A universal reagent for detection of emerging diseases using bioengineered multifunctional yeast nanofragments

Accurate and early detection of biomarkers provides the molecular evidence for disease management, allowing prompt actions and timely treatments to save lives. Multivalent biomolecular interactions between the probe and biomarker as well as controlled probe orientation on material surfaces are keys for highly sensitive detection. Here we report the bioengineering of programmable and multifunctional nanoprobes, which can provide rapid, specific and highly sensitive detection of emerging diseases in a range of widely used diagnostic systems. These nanoprobes composed of nanosized cell wall fragments, termed as synthetic bionanofragments (SynBioNFs), are generated by the fragmentation of genetically programmed yeast cells. SynBioNFs display multiple copies of biomolecules for high-affinity target binding and molecular handles for the precisely orientated attachment on surfaces used in diagnostic platforms. SynBioNFs are demonstrated for the capture and detection of SARS-CoV-2 virions using multiple diagnostic platforms, including surface-enhanced Raman scattering, fluorescence, electrochemical and colorimetric-based lateral flow systems with sensitivity comparable with the gold-standard reverse-transcription quantitative polymerase chain reaction.

Exploring Performance Parameters of Artificial Allosteric Protein Switches

Biological information processing networks rely on allosteric protein switches that dynamically interconvert biological signals. Construction of their artificial analogues is a central goal of synthetic biology and bioengineering. Receptor domain insertion is one of the leading methods for constructing chimeric protein switches. Here we present an in vitro expression-based platform for the analysis of chimeric protein libraries for which traditional cell survival or cytometric high throughput assays are not applicable. We utilise this platform to screen a focused library of chimeras between PQQ-glucose dehydrogenase and calmodulin. Using this approach, we identified 50 chimeras (approximately 23% of the library) that were activated by calmodulin-binding peptides. We analysed performance parameters of the active chimeras and demonstrated that their dynamic range and response times are anticorrelated, pointing to the existence of an inherent thermodynamic trade-off. We show that the structure of the ligand peptide affects both the response and activation kinetics of the biosensors suggesting that the structure of a ligand:receptor complex can influence the chimera's activation pathway. In order to understand the extent of structural changes in the reporter protein induced by the receptor domains, we have analysed one of the chimeric molecules by CD spectroscopy and hydrogen-deuterium exchange mass spectrometry. We concluded that subtle ligand-induced changes in the receptor domain propagated into the GDH domain and affected residues important for substrate and cofactor binding. Finally, we used one of the identified chimeras to construct a two-component rapamycin biosensor and demonstrated that core switch optimisation translated into improved biosensor performance.

Generation of Nanoyeast Single-Chain Variable Fragments as High-Avidity Biomaterials for Dengue Virus Detection

Bioengineered yeast bio-nanomaterials termed nanoyeasts displaying antibody single-chain variable fragments (scFvs) against diagnostic targets are a promising alternative to monoclonal antibodies (mAbs). A potential limitation for translating nanoyeasts into diagnostic tools is batch-to-batch variability. Herein, we demonstrate a systematic approach for cost-efficient production of highly specific nanoyeasts that enabled accurate dengue virus (DENV) detection by immunoassay (2.5% CV). Yeasts bioengineered to surface express DENV-specific scFvs (up to 66% of the total cell population) were fragmented into nanoyeast fractions trialing sonication, bead beating, and high-pressure disruption methods. Nanoyeast fractions from sonication had optimal target binding, uniform particle size (±89 nm), were stable, and retained diagnostic activity for 7 days at 37 °C compared to traditional mAbs that lost activity after 1 day at 37 °C. We engineered a panel of nanoyeast scFvs targeting DENV nonstructural protein 1 (NS1): (i) specific for serotyping DENV 1-4 and (ii) cross-reactive anti-DENV scFvs that are suitable for "yes/no" diagnostic applications. We demonstrate highly specific nanoyeast scFvs for serotyping DENV. We show that nanoyeast scFvs specifically detect NS1 in simulated patient plasma with a limit of detection of 250 ng/mL, the concentration found in infected patients.

Connecting Artificial Proteolytic and Electrochemical Signaling Systems with Caged Messenger Peptides

Enzymatic polypeptide proteolysis is a widespread and powerful biological control mechanism. Over the last few years, substantial progress has been made in creating artificial proteolytic systems where an input of choice modulates the protease activity and thereby the activity of its substrates. However, all proteolytic systems developed so far have relied on the direct proteolytic cleavage of their effectors. Here, we propose a new concept where protease biosensors with a tunable input uncage a signaling peptide, which can then transmit a signal to an allosteric protein reporter. We demonstrate that both the cage and the regulatory domain of the reporter can be constructed from the same peptide-binding domain, such as calmodulin. To demonstrate this concept, we constructed a proteolytic rapamycin biosensor and demonstrated its quantitative actuation on fluorescent, luminescent, and electrochemical reporters. Using the latter, we constructed sensitive bioelectrodes that detect the messenger peptide release and quantitatively convert the recognition event into electric current. We discuss the application of such systems for the construction of in vitro sensory arrays and in vivo signaling circuits.

Amplification-Free SARS-CoV-2 Detection Using Nanoyeast-scFv and Ultrasensitive Plasmonic Nanobox-Integrated Nanomixing Microassay

The implementation of accurate and sensitive molecular detection for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is paramount to effectively control the ongoing coronavirus disease 2019 (COVID-19) pandemic. In this regard, we herein propose the specific and highly sensitive SARS-CoV-2 detection based on nanoyeast single-chain-variable fragment (scFv) and ultrasensitive plasmonic nanobox-integrated nanomixing microassay. Importantly, this designed platform showcases the utility of nanoyeast-scFvs as specific capture reagents targeting the receptor-binding domain (RBD) of the virus and as monoclonal antibody alternatives suitable for cost-effective mass production and frequent testing. By capitalizing on single-particle active nanoboxes as plasmonic nanostructures for surface-enhanced Raman scattering (SERS), the microassay utilizes highly sensitive Raman signals to indicate virus infection. The developed microassay further integrated nanomixing for accelerating molecular collisions. Through the synergistic working of nanoyeast-scFv, plasmonic nanoboxes, and nanomixing, the highly specific and sensitive SARS-CoV-2 detection is achieved as low as 17 virus/μL without any molecular amplification. We successfully demonstrate SARS-CoV-2 detection in saliva samples of simulated patients at clinically relevant viral loads, suggesting the possibility of this platform for accurate and noninvasive patient screening.

Self-powered molecule release systems activated with chemical signals processed through reconfigurable Implication or Inhibition Boolean logic gates

The Implication (IMPLY) and Inhibition (INHIB) Boolean logic gates were realized using switchable chimeric pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH-Clamp) containing a fused affinity clamp unit recognizing a signal-peptide. The second component of the logic gate was the wild-type PQQ-glucose dehydrogenase working cooperatively with the PQQ-GDH-Clamp enzyme. The IMPLY and INHIB gates were realized using the same enzyme composition activated with differently defined input signals, thus representing reconfigurable logic systems. The logic gates were first tested while operating in a solution with optical analysis of the output signals. Then, the enzymes were immobilized on a buckypaper electrode for electrochemical transduction of the output signals. The switchable modified electrodes mimicking the IMPLY or INHIB logic gates were integrated with an oxygen-reducing electrode modified with bilirubin oxidase to operate as a biofuel cell activated/inhibited by various input signal combinations processed either by IMPLY or INHIB logic gates. The switchable biofuel cell was used as a self-powered device triggering molecule release function controlled by the logically processed molecule signals.

Control of Allosteric Protein Electrochemical Switches with Biomolecular and Electronic Signals

The construction of allosteric protein switches is a key goal of synthetic biology. Such switches can be compiled into signaling systems mimicking information and energy processing systems of living organisms. Here we demonstrate construction of a biocatalytic electrode functionalized with a recombinant chimeric protein between pyrroloquinoline quinone-dependent glucose dehydrogenase and calmodulin. This electrode could be activated by calmodulin-binding peptide and showed a high bioelectrocatalytic current (ca. 300 μA) due to efficient direct electron transfer. In order to expand the types of inputs that can be used to activate the developed electrode, we constructed a caged version of calmodulin-binding peptide that could be proteolytically uncaged using a protease of choice. Finally, the complexity of the switchable bioelectrochemical system was further increased by the use of almost any kind of molecule/biomolecule or electronic signal, unequivocally proving the orthogonality of the aforementioned system.

Caged Activators of Artificial Allosteric Protein Biosensors

The ability of proteins to interconvert unrelated biochemical inputs and outputs underlays most energy and information processing in biology. A common conversion mechanism involves a conformational change of a protein receptor in response to a ligand binding or a covalent modification, leading to allosteric activity modulation of the effector domain. Designing such systems rationally is a central goal of synthetic biology and protein engineering. A two-component sensory system based on the scaffolding of modules in the presence of an analyte is one of the most generalizable biosensor architectures. An inherent problem of such systems is dependence of the response on the absolute and relative concentrations of the components. Here we use the example of two-component sensory systems based on calmodulin-operated synthetic switches to analyze and address this issue. We constructed "caged" versions of the activating domain thereby creating a thermodynamic barrier for spontaneous activation of the system. We demonstrate that the caged biosensor architectures could operate at concentrations spanning 3 orders of magnitude and are applicable to electrochemical, luminescent, and fluorescent two-component biosensors. We analyzed the activation kinetics of the caged biosensors and determined that the core allosteric switch is likely to be the rate limiting component of the system. These findings provide guidance for predictable engineering of robust sensory systems with inputs and outputs of choice.

Control of allosteric electrochemical protein switch using magnetic signals

The artificial chimeric enzyme with allosteric features was activated with a magnetic field applied at a distance.

Rational Design of an Anticalin-Type Sugar-Binding Protein Using a Genetically Encoded Boronate Side Chain

The molecular recognition of carbohydrates plays a fundamental role in many biological processes. However, the development of carbohydrate-binding reagents for biomedical research and use poses a challenge due to the generally poor affinity of proteins toward sugars in aqueous solution. Here, we describe the effective molecular recognition of pyranose monosaccharides (in particular, galactose and mannose) by a rationally designed protein receptor based on the human lipocalin scaffold (Anticalin). Complexation relies on reversible covalent cis-diol boronate diester formation with a genetically encoded l-boronophenylalanine (Bpa) residue which was incorporated as a non-natural amino acid at a sterically permissive position in the ligand pocket of the Anticalin, as confirmed by X-ray crystallography. Compared with the metal-ion and/or avidity-dependent oligovalent lectins that prevail in nature, our approach offers a novel and promising route to generate tight sugar-binding reagents both as research reagents and for biomedical applications.

Biochemical and spectroscopic characterization of dinuclear Mn-sites in artificial four-helix bundle proteins

To better understand metalloproteins with Mn-clusters, we have designed artificial four-helix bundles to have one, two, or three dinuclear metal centers able to bind Mn(II). Circular dichroism measurements showed that the Mn-proteins have substantial α-helix content, and analysis of electron paramagnetic resonance spectra is consistent with the designed number of bound Mn-clusters. The Mn-proteins were shown to catalyze the conversion of hydrogen peroxide into molecular oxygen. The loss of hydrogen peroxide was dependent upon the concentration of protein with bound Mn, with the proteins containing multiple Mn-clusters showing greater activity. Using an oxygen sensor, the oxygen concentration was found to increase with a rate up to 0.4μM/min, which was dependent upon the concentrations of hydrogen peroxide and the Mn-protein. In addition, the Mn-proteins were shown to serve as electron donors to bacterial reaction centers using optical spectroscopy. Similar binding of the Mn-proteins to reaction centers was observed with an average dissociation constant of 2.3μM. The Mn-proteins with three metal centers were more effective at this electron transfer reaction than the Mn-proteins with one or two metal centers. Thus, multiple Mn-clusters can be incorporated into four-helix bundles with the capability of performing catalysis and electron transfer to a natural protein.

Design of dinuclear manganese cofactors for bacterial reaction centers

A compelling target for the design of electron transfer proteins with novel cofactors is to create a model for the oxygen-evolving complex, a Mn4Ca cluster, of photosystem II. A mononuclear Mn cofactor can be added to the bacterial reaction center, but the addition of multiple metal centers is constrained by the native protein architecture. Alternatively, metal centers can be incorporated into artificial proteins. Designs for the addition of dinuclear metal centers to four-helix bundles resulted in three artificial proteins with ligands for one, two, or three dinuclear metal centers able to bind Mn. The three-dimensional structure determined by X-ray crystallography of one of the Mn-proteins confirmed the design features and revealed details concerning coordination of the Mn center. Electron transfer between these artificial Mn-proteins and bacterial reaction centers was investigated using optical spectroscopy. After formation of a light-induced, charge-separated state, the experiments showed that the Mn-proteins can donate an electron to the oxidized bacteriochlorophyll dimer of modified reaction centers, with the Mn-proteins having additional metal centers being more effective at this electron transfer reaction. Modeling of the structure of the Mn-protein docked to the reaction center showed that the artificial protein likely binds on the periplasmic surface similarly to cytochrome c2, the natural secondary donor. Combining reaction centers with exogenous artificial proteins provides the opportunity to create ligands and investigate the influence of inhomogeneous protein environments on multinuclear redox-active metal centers. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

Targeted delivery of ubiquitin-conjugated BH3 peptide-based Mcl-1 inhibitors into cancer cells

BH3 peptides are key mediators of apoptosis and have served as the lead structures for the development of anticancer therapeutics. Previously, we reported the application of a simple cysteine-based side chain cross-linking chemistry to NoxaBH3 peptides that led to the generation of the cross-linked NoxaBH3 peptides with increased cell permeability and higher inhibitory activity against Mcl-1 ( Muppidi, A., Doi, K., Edwardraja, S., Drake, E. J., Gulick, A. M., Wang, H.-G., Lin, Q. ( 2012 ) J. Am. Chem. Soc. 134 , 14734 ). To deliver cross-linked NoxaBH3 peptides selectively into cancer cells for enhanced efficacy and reduced systemic toxicity, here we report the conjugation of the NoxaBH3 peptides with the extracellular ubiquitin, a recently identified endogenous ligand for CXCR4, a chemokine receptor overexpressed in cancer cells. The resulting ubiquitin-NoxaBH3 peptide conjugates showed increased inhibitory activity against Mcl-1 and selective killing of the CXCR4-expressing cancer cells. The successful delivery of the NoxaBH3 peptides by ubiquitin into cancer cells suggests that the ubiquitin/CXCR4 axis may serve as a general route for the targeted delivery of anticancer agents.

Cloning, expression and characterization of 3-hydroxyisobutyrate dehydrogenase from Pseudomonas denitrificans ATCC 13867

The gene encoding an NAD⁺-dependent, 3-hydroxyisobutyrate dehydrogenase (3HIBDH-IV) from Pseudomonas denitrificans ATCC 13867 was cloned and expressed in Escherichia coli BL 21 (DE3) and characterized to understand its physiological relevance in the degradation of 3-hydroxypropionic acid (3-HP). The deduced amino acid sequence showed high similarity to other 3-hydroxyisobutyrate dehydrogenase isozymes (3HIBDHs) of P. denitrificans ATCC 13867. A comparison of 3HIBDH-IV with its relevant enzymes along with molecular docking studies suggested that Lys171, Asn175 and Gly123 are important for its catalytic function on 3-hydroxyacids. The recombinant 3HIBDH-IV was purified to homogeneity utilizing a Ni-NTA-HP resin column in high yield. 3HIBDH-IV was very specific to (S)-3-hydroxyisobutyrate, but also catalyzed the oxidation of 3-HP to malonate semialdehyde. The specific activity and half-saturation constant (K_m) for 3-HP at 30°C and pH 9.0 were determined to be 17 U/mg protein and 1.0 mM, respectively. Heavy metals, such as Ag⁺ and Hg²⁺, completely inhibited the 3HIBDH-IV activity, whereas dithiothreitol, 2-mercaptoethanol and ethylenediaminetetraacetic acid increased its activity 1.5–1.8-fold. This paper reports the characteristics of 3HIBDH-IV as well as its probable role in 3-HP degradation.

Rational design of proteolytically stable, cell-permeable peptide-based selective Mcl-1 inhibitors

Direct chemical modifications provide a simple and effective means to "translate" bioactive helical peptides into potential therapeutics targeting intracellular protein-protein interactions. We previously showed that distance-matching bisaryl cross-linkers can reinforce peptide helices containing two cysteines at the i and i+7 positions and confer cell permeability to the cross-linked peptides. Here we report the first crystal structure of a biphenyl-cross-linked Noxa peptide in complex with its target Mcl-1 at 2.0 Å resolution. Guided by this structure, we remodeled the surface of this cross-linked peptide through side-chain substitution and N-methylation and obtained a pair of cross-linked peptides with substantially increased helicity, cell permeability, proteolytic stability, and cell-killing activity in Mcl-1-overexpressing U937 cells.

Copper-free Sonogashira cross-coupling for functionalization of alkyne-encoded proteins in aqueous medium and in bacterial cells

Bioorthogonal reactions suitable for functionalization of genetically or metabolically encoded alkynes, for example, copper-catalyzed azide-alkyne cycloaddition reaction ("click chemistry"), have provided chemical tools to study biomolecular dynamics and function in living systems. Despite its prominence in organic synthesis, copper-free Sonogashira cross-coupling reaction suitable for biological applications has not been reported. In this work, we report the discovery of a robust aminopyrimidine-palladium(II) complex for copper-free Sonogashira cross-coupling that enables selective functionalization of a homopropargylglycine (HPG)-encoded ubiquitin protein in aqueous medium. A wide range of aromatic groups including fluorophores and fluorinated aromatic compounds can be readily introduced into the HPG-containing ubiquitin under mild conditions with good to excellent yields. The suitability of this reaction for functionalization of HPG-encoded ubiquitin in Escherichia coli was also demonstrated. The high efficiency of this new catalytic system should greatly enhance the utility of Sonogashira cross-coupling in bioorthogonal chemistry.

Improving the productivity of single-chain Fv antibody against c-Met by rearranging the order of its variable domains

Single-chain Fv (scFv) antibody against c-Met is expected to be employed in clinical treatment or imaging of cancer cells owing to the important biological roles of c-Met in the proliferation of malignancies. Here, we show that the productivity of scFv against c-Met in Escherichia coli is significantly influenced by the orientation of its variable domains. We generated anti-c-Met scFv antibodies with two different domain orders (i.e., VL-linker-VH and VH-linker-VL), expressed them in the cytoplasm of E. coli trx/ gor deleted mutant, and compared their specific activities as well as their productivities. Productivity of total and functional anti-c-Met scFv with VH/VL orientation was more than five times higher than that with VL/VH format. Coexpression of DsbC enhanced the yield of soluble amounts of anti-c-Met scFv protein for both constructs. The purified scFv antibodies of the two different formats exhibited almost the same antigen-binding activities. We also compared the productivities and specific activities of anti-c-Met diabodies with VH/VL or VL/VH formats and obtained similar results to the case of scFv antibodies.