Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Progressing Antimicrobial Resistance Sensing Technologies across Human, Animal, and Environmental Health Domains

The spread of antimicrobial resistance (AMR) is a rapidly growing threat to humankind on both regional and global scales. As countries worldwide prepare to embrace a One Health approach to AMR management, which is one that recognizes the interconnectivity between human, animal, and environmental health, increasing attention is being paid to identifying and monitoring key contributing factors and critical control points. Presently, AMR sensing technologies have significantly progressed phenotypic antimicrobial susceptibility testing (AST) and genotypic antimicrobial resistance gene (ARG) detection in human healthcare. For effective AMR management, an evolution of innovative sensing technologies is needed for tackling the unique challenges of interconnected AMR across various and different health domains. This review comprehensively discusses the modern state-of-play for innovative commercial and emerging AMR sensing technologies, including sequencing, microfluidic, and miniaturized point-of-need platforms. With a unique view toward the future of One Health, we also provide our perspectives and outlook on the constantly changing landscape of AMR sensing technologies beyond the human health domain.

The Requirement of Genetic Diagnostic Technologies for Environmental Surveillance of Antimicrobial Resistance

Antimicrobial resistance (AMR) is threatening modern medicine. While the primary cost of AMR is paid in the healthcare domain, the agricultural and environmental domains are also reservoirs of resistant microorganisms and hence perpetual sources of AMR infections in humans. Consequently, the World Health Organisation and other international agencies are calling for surveillance of AMR in all three domains to guide intervention and risk reduction strategies. Technologies for detecting AMR that have been developed for healthcare settings are not immediately transferable to environmental and agricultural settings, and limited dialogue between the domains has hampered opportunities for cross-fertilisation to develop modified or new technologies. In this feature, we discuss the limitations of currently available AMR sensing technologies used in the clinic for sensing in other environments, and what is required to overcome these limitations.

Engineering a solid-state metalloprotein hydrogen evolution catalyst

Hydrogen has the potential to play an important role in decarbonising our energy systems. Crucial to achieving this is the ability to produce clean sources of hydrogen using renewable energy sources. Currently platinum is commonly used as a hydrogen evolution catalyst, however, the scarcity and expense of platinum is driving the need to develop non-platinum-based catalysts. Here we report a protein-based hydrogen evolution catalyst based on a recombinant silk protein from honeybees and a metal macrocycle, cobalt protoporphyrin (CoPPIX). We enhanced the hydrogen evolution activity three fold compared to the unmodified silk protein by varying the coordinating ligands to the metal centre. Finally, to demonstrate the use of our biological catalyst, we built a proton exchange membrane (PEM) water electrolysis cell using CoPPIX-silk as the hydrogen evolution catalyst that is able to produce hydrogen with a 98% Faradaic efficiency. This represents an exciting advance towards allowing protein-based catalysts to be used in electrolysis cells.

Enhancement of metallomacrocycle-based oxygen reduction catalysis through immobilization in a tunable silk-protein scaffold

Fuel cells convert chemical energy into electrical current with the use of an oxidant such as oxygen and have the potential to reduce our reliance on fossil fuels. To overcome the slow kinetics of the oxygen reduction reaction (ORR), platinum is often used as the catalyst. However, the scarcity and expense of platinum limits the wide-spread use of fuel cells. In the search for non-platinum oxygen reduction catalysts, metallomacrocycles have attracted significant attention. While progress has been made in understanding how metallomacrocycle-based molecules can catalyze the ORR, their low stability, remains an on-going challenge. Here we report an immobilization strategy whereby hemin (iron protoporphyrin IX, heme b) is converted into an oxygen reduction catalyst which could be operated for over 96 h, with turnover numbers >10⁷. This represents a 3 orders of magnitude improvement over the best reported iron porphyrin ORR catalyst to date. The basis for this improvement in turnover is specific binding of the heme within a recombinant silk protein, which allows for separation of the porphyrin active sites. Use of the silk protein provides a scaffold that can be engineered to improve selectivity and efficiency. Through rational design of the heme binding site, a > 95% selectivity for a four-electron reduction of oxygen to water was obtained, equal to the selectivity obtained using platinum-based catalysts. This work represents an important advance in the field, demonstrating that metallomacrocycle-based ORR catalysts are viable for use in fuel cells.

Biocompatibility and immunogenic response to recombinant honeybee silk material

If tolerated in biological environments, recombinant structural proteins offer the advantage that biological cues dictating cell attachment and material degradation can be modified as required for clinical application using genetic engineering. In this study, we investigate the biological response to materials generated from the recombinant honeybee silk protein, AmelF3, a structural protein that can be produced at high levels by fermentation in Escherichia coli. The protein can be readily purified from E. coli host cell proteins after transgenic production and fabricated into various material formats. When implanted subcutaneously according to International Standard ISO 10993 tests, materials generated from the purified recombinant protein were found to be noncytotoxic, inducing a transient weak immunogenic response and a chronic inflammatory response that resolved over time. While preliminary, this study supports the ongoing development of materials generated from this protein for biomedical applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1763-1770, 2019.

Did aculeate silk evolve as an antifouling material?

Many of the challenges we currently face as an advanced society have been solved in unique ways by biological systems. One such challenge is developing strategies to avoid microbial infection. Social aculeates (wasps, bees and ants) mitigate the risk of infection to their colonies using a wide range of adaptations and mechanisms. These adaptations and mechanisms are reliant on intricate social structures and are energetically costly for the colony. It seems likely that these species must have had alternative and simpler mechanisms in place to ensure the maintenance of hygienic domicile conditions prior to the evolution of these complex behaviours. Features of the aculeate coiled-coil silk proteins are reminiscent of those of naturally occurring α-helical antimicrobial peptides (AMPs). In this study, we demonstrate that peptides derived from the aculeate silk proteins have antimicrobial activity. We reconstruct the predicted ancestral silk sequences of an aculeate ancestor that pre-dates the evolution of sociality and demonstrate that these ancestral sequences also contained peptides with antimicrobial properties. It is possible that the silks evolved as an antifouling material and facilitated the evolution of sociality. These materials serve as model materials for consideration in future biomaterial development.

Confirmation of Bioinformatics Predictions of the Structural Domains in Honeybee Silk

Honeybee larvae produce a silk made up of proteins in predominantly a coiled coil molecular structure. These proteins can be produced in recombinant systems, making them desirable templates for the design of advanced materials. However, the atomic level structure of these proteins is proving difficult to determine: firstly, because coiled coils are difficult to crystalize; and secondly, fibrous proteins crystalize as fibres rather than as discrete protein units. In this study, we synthesised peptides from the central structural domain, as well as the N- and C-terminal domains, of the honeybee silk. We used circular dichroism spectroscopy, infrared spectroscopy, and molecular dynamics to investigate the folding behaviour of the central domain peptides. We found that they folded as predicted by bioinformatics analysis, giving the protein engineer confidence in bioinformatics predictions to guide the design of new functionality into these protein templates. These results, along with the infrared structural analysis of the N- and C-terminal domain peptides and the comparison of peptide film properties with those of the full-length AmelF3 protein, provided significant insight into the structural elements required for honeybee silk protein to form into stable materials.

Rational design of new materials using recombinant structural proteins: Current state and future challenges

Sequence-definable polymers are seen as a prerequisite for design of future materials, with many polymer scientists regarding such polymers as the holy grail of polymer science. Recombinant proteins are sequence-defined polymers. Proteins are dictated by DNA templates and therefore the sequence of amino acids in a protein is defined, and molecular biology provides tools that allow redesign of the DNA as required. Despite this advantage, proteins are underrepresented in materials science. In this publication we investigate the advantages and limitations of using proteins as templates for rational design of new materials.

Modification of Honeybee Silk by the Addition of Antimicrobial Agents

Honeybee silk proteins can be produced at high levels in recombinant systems, fabricated into materials, and are tolerant of amino acid modifications: properties that make them exciting templates for designing new functional materials. Here, we explore the properties of materials either made from silk-antimicrobial peptide (AMP) fusion proteins or silk containing entrapped AMPs or silver nanoparticles. Inclusion of AMP within the silk protein sequence did not affect our ability to express the proteins or process them into films. When AMP-silk proteins and Escherichia coli cells were coincubated in solution, a reduction in cell numbers was observed after degradation of the chimeric protein to release a truncated version of the AMP. In films, the AMP was retained in the silk with leaching rates of <1% per day. Films containing silver nanoparticles were antimicrobial, with the silk preventing aggregation of nanoparticles and slowing the rate of dissolution of the particles.

Recombinant Structural Proteins and Their Use in Future Materials

Recombinant proteins are polymers that offer the materials engineer absolute control over chain length and composition: key attributes required for design of advanced polymeric materials. Through this control, these polymers can be encoded to contain information that enables them to respond as the environment changes. However, despite their promise, protein-based materials are under-represented in materials science. In this chapter we investigate why this is and describe recent efforts to address this. We discuss constraints limiting rational design of structural proteins for advanced materials; advantages and disadvantages of different recombinant expression platforms; and, methods to fabricate proteins into solid-state materials. Finally, we describe the silk proteins used in our laboratory as templates for information-containing polymers.

Phosphorescent oxygen-sensing and singlet oxygen production by a biosynthetic silk

A recombinant coiled-coil silk was utilised to immobilise heavy-metal-macrocycles which are known to undergo efficient intersystem crossing from the singlet state to the triplet state following excitation with visible light.

More than one way to spin a crystallite: multiple trajectories through liquid crystallinity to solid silk

Arthropods face several key challenges in processing concentrated feedstocks of proteins (silk dope) into solid, semi-crystalline silk fibres. Strikingly, independently evolved lineages of silk-producing organisms have converged on the use of liquid crystal intermediates (mesophases) to reduce the viscosity of silk dope and assist the formation of supramolecular structure. However, the exact nature of the liquid-crystal-forming-units (mesogens) in silk dope, and the relationship between liquid crystallinity, protein structure and silk processing is yet to be fully elucidated. In this review, we focus on emerging differences in this area between the canonical silks containing extended-β-sheets made by silkworms and spiders, and 'non-canonical' silks made by other insect taxa in which the final crystallites are coiled-coils, collagen helices or cross-β-sheets. We compared the amino acid sequences and processing of natural, regenerated and recombinant silk proteins, finding that canonical and non-canonical silk proteins show marked differences in length, architecture, amino acid content and protein folding. Canonical silk proteins are long, flexible in solution and amphipathic; these features allow them both to form large, micelle-like mesogens in solution, and to transition to a crystallite-containing form due to mechanical deformation near the liquid-solid transition. By contrast, non-canonical silk proteins are short and have rod or lath-like structures that are well suited to act both as mesogens and as crystallites without a major intervening phase transition. Given many non-canonical silk proteins can be produced at high yield in E. coli, and that mesophase formation is a versatile way to direct numerous kinds of supramolecular structure, further elucidation of the natural processing of non-canonical silk proteins may to lead to new developments in the production of advanced protein materials.

Folding behavior of four silks of giant honey bee reflects the evolutionary conservation of aculeate silk proteins

Multiple gene duplication events in the precursor of the Aculeata (bees, ants, hornets) gave rise to four silk genes. Whilst these homologs encode proteins with similar amino acid composition and coiled coil structure, the retention of all four homologs implies they each are important. In this study we identified, produced and characterized the four silk proteins from Apis dorsata, the giant Asian honeybee. The proteins were readily purified, allowing us to investigate the folding behavior of solutions of individual proteins in comparison to mixtures of all four proteins at concentrations where they assemble into their native coiled coil structure. In contrast to solutions of any one protein type, solutions of a mixture of the four proteins formed coiled coils that were stable against dilution and detergent denaturation. The results are consistent with the formation of a heteromeric coiled coil protein complex. The mechanism of silk protein coiled coil formation and evolution is discussed in light of these results.

Stabilization of viruses by encapsulation in silk proteins

Viruses are important for a range of modern day applications. However, their utility is limited by their susceptibility to temperature degradation. In this study, we report a simple system to compare the ability of different dried protein films to stabilize viruses against exposure to elevated temperatures. Films from each of three different silks, silkworm, honeybee silk and hornet silk, stabilized entrapped viruses at 37 °C better than films of albumin from bovine serum (BSA) and all four proteins provided substantially more stabilization than no protein controls. A comparison of the molecular structure of the silks and BSA films showed no correlation between the ability of the proteins to stabilize the virus and the secondary structure of the protein in the films. The mechanism of stabilization is discussed and a hypothesis is suggested to explain the superior performance of the silk proteins.

Recombinant production and film properties of full-length hornet silk proteins

Full-length versions of the four main components of silk cocoons of Vespa simillima hornets, Vssilk1-4, were produced as recombinant proteins in Escherichia coli. In shake flasks, the recombinant Vssilk proteins yielded 160-330mg recombinant proteinl(-1). Films generated from solutions of single Vssilk proteins had a secondary structure similar to that of films generated from native hornet silk. The films made from individual recombinant hornet silk proteins had similar or enhanced mechanical performance compared with films generated from native hornet silk, possibly reflecting the homogeneity of the recombinant proteins. The pH-dependent changes in zeta (ζ) potential of each Vssilk film were measured, and isoelectric points (pI) of Vssilk1-4 were determined as 8.9, 9.1, 5.0 and 4.2, respectively. The pI of native hornet silk, a combination of the four Vssilk proteins, was 4.7, a value similar to that of Bombyx mori silkworm silk. Films generated from Vssilk1 and 2 had net positive charge under physiological conditions and showed significantly higher cell adhesion activity. It is proposed that recombinant hornet silk is a valuable new material with potential for cell culture applications.

Cross-linking in the silks of bees, ants and hornets

Silk production is integral to the construction of nests or cocoons for many Aculeata, stinging Hymenopterans such as ants, bees and wasps. Here we report the sequences of new aculeate silk proteins and compare cross-linking among nine native silks from three bee species (Apis mellifera, Bombus terrestris and Megachile rotundata), three ant species (Myrmecia forficata, Oecophylla smaragdina and Harpegnathos saltator) and three hornets (Vespa analis, Vespa simillima and Vespa mandarinia). The well studied silks of spiders and silkworms are comprised of large proteins that are cross-linked and stabilized predominantly by intra and intermolecular beta sheet structure. In contrast, the aculeate silks are comprised of relatively small proteins that contain central coiled coil domains and comparatively reduced amounts of beta sheet structure. The hornet silks, which have the most beta sheet structure and the greatest amount of amino acid sequence outside the coiled-coil domains, dissolve in concentrated LiBr solution and appear to be stabilized predominantly by beta sheet structure like the classic silks. In contrast, the ant and bee silks, which have less beta sheet and less sequence outside the coiled-coil domains, could not be dissolved in LiBr and appear to be predominantly stabilized by covalent cross-linking. The iso-peptide cross-linker, ε-(γ-glutamyl)-lysine that is produced by transglutaminase enzymes, was demonstrated to be present in all silks by mass spectrometry, but at greater levels in silks of ants and bees. The bee silks and ant cocoons, but not the Oecophylla nest silks, appeared to be further stabilized by tanning reactions.

A new class of animal collagen masquerading as an insect silk

Collagen is ubiquitous throughout the animal kingdom, where it comprises some 28 diverse molecules that form the extracellular matrix within organisms. In the 1960s, an extracorporeal animal collagen that forms the cocoon of a small group of hymenopteran insects was postulated. Here we categorically demonstrate that the larvae of a sawfly species produce silk from three small collagen proteins. The native proteins do not contain hydroxyproline, a post translational modification normally considered characteristic of animal collagens. The function of the proteins as silks explains their unusual collagen features. Recombinant proteins could be produced in standard bacterial expression systems and assembled into stable collagen molecules, opening the door to manufacture a new class of artificial collagen materials.

Silverfish silk is formed by entanglement of randomly coiled protein chains

Silks are semi-crystalline solids in which protein chains are associated by intermolecular hydrogen bonding within ordered crystallites, and by entanglement within unordered regions. By varying the type of protein secondary structure within crystallites and the overall degree of molecular order within fibers, arthropods produce fibers with a variety of physical properties suited to many purposes. We characterized silk produced as a tactile stimulus during mating by the grey silverfish (Ctenolepisma longicaudata) using Fourier transform infrared spectroscopy, polarized Raman spectroscopy, gel electrophoresis and amino acid analysis. Fibers were proteinaceous-the main component being a 220 kDa protein-and were rich in Gln/Glu, Leu, and Lys. The protein structure present was predominantly random coil, with a lesser amount of beta-structure. Silk fibers could readily be solubilized in aqueous solutions of a mild chaotrope, sodium dodecyl sulfate, indicating protein chains were not cross-linked by disulfide or other covalent bonds. We conclude that entanglement is the major mechanism by which these silk proteins cohere into a solid material. We propose silks used as short-term tactile cues are subject to less stringent requirements for molecular order relative to other silks, allowing the random coil structure to be favored as an adaptation promoting maximal entanglement and adhesion.

Controlling the molecular structure and physical properties of artificial honeybee silk by heating or by immersion in solvents

Honeybee larvae produce silken cocoons that provide mechanical stability to the hive. The silk proteins are small and non-repetitive and therefore can be produced at large scale by fermentation in E. coli. The recombinant proteins can be fabricated into a range of forms; however the resultant material is soluble in water and requires a post production stabilizing treatment. In this study, we describe the structural and mechanical properties of sponges fabricated from artificial honeybee silk proteins that have been stabilized in aqueous methanol baths or by dry heating. Aqueous methanol treatment induces formation of ß-sheets, with the amount of ß-sheet dictated by methanol concentration. Formation of ß-sheets renders sponges insoluble in water and generates a reversibly compressible material. Dry heat treatments at 190°C produce a water insoluble material, that is stiffer than the methanol treated equivalent but without significant secondary structural changes. Honeybee silk proteins are particularly high in Lys, Ser, Thr, Glu and Asp. The properties of the heat treated material are attributed to generation of lysinoalanine, amide (isopeptide) and/or ester covalent cross-links. The unique ability to stabilize material by controlling secondary structure rearrangement and covalent cross-linking allows us to design recombinant silk materials with a wide range of properties.

Silk from crickets: a new twist on spinning

Raspy crickets (Orthoptera: Gryllacrididae) are unique among the orthopterans in producing silk, which is used to build shelters. This work studied the material composition and the fabrication of cricket silk for the first time. We examined silk-webs produced in captivity, which comprised cylindrical fibers and flat films. Spectra obtained from micro-Raman experiments indicated that the silk is composed of protein, primarily in a beta-sheet conformation, and that fibers and films are almost identical in terms of amino acid composition and secondary structure. The primary sequences of four silk proteins were identified through a mass spectrometry/cDNA library approach. The most abundant silk protein was large in size (300 and 220 kDa variants), rich in alanine, glycine and serine, and contained repetitive sequence motifs; these are features which are shared with several known beta-sheet forming silk proteins. Convergent evolution at the molecular level contrasts with development by crickets of a novel mechanism for silk fabrication. After secretion of cricket silk proteins by the labial glands they are fabricated into mature silk by the labium-hypopharynx, which is modified to allow the controlled formation of either fibers or films. Protein folding into beta-sheet structure during silk fabrication is not driven by shear forces, as is reported for other silks.

Production, structure and in vitro degradation of electrospun honeybee silk nanofibers

Honeybees produce silken cocoons containing four related fibrous proteins. High levels of each of the honeybee silk proteins can be produced recombinantly by fermentation in Escherichia coli. In this study we have used electrospinning to fabricate a single recombinant honeybee silk protein, AmelF3, into nanofibers of around 200 nm diameter. Infrared spectroscopy found that the molecular structure of the nanofibers was predominantly coiled coil, essentially the same as native honeybee silk. Mats of the honeybee nanofibers were treated with methanol or by water annealing, which increased their β-sheet content and rendered them water insensitive. The insoluble mats were degraded by protease on a time scale of hours to days. The protease gradually released proteins from the solid state and these were subsequently rapidly degraded into small peptides without the accumulation of partial degradation products. Cell culture assays demonstrated that the mats allowed survival, attachment and proliferation of fibroblasts. These results indicate that honeybee silk proteins meet many prerequisites for use as a biomaterial.

Single honeybee silk protein mimics properties of multi-protein silk

Honeybee silk is composed of four fibrous proteins that, unlike other silks, are readily synthesized at full-length and high yield. The four silk genes have been conserved for over 150 million years in all investigated bee, ant and hornet species, implying a distinct functional role for each protein. However, the amino acid composition and molecular architecture of the proteins are similar, suggesting functional redundancy. In this study we compare materials generated from a single honeybee silk protein to materials containing all four recombinant proteins or to natural honeybee silk. We analyse solution conformation by dynamic light scattering and circular dichroism, solid state structure by Fourier Transform Infrared spectroscopy and Raman spectroscopy, and fiber tensile properties by stress-strain analysis. The results demonstrate that fibers artificially generated from a single recombinant silk protein can reproduce the structural and mechanical properties of the natural silk. The importance of the four protein complex found in natural silk may lie in biological silk storage or hierarchical self-assembly. The finding that the functional properties of the mature material can be achieved with a single protein greatly simplifies the route to production for artificial honeybee silk.

Dual structural color mechanisms in a scarab beetle

The cuticle of a Mycterophallus cetoniine scarab species displays both red iridescence due to a multilayer reflector mechanism and rainbow iridescence due to a superimposed diffraction grating mechanism. This is the first reported example of an animal possessing two independent classes of structural colors arising from interference at the wavelengths of visible light. In this work, the Mycterophallus cuticle is characterized by light microscopy, spectrophotometry, scanning electron microscopy, and transmission electron microscopy. We compare the cuticle of the Mycterophallus species to two closely related Lomaptera scarab species, one with only a multilayer reflector and the second with only a diffraction grating. We calculate the correspondence between the nanostructural parameters and the optical properties of the Mycterophallus cuticle to determine the relative optical contributions of the two color mechanisms and the interactions between them.

Harnessing disorder: onychophorans use highly unstructured proteins, not silks, for prey capture

Onychophora are ancient, carnivorous soft-bodied invertebrates which capture their prey in slime that originates from dedicated glands located on either side of the head. While the biochemical composition of the slime is known, its unusual nature and the mechanism of ensnaring thread formation have remained elusive. We have examined gene expression in the slime gland from an Australian onychophoran, Euperipatoides rowelli, and matched expressed sequence tags to separated proteins from the slime. The analysis revealed three categories of protein present: unique high-molecular-weight proline-rich proteins, and smaller concentrations of lectins and small peptides, the latter two likely to act as protease inhibitors and antimicrobial agents. The predominant proline-rich proteins (200 kDa+) are composed of tandem repeated motifs and distinguished by an unusually high proline and charged residue content. Unlike the highly structured proteins such as silks used for prey capture by spiders and insects, these proteins lack ordered secondary structure over their entire length. We propose that on expulsion of slime from the gland onto prey, evaporative water loss triggers a glass transition change in the protein solution, resulting in adhesive and enmeshing thread formation, assisted by cross-linking of complementary charged and hydrophobic regions of the protein. Euperipatoides rowelli has developed an entirely new method of capturing prey by harnessing disordered proteins rather than structured, silk-like proteins.

Insect silk: one name, many materials

Silks play a crucial role in the survival and reproduction of many insects. Labial glands, Malpighian tubules, and a variety of dermal glands have evolved to produce these silks. The glands synthesize silk proteins, which become semicrystalline when formed into fibers. Although each silk contains one dominant crystalline structure, the range of molecular structures that can form silk fibers is greater than any other structural protein group. On the basis of silk gland type, silk protein molecular structure, and the phylogenetic relationship of silk-producing species, we grouped insect silks into 23 distinct categories, each likely to represent an independent evolutionary event. Despite having diverse functions and fundamentally different protein structures, these silks typically have high levels of protein crystallinity and similar amino acid compositions. The substantial crystalline content confers extraordinary mechanical properties and stability to silk and appears to be required for production of fine protein fibers.

An unlikely silk: the composite material of green lacewing cocoons

Spiders routinely produce multiple types of silk; however, common wisdom has held that insect species produce one type of silk each. This work reports that the green lacewing ( Mallada signata, Neuroptera) produces two distinct classes of silk. We identified and sequenced the gene that encodes the major protein component of the larval lacewing cocoon silk and demonstrated that it is unrelated to the adult lacewing egg-stalk silk. The cocoon silk protein is 49 kDa in size and is alanine rich (>40%), and it contains an alpha-helical secondary structure. The final instar lacewing larvae spin protein fibers of approximately 2 microm diameter to construct a loosely woven cocoon. In a second stage of cocoon construction, the insects lay down an inner wall of lipids that uses the fibers as a scaffold. We propose that the silk protein fibers provide the mechanical strength of the composite lacewing cocoon whereas the lipid layer provides a barrier to water loss during pupation.

An Australian webspinner species makes the finest known insect silk fibers

Aposthonia gurneyi, an Australian webspinner species, is a primitive insect that constructs and lives in a silken tunnel which screens it from the attentions of predators. The insect spins silk threads from many tiny spines on its forelegs to weave a filmy sheet. We found that the webspinner silk fibers have a mean diameter of only 65 nm, an order of magnitude smaller than any previously reported insect silk. The purpose of such fine silk may be to reduce the metabolic cost of building the extensive tunnels. At the molecular level, the A. gurneyi silk has a predominantly beta-sheet protein structure. The most abundant clone in a cDNA library produced from the webspinner silk glands encoded a protein with extensive glycine-serine repeat regions. The GSGSGS repeat motif of the A. gurneyi silk protein is similar to the well-known GAGAGS repeat motif found in the heavy fibroin of silkworm silk, which also has beta-sheet structure. As the webspinner silk gene is unrelated to the silk gene of the phylogenetically distant silkworm, this is a striking example of convergent evolution.

OpdA, a bacterial organophosphorus hydrolase, prevents lethality in rats after poisoning with highly toxic organophosphorus pesticides

Organophosphorus (OP) pesticides poison more than 3,000,000 people every year in the developing world, mostly through intentional self-poisoning. Advances in medical therapy for OP poisoning have lagged, and current treatment is not highly effective with mortality of up to 40% in even the most advanced Western medical facilities. Administration of a broadly active bacterial OP hydrolase to patients in order to hydrolyze OPs in circulation might allow current therapies to be more effective. The objective of this work was to evaluate the efficacy of a new recombinant bacterial OP hydrolase (OpdA), cloned from Agrobacterium radiobacter, in rat models of two chemically distinct but highly toxic and rapidly acting OP pesticides: dichlorvos and parathion. Without OpdA treatment, median time to death in rats poisoned with 3x LD(50) of dichlorvos or parathion was 6 min and 25.5 min, respectively. Administration of a single dose of OpdA immediately after dichlorvos resulted in 100% survival at 24h, with no additional antidotal therapy. After parathion poisoning, OpdA alone caused only a delay to death. However, an additional two doses of OpdA resulted in 62.5% survival at 24 h after parathion poisoning. In combination with pralidoxime therapy, a single dose of OpdA increased survival to 75% after parathion poisoning. Our results demonstrate that OpdA is able to improve survival after poisoning by two chemically distinct and highly toxic OP pesticides.

Jhe in Gryllus assimilis: cloning, sequence-activity associations and phylogeny

The 458 amino acid sequence of a mature JHE protein from the cricket Gryllus assimilis was identified after isolating the partial cDNA sequence encoding this protein from a fat body and midgut cDNA library. This hemimetabolan JHE sequence shows over 40% amino acid similarity to the known JHE sequences of several holometabolous insects. It also includes previously determined peptide sequences for G. assimilis JHE as well as two other motifs associated with JHE enzymes in holometabolous insects. The predicted molecular weight of the protein agrees with that of the JHE previously purified from G. assimilis. Partial genomic sequence encoding the Jhe contains two large (1330 and 2918bp) introns. No coding DNA sequence variation was observed over a 1293bp region between selected lines differing six to eight-fold in hemolymph JHE activity. However, a 19bp indel was found in one of the introns; the insertion was strongly associated with elevated hemolymph activity, both in the selected lines and in the F(2) progeny of crosses between them. Phylogenetic analyses localised the G. assimilis JHE to a clade containing dipteran and coleopteran JHEs, with lepidopteran JHEs occurring in a separate clade.

An independently evolved Dipteran silk with features common to Lepidopteran silks

Male hilarine flies (Diptera: Empididae: Empidinae) present prospective mates with silk-wrapped gifts. The silk is produced by specialised cells located in the foreleg basitarsus of the fly. In this report, we describe 2.3 kbp of the silk gene from a hilarine fly (Hilara spp.) that was identified from highly expressed mRNA extracted from the prothoracic basitarsus of males. Using specific primers, we found that the silk gene is expressed in the basitarsi and not in any other part of the male fly. The silk gene from the basitarsi cDNA library matched an approximately 220 kDa protein from the silk-producing basitarsus. Although the predicted silk protein sequence was unlike any other protein sequence in available databases, the architecture and composition of the predicted protein had features in common with previously described silks. The convergent evolution of these features in the Hilarini silk and other silks emphasises their importance in the functional requirements of silk proteins.

Conservation of Essential Design Features in Coiled Coil Silks

Silks are strong protein fibers produced by a broad array of spiders and insects. The vast majority of known silks are large, repetitive proteins assembled into extended beta-sheet structures. Honeybees, however, have found a radically different evolutionary solution to the need for a building material. The 4 fibrous proteins of honeybee silk are small ( approximately 30 kDa each) and nonrepetitive and adopt a coiled coil structure. We examined silks from the 3 superfamilies of the Aculeata (Hymenoptera: Apocrita) by infrared spectroscopy and found coiled coil structure in bees (Apoidea) and in ants (Vespoidea) but not in parasitic wasps of the Chrysidoidea. We subsequently identified and sequenced the silk genes of bumblebees, bulldog ants, and weaver ants and compared these with honeybee silk genes. Each species produced orthologues of the 4 small fibroin proteins identified in honeybee silk. Each fibroin contained a continuous predicted coiled coil region of around 210 residues, flanked by 23-160 residue length N- and C-termini. The cores of the coiled coils were unusually rich in alanine. There was extensive sequence divergence among the bee and ant silk genes (<50% similarity between the alignable regions of bee and ant sequences), consistent with constant and equivalent divergence since the bee/ant split (estimated to be 155 Myr). Despite a high background level of sequence diversity, we have identified conserved design elements that we propose are essential to the assembly and function of coiled coil silks.

Only one esterase of Drosophila melanogaster is likely to degrade juvenile hormone in vivo

Previously we identified juvenile hormone esterase (JHE) from Drosophila melanogaster by the criteria that it showed both appropriate developmental expression and kinetics for juvenile hormone (JH). We also noted three further esterases of D. melanogaster with some JHE-like characteristics, such as a GQSAG active site motif, a particular amphipathic helix, or close phylogenetic relationship with other JHEs. In this study, these JHE-like enzymes were expressed in vitro and their kinetic parameters compared with those of the previously identified JHE. Despite considerable phylogenetic distance between some of the esterases, they could all hydrolyse racemic JHIII. However, only the previously identified JHE had kinetic parameters (K(M) and k(cat)) towards various forms of JH (racemic or individual isomers of JHIII, JHII, JHI, and methyl farnesoate) consistent with a physiological role in JH regulation. Furthermore, only this JHE showed a preference for artificial substrates with acyl chain lengths similar to that of JH. This suggests that there is probably only one physiologically functional JHE in D. melanogaster but multiple esterases with JH esterase activity. Genomic comparisons of the selective JHE across 11 other Drosophila species showed a single orthologue in 10 of them but Drosophila willistoni has 16 full-length copies, five of them with the GQSAG motif and amphipathic helix.

A global response to sulfur starvation in Pseudomonas putida and its relationship to the expression of low-sulfur-content proteins

Sulfur is essential for life on Earth, but its availability is limited in many environments. Here the sulfur-starvation response of the model soil bacterium Pseudomonas putida KT2440 is shown to be associated with an approximately fivefold reduction in the total soluble thiol content of the cell. A bioinformatic survey of the P. putida KT2440 genome identified 646 genes encoding proteins with a significantly lower than average sulfur content (low sulfur-content proteins, LSPs), the expression of which may have a role in the global reduction of cellular thiol content during sulfur starvation. Analysis of the genetic organization of the LSP-encoding genes showed that 31% were potentially transcriptionally associated with at least one other gene encoding a protein defined as an LSP. In particular, 55 LSP genes were located in three large clusters, termed low-sulfur islands (LSIs) here. The predicted identities of the proteins encoded by the LSIs strongly suggest that the LSIs have a role in acquiring sulfur from organic sulfur sources during sulfur starvation. This hypothesis was supported by transcription fusion studies on a limited number of LSP promoters under low-sulfur conditions. In a wider survey of bacterial species, LSIs were found to be more prevalent in free-living, Gram-negative bacteria than in Gram-positive or obligately intracellular bacteria.

A highly divergent gene cluster in honey bees encodes a novel silk family

The pupal cocoon of the domesticated silk moth Bombyx mori is the best known and most extensively studied insect silk. It is not widely known that Apis mellifera larvae also produce silk. We have used a combination of genomic and proteomic techniques to identify four honey bee fiber genes (AmelFibroin1-4) and two silk-associated genes (AmelSA1 and 2). The four fiber genes are small, comprise a single exon each, and are clustered on a short genomic region where the open reading frames are GC-rich amid low GC intergenic regions. The genes encode similar proteins that are highly helical and predicted to form unusually tight coiled coils. Despite the similarity in size, structure, and composition of the encoded proteins, the genes have low primary sequence identity. We propose that the four fiber genes have arisen from gene duplication events but have subsequently diverged significantly. The silk-associated genes encode proteins likely to act as a glue (AmelSA1) and involved in silk processing (AmelSA2). Although the silks of honey bees and silkmoths both originate in larval labial glands, the silk proteins are completely different in their primary, secondary, and tertiary structures as well as the genomic arrangement of the genes encoding them. This implies independent evolutionary origins for these functionally related proteins.

A single monooxygenase, ese, is involved in the metabolism of the organochlorides endosulfan and endosulfate in an Arthrobacter sp

In this paper we describe isolation of a bacterium capable of degrading both isomers of the organochloride insecticide endosulfan and its toxic metabolite, endosulfate. The bacterium was isolated from a soil microbial population that was enriched with continuous pressure to use endosulfate as the sole source of sulfur. Analysis of the 16S rRNA sequence of the bacterium indicated that it was an Arthrobacter species. The organochloride-degrading activity was not observed in the presence of sodium sulfite as an alternative sulfur source, suggesting that the activity was part of the sulfur starvation response of the strain. A gene, ese, encoding an enzyme capable of degrading both isomers of endosulfan and endosulfate was isolated from this bacterium. The enzyme belongs to the two-component flavin-dependent monooxygenase family whose members require reduced flavin for activity. Nuclear magnetic resonance analyses identified the metabolite of endosulfan as endosulfan monoalcohol and the metabolite of endosulfate as endosulfan hemisulfate. The ese gene was located in a cluster of 10 open reading frames encoding proteins with low levels of sulfur-containing amino acids. These open reading frames were organized into two apparent divergently orientated operons and a gene encoding a putative LysR-type transcriptional regulator. The operon not containing ese did contain a homologue whose product exhibited 62% amino acid identity to the ese-encoded protein.

Comparing the organophosphorus and carbamate insecticide resistance mutations in cholin- and carboxyl-esterases

Mutant insect carboxyl/cholinesterases underlie over 60 cases of resistance to organophosphorus and/or carbamate insecticides. Biochemical and molecular data on about 20 of these show recurrent use of a very small number of mutational options to generate either target site or metabolic resistance. Moreover, the mutant enzymes are often kinetically inefficient and associated with significant fitness costs, due to impaired performance of the enzymes' original function. By contrast many bacterial enzymes are now known which can effectively detoxify these pesticides. It appears that the constraints of the genetic code and eukaryote genetic systems have severely limited the evolutionary response of insects to the widespread use of the insecticides over the last 60 years.

A Brevibacillus choshinensis System That Secretes Cytoplasmic Proteins

Brevibacillus choshinensis has previously been shown to be a useful strain for the secretion of heterologous proteins via the Sec secretory pathway. This pathway involves the secretion of proteins prior to folding, whereas the alternative TAT (twin-arginine translocation) pathway enables pre-folded proteins to be secreted. We have modified the signal peptide of the Brevibacillus expression vector pNCMO2 to accommodate a Sec avoidance signal as well as the twin arginines required for secretion via the TAT system. Use of this modified signal peptide with the phosphotriesterase OpdA enabled B. choshinensis transformants to express and secrete the enzyme in an active and substantially pure form. The system was also used successfully to secrete two cytoplasmic proteins, the phosphotriesterase HocA from Pseudomonas monteilii and the phenylcarbamate-degrading enzyme, PCD, from Arthrobacter oxydans. The inhibitors carbonyl cyanide m-chlorophenyl hydrazine and sodium azide were used to confirm that secretion was occurring via the TAT secretion pathway. The modified B. choshinensis system we have developed may have general utility in secreting a wide range of heterologous proteins in active and conveniently processed form.