Esterification Delivers a Functional Enzyme into a Human Cell

Unnatural lipids for simultaneous mRNA delivery and metabolic cell labeling

Lipids have demonstrated tremendous promise for mRNA delivery, as evidenced by the success of Covid-19 mRNA vaccines. However, existing lipids are mostly used as delivery vehicles and lack the ability to monitor and further modulate the target cells. Here, for the first time, we report a class of unnatural lipids (azido-DOTAP) that can efficiently deliver mRNAs into cells and meanwhile metabolically label cells with unique chemical tags (e.g., azido groups). The azido tags expressed on the cell membrane enable the monitoring of transfected cells, and can mediate subsequent conjugation of cargos via efficient click chemistry for further modulation of transfected cells. We further demonstrate that the dual-functional unnatural lipid is applicable to different types of cells including dendritic cells, the prominent type of antigen presenting cells, potentially opening a new avenue to developing enhanced mRNA vaccines.

Evaluation of the RNA-dependence of PRC2 binding to chromatin in human pluripotent stem cells

Polycomb Repressive Complex 2 (PRC2), an important histone modifier and epigenetic repressor, has been known to interact with RNA for almost two decades. In our previous publication (Long, Hwang et al. 2020), we presented data supporting the functional importance of RNA interaction in maintaining PRC2 occupancy on chromatin, using comprehensive approaches including an RNA-binding mutant of PRC2 and an rChIP-seq assay. Recently, concerns have been expressed regarding whether the RNA-binding mutant has impaired histone methyltransferase activity and whether the rChIP-seq assay can potentially generate artifacts. Here we provide new data that support a number of our original findings. First, we found the RNA-binding mutant to be fully capable of maintaining H3K27me3 levels in human induced pluripotent stem cells. The mutant had reduced methyltransferase activity in vitro, but only on some substrates at early time points. Second, we found that our rChIP-seq method gave consistent data across antibodies and cell lines. Third, we further optimized rChIP-seq by using lower concentrations of RNase A and incorporating a catalytically inactive mutant RNase A as a control, as well as using an alternative RNase (RNase T1). The EZH2 rChIP-seq results using the optimized protocols supported our original finding that RNA interaction contributes to the chromatin occupancy of PRC2.

Evaluation of the Cytosolic Uptake of HaloTag Using a pH-Sensitive Dye

The efficient cytosolic delivery of proteins is critical for advancing novel therapeutic strategies. Current delivery methods are severely limited by endosomal entrapment, and detection methods lack sophistication in tracking the fate of delivered protein cargo. HaloTag, a commonly used protein in chemical biology and a challenging delivery target, is an exceptional model system for understanding and exploiting cellular delivery. Here, we employed a combinatorial strategy to direct HaloTag to the cytosol. We established the use of Virginia Orange, a pH-sensitive fluorophore, and Janelia Fluor 585, a similar but pH-agnostic fluorophore, in a fluorogenic assay to ascertain protein localization within human cells. Using this assay, we investigated HaloTag delivery upon modification with cell-penetrating peptides, carboxyl group esterification, and cotreatment with an endosomolytic agent. We found efficacious cytosolic entry with two distinct delivery methods. This study expands the toolkit for detecting the cytosolic access of proteins and highlights that multiple intracellular delivery strategies can be used synergistically to effect cytosolic access. Moreover, HaloTag is poised to serve as a platform for the delivery of varied cargo into human cells.

α-Silylated Diazoalkynes: New Tools for Bioconjugation of Proteins

α-Silylated diazoalkynes are stabilized diazo compounds that can selectively react with carboxylic residues in buffered aqueous media. In-situ fluoride induced desilylation increases this reactivity, leading to a very fast reaction. Application to the selective functionalization of RNase A, followed by post-functionalization using click chemistry, is described. These new reagents expand the toolbox for native protein modification at carboxylic residues.

Pinpointing Acidic Residues in Proteins

It is of great importance to pinpoint specific residues or sites of a protein in biological contexts to enable desired mechanism of action for small molecules or to precisely control protein function. In this regard, acidic residues including aspartic acid (Asp) and glutamic acid (Glu) hold great potential due to their great prevalence and unique function. To unlock the largely untapped potential, great efforts have been made recently by synthetic chemists, chemical biologists and pharmacologists. Herein, we would like to highlight the remarkable progress and particularly introduce the electrophiles that exhibit reactivity to carboxylic acids, the light-induced reactivities to carboxylic acids and the genetically encoded noncanonical amino acids that allow protein manipulations at acidic residues. We also comment on certain unresolved challenges, hoping to draw more attention to this rapidly developing area.

Investigating the Cytosolic Delivery of Proteins by Lipid Nanoparticles Using the Chloroalkane Penetration Assay

Protein therapeutics are an expanding area for research and drug development, and lipid nanoparticles (LNPs) are the most prominent nonviral vehicles for protein delivery. The most common methods for assessing protein delivery by LNPs include assays that measure the total amount of protein taken up by cells and assays that measure the phenotypic changes associated with protein delivery. However, assays for total cellular uptake include large amounts of protein that are trapped in endosomes or are otherwise nonfunctional. Assays for functional delivery are important, but the readouts are indirect and amplified, limiting the quantitative interpretation. Here, we apply an assay for cytosolic delivery, the chloroalkane penetration assay (CAPA), to measure the cytosolic delivery of a (-30) green fluorescent protein (GFP) fused to Cre recombinase (Cre(-30)GFP) fusion protein by LNPs. We compare these data to the data from total cellular uptake and functional delivery assays to provide a richer analysis of uptake and endosomal escape for LNP-mediated protein delivery. We also use CAPA for a screen of a small library of lipidoids, identifying those with a promising ability to deliver Cre(-30)GFP to the cytosol of mammalian cells. With careful controls and optimized conditions, we expect that CAPA will be a useful tool for investigating the rate, efficiency, and mechanisms of LNP-mediated delivery of therapeutic proteins.

Photocatalytic Activation of Aryl(trifluoromethyl) Diazos to Carbenes for High-Resolution Protein Labeling with Red Light

State-of-the-art methods in photoproximity labeling center on the targeted generation and capture of short-lived reactive intermediates to provide a snapshot of local protein environments. Diazirines are the current gold standard for high-resolution proximity labeling, generating short-lived aryl(trifluoromethyl) carbenes. Here, we present a method to access aryl(trifluoromethyl) carbenes from a stable diazo source via tissue-penetrable, deep red to near-infrared light (600-800 nm). The operative mechanism of this activation involves Dexter energy transfer from photoexcited osmium(II) photocatalysts to the diazo, thus revealing an aryl(trifluoromethyl) carbene. The labeling preferences of the diazo probe with amino acids are studied, showing high reactivity toward heteroatom-H bonds. Upon the synthesis of a biotinylated diazo probe, labeling studies are conducted on native proteins as well as proteins conjugated to the Os photocatalyst. Finally, we demonstrate that the conjugation of a protein inhibitor to the photocatalyst also enables selective protein labeling in the presence of spectator proteins and achieves specific labeling of a membrane protein on the surface of mammalian cells via a two-antibody photocatalytic system.

Diazo-carboxyl Click Derivatization Enables Sensitive Analysis of Carboxylic Acid Metabolites in Biosamples

Carboxylic acids are central metabolites in bioenergetics, signal transduction, and post-translation protein regulation. However, the quantitative analysis of carboxylic acids as an indispensable part of metabolomics is prohibitively challenging, particularly in trace amounts of biosamples. Here we report a diazo-carboxyl/hydroxylamine-ketone double click derivatization method for the sensitive analysis of hydrophilic, low-molecular-weight carboxylic acids. In general, our method renders a 5- to 2000-fold higher response in mass spectrometry along with improved chromatographic separation. With this method, we presented the near-single-cell analysis of carboxylic acid metabolites in 10 mouse egg cells before and after fertilization. Malate, fumarate, and β-hydroxybutyrate were found to decrease after fertilization. We also monitored the isotope labeling kinetics of carboxylic acids inside adherent cells cultured in 96-well plates during drug treatment. Finally, we applied this method to plasma or serum samples (5 μL) collected from mice and humans under pathological and physiological conditions. The double click derivatization method paves a way toward single-cell metabolomics and bedside diagnostics.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

Engineered Synthetic STxB for Enhanced Cytosolic Delivery

Many molecular targets for cancer therapy are located in the cytosol. Therapeutic macromolecules are generally not able to spontaneously translocate across membranes to reach these cytosolic targets. Therefore a strong need exists for tools that enhance cytosolic delivery. Shiga toxin B-subunit (STxB) is used to deliver therapeutic principles to disease-relevant cells that express its receptor, the glycolipid Gb3. Based on its naturally existing membrane translocation capacity, STxB delivers antigens to the cytosol of Gb3-positive dendritic cells, leading to the induction of CD8⁺ T cells. Here, we have explored the possibility of further increasing the membrane translocation of STxB to enable other therapeutic applications. For this, our capacity to synthesize STxB chemically was exploited to introduce unnatural amino acids at different positions of the protein. These were then functionalized with hydrophobic entities to locally destabilize endosomal membranes. Intracellular trafficking of these functionalized STxB was measured by confocal microscopy and their cytosolic arrival with a recently developed highly robust, sensitive, and quantitative translocation assay. From different types of hydrophobic moieties that were linked to STxB, the most efficient configuration was determined. STxB translocation was increased by a factor of 2.5, paving the path for new biomedical opportunities.

Modular Diazo Compound for the Bioreversible Late-Stage Modification of Proteins

We introduce a versatile strategy for the bioreversible modification of proteins. Our strategy is based on a tricomponent molecule, synthesized in three steps, that incorporates a diazo moiety for chemoselective esterification of carboxyl groups, a pyridyl disulfide group for late-stage functionalization with thiolated ligands, and a self-immolative carbonate group for esterase-mediated cleavage. Using cytochrome c (Cyt c) and the green fluorescent protein (GFP) as models, we generated protein conjugates modified with diverse domains for cellular delivery that include a small molecule, targeting and cell-penetrating peptides (CPPs), and a large polysaccharide. As a proof of concept, we used our strategy to effect the delivery of proteins into the cytosol of live mammalian cells in the presence of serum. The cellular delivery of functional Cyt c, which induces apoptosis, highlighted the advantage of bioreversible conjugation on a carboxyl group versus irreversible conjugation on an amino group. The ease and utility of this traceless modification provide new opportunities for chemical biologists.

Hydrolysis-Resistant Ester-Based Linkers for Development of Activity-Based NIR Bioluminescence Probes

Activity-based sensing (ABS) probes equipped with a NIR bioluminescence readout are promising chemical tools to study cancer biomarkers owing to their high sensitivity and deep tissue compatibility. Despite the demand, there is a dearth of such probes because NIR substrates (e.g., BL660 (a NIR luciferin analog)) are not equipped with an appropriate attachment site for ABS trigger installation. For instance, our attempts to mask the carboxylic acid moiety with standard self-immolative benzyl linkers resulted in significant background signals owing to undesirable ester hydrolysis. In this study, we overcame this longstanding challenge by rationally designing a new hydrolysis-resistant ester-based linker featuring an isopropyl shielding arm. Compared to the parent, the new design is 140.5-fold and 67.8-fold more resistant toward spontaneous and esterase-mediated hydrolysis, respectively. Likewise, we observed minimal cleavage of the ester moiety when incubated with a panel of enzymes possessing ester-hydrolyzing activity. These impressive in vitro results were corroborated through a series of key experiments in live cells. Further, we showcased the utility of this technology by developing the first NIR bioluminescent probe for nitroreductase (NTR) activity and applied it to visualize elevated NTR expression in oxygen deficient lung cancer cells and in a murine model of non-small cell lung cancer. The ability to monitor the activity of this key biomarker in a deep tissue context is critical because it is associated with tumor hypoxia, which in turn is linked to drug resistance and aggressive cancer phenotypes.

Endocytosis-Independent and Cancer-Selective Cytosolic Protein Delivery via Reversible Tagging with LAT1 substrate

Protein drugs targeting intracellular machineries have shown profound therapeutic potentials, but their clinical utilities are greatly hampered by the lack of efficient cytosolic delivery techniques. Existing strategies mainly rely on nanocarriers or conjugated cell-penetrating peptides (CPPs), which often have drawbacks such as materials complexity/toxicity, lack of cell specificity, and endolysosomal entrapment. Herein, a unique carrier-free approach is reported for mediating cancer-selective and endocytosis-free cytosolic protein delivery. Proteins are sequentially modified with 4-nitrophenyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) benzyl carbonate as the H₂ O₂ -responsive domain and 3,4-dihydroxy-l-phenylalanine as the substrate of l-type amino acid transporter 1 (LAT1). Thus, the pro-protein can be directly transported into tumor cells by overexpressed LAT1 on cell membranes, bypassing endocytosis and endolysosomal entrapment. In the cytosol, overproduced H₂ O₂ restores the protein structure and activity. Using this technique, versatile proteins are delivered into tumor cells with robust efficiency, including toxins, enzymes, CRISPR-Cas9 ribonucleoprotein, and antibodies. Furthermore, intravenously injected pro-protein of saporin shows potent anticancer efficacy in 4T1-tumor-bearing mice, without provoking systemic toxicity. Such a facile and versatile pro-protein platform may benefit the development of protein pharmaceuticals.

Host-Guest Complexation by β-Cyclodextrin Enhances the Solubility of an Esterified Protein

The carboxyl groups of a protein can be esterified by reaction with a diazo compound, 2-diazo-2-(p-methylphenyl)-N,N-dimethylacetamide. This esterification enables the entry of the protein into the cytosol of a mammalian cell, where the nascent ester groups are hydrolyzed by endogenous esterases. The low aqueous solubility of the ensuing esterified protein is, however, a major practical challenge. Solubility screening revealed that β-cyclodextrin (β-CD) is an optimal solubilizing agent for esterified green fluorescent protein (est-GFP). Its addition can increase the recovery of est-GFP by 10-fold. α-CD, γ-CD, and cucurbit-7-uril are less effective excipients. ¹H NMR titration experiments revealed that β-CD encapsulates the hydrophobic tolyl group of ester conjugates with K_a = 321 M^-1. Combining l-arginine and sucrose with β-CD enables the nearly quantitative recovery of est-GFP. Thus, the insolubility of esterified proteins can be overcome with excipients.

Harnessing the Therapeutic Potential of Biomacromolecules through Intracellular Delivery of Nucleic Acids, Peptides, and Proteins

Biomacromolecules have long been at the leading edge of academic and pharmaceutical drug development and clinical translation. With the clinical advances of new therapeutics, such as monoclonal antibodies and nucleic acids, the array of medical applications of biomacromolecules has broadened considerably. A major on-going effort is to expand therapeutic targets within intracellular locations. Owing to their large sizes, abundant charges, and hydrogen-bond donors and acceptors, advanced delivery technologies are required to deliver biomacromolecules effectively inside cells. In this review, strategies used for the intracellular delivery of three major forms of biomacromolecules: nucleic acids, proteins, and peptides, are highlighted. An emphasis is placed on synthetic delivery approaches and the major hurdles needed to be overcome for their ultimate clinical translation.

"Clickable" ZIF-8 for Cell-Type-Specific Delivery of Functional Proteins

Protein therapy provides a powerful alternative to small-molecule-based therapy, especially on cellular targets that are normally considered to be less druggable. Intracellular protein delivery, in particular, in a cell-type-specific manner, is still highly challenging. At present, few general strategies are available for the robust and selective intracellular delivery of proteins. In this Letter, by using zeolitic imidazolate framework-8 (ZIF-8) as protein-encapsulated nanoparticles and simultaneous doping with norbornene-modified imidazole (MIM-Nor), followed by surface attachment of the resulting nanoparticles with cetuximab (Cet) through click chemistry, we successfully synthesized Cet@protein@ZIF-8N, which was subsequently used for the selective intracellular delivery of functional proteins to epidermal-growth-factor-receptor (EGFR)-overexpressed cells. Both in-cell and in vivo experiments proved that Cet@RNase A@ZIF-8N can effectively deliver RNase A with the retention of selective inhibition. Furthermore, the same strategy was successfully applied to cell-type-specific gene editing through the delivery of a Cas9/sgRNA complex to knockdown the endogenous expression of glutathione peroxidase (GPX4), a key protein in ferroptosis. Our new system thus has potential implications in future cancer treatment and the development of precision medicine.

Genetic and Covalent Protein Modification Strategies to Facilitate Intracellular Delivery

Protein-based therapeutics represent a rapidly growing segment of approved disease treatments. Successful intracellular delivery of proteins is an important precondition for expanded in vivo and in vitro applications of protein therapeutics. Direct modification of proteins and peptides for improved cytosolic translocation are a promising method of increasing delivery efficiency and expanding the viability of intracellular protein therapeutics. In this Review, we present recent advances in both synthetic and genetic protein modifications for intracellular delivery. Active endocytosis-based and passive internalization pathways are discussed, followed by a review of modification methods for improved cytosolic delivery. After establishing how proteins can be modified, general strategies for facilitating intracellular delivery, such as chemical supercharging or inclusion of cell-penetrating motifs, are covered. We then outline protein modifications that promote endosomal escape. We finally examine the delivery of two potential classes of therapeutic proteins, antibodies and associated antibody fragments, and gene editing proteins, such as cas9.

Ribonuclease zymogen induces cytotoxicity upon HIV-1 infection

BACKGROUND

Targeting RNA is a promising yet underdeveloped modality for the selective killing of cells infected with HIV-1. The secretory ribonucleases (RNases) found in vertebrates have cytotoxic ribonucleolytic activity that is kept in check by a cytosolic ribonuclease inhibitor protein, RI.

METHODS

We engineered amino acid substitutions that enable human RNase 1 to evade RI upon its cyclization into a zymogen that is activated by the HIV-1 protease. In effect, the zymogen has an HIV-1 protease cleavage site between the termini of the wild-type enzyme, thereby positioning a cleavable linker over the active site that blocks access to a substrate.

RESULTS

The amino acid substitutions in RNase 1 diminish its affinity for RI by 106-fold and confer high toxicity for T-cell leukemia cells. Pretreating these cells with the zymogen leads to a substantial drop in their viability upon HIV-1 infection, indicating specific toxicity toward infected cells.

CONCLUSIONS

These data demonstrate the utility of ribonuclease zymogens as biologic prodrugs.

Adapting protein sequences for optimized therapeutic efficacy

Therapeutic proteins alleviate disease pathology by supplementing missing or defective native proteins, sequestering superfluous proteins, or by acting through designed non-natural mechanisms. Although therapeutic proteins often have the same amino acid sequence as their native counterpart, their maturation paths from expression to the site of physiological activity are inherently different, and optimizing protein sequences for properties that 100s of millions of years of evolution did not need to address presents an opportunity to develop better biological treatments. Because therapeutic proteins are inherently non-natural entities, optimization for their desired function should be considered analogous to that of small molecule drug candidates, which are optimized through expansive combinatorial variation by the medicinal chemist. Here, we review recent successes and challenges of protein engineering for optimized therapeutic efficacy.

Two-Step Synthesis of α-Aryl-α-diazoamides as Modular Bioreversible Labels

α-Aryl-α-diazoamides were synthesized in two steps under mild conditions. This expeditious route employs Pd-catalyzed C-H arylation of N-succinimidyl 2-diazoacetate to obtain N-succinimidyl 2-aryl-2-diazoacetates, followed by aminolysis. The ensuing diazo compounds can esterify carboxyl groups in aqueous solution, and the ester products are substrates for an esterase. The broad scope of the synthetic route enables the continued development of diazo compounds in chemical biology.

Strengths and Challenges of Secretory Ribonucleases as AntiTumor Agents

Approaches to develop effective drugs to kill cancer cells are mainly focused either on the improvement of the currently used chemotherapeutics or on the development of targeted therapies aimed at the selective destruction of cancer cells by steering specific molecules and/or enhancing the immune response. The former strategy is limited by its genotoxicity and severe side effects, while the second one is not always effective due to tumor cell heterogeneity and variability of targets in cancer cells. Between these two strategies, several approaches target different types of RNA in tumor cells. RNA degradation alters gene expression at different levels inducing cell death. However, unlike DNA targeting, it is a pleotropic but a non-genotoxic process. Among the ways to destroy RNA, we find the use of ribonucleases with antitumor properties. In the last few years, there has been a significant progress in the understanding of the mechanism by which these enzymes kill cancer cells and in the development of more effective variants. All the approaches seek to maintain the requirements of the ribonucleases to be specifically cytotoxic for tumor cells. These requirements start with the competence of the enzymes to interact with the cell membrane, a process that is critical for their internalization and selectivity for tumor cells and continue with the downstream effects mainly relying on changes in the RNA molecular profile, which are not only due to the ribonucleolytic activity of these enzymes. Although the great improvements achieved in the antitumor activity by designing new ribonuclease variants, some drawbacks still need to be addressed. In the present review, we will focus on the known mechanisms used by ribonucleases to kill cancer cells and on recent strategies to solve the shortcomings that they show as antitumor agents, mainly their pharmacokinetics.

Transforming nanobodies into high-precision tools for protein function analysis

Single-domain antibodies, derived from camelid heavy antibodies (nanobodies) or shark variable new antigen receptors, have attracted increasing attention in recent years due to their extremely versatile nature and the opportunities they offer for downstream modification. Discovered more than three decades ago, these 120-amino acid (∼15-kDa) antibody fragments are known to bind their target with high specificity and affinity. Key features of nanobodies that make them very attractive include their single-domain nature, small size, and affordable high-level expression in prokaryotes, and their cDNAs are routinely obtained in the process of their isolation. This facilitates and stimulates new experimental approaches. Hence, it allows researchers to formulate new answers to complex biomedical questions. Through elementary PCR-based technologies and chemical modification strategies, their primary structure can be altered almost at leisure while retaining their specificity and biological activity, transforming them into highly tailored tools that meet the increasing demands of current-day biomedical research. In this review, various aspects of camelid nanobodies are expounded, including intracellular delivery in recombinant format for manipulation of, i.e., cytoplasmic targets, their derivatization to improve nanobody orientation as a capturing device, approaches to reversibly bind their target, their potential as protein-silencing devices in cells, the development of strategies to transfer nanobodies through the blood-brain barrier and their application in CAR-T experimentation. We also discuss some of their disadvantages and conclude with future prospects.

Probing the Mechanism of Photoaffinity Labeling by Dialkyldiazirines through Bioorthogonal Capture of Diazoalkanes

Dialkyldiazirines have emerged as reagents of choice for biological photoaffinity labeling studies. The mechanism of crosslinking has dramatic consequences for biological applications where instantaneous labeling is desirable, as carbene insertions display different chemoselectivity and are much faster than competing mechanisms involving diazo or ylide intermediates. Here, deuterium labeling and diazo compound trapping experiments are employed to demonstrate that both carbene and diazo mechanisms operate in the reactions of a dialkyldiazirine motif that is commonly utilized for biological applications. For the fraction of intermolecular labeling that does involve a carbene mechanism, direct insertion is not necessarily involved, as products derived from a carbonyl ylide are also observed. We demonstrate that a strained cycloalkyne can intercept diazo compound intermediates and serve as a bioorthogonal probe for studying the contribution of the diazonium mechanism of photoaffinity labeling on a model protein under aqueous conditions.

Intracellular Delivery of Adamantane-Tagged Small Molecule, Proteins, and Liposomes Using an Octaarginine-Conjugated β-Cyclodextrin

Herein, we demonstrate a convenient technique for the intracellular delivery of proteins and liposomes based on supramolecular host-guest chemistry. First, we prepared the R8-CD^OH carrier molecule, which is a β-cyclodextrin derivative bearing an octaarginine (R8) chain, as a cell-penetrating peptide, at the primary hydroxyl group. The surface amino groups of proteins (GFP, β-gal, and IgG) were then partly modified with adamantane (Ad) tags using 1-Ad-carboxylic acid N-hydroxysuccinimide ester (Ad-NHS). These Ad-tagged proteins were effectively delivered into HeLa cells though supramolecular host-guest interactions with R8-CD^OH. A 100 nm sized liposome bearing Ad-tags on its surface was also delivered into these cells by the action of R8-CD^OH. The present method does not require any genetic manipulation, and only easy chemical modification processes are used to facilitate intracellular delivery; therefore, we believe that the present method is applicable to a variety of bioengineering processes, such as protein-based therapeutics, cellular reprogramming, and genome-editing, among others.

Partitioning of amino acids and proteins into decanol using phase transfer agents towards understanding life in non-polar liquids

Water has many roles in the context of life on Earth, however throughout the universe, other liquids may be able to support the emergence of life. We looked at the ability of amino acids, peptides, a depsipeptide, and proteins to partition into a non-polar decanol phase, with and without the addition of a phase transfer agent. Partitioning evaluated using UV detection, or with HPLC coupled to either charged aerosol detection or ESI-MS. For amino acids and short peptides, phase transfer agents were used to move the biomolecules to the decanol phase, and this transfer was pH dependent. For larger molecules, phase transfer agents did not seem to affect the transfer. Both the depsipetide, valinomycin, and the protein Taq DNA polymerase had solubility in the decanol phase. Additionally, valinomycin appeared to retain its biological ability to bind to potassium ions. These results show that most terrestrial biological molecules are not compatible with non-polar solvents, but it is possible to find and perhaps evolve polymers that are functional in such phases.

Circular zymogens of human ribonuclease 1

The endogenous production of enzymes as zymogens provides a means to control catalytic activities. Here, we describe the heterologous production of ribonuclease 1 (RNase 1), which is the most prevalent secretory ribonuclease in humans, as a zymogen. In folded RNase 1, the N and C termini flank the enzymic active site. By using intein-mediated cis-splicing, we created circular proteins in which access to the active site of RNase 1 is obstructed by an amino-acid sequence that is recognized by the HIV-1 protease. Installing a sequence that does not perturb the RNase 1 fold led to only modest inactivation. In contrast, the ancillary truncation of residues from each terminus led to a substantial decrease in the catalytic activity of the zymogen with the maintenance of thermostability. For optimized zymogens, activation by HIV-1 protease led to a > 104 -fold increase in ribonucleolytic activity at a rate comparable to that for the cleavage of endogenous viral substrates. Molecular modeling indicated that these zymogens are inactivated by conformational distortion in addition to substrate occlusion. Because protease levels are elevated in many disease states and ribonucleolytic activity can be cytotoxic, RNase 1 zymogens have potential as generalizable prodrugs.