 17% faster diffusion kinetic for FhuA Δ1-159 Exp as compared to FhuA Δ1-159, well correlated to the expected channel surface area increase of ~16%.</p> <p>Conclusion</p> <p>In this study using a simple "semi rational" approach the FhuA Δ1-159 diameter was enlarged. By combining the actual results with the previous ones on the FhuA Δ1-159 lengthening a new set of synthetic nanochannels with desired lengths and diameters can be produced, broadening the FhuA Δ1-159 applications. As large scale protein production is possible our approach can give a contribution to nanochannel industrial applications.</p

Atomic resolution structure of full-length human insulin fibrils

International audiencePatients with type 1 diabetes mellitus who are dependent on an external supply of insulin develop insulin-derived amyloidosis at the sites of insulin injection. A major component of these plaques is identified as full-length insulin consisting of the two chains A and B. While there have been several reports that characterize insulin misfolding and the biophysical properties of the fibrils, atomic-level information on the insulin fibril architecture remains elusive. We present here an atomic resolution structure of a monomorphic insulin amyloid fibril that has been determined using magic angle spinning solid-state NMR spectroscopy. The structure of the insulin monomer yields a U-shaped fold in which the two chains A and B are arranged in parallel to each other and are oriented perpendicular to the fibril axis. Each chain contains two β‐strands. We identify two hydrophobic clusters that together with the three preserved disulfide bridges define the amyloid core structure. The surface of the monomeric amyloid unit cell is hydrophobic implicating a potential dimerization and oligomerization interface for the assembly of several protofilaments in the mature fibril. The structure provides a starting point for the development of drugs that bind to the fibril surface and disrupt secondary nucleation as well as for other therapeutic approaches to attenuate insulin aggregation

A model‐based framework for parallel scale‐down fed‐batch cultivations in mini‐bioreactors for accelerated phenotyping

Concentration gradients that occur in large industrial‐scale bioreactors due to mass transfer limitations have significant effects on process efficiency. Hence, it is desirable to investigate the response of strains to such heterogeneities to reduce the risk of failure during process scale‐up. Although there are various scale‐down techniques to study these effects, scale‐down strategies are rarely applied in the early developmental phases of a bioprocess, as they have not yet been implemented on small‐scale parallel cultivation devices. In this study, we combine mechanistic growth models with a parallel mini‐bioreactor system to create a high‐throughput platform for studying the response of Escherichia coli strains to concentration gradients. As a scaled‐down approach, a model‐based glucose pulse feeding scheme is applied and compared with a continuous feed profile to study the influence of glucose and dissolved oxygen gradients on both cell physiology and incorporation of noncanonical amino acids into recombinant proinsulin. The results show a significant increase in the incorporation of the noncanonical amino acid norvaline in the soluble intracellular extract and in the recombinant product in cultures with glucose/oxygen oscillations. Interestingly, the amount of norvaline depends on the pulse frequency and is negligible with continuous feeding, confirming observations from large‐scale cultivations. Most importantly, the results also show that a larger number of the model parameters are significantly affected by the scale‐down scheme, compared with the reference cultivations. In this example, it was possible to describe the effects of oscillations in a single parallel experiment. The platform offers the opportunity to combine strain screening with scale‐down studies to select the most robust strains for bioprocess scale‐up.ISSN:0006-3592ISSN:1097-029