A bioinspired snap-through metastructure for manipulating micro-objects

Micro-objects stick tenaciously to each other-a well-known show-stopper in microtechnology and in handling micro-objects. Inspired by the trigger plant, we explore a mechanical metastructure for overcoming adhesion involving a snap-action mechanism. We analyze the nonlinear mechanical response of curved beam architectures clamped by a tunable spring, incorporating mono- and bistable states. As a result, reversible miniaturized snap-through devices are successfully realized by micron-scale direct printing, and successful pick-and-place handling of a micro-object is demonstrated. The technique is applicable to universal scenarios, including dry and wet environment, or smooth and rough counter surfaces. With an unprecedented switching ratio (between high and low adhesion) exceeding 10⁴, this concept proposes an efficient paradigm for handling and placing superlight objects.

Film-Terminated Fibrillar Microstructures with Improved Adhesion on Skin-like Surfaces

Adhesives for interaction with human skin and tissues are needed for multiple applications. Micropatterned dry adhesives are potential candidates, allowing for a conformal contact and glue-free adhesion based on van der Waals interactions. In this study, we investigate the superior adhesion of film-terminated fibrillar microstructures (fibril diameter, 60 μm; aspect ratio, 3) in contact with surfaces of skin-like roughness (Rz 50 μm). Adhesion decays only moderately with increasing roughness, in contrast to unstructured samples. Sinusoidal model surfaces adhere when their wavelengths exceed about four fibril diameters. The film-terminated microstructure exhibits a saturation of the compressive force during application, implying a pressure safety regime protecting delicate counter surfaces. Applications of this novel adhesive concept are foreseen in the fields of wearable electronics and wound dressing.

Attachment of bioinspired microfibrils in fluids: transition from a hydrodynamic to hydrostatic mechanism

Reversible and switchable adhesion of elastomeric microstructures has attracted significant interest in the development of grippers for object manipulation. Their applications, however, have often been limited to dry conditions and adhesion of such deformable microfibrils in the fluid environment is less understood. In the present study, we performed adhesion tests in silicone oil using single cylindrical microfibrils of a flat-punch shape with a radius of 80 µm. Stiff fibrils were created using three-dimensional printing of an elastomeric resin with an elastic modulus of 500 MPa, and soft fibrils, with a modulus of 3.3 MPa, were moulded in polyurethane. Our results suggest that adhesion is dominated by hydrodynamic forces, which can be maximized by stiff materials and high retraction velocities, in line with theoretical predictions. The maximum pull-off stress of stiff cylindrical fibrils is 0.6 MPa, limited by cavitation and viscous fingering, occurring at retraction velocities greater than 2 µm s^-1. Next, we add a mushroom cap to the microfibrils, which, in the case of the softer material, deforms upon retraction and leads to a transition to a hydrostatic suction regime with higher pull-off stresses ranging from 0.7 to 0.9 MPa. The effects of elastic modulus, fibril size and viscosity for underwater applications are illustrated in a mechanism map to provide guidance for design optimization.

Water as a "glue": Elasticity-enhanced wet attachment of biomimetic microcup structures

Octopus, clingfish, and larva use soft cups to attach to surfaces under water. Recently, various bioinspired cups have been engineered. However, the mechanisms of their attachment and detachment remain elusive. Using a novel microcup, fabricated by two-photon lithography, coupled with in situ pressure sensor and observation cameras, we reveal the detailed nature of its attachment/detachment under water. It involves elasticity-enhanced hydrodynamics generating "self-sealing" and high suction at the cup-substrate interface, converting water into "glue." Detachment is mediated by seal breaking. Three distinct mechanisms of breaking are identified, including elastic buckling of the cup rim. A mathematical model describes the interplay between the attachment/detachment process, geometry, elasto-hydrodynamics, and cup retraction speed. If the speed is too slow, then the octopus cannot attach; if the tide is too gentle for the larva, then water cannot serve as a glue. The concept of "water glue" can innovate underwater transport and manufacturing strategies.

Preventing Catastrophic Failure of Microfibrillar Adhesives in Compliant Systems Based on Statistical Analysis of Adhesive Strength

Adhesives based on fibrillar surface microstructures have shown great potential for handling applications requiring strong, reversible, and switchable adhesion. Recently, the importance of the statistical distribution of adhesive strength of individual fibrils in controlling the overall performance was revealed. Strength variations physically correspond to different interfacial defect sizes, which, among other factors, are related to surface roughness. For analysis of the strength distribution, Weibull's statistical theory of fracture was introduced. In this study, the importance of the statistical properties in controlling the stability of attachment is explored. Considering the compliance of the loading system, we develop a stability criterion based on the Weibull statistical parameters. It is shown that when the distribution in fibril adhesive strength is narrow, the global strength is higher but unstable detachment is more likely. Experimental variation of the loading system compliance for a specimen of differing statistical properties shows a transition to unstable detachment at low system stiffness, in good agreement with the theoretical stability map. This map serves to inform the design of gripper compliance, when coupled with statistical analysis of strength on the target surface of interest. Such a treatment could prevent catastrophic failure by spontaneous detachment of an object from an adhesive gripper.

Elastohydrodynamic Dewetting of Thin Liquid Films: Elucidating Underwater Adhesion of Topographically Patterned Surfaces

In underwater adhesion of a topographically patterned surface with a very soft material such as human skin, the elastic deformation can be large enough to achieve solid-on-solid contact not only on top of the hills but also in the valleys of the substrate topography. In this context, we have studied the dynamics of dewetting of a thin liquid film confined between a rigid, periodic micropillar array and a soft, elastic sphere. In our experiments, we observed two very distinct dewetting morphologies. For large ratios of array period to micropillar height and width, the dewetted areas tend to have a diamond-like shape and expand with a rate similar to a flat, unpatterned substrate. When the array period is reduced, the morphology of the dry spot becomes irregular and its expansion rate is significantly reduced. We developed a fully coupled numerical model of the dewetting process that reproduces the key features observed in experiments. Moreover, we performed contact mechanics simulations to characterize the deformation of the elastomer and the shape of the dewetted area in a unit cell of the micropillar array.

Enhancing Dry Adhesion of Polymeric Micropatterns by Electric Fields

Micropatterned dry adhesives rely mainly on van der Waals interactions. In this paper, we explore the adhesion strength increase that can be achieved by superimposing an electrostatic field through interdigitated subsurface electrodes. Micropatterns were produced by replica molding in silicone. The adhesion forces were characterized systematically by means of experiments and numerical modeling. The force increased with the square of the applied voltage for electric fields up to 800 V. For larger fields, a less-than-quadratic scaling was observed, which is likely due to the small, field-dependent electrical conductivity of the materials involved. The additional adhesion force was found to be up to twice of the field-free adhesion. The results suggest an alternative method for the controlled handling of fragile or miniaturized objects.

Statistical properties of defect-dependent detachment strength in bioinspired dry adhesives

Dry adhesives using surface microstructures inspired by climbing animals have been recognized for their potentially novel capabilities, with relevance to a range of applications including pick-and-place handling. Past work has suggested that performance may be strongly dependent on variability in the critical defect size among fibrillar sub-contacts. However, it has not been directly verified that the resulting adhesive strength distribution is well described by the statistical theory of fracture used. Using in situ contact visualization, we characterize adhesive strength on a fibril-by-fibril basis for a synthetic fibrillar adhesive. Two distinct detachment mechanisms are observed. The fundamental, design-dependent mechanism involves defect propagation from within the contact. The secondary mechanism involves defect propagation from fabrication imperfections at the perimeter. The existence of two defect populations complicates characterization of the statistical properties. This is addressed by using the mean order ranking method to isolate the fundamental mechanism. The statistical properties obtained are subsequently used within a bimodal framework, allowing description of the secondary mechanism. Implications for performance are discussed, including the improvement of strength associated with elimination of fabrication imperfections. This statistical analysis of defect-dependent detachment represents a more complete approach to the characterization of fibrillar adhesives, offering new insight for design and fabrication.

Strong Wet and Dry Adhesion by Cupped Microstructures

Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design-cupped microstructures (CM)-that generates strong controllable adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an adhesion strength (force per real contact area) of up to 1.3 MPa, but underwater, 15°CM achieved 20 times stronger adhesion than MSM (∼1 MPa versus ∼0.05 MPa). Furthermore, the cupped microstructures exhibit self-sealing properties, whereby stronger pulls lead to longer stable attachment and much higher adhesion through the formation of a better seal.

Roll-to-Roll Manufacturing of Micropatterned Adhesives by Template Compression

For the next generation of handling systems, reversible adhesion enabled by micropatterned dry adhesives exhibits high potential. The versatility of polymeric micropatterns in handling objects made from various materials has been demonstrated by several groups. However, specimens reported in most studies have been restricted to the laboratory scale. Upscaling the size and quantity of micropatterned adhesives is the next step to enable successful technology transfer. Towards this aim, we introduce a continuous roll-to-roll replication process for fabrication of high-performance, mushroom-shaped micropatterned dry adhesives. The micropatterns were made from UV-curable polyurethane acrylates. To ensure the integrity of the complex structure during the fabrication process, flexible templates were used. The compression between the template and the wet prepolymer coating was investigated to optimize replication results without structural failures, and hence, to improve adhesion. As a result, we obtained micropatterned adhesive tapes, 10 cm in width and several meters in length, with adhesion strength about 250 kPa to glass, suitable for a wide range of applications.

Adhesion and relaxation of a soft elastomer on surfaces with skin like roughness

For designing new skin adhesives, the complex mechanical interaction of soft elastomers with surfaces of various roughnesses needs to be better understood. We systematically studied the effects of a wide set of roughness characteristics, film thickness, hold time and material relaxation on the adhesive behaviour of the silicone elastomer SSA 7-9800 (Dow Corning). As model surfaces, we used epoxy replicas obtained from substrates with roughness ranging from very smooth to skin-like. Our results demonstrate that films of thin and intermediate thickness (60 and 160 µm) adhered best to a sub-micron rough surface, with a pull-off stress of about 50 kPa. Significant variations in pull-off stress and detachment mechanism with roughness and hold time were found. In contrast, 320 µm thick films adhered with lower pull-off stress of about 17 kPa, but were less sensitive to roughness and hold time. It is demonstrated that the adhesion performance of the silicone films to rough surfaces can be tuned by tailoring the film thickness and contact time.

Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates

The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young's moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent.

The multi-layered protective cuticle of Collembola: a chemical analysis

Collembola, also known as springtails, are soil-dwelling arthropods that typically respire through the cuticle. To avoid suffocating in wet conditions, Collembola have evolved a complex, hierarchically nanostructured, cuticle surface that repels water with remarkable efficiency. In order to gain a more profound understanding of the cuticle characteristics, the chemical composition and architecture of the cuticle of Tetrodontophora bielanensis was studied. A stepwise removal of the different cuticle layers enabled controlled access to each layer that could be analysed separately by chemical spectrometry methods and electron microscopy. We found a cuticle composition that consisted of three characteristic layers, namely, a chitin-rich lamellar base structure overlaid by protein-rich nanostructures, and a lipid-rich envelope. The specific functions, composition and biological characteristics of each cuticle layer are discussed with respect to adaptations of Collembola to their soil habitat. It was found that the non-wetting characteristics base on a rather typical arthropod cuticle surface chemistry which confirms the decisive role of the cuticle topography.

The springtail cuticle as a blueprint for omniphobic surfaces

Omniphobic surfaces found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies. One example is the water and even oil-repellent cuticle of springtails (Collembola). The wingless arthropods evolved a highly textured, hierarchically arranged surface pattern that affords mechanical robustness and wetting resistance even at elevated hydrostatic pressures. Springtail cuticle-derived surfaces therefore promise to overcome limitations of lotus-inspired surfaces (low durability, insufficient repellence of low surface tension liquids). In this review, we report on the liquid-repellent natural surfaces of arthropods living in aqueous or temporarily flooded habitats including water-walking insects or water spiders. In particular, we focus on springtails presenting an overview on the cuticular morphology and chemistry and their biological relevance. Based on the obtained liquid repellence of a variety of liquids with remarkable efficiency, the review provides general design criteria for robust omniphobic surfaces. In particular, the resistance against complete wetting and the mechanical stability strongly both depend on the topographical features of the nano- and micropatterned surface. The current understanding of the underlying principles and approaches to their technological implementation are summarized and discussed.

In situ experiments to reveal the role of surface feature sidewalls in the Cassie-Wenzel transition

Waterproof and self-cleaning surfaces continue to attract much attention as they can be instrumental in various different technologies. Such surfaces are typically rough, allowing liquids to contact only the outermost tops of their asperities, with air being entrapped underneath. The formed solid-liquid-air interface is metastable and, hence, can be forced into a completely wetted solid surface. A detailed understanding of the wetting barrier and the dynamics of this transition is critically important for the practical use of the related surfaces. Toward this aim, wetting transitions were studied in situ at a set of patterned perfluoropolyether dimethacrylate (PFPEdma) polymer surfaces exhibiting surface features with different types of sidewall profiles. PFPEdma is intrinsically hydrophobic and exhibits a refractive index very similar to water. Upon immersion of the patterned surfaces into water, incident light was differently scattered at the solid-liquid-air and solid-liquid interface, which allows for distinguishing between both wetting states by dark-field microscopy. The wetting transition observed with this methodology was found to be determined by the sidewall profiles of the patterned structures. Partial recovery of the wetting was demonstrated to be induced by abrupt and continuous pressure reductions. A theoretical model based on Laplace's law was developed and applied, allowing for the analytical calculation of the transition barrier and the potential to revert the wetting upon pressure reduction.

Directed assembly of nanoparticles to isolated diatom valves using the non-wetting characteristics after pyrolysis

A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is presented. After pyrolysis, the valves exhibit incomplete wetting due to their characteristic T-shaped profiles as a prerequisite for a regioselective coupling reaction. A micromanipulation system allows for precise handling and their immobilization onto an adhesive substrate and manipulation into arrays.

Biologically inspired omniphobic surfaces by reverse imprint lithography

Springtail skin morphology is translated into robust omniphobic polymer membranes by reverse imprint lithography. The combination of overhanging cross-sections and their arrangement in a self-supporting comblike pattern are crucial for mechanically stable coatings that can be even applied to curved surfaces.

Wetting resistance at its topographical limit: the benefit of mushroom and serif T structures

Springtails (Collembola) are wingless arthropods adapted to cutaneous respiration in temporarily rain-flooded habitats. They immediately form a plastron, protecting them against suffocation upon immersion into water and even low-surface-tension liquids such as alkanes. Recent experimental studies revealed a high-pressure resistance of such plastrons against collapse. In this work, skin sections of Orthonychiurus stachianus are studied by transmission electron microscopy. The micrographs reveal cavity side-wall profiles with characteristic overhangs. These were fitted by polynomials to allow access for analytical and numerical calculations of the breakthrough pressure, that is, the barrier against plastron collapse. Furthermore, model profiles with well-defined geometries were used to set the obtained results into context and to develop a general design principle for the most robust surface structures. Our results indicate the decisive role of the sectional profile of overhanging structures to form a robust heterogeneous wetting state for low-surface-tension liquids that enables the omniphobicity. Furthermore, the design principles of mushroom and serif T structures pave the way for omniphobic surfaces with a high-pressure resistance irrespective of solid surface chemistry.

Structure, function and evolution of the Archaeal class I fructose-1,6-bisphosphate aldolase

FBPA (fructose-1,6-bisphosphate aldolase) catalyses the reversible aldol condensation of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate to form fructose 1,6-bisphosphate. Two classes of FBPA, which rely on different reaction mechanisms, have so far been discovered, class I mainly found in Eucarya and class II mainly in Bacteria. Only recently were genes encoding proteins with FBPA activity identified in Archaea. Archaeal FBPAs do not share any significant overall sequence identity with members of the traditional classes of FBPAs, raising the interesting question of whether they have evolved independently by convergent evolution or diverged from a common ancestor. Biochemical characterization of FBPAs of the two hyperthermophilic Archaea Thermoproteus tenax and Pyrococcus furiosus showed that the enzymes use a Schiff-base mechanism and thus belong to the class I aldolases. The crystal structure of the archaeal FBPA from T. tenax revealed that the protein fold, as for the classical FBPA I and II, is that of a parallel (betaalpha)(8) barrel. A substrate-bound crystal structure allowed detailed active-site comparisons which showed the conservation of six important catalytic and substrate-binding residues between the archaeal and the classical FBPA I. This observation provides further evidence that the two sequence families of proteins share a common evolutionary origin. Furthermore, structure and sequence analysis indicate that the class I FBPA shares a common evolutionary origin with several other enzyme superfamilies of the (betaalpha)(8) barrel fold.

Embden-Meyerhof-Parnas and Entner-Doudoroff pathways in Thermoproteus tenax: metabolic parallelism or specific adaptation?

Genome data as well as biochemical studies have indicated that--as a peculiarity within hyperthermophilic Archaea--Thermoproteus tenax uses three different pathways for glucose metabolism, a variant of the reversible EMP (Embden-Meyerhof-Parnas) pathway and two different modifications of the ED (Entner-Doudoroff) pathway, a non-phosphorylative and a semi-phosphorylative version. An overview of the three different pathways is presented and the physiological function of the variants is discussed.

Triosephosphate isomerase of the hyperthermophile Thermoproteus tenax: thermostability is not everything

The triosephosphate isomerase of the hyperthermophilic crenarchaeum Thermoproteus tenax (TtxTIM) represents a homomeric tetramer. Unlike the triosephosphate isomerases of other hyperthermophiles, however, the association of the TtxTIM tetramers is looser, allowing a reversible dissociation into inactive dimers. The dimer/tetramer equilibrium of TtxTIM is shifted to the tetrameric state through a specific interaction with glycerol-1-phosphate dehydrogenase of T. tenax, suggesting that higher oligomerization of the TtxTIM serves functional rather than stabilizing purposes.

Role of two different glyceraldehyde-3-phosphate dehydrogenases in controlling the reversible Embden-Meyerhof-Parnas pathway in Thermoproteus tenax: regulation on protein and transcript level

The hyperthermophilic archaeum Thermoproteus tenax uses a variant of the Embden-Meyerhof-Parnas (EMP) pathway as the main route for carbohydrate metabolism. This variant is characterized by a reversible nonallosteric PPi-dependent phosphofructokinase and two glyceraldehyde-3-phosphate dehydrogenases differing in cosubstrate specificity, phosphate dependence, and allosteric behavior. Although the nonphosphorylating NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN; E.C. 1.2.1.8) fulfills exclusively catabolic purposes, the phosphorylating NADP+-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP+-GAPDH; E.C. 1.2.1.13) exhibits anabolic features. The gene encoding the NADP+-GAPDH was cloned, sequenced, and expressed in Escherichia coli. The deduced protein sequence displayed 47%-53% sequence identity to archaeal phosphorylating GAPDHs. The kinetic parameters of the NADP+-GAPDH showed a clear preference for the reductive reaction with a 5-fold-higher specific activity in the reductive reaction as compared to the oxidative reaction and a 20-fold-lower Km for 1,3-bisphosphoglycerate as compared to glyceraldehyde-3-phosphate. Contrary to GAPN, the enzyme is not allosterically regulated. The coding gene overlaps by 1 bp with a preceding open reading frame coding for 3-phosphoglycerate kinase (PGK; E.C. 2.7.2.3). Northern analyses identified mono- and bicistronic messages of both genes in an equimolar ratio. Transcript levels and specific activity of NADP+-GAPDH and PGK were 3- to 4-fold higher under autotrophic conditions as compared to heterotrophic conditions, whereas transcript abundance and specific activity of GAPN remained constant in autotrophically and heterotrophically grown cells. The different regulation of the two counteracting glyceraldehyde-3-phosphate dehydrogenases is discussed with respect to the flux control of the T. tenax-specific EMP variant.

Tiny TIM: a small, tetrameric, hyperthermostable triosephosphate isomerase

Comparative structural studies on proteins derived from organisms with growth optima ranging from 15 to 100 degrees C are beginning to shed light on the mechanisms of protein thermoadaptation. One means of sustaining hyperthermostability is for proteins to exist in higher oligomeric forms than their mesophilic homologues. Triosephosphate isomerase (TIM) is one of the most studied enzymes, whose fold represents one of nature's most common protein architectures. Most TIMs are dimers of approximately 250 amino acid residues per monomer. Here, we report the 2.7 A resolution crystal structure of the extremely thermostable TIM from Pyrococcus woesei, a hyperthermophilic archaeon growing optimally at 100 degrees C, representing the first archaeal TIM structure. P. woesei TIM exists as a tetramer comprising monomers of only 228 amino acid residues. Structural comparisons with other less thermostable TIMs show that although the central beta-barrel is largely conserved, severe pruning of several helices and truncation of some loops give rise to a much more compact monomer in the small hyperthermophilic TIM. The classical TIM dimer formation is conserved in P. woesei TIM. The extreme thermostability of PwTIM appears to be achieved by the creation of a compact tetramer where two classical TIM dimers interact via an extensive hydrophobic interface. The tetramer is formed through largely hydrophobic interactions between some of the pruned helical regions. The equivalent helical regions in less thermostable dimeric TIMs represent regions of high average temperature factor. The PwTIM seems to have removed these regions of potential instability in the formation of the tetramer. This study of PwTIM provides further support for the role of higher oligomerisation states in extreme thermal stabilisation.

A mass balance study to evaluate the biotransformation and excretion of [14C]-triamcinolone acetonide following oral administration

The principle objective of this study was to characterize the absorption, metabolism, and disposition of orally administered [14C]-triamcinolone acetonide. Six healthy male subjects each received a single 100 microCi (approximately 800 micrograms) oral dose of [14C]-triamcinolone acetonide. Plasma, urine, and fecal samples were collected at selected times and analyzed for triamcinolone acetonide and [14C]-derived radioactivity. Plasma protein binding of triamcinolone acetonide was also determined. Metabolite profiling and identification were carried out in plasma and excreta. Principle metabolites were assessed for activity with in vitro anti-inflammatory models. [14C]-triamcinolone acetonide was found to be systemically absorbed following oral administration. The presystemic metabolism and clearance of triamcinolone acetonide were extensive, with only a small fraction of the total plasma radioactivity being made up of triamcinolone acetonide. Little to no parent compound was detected in the plasma 24 hours after administration. Most of the urinary and fecally [14C]-derived radioactivity was also excreted within 24 and 72 hours postdose, respectively. Mean plasma protein binding of triamcinolone acetonide was constant, predictable, and a relatively low 68% over a 24-fold range of plasma concentrations. Three principle metabolites of triamcinolone acetonide were profiled in plasma, urine, and feces. These metabolites were identified as 6 beta-hydroxy triamcinolone, 21-carboxylic acid triamcinolone acetonide, and 6 beta-hydroxy-21-oic triamcinolone acetonide. All three metabolites failed to show any concentration-dependent effects in anti-inflammatory models evaluating IL-5-sustained eosinophil viability and IgE-induced basophil histamine release.

Production of volatile derivatives of metal(loid)s by microflora involved in anaerobic digestion of sewage sludge

Gases released from anaerobic wastewater treatment facilities contain considerable amounts of volatile methyl and hydride derivatives of metals and metalloids, such as arsine (AsH(3)), monomethylarsine, dimethylarsine, trimethylarsine, trimethylbismuth (TMBi), elemental mercury (Hg(0)), trimethylstibine, dimethyltellurium, and tetramethyltin. Most of these compounds could be shown to be produced by pure cultures of microorganisms which are representatives of the anaerobic sewage sludge microflora, i.e., methanogenic archaea (Methanobacterium formicicum, Methanosarcina barkeri, Methanobacterium thermoautotrophicum), sulfate-reducing bacteria (Desulfovibrio vulgaris, D. gigas), and a peptolytic bacterium (Clostridium collagenovorans). Additionally, dimethylselenium and dimethyldiselenium could be detected in the headspace of most of the pure cultures. This is the first report of the production of TMBi, stibine, monomethylstibine, and dimethylstibine by a pure culture of M. formicicum.

Pyruvate kinase of the hyperthermophilic crenarchaeote Thermoproteus tenax: physiological role and phylogenetic aspects

Pyruvate kinase (PK; EC 2.7.1.40) of Thermoproteus tenax was purified to homogeneity, and its coding gene was cloned and expressed in Escherichia coli. It represents a homomeric tetramer with a molecular mass of 49 kDa per subunit. PK exhibits positive binding cooperativity with respect to phosphoenolpyruvate and metal ions such as Mg(2+) and Mn(2+). Heterotropic effects, as commonly found for PKs from bacterial and eucaryal sources, could not be detected. The enzyme does not depend on K(+) ions. Heterotrophically grown cells exhibit specific activity of PK four times higher than autotrophically grown cells. Since the mRNA level of the PK coding gene is also accordingly higher in heterotrophic cells, we conclude that the PK activity is adjusted to growth conditions mainly on the transcript level. The enzymic properties of the PK and the regulation of its expression are discussed with respect to the physiological framework given by the T. tenax-specific variant of the Embden-Meyerhof-Parnas pathway. T. tenax PK shows moderate overall sequence similarity (25 to 40% identity) to its bacterial and eucaryal pendants. Phylogenetic analyses of the known PK sequences result in a dichotomic tree topology that divides the enzymes into two major PK clusters, probably diverged by an early gene duplication event. The phylogenetic divergence is paralleled by a striking phenotypic differentiation of PKs: PKs of cluster I, which occur in eucaryal cytoplasm, some gamma proteobacteria, and low-GC gram-positive bacteria, are only active in the presence of fructose-1,6-bisphosphate or other phosphorylated sugars, whereas PKs of cluster II, found in various bacterial phyla, plastids, and in Archaea, show activity without effectors but are commonly regulated by the energy charge of the cell.

Crystallization and preliminary X-ray diffraction analysis of the NAD-dependent non--phosphorylating GAPDH of the hyperthermophilic archaeon Thermoproteus tenax

Recombinant non-phosphorylating NAD(+)-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN) of the hyperthermophilic crenarchaeote Thermoproteus tenax has been overexpressed, purified and crystallized using the hanging-drop vapour-diffusion technique. Crystals of different habits were obtained from several precipitant solutions (salts and polyethylene glycols). Preliminary X-ray analysis was performed with crystals grown in ammonium formate, which belonged to the primitive hexagonal space group P622, and had unit-cell parameters a = b = 184.8, c = 133.0 A, gamma = 120 degrees. Assuming a molecular weight of 55 kDa, a Matthews parameter of 3.3 A(3) Da(-1) is calculated assuming two molecules per asymmetric unit. The diffraction limit of these crystals is 2.5 A resolution.

Microbial degradation of octamethylcyclotetrasiloxane

The microbial degradation of low-molecular-weight polydimethylsiloxanes was investigated through laboratory experiments. Octamethylcyclotetrasiloxane was found to be biodegraded under anaerobic conditions in composted sewage sludge, as monitored by the occurrence of the main polydimethylsiloxane degradation product, dimethylsilanediol, compared to that found in experiments with sterilized control samples.

Preliminary crystallographic studies of triosephosphate isomerase (TIM) from the hyperthermophilic Archaeon Pyrococcus woesei

Recombinant triosephosphate isomerase (TIM) from a hyperthermophilic Archaeon, Pyrococcus woesei, has been crystallized. Three crystal forms have been obtained: monoclinic, orthorhombic and hexagonal. The monoclinic crystals belong to space group P21 with cell dimensions a = 79.1, b = 89.2, c = 145.4 A and beta = 92.8 degrees, and diffract to at least 2.6 A. The orthorhombic crystals belong to space group P21212 with a = 89.4, b = 155.9, c = 79.5 A, and diffract to 2.9 A. Diffraction from the hexagonal form showed extensive disorder. The monoclinic form contains two tetramers in the asymmetric unit, which are in the same orientation but related by a pseudo-centering. The orthorhombic form contains one tetramer in the asymmetric unit which is in approximately the same orientation as in the monoclinic form. Knowledge of the structure of this hyperthermostable TIM, which is tetrameric in contrast to dimeric forms previously observed, will add to our understanding of protein thermostability.

Cloning, sequencing, and expression of the gene encoding cyclic 2, 3-diphosphoglycerate synthetase, the key enzyme of cyclic 2, 3-diphosphoglycerate metabolism in Methanothermus fervidus

Cyclic 2,3-diphosphoglycerate synthetase (cDPGS) catalyzes the synthesis of cyclic 2,3-diphosphoglycerate (cDPG) by formation of an intramolecular phosphoanhydride bond in 2,3-diphosphoglycerate. cDPG is known to be accumulated to high intracellular concentrations (>300 mM) as a putative thermoadapter in some hyperthermophilic methanogens. For the first time, we have purified active cDPGS from a methanogen, the hyperthermophilic archaeon Methanothermus fervidus, sequenced the coding gene, and expressed it in Escherichia coli. cDPGS purification resulted in enzyme preparations containing two isoforms differing in their electrophoretic mobility under denaturing conditions. Since both polypeptides showed the same N-terminal amino acid sequence and Southern analyses indicate the presence of only one gene coding for cDPGS in M. fervidus, the two polypeptides originate from the same gene but differ by a not yet identified modification. The native cDPGS represents a dimer with an apparent molecular mass of 112 kDa and catalyzes the reversible formation of the intramolecular phosphoanhydride bond at the expense of ATP. The enzyme shows a clear preference for the synthetic reaction: the substrate affinity and the Vmax of the synthetic reaction are a factor of 8 to 10 higher than the corresponding values for the reverse reaction. Comparison with the kinetic properties of the electrophoretically homogeneous, apparently unmodified recombinant enzyme from E. coli revealed a twofold-higher Vmax of the enzyme from M. fervidus in the synthesizing direction.

PPi-dependent phosphofructokinase from Thermoproteus tenax, an archaeal descendant of an ancient line in phosphofructokinase evolution

Flux into the glycolytic pathway of most cells is controlled via allosteric regulation of the irreversible, committing step catalyzed by ATP-dependent phosphofructokinase (PFK) (ATP-PFK; EC 2.7.1.11), the key enzyme of glycolysis. In some organisms, the step is catalyzed by PPi-dependent PFK (PPi-PFK; EC 2.7.1.90), which uses PPi instead of ATP as the phosphoryl donor, conserving ATP and rendering the reaction reversible under physiological conditions. We have determined the enzymic properties of PPi-PFK from the anaerobic, hyperthermophilic archaeon Thermoproteus tenax, purified the enzyme to homogeneity, and sequenced the gene. The approximately 100-kDa PPi-PFK from T. tenax consists of 37-kDa subunits; is not regulated by classical effectors of ATP-PFKs such as ATP, ADP, fructose 2,6-bisphosphate, or metabolic intermediates; and shares 20 to 50% sequence identity with known PFK enzymes. Phylogenetic analyses of biochemically characterized PFKs grouped the enzymes into three monophyletic clusters: PFK group I represents only classical ATP-PFKs from Bacteria and Eucarya; PFK group II contains only PPi-PFKs from the genus Propionibacterium, plants, and amitochondriate protists; whereas group III consists of PFKs with either cosubstrate specificity, i.e., the PPi-dependent enzymes from T. tenax and Amycolatopsis methanolica and the ATP-PFK from Streptomyces coelicolor. Comparative analyses of the pattern of conserved active-site residues strongly suggest that the group III PFKs originally bound PPi as a cosubstrate.

NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase from Thermoproteus tenax. The first identified archaeal member of the aldehyde dehydrogenase superfamily is a glycolytic enzyme with unusual regulatory properties

The hyperthermophilic archaeum Thermoproteus tenax possesses two glyceraldehyde-3-phosphate dehydrogenases differing in cosubstrate specificity and phosphate dependence of the catalyzed reaction. NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphate-independent irreversible oxidation of D-glyceraldehyde 3-phosphate to 3-phosphoglycerate. The coding gene was cloned, sequenced, and expressed in Escherichia coli. Sequence comparisons showed no similarity to phosphorylating glyceraldehyde-3-phosphate dehydrogenases but revealed a relationship to aldehyde dehydrogenases, with the highest similarity to the subgroup of nonphosphorylating glyceraldehyde-3-phosphate dehydrogenases. The activity of the enzyme is affected by a series of metabolites. All effectors tested influence the affinity of the enzyme for its cosubstrate NAD+. Whereas NADP(H), NADH, and ATP reduce the affinity for the cosubstrate, AMP, ADP, glucose 1-phosphate, and fructose 6-phosphate increase the affinity for NAD+. Additionally, most of the effectors investigated induce cooperativity of NAD+ binding. The irreversible catabolic oxidation of glyceraldehyde 3-phosphate, the control of the enzyme by energy charge of the cell, and the regulation by intermediates of glycolysis and glucan degradation identify the NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase as an integral constituent of glycolysis in T. tenax. Its regulatory properties substitute for those lacking in the reversible nonregulated pyrophosphate-dependent phosphofructokinase in this variant of the Embden-Meyerhof-Parnas pathway.

Carbohydrate metabolism in Thermoproteus tenax: in vivo utilization of the non-phosphorylative Entner-Doudoroff pathway and characterization of its first enzyme, glucose dehydrogenase

Thermoproteus tenax is a hyperthermophilic, facultative heterotrophic archaeum. In this organism the utilization of the two catabolic pathways, a variant of the Embden-Meyerhof-Parnas (EMP) pathway and the modified (nonphosphorylative) Entner-Doudoroff (ED) pathway, was investigated and the first enzyme of the ED pathway, glucose dehydrogenase, was characterized. The distribution of the 13C label in alanine synthesized by cells grown with [1-13C]glucose indicated that in vivo the EMP pathway and the modified ED pathway operate parallel, with glucose metabolization via the EMP pathway being prominent. To initiate studies on the regulatory mechanisms governing carbon flux via these pathways, the first enzyme of the ED pathway, glucose dehydrogenase, was purified to homogeneity and its phenotypic properties were characterized. The pyridine-nucleotide-dependent enzyme used both NAD+ and NADP+ as cosubstrates, showing a 100-fold higher affinity for NADP+. Besides glucose, xylose was used as substrate, but with significantly lower affinity. These data suggest that the physiological function of the enzyme is the oxidation of glucose by NADP+. A striking feature was the influence of NADP+ and NAD+ on the quaternary structure and activity state of the enzyme. Without cosubstrate, the enzyme was highly aggregated (mol. mass > 600 kDa) but inactive, whereas in the presence of the cosubstrate the aggregates dissociated into enzymatically active, homomeric dimers with a mol. mass of 84 kDa (mol. mass of subunits: 41 kDa). The N-terminal amino acid sequence showed striking similarity to the respective partial sequences of alcohol dehydrogenases and sorbitol dehydrogenases, but no resemblance to the known pyridine-nucleotide-dependent archaeal and bacterial glucose dehydrogenases.

Disposition of a novel recombinant antithrombotic agent, RG 12986, in cynomolgus monkeys

RG 12986, a novel antagonist of platelet aggregation, is a recombinant peptide based on the sequence in von Willebrand factor, which contains the GP1b binding site. Disposition of the peptide in cynomolgus monkeys was determined using nonlabeled and 35S-labeled product. After iv administration, the peptide underwent a triphasic decay in the plasma. The first phase of elimination, after distribution, had a t1/2 (approximately 20 min) similar to that observed for inhibition of platelet aggregation (approximately 25 min). The correlation between the logarithm of the plasma peptide concentration and activity was r = 0.9989. The effective duration of pharmacological activity was approximately 2 hr. After this period, a slower terminal phase of plasma elimination was observed (t1/2 approximately 2 hr). Plasma clearance (7-15 ml/min/kg) and volume of distribution at steady-state (0.4-0.9 L/kg) estimates appeared to have a slight dose dependency, but the scope of the investigation did not allow this to be verified. There was a linear correlation between dose and AUC (r2 = 0.9998), but for each 4-fold increase in dose there was a greater than 4-fold increase in AUC. Immediately after iv administration, significant fragmentation of the peptide was observed with polyacrylamide gel electrophoresis analysis of the plasma. This initial rate of metabolism was subsequently slowed to t1/2 estimates of 2 hr, followed by a very long terminal half-life of plasma radioactivity of 12 days. It is likely that this terminal half-life represents metabolic recycling of 35S. Elimination of the label was primarily via the kidneys.

The 3-phosphoglycerate kinase of the hyperthermophilic archaeum Pyrococcus woesei produced in Escherichia coli: loss of heat resistance due to internal translation initiation and its restoration by site-directed mutagenesis

Heterologous expression of the gene coding for 3-phosphoglycerate kinase (PGK) of the hyperthermophilic archaeum, Pyrococcus woesei (Pw), in Escherichia coli (Ec) yielded only low recovery of recombinant PGK (re-PGK) in heat-precipitated crude extracts. Moreover, we noticed contamination with a 28-kDa protein, from which PGK could hardly be separated, even under stringent conditions after tagging the re-PGK with a His6-tag. The preparations contaminated with the 28-kDa protein showed an unexpectedly low thermal stability. Under the same conditions (85 degrees C, 30 min), however, the enzyme from the original organism was completely resistant to heat inactivation. As shown by size-exclusion chromatography, re-PGK forms tight associations with the 28-kDa protein, which was found to represent a C-terminal fragment of PGK and to arise as a product of internal translation initiation within the pgk gene. Mutations changing the internal ribosome-binding site effectively suppressed the production of the 28-kDa protein and restored the thermal stability of the Pw re-PGK.

Tetrameric triosephosphate isomerase from hyperthermophilic Archaea

Triosephosphate isomerase (TIM) of the hyperthermophilic Archaea Pyrococcus woesei and Methanothermus fervidus have been purified to homogeneity. The enzymes from the two hyperthermophiles represent homo-tetramers of 100 kDa, contrary to all known bacterial and eukaryotic TIMs, which are dimers of 48-60 kDa. Molecular size determination of the TIM from the mesophilic methanogen Methanobacterium bryantii yielded the usual molecular mass of only 57 kDa, indicating that the tetrameric aggregation state does not represent an archaeal feature but rather correlates with thermoadaptation. A similar preference for higher protein aggregates in hyperthermophilic Archaea has previously been demonstrated for 3-phosphoglycerate kinases. The gene of the P. woesei TIM was cloned and sequenced. The archaeal TIM proved to be homologous to its bacterial and eukaryotic pendants. Most strikingly, the deduced protein sequence comprises only 224 residues and thus represents the shortest TIM sequence known as yet. Taking the three-dimensional structure of the eucaryal TIM as a basis, from the shortenings of the chain considerable rearrangements at the bottom of the alpha/beta barrel and at its functionally inactive flank are expected, which are interpreted in terms of the formation of new subunit contacts.

Dimeric 3-phosphoglycerate kinases from hyperthermophilic Archaea. Cloning, sequencing and expression of the 3-phosphoglycerate kinase gene of Pyrococcus woesei in Escherichia coli and characterization of the protein. Structural and functional comparison with the 3-phosphoglycerate kinase of Methanothermus fervidus

The gene coding for the 3-phosphoglycerate kinase (EC 2.7.2.3) of Pyrococcus woesei was cloned and sequenced. The gene sequence comprises 1230 bp coding for a polypeptide with the theoretical M(r) of 46,195. The deduced protein sequence exhibits a high similarity (46.1% and 46.6% identity) to the other known archaeal 3-phosphoglycerate kinases of Methanobacterium bryantii and Methanothermus fervidus [Fabry, S., Heppner, P., Dietmaier, W. & Hensel, R. (1990) Gene 91, 19-25]. By comparing the 3-phosphoglycerate kinase sequences of the mesophilic and the two thermophilic Archaea, trends in thermoadaptation were confirmed that could be deduced from comparisons of glyceraldehyde-3-phosphate dehydrogenase sequences from the same organisms [Zwickl, P., Fabry, S., Bogedain, C., Haas, A. & Hensel, R. (1990) J. Bacteriol. 172, 4329-4338]. With increasing temperature the average hydrophobicity and the portion of aromatic residues increases, whereas the chain flexibility as well as the content in chemically labile residues (Asn, Cys) decreases. To study the phenotypic properties of the 3-phosphoglycerate kinases from thermophilic Archaea in more detail, the 3-phosphoglycerate kinase genes from P. woesei and M. fervidus were expressed in Escherichia coli. Comparisons of kinetic and molecular properties of the enzymes from the original organisms and from E. coli indicate that the proteins expressed in the mesophilic host are folded correctly. Besides their higher thermostability according to their origin from hyperthermophilic organisms, both enzymes differ from their bacterial and eucaryotic homologues mainly in two respects. (a) The 3-phosphoglycerate kinases from P. woesei and M. fervidus are homomeric dimers in their native state contrary to all other known 3-phosphoglycerate kinases, which are monomers including the enzyme from the mesophilic Archaeum M. bryantii. (b) Monovalent cations are essential for the activity of both archaeal enzymes with K+ being significantly more efficient than Na+. For the P. woesei enzyme, non-cooperative K+ binding with an apparent Kd (K+) of 88 mM could be determined by kinetic analysis, whereas for the M. fervidus 3-phosphoglycerate kinase the K+ binding is rather complex: from the fitting of the saturation data, non-cooperative binding sites with low selectivity for K+ and Na+ (apparent Kd = 270 mM) and at least three cooperative and highly specific K+ binding sites/subunit are deduced. At the optimum growth temperature of P. woesei (100 degrees C) and M. fervidus (83 degrees C), the 3-phosphoglycerate kinases show half-lives of inactivation of only 28 min and 44 min, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)