Engineered mosaic protein polymers; a simple route to multifunctional biomaterials

Abstract: Background: Engineered living materials (ELMs) are an exciting new frontier, where living organisms create highly functional materials. In particular, protein ELMs have the advantage that their properties can be manipulated via simple molecular biology. Caf1 is a protein ELM that is especially attractive as a biomaterial on account of its unique combination of properties: bacterial cells export it as a massive, modular, non-covalent polymer which is resistant to thermal and chemical degradation and free from animal material. Moreover, it is biologically inert, allowing the bioactivity of each 15 kDa monomeric Caf1 subunit to be specifically engineered by mutagenesis and co-expressed in the same Escherichia coli cell to produce a mixture of bioactive Caf1 subunits. Results: Here, we show by gel electrophoresis and transmission electron microscopy that the bacterial cells combine these subunits into true mosaic heteropolymers. By combining two separate bioactive motifs in a single mosaic polymer we demonstrate its utility by stimulating the early stages of bone formation by primary human bone marrow stromal cells. Finally, using a synthetic biology approach, we engineer a mosaic of three components, demonstrating that Caf1 complexity depends solely upon the variety of monomers available. Conclusions: These results demonstrate the utility of engineered Caf1 mosaic polymers as a simple route towards the production of multifunctional biomaterials that will be useful in biomedical applications such as 3D tissue culture and wound healing. Additionally, in situ Caf1 producing cells could create complex bacterial communities for biotechnology. Graphical abstract

A generic expression system to produce proteins that co-assemble with alkane thiol SAM

Surface biology aims to observe and control biological processes by combining bio-, surface, and physical chemistry. Self-assembled monolayers (SAM) on gold surfaces have provided excellent methods for nanoscale surface preparation for such studies. However, extension of this work requires the specific immobilization of whole protein domains and the direct incorporation of recombinant proteins into SAM is still problematic. In this study a short random coil peptide has been designed to insert into thioalkane layers by formation of a hydrophobic helix. Surface plasmon resonance (SPR) studies show that specific immobilization via the internal cysteine is achieved. Addition of the peptide sequence to the terminus of a protein at the genetic level enables the production of a range of recombinant fusion-proteins with good yield. SPR shows that the proteins display the same gold-binding behavior as the peptide. It is shown that cell growth control can be achieved by printing the proteins using soft lithography with subsequent infilling with thioalkanes The expression plasmid is constructed so that any stable protein domain can be easily cloned, expressed, purified and immobilized

mAMSA resistant human topoisomerase IIβ mutation G465D has reduced ATP hydrolysis activity

Type II Human DNA Topoisomerases (topos II) play an essential role in DNA replication and transcription and are important targets for cancer chemotherapeutic drugs. Topoisomerase II causes transient double-strand breaks in DNA, forming a gate through which another double helix is passed, and acts as a DNA dependent ATPase. Mutations in topoII have been linked to atypical multi-drug resistance. Both human Topoisomerase II isoforms, α and β, are targeted by amsacrine. We have used a forced molecular evolution approach to identify mutations conferring resistance to acridines. Here we report mutation βG465D, which was selected with mAMSA and DACA and is cross-resistant to etoposide, ellipticine and doxorubicin. Resistance to mAMSA appears to decrease over time indicating a previously unreported resistance mechanism. G465D lies within the B′ domain in the region that contacts the cleaved gate helix. There is a 3-fold decrease in ATP affinity and ATP hydrolysis and an altered requirement for magnesium in decatenation assays. The decatenation rate is decreased for the mutated G465D protein. And we report for the first time the use of fluorescence anisotropy with intact human topoisomerase II

pH-dependent Stability and Membrane Interaction of the Pore-forming Domain of Colicin A*

Thermal stability of the pore-forming domain of colicin A was studied by high sensitivity differential scanning calorimetry and circular dichroism spectroscopy. In the pH range between 8 and 5, the thermal denaturation of the protein in solution occurs at 66-69 degrees C and is characterized by the calorimetric enthalpy of approximately 90 kcal/M. At pH below 5, there is a rapid pH-dependent destabilization of the pore-forming domain resulting in the lowering of the midpoint denaturation temperature and a decrease in the calorimetric enthalpy of denaturation. Circular dichroism spectra in the near and far ultraviolet show that the thermotropic transition is associated with collapse of the native tertiary structure of the pore-forming domain, although a large proportion of the helical secondary structure remains preserved. The present data indicate some similarity also between acid-induced and temperature-induced denaturation of the pore-forming domain of colicin A. Association of the pore-forming domain with phospholipid vesicles of dioleoylphosphatidylglycerol results in total disappearance of the calorimetric transition, even at pH values as high as 7. Since lipid binding also induces collapse of the near ultraviolet circular dichroism spectrum, these data indicate that interaction with the membrane facilitates a conformational change within the pore-forming domain to a looser (denaturated-like) state. These findings are discussed in relation to the recent model (van der Goot, F. G., Gonzalez-Manas, J. M., Lakey, J. H., Pattus, F. (1991) Nature 354, 408-410) which postulates that a flexible "molten globule" state is an intermediate on the pathway to membrane insertion of colicin A

Controlled spatial and conformational display of immobilised bone morphogenetic protein-2 and osteopontin signalling motifs regulates osteoblast adhesion and differentiation in vitro

<p>Abstract</p> <p>Background</p> <p>The interfacial molecular mechanisms that regulate mammalian cell growth and differentiation have important implications for biotechnology (production of cells and cell products) and medicine (tissue engineering, prosthetic implants, cancer and developmental biology). We demonstrate here that engineered protein motifs can be robustly displayed to mammalian cells <it>in vitro </it>in a highly controlled manner using a soluble protein scaffold designed to self assemble on a gold surface.</p> <p>Results</p> <p>A protein was engineered to contain a C-terminal cysteine that would allow chemisorption to gold, followed by 12 amino acids that form a water soluble coil that could switch to a hydrophobic helix in the presence of alkane thiols. Bioactive motifs from either bone morphogenetic protein-2 or osteopontin were added to this scaffold protein and when assembled on a gold surface assessed for their ability to influence cell function. Data demonstrate that osteoblast adhesion and short-term responsiveness to bone morphogenetic protein-2 is dependent on the surface density of a cell adhesive motif derived from osteopontin. Furthermore an immobilised cell interaction motif from bone morphogenetic protein supported bone formation <it>in vitro </it>over 28 days (in the complete absence of other osteogenic supplements). In addition, two-dimensional patterning of this ligand using a soft lithography approach resulted in the spatial control of osteogenesis.</p> <p>Conclusion</p> <p>These data describe an approach that allows the influence of immobilised protein ligands on cell behaviour to be dissected at the molecular level. This approach presents a durable surface that allows both short (hours or days) and long term (weeks) effects on cell activity to be assessed. This widely applicable approach can provide mechanistic insight into the contribution of immobilised ligands in the control of cell activity.</p

An accurate in vitro model of the E. coli envelope

Gram-negative bacteria are an increasingly serious source of antibiotic-resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir-Blodgett and Langmuir-Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development

An oomycete NLP cytolysin forms transient small pores in lipid membranes

Microbial plant pathogens secrete a range of effector proteins that damage host plants and consequently constrain global food production. Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) are produced by numerous phytopathogenic microbes that cause important crop diseases. Many NLPs are cytolytic, causing cell death and tissue necrosis by disrupting the plant plasma membrane. Here, we reveal the unique molecular mechanism underlying the membrane damage induced by the cytotoxic model NLP. This membrane disruption is a multistep process that includes electrostatic-driven, plant-specific lipid recognition, shallow membrane binding, protein aggregation, and transient pore formation. The NLP-induced damage is not caused by membrane reorganization or large-scale defects but by small membrane ruptures. This distinct mechanism of lipid membrane disruption is highly adapted to effectively damage plant cells.Peer reviewe

The Two-State Prehensile Tail of the Antibacterial Toxin Colicin N

Intrinsically disordered regions within proteins are critical elements in many biomolecular interactions and signaling pathways. Antibacterial toxins of the colicin family, which could provide new antibiotic functions against resistant bacteria, contain disordered N-terminal translocation domains (T-domains) that are essential for receptor binding and the penetration of the Escherichia coli outer membrane. Here we investigate the conformational behavior of the T-domain of colicin N (ColN-T) to understand why such domains are widespread in toxins that target Gram-negative bacteria. Like some other intrinsically disordered proteins in the solution state of the protein, ColN-T shows dual recognition, initially interacting with other domains of the same colicin N molecule and later, during cell killing, binding to two different receptors, OmpF and TolA, in the target bacterium. ColN-T is invisible in the high-resolution x-ray model and yet accounts for 90 of the toxin’s 387 amino acid residues. To reveal its solution structure that underlies such a dynamic and complex system, we carried out mutagenic, biochemical, hydrodynamic and structural studies using analytical ultracentrifugation, NMR, and small-angle x-ray scattering on full-length ColN and its fragments. The structure was accurately modeled from small-angle x-ray scattering data by treating ColN as a flexible system, namely by the ensemble optimization method, which enables a distribution of conformations to be included in the final model. The results reveal, to our knowledge, for the first time the dynamic structure of a colicin T-domain. ColN-T is in dynamic equilibrium between a compact form, showing specific self-recognition and resistance to proteolysis, and an extended form, which most likely allows for effective receptor binding