Recent developments in sustainably sourced protein-based biomaterials.

Research into the development of sustainable biomaterials is increasing in both interest and global importance due to the increasing demand for materials with decreased environmental impact. This research field utilises natural, renewable resources to develop innovative biomaterials. The development of sustainable biomaterials encompasses the entire material life cycle, from desirable traits, and environmental impact from production through to recycling or disposal. The main objective of this review is to provide a comprehensive definition of sustainable biomaterials and to give an overview of the use of natural proteins in biomaterial development. Proteins such as collagen, gelatin, keratin, and silk, are biocompatible, biodegradable, and may form materials with varying properties. Proteins, therefore, provide an intriguing source of biomaterials for numerous applications, including additive manufacturing, nanotechnology, and tissue engineering. We give an insight into current research and future directions in each of these areas, to expand knowledge on the capabilities of sustainably sourced proteins as advanced biomaterials.

Carbonic anhydrase generates a pH gradient in Bombyx mori silk glands.

Silk is a protein of interest to both biological and industrial sciences. The silkworm, Bombyx mori, forms this protein into strong threads starting from soluble silk proteins using a number of biochemical and physical cues to allow the transition from liquid to fibrous silk. A pH gradient has been measured along the gland, but the methodology employed was not able to precisely determine the pH at specific regions of interest in the silk gland. Furthermore, the physiological mechanisms responsible for the generation of this pH gradient are unknown. In this study, concentric ion selective microelectrodes were used to determine the luminal pH of B. mori silk glands. A gradient from pH 8.2 to 7.2 was measured in the posterior silk gland, with a pH 7 throughout the middle silk gland, and a gradient from pH 6.8 to 6.2 in the beginning of the anterior silk gland where silk processing into fibers occurs. The small diameter of the most anterior region of the anterior silk gland prevented microelectrode access in this region. Using a histochemical method, the presence of active carbonic anhydrase was identified in the funnel and anterior silk gland of fifth instar larvae. The observed pH gradient collapsed upon addition of the carbonic anhydrase inhibitor methazolamide, confirming an essential role for this enzyme in pH regulation in the B. mori silk gland. Plastic embedding of whole silk glands allowed clear visualization of the morphology, including the identification of four distinct epithelial cell types in the gland and allowed correlations between silk gland morphology and silk stages of assembly related to the pH gradient. B. mori silk glands have four different epithelial cell types, one of which produces carbonic anhydrase. Carbonic anhydrase is necessary for the mechanism that generates an intraluminal pH gradient, which likely regulates the assembly of silk proteins and then the formation of fibers from soluble silk proteins. These new insights into native silk formation may lead to a more efficient production of artificial or regenerated silkworm silk fibers.

Self-assembled insect muscle bioactuators with long term function under a range of environmental conditions.

The use of mammalian muscles as device actuators is severely limited by their sensitivity to environmental conditions and short lifetime. To overcome these limitations insect muscle stem cells were used to generate organized 3D muscle constructs with significant enhancements in environmental tolerance and long term function. These tissues self-assembled, self-repaired, survived for months in culture without media replenishment and produced stresses of up to 2 kPa, all under ambient conditions. The muscle tissues continued to function for days even under biologically extreme temperature and pH. Furthermore, the dimensions and geometry of these tissues can be easily scaled to MEMS or meso-scale devices. The versatility, environmental hardiness and long term function provide a new path forward for biological actuators for device needs.

Characterisation of dihydrodipicolinate synthase (DHDPS) from Bacillus anthracis.

Bacillus anthracis is a Gram-positive spore-forming bacterium that is the causative agent of anthrax disease. The use of anthrax as a bioweapon has increased pressure for the development of an effective treatment. Dihydrodipicolinate synthase (DHDPS) catalyses the first committed step in the biosynthetic pathway yielding two essential bacterial metabolites, meso-diaminopimelate (DAP) and (S)-lysine. DHDPS is therefore a potential antibiotic target, as microbes require either lysine or DAP as a component of the cell wall. This paper is the first biochemical description of DHDPS from B. anthracis. Enzyme kinetic analyses, isothermal titration calorimetry (ITC), mass spectrometry and differential scanning fluorimetry (DSF) were used to characterise B. anthracis DHDPS and compare it with the well characterised Escherichia coli enzyme. B. anthracis DHDPS exhibited different kinetic behaviour compared with E. coli DHDPS, in particular, substrate inhibition by (S)-aspartate semi-aldehyde was observed for the B. anthracis enzyme (K(si(ASA))=5.4+/-0.5 mM), but not for the E. coli enzyme. As predicted from a comparison of the X-ray crystal structures, the B. anthracis enzyme was not inhibited by lysine. The B. anthracis enzyme was thermally stabilised by the first substrate, pyruvate, to a greater extent than its E. coli counterpart, but has a weaker affinity for pyruvate based on enzyme kinetics and ITC studies. This characterisation will provide useful information for the design of inhibitors as new antibiotics targeting B. anthracis.