Materials Synthetic Biology

Light is fundamental to life on earth. Therefore, nature has evolved a multitude of photoreceptors that sense light across all kingdoms. This natural resource provides synthetic biology with a vast pool of light-sensing components with distinct spectral properties that can be harnessed to engineer novel optogenetic tools. These devices enable control over gene expression, cell morphology and signaling pathways with superior spatiotemporal resolution and are maturing towards elaborate applications in basic research, in the production of biopharmaceuticals and in biomedicine. This article provides a summary of the recent advances in optogenetics that use light for the precise control of biological functions in mammalian cells. © 2013 The Royal Society of Chemistry.

Time-resolved quantitative analysis of auxin-mediated processes in plant cells is as of yet limited. By applying a synergistic mammalian and plant synthetic biology approach, we have developed a novel ratiometric luminescent biosensor with wide applicability in the study of auxin metabolism, transport, and signalling. The sensitivity and kinetic properties of our genetically encoded biosensor open new perspectives for the analysis of highly complex auxin dynamics in plant growth and development.

The design of synthetic biology-inspired control devices enabling entire mammalian cells to receive, process and transfer metabolic information and so communicate with each other via synthetic multichannel networks may provide new insight into the organization of multicellular organisms and future clinical interventions. Here we describe communication networks that orchestrate behavior in individual mammalian cells in response to cell-to-cell metabolic signals. We engineered sender, processor and receiver cells that interact with each other in ways that resemble natural intercellular communication networks such as multistep information processing cascades, feed-forward-based signaling loops, and two-way communication. The engineered two-way communication devices mimicking natural control systems in the development of vertebrate extremities and vasculature was used to program temporal permeability in vascular endothelial cell layers. These synthetic multicellular communication systems may inspire future therapies or tissue engineering strategies. © 2012 Nature America, Inc. All rights reserved.

The Cu(i)-catalyzed cycloaddition of terminal azides and alkynes (click chemistry) represents a highly specific reaction for the functionalization of biomolecules with chemical moieties such as dyes or polymer matrices. In this study we evaluate the use of bicinchoninic acid (BCA) as a ligand for Cu(i) under physiological reaction conditions. We demonstrate that the BCA-Cu(i)-complex represents an efficient catalyst for the conjugation of fluorophores or biotin to alkyne- or azide-functionalized proteins resulting in increased or at least equal reaction yields compared to commonly used catalysts like Cu(i) in complex with TBTA (tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl] amine) or BPAA (bathophenanthroline disulfonic acid). The stabilization of Cu(i) with BCA represents a new strategy for achieving highly efficient bioconjugation reactions under physiological conditions in many application fields. © 2012 The Royal Society of Chemistry.

Metabolite-responsive hydrogels that detect pathological metabolite concentrations and react by releasing a therapeutic stimulus hold high promises in treating metabolic diseases. In this study, a hydrogel is described that discriminates between physiological and pathological concentrations of urate, the causative agent of gouty arthritis. The hydrogel is synthesized by coupling a dimeric variant of the Deinococcus radiodurans-derived urate repressor HucR to linear polyacrylamide. The protein-grafted polymer is crosslinked to form a hydrogel by a multimeric hucO DNA sequence [hucO]n specifically binding HucR. At elevated urate concentrations, HucR dissociates from [hucO]n thereby weakening the hydrogel structure and resulting in its dissolution. A stimulus-responsive biohybrid material is described that rapidly dissolves at pathological concentrations of the gouty arthritis-causing metabolite urate. The gel consists of polyacrylamide and DNA that are crosslinked by the Deinococcus radiodurans-derived urate sensor HucR, which binds its specific target DNA motif at physiological urate concentrations and dissociates thereof at pathological concentrations. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Trigger-inducible transcription-control devices that reversibly fine-tune transgene expression in response to molecular cues have significantly advanced the rational reprogramming of mammalian cells. When designed for use in future gene-and cell-based therapies the trigger molecules have to be carefully chosen in order to provide maximum specificity, minimal side-effects and optimal pharmacokinetics in a mammalian organism. Capitalizing on control components that enable Caulobacter crescentus to metabolize vanillic acid originating from lignin degradation that occurs in its oligotrophic freshwater habitat, we have designed synthetic devices that specifically adjust transgene expression in mammalian cells when exposed to vanillic acid. Even in mice transgene expression was robust, precise and tunable in response to vanillic acid. As a licensed food additive that is regularly consumed by humans via flavoured convenience food and specific fresh vegetable and fruits, vanillic acid can be considered as a safe trigger molecule that could be used for diet-controlled transgene expression in future gene-and cell-based therapies. © 2011 The Author(s).

Interactive materials being responsive to a biocompatible stimulus represent a promising approach for future therapeutic applications. In this study, we present a novel biohybrid material synthesized from biocompatible components being stimulus-responsive to the pharmaceutically approved small-molecule novobiocin. The hydrogel design is based on the gyrase B (GyrB) protein, which is covalently grafted to multi-arm polyethylene glycol (PEG) using a Michael-type addition reaction. Upon addition of the GyrB-dimerizing substance coumermycin, stable hydrogels form which can be dissolved in a dose-adjustable manner by the antibiotic novobiocin. The switchable properties of this PEG-based hydrogel are favorable for future applications in tissue engineering and as externally controlled drug depot. A polyethylenglycol(PEG)- based biohybrid material is presented being dose-responsive to the small-molecule drug novobiocin. The design is based on a multi-arm PEG functionalized with the protein gyrase B, which can be crosslinked to a hydrogel by coumermycin. Hydrogel dissolution can be triggered dose dependently by the addition of novobiocin. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iatrogenic preterm prelabor rupture of membranes (iPPROM) remains the main complication after invasive interventions into the intrauterine cavity. Here, the proteolytic stability of mussel-mimetic tissue adhesive (mussel glue) and its sealing behavior on punctured fetal membranes are evaluated. The proteolytic degradation of mussel glue and fibrin glue were compared in vitro. Critical pressures of punctured and sealed fetal membranes were determined under close to physiological conditions using a custom-made inflation device. An inverse finite element procedure was applied to estimate mechanical parameters of mussel glue. Mussel glue was insensitive whereas fibrin glue was sensitive towards proteolytic degradation. Mussel glue sealed 3.7 mm fetal membrane defect up to 60 mbar (45 mm Hg) when applied under wet conditions, whereas fibrin glue needed dry membrane surfaces for reliable sealing. The mussel glue can be represented by a neo-Hookean material model with elastic coefficient C1 = 9.63 kPa. Ex-vivo-tested mussel glue sealed fetal membranes and resisted pressures achieved during uterine contractions. Together with good stability in proteolytic environments, this makes mussel glue a promising sealing material for future applications. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The emerging field of synthetic biology is a novel biological discipline at the interface between traditional biology, chemistry, and engineering sciences. Synthetic biology aims at the rational design of complex synthetic biological devices and systems with desired properties by combining compatible, modular biological parts in a systematic manner.While the first engineered systems were mainly proof-of-principle studies to demonstrate the power of the modular engineering approach of synthetic biology, subsequent systems focus on applications in the health, environmental, and energy sectors. This review describes recent approaches for biomedical applications that were developed along the synthetic biology design hierarchy, at the level of individual parts, of devices, and of complex multicellular systems. It describes how synthetic biological parts can be used for the synthesis of drug-delivery tools, how synthetic biological devices can facilitate the discovery of novel drugs, and how multicellular synthetic ecosystems can give insight into population dynamics of parasites and hosts. These examples demonstrate how this new discipline could contribute to novel solutions in the biopharmaceutical industry. © 2013 by The Johns Hopkins University Press.