A molecular method for the delivery of small molecules and proteins across the cell wall of algae using molecular transporters

Cell-Penetrating Peptide-Based Triple Nanocomplex Enables Efficient Nuclear Gene Delivery in Chlamydomonas reinhardtii

Microalgae are a promising solution for mitigating climate change due to their ability to capture greenhouse gases and produce renewable materials. However, their effective application is often hindered by barriers that necessitate advances in genetic engineering to improve photosynthesis and productivity. One major obstacle is the microalgal cell wall, which complicates the delivery of genetic material into these organisms. To address these challenges, we developed a novel triple nanocomplex system integrating cell-penetrating peptides (CPPs), nuclear localization signal (NLS) peptides, and plasmid DNA. This system allows simple preparation while achieving efficient nuclear translocation of plasmid DNA. We evaluated two CPPs, pVEC-ORI and pVEC-R6A, for their efficacy in facilitating intracellular transfer of DNA into wild-type Chlamydomonas reinhardtii cells. Notably, pVEC-R6A demonstrated a 6.88-fold increase in efficiency compared to pVEC-ORI, despite the presence of thick cell walls. The optimal CPP:DNA ratio for stable nanocomplex formation was determined to be 5:1 for pVEC-ORI and 10:1 for pVEC-R6A. By incorporating the simian virus 40 (SV40) NLS into CPP/DNA nanocomplexes, we successfully directed the localization of plasmid DNA into the nucleus. Our findings indicate that this simple and efficient DNA delivery system has significant potential as a tool to advance microalgal synthetic biology.

The need for smart microalgal bioprospecting

Microalgae's adaptability and resilience to Earth's diverse environments have evolved these photosynthetic microorganisms into a biotechnological source of industrially relevant physiological functions and biometabolites. Despite this, microalgae-based industries only exploit a handful of species. This lack of biodiversity hinders the expansion of the microalgal industry. Microalgal bioprospecting, searching for novel biological algal resources with new properties, remains a low throughput and time-consuming endeavour due to inefficient workflows that rely on non-selective sampling, monoalgal culture status and outdated, non-standardized characterization techniques. This review will highlight the importance of microalgal bioprospecting and critically explore commonly employed methodologies. We will also explore current advances driving the next generation of smart algal bioprospecting focusing on novel workflows and transdisciplinary methodologies with the potential to enable high-throughput microalgal biodiscoveries. Images adapted from (Addicted04 in Wikipedia File: Australia on the globe (Australia centered).svg. 2014.; Jin et al. in ACS Appl Bio Mater 4:5080-5089, 2021; Kim et al. in Microchim Acta 189:88, 2022; Tony et al. in Lab on a Chip 15, 19:3810-3810; Thermo Fisher Scientific INC. in CTS Rotea Brochure).

Cell-Penetrating Peptide Delivery of Nucleic Acid Cargo to Emiliania huxleyi, a Calcifying Marine Coccolithophore

Coccolithophores are a group of unicellular marine phytoplankton that exhibit a prolific capacity for carbon conversion and are critical to ocean biogeochemistry. A fundamental understanding of coccolithophore biomineralization has been limited, in part, by the lack of genetic and molecular tools to investigate the organisms. In particular, it has proven to be difficult to deliver macromolecules across the coccosphere-membrane complex. To overcome this barrier, we employed cell-penetrating peptides (CPP) in the Emiliania huxleyi coccolithophores. We evaluated three established CPPs (TAT, R9, and KFF) and designed a CPP that incorporates a high proline content identified in the protein transduction domain of EhV060, an E. huxleyi virus lectin protein. To measure the delivery performance, we covalently linked CPPs to synthetic peptide nucleic acids (PNA) and attached a fluorescein marker. CPP-PNA-FITC complexes were efficiently delivered across the coccosphere-membrane complex to the cytoplasm of E. huxleyi cells. Characterization of E. huxleyi demonstrates that CPP-PNA are nontoxic and reveals specific effects of CPP-PNA on cell biology and calcification. Direct delivery and characterization of synthetic nucleic acids represent a step forward in synthetic biology to explore coccolithophore biomineralization.

Biohybrid Microalgae Robots: Design, Fabrication, Materials, and Applications

The integration of microorganisms and engineered artificial components has shown considerable promise for creating biohybrid microrobots. The unique features of microalgae make them attractive candidates as natural actuation materials for the design of biohybrid microrobotic systems. In this review, microalgae-based biohybrid microrobots are introduced for diverse biomedical and environmental applications. The distinct propulsion and phototaxis behaviors of green microalgae, as well as important properties from other photosynthetic microalga systems (blue-green algae and diatom) that are crucial to constructing powerful biohybrid microrobots, will be described first. Then the focus is on chemical and physical routes for functionalizing the algae surface with diverse reactive materials toward the fabrication of advanced biohybrid microalgae robots. Finally, representative applications of such algae-driven microrobots are presented, including drug delivery, imaging, and water decontamination, highlighting the distinct advantages of these active biohybrid robots, along with future prospects and challenges.

Detection of intact vancomycin-arginine as the active antibacterial conjugate in E. coli by whole-cell solid-state NMR

The introduction of new and improved antibacterial agents based on facile synthetic modifications of existing antibiotics represents a promising strategy to deliver urgently needed antibacterial candidates to treat multi-drug resistant bacterial infections. Using this strategy, vancomycin was transformed into a highly active agent against antibiotic-resistant Gram-negative organisms in vitro and in vivo through the addition of a single arginine to yield vancomycin-arginine (V-R). Here, we report detection of the accumulation of V-R in E. coli by whole-cell solid-state NMR using 15N-labeled V-R. 15N CPMAS NMR revealed that the conjugate remained fully amidated without loss of arginine, demonstrating that intact V-R represents the active antibacterial agent. Furthermore, C{N}REDOR NMR in whole cells with all carbons at natural abundance 13C levels exhibited the sensitivity and selectivity to detect the directly bonded 13C-15N pairs of V-R within E. coli cells. Thus, we also present an effective methodology to directly detect and evaluate active drug agents and their accumulation within bacteria without the need for potentially perturbative cell lysis and analysis protocols.

Nuclear localization signal peptides enhance genetic transformation of Dunaliella salina

BACKGROUND

Dunaliella salina (D. salina) expression system shows a very attractive application prospect, but it currently has a technical bottleneck, namely the low or unstable expression of recombinant proteins. Given the characteristics of cell-penetrating peptides or/and nuclear localization signal (NLS) peptides, this study is the first attempt to improve the transformation rate of foreign gene with trans-activating transcriptional (TAT) protein or/and NLS peptides.

METHODS AND RESULTS

Using salt gradient method, exogenous plasmids were transferred into D. salina cells with TAT or TAT/NLS complexes simultaneously. The β-glucuronidase gene expression was identified by means of histochemical stain and RT-qPCR detection. Through observation with light microscope, TAT-mediating cells exhibit an apparent cytotoxicity even at ratios of 0.5, no significant toxicity was noted in the TAT/plasmid/NLS complex group. It is obvious that with the addition of peptides the toxicity decreases significantly. Histochemical staining showed that the transformants presented blue color under light microscope, but the negative control and blank control are not. Furthermore, based on a TAT/plasmids ratio of 4 with 10 µg NLS peptides mediation, RT-qPCR results demonstrated that the transcripts of target gene were increased by 269 times than that of control group.

CONCLUSIONS

This study demonstrated that combination of TAT and NLS peptides can significantly improve the transformation rate and expression level of foreign gene in D. salina system. It offers a promising way for promoting the application and development of D. salina bioreactor.

Extremophile-based biohybrid micromotors for biomedical operations in harsh acidic environments

The function of robots in extreme environments is regarded as one of the major challenges facing robotics. Here, we demonstrate that acidophilic microalgae biomotors can maintain their swimming behavior over long periods of time in the harsh acidic environment of the stomach, thus enabling them to be applied for gastrointestinal (GI) delivery applications. The biomotors can also be functionalized with a wide range of cargos, ranging from small molecules to nanoparticles, without compromising their ability to self-propel under extreme conditions. Successful GI delivery of model payloads after oral administration of the acidophilic algae motors is confirmed using a murine model. By tuning the surface properties of cargos, it is possible to modulate their precise GI localization. Overall, our findings indicate that multifunctional acidophilic algae-based biomotors offer distinct advantages compared to traditional biohybrid platforms and hold great potential for GI-related biomedical applications.

Combination of vancomycin and guanidinium-functionalized helical polymers for synergistic antibacterial activity and biofilm ablation

The emergence of various resistant bacteria and overuse of antibiotics have led to severe side effects. Therefore, developing efficient and safe antibacterial systems is important. Herein, well-defined antimicrobial material–helical poly(phenyl guanidinium isocyanide) block copolymers with different conformations (l-P3-van, d-P3-van, and dl-P3-van) that connect vancomycin (van) to the polymer through a disulfide bond were synthesized. The prepared antimicrobial materials exhibit broad-spectrum antimicrobial activity, low bacterial resistance, and good proteolytic stability. They also overcome the intrinsic resistance of Gram-negative bacteria to van with a 100-fold increase in antimicrobial activity. Interestingly, the conformation of the material promotes its antimicrobial activity. The left-handed helix conformation shows five-fold more antimicrobial activity than the right-handed helical conformation, thereby opening a path for the application of nanochirality in the field of antibiotics.

Helical poly(phenyl isocyanide)-based antibacterial materials have been developed, which have a broad antibacterial spectrum and high antibacterial activity and can effectively destroy preformed biofilms.

Reduced cytotoxicity of polyethyleneimine by covalent modification of antioxidant and its application to microalgal transformation

The conversion of carbon dioxide into valuable chemicals is an effective strategy for combating augmented concentrations of carbon dioxide in the environment. Microalgae photosynthetically produce valuable chemicals that are used as biofuels, sources for industrial materials, medicinal leads, and food additives. Thus, improvements in microalgal technology via genetic engineering may prove to be promising for the tailored production of novel metabolites. For the transformation of microalgae, nucleic acids such as plasmid DNA (pDNA) are delivered into the cells using physical and mechanical techniques, such as electroporation, bombardment with DNA-coated microprojectiles, and vortexing with glass beads. However, owing to the electrostatic repulsion between negatively charged cell walls and nucleic acids, the delivery of nucleic acids into the microalgal cells is challenging. To solve this issue, in this study, we investigated microalgal transformation via electroporation using polyplexes with linear polyethyleneimine (LPEI) and pDNA. However, the high toxicity of LPEI decreased the transformation efficiency in Chlamydomonas reinhardtii cells. We revealed that the toxicity of LPEI was due to oxidative stress resulting from the cellular uptake of LPEI. To suppress the toxicity of LPEI, an antioxidant, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), was covalently conjugated with LPEI; the conjugate was named as TEMPO-LPEI. Interestingly, with a cellular uptake tendency similar to that of LPEI, TEMPO-LPEI dramatically decreased oxidative stress and cytotoxicity. Electroporation using polyplexes of TEMPO-LPEI and pDNA enhanced the transformation efficiency, compared to those treated with bare pDNA and polyplexes of LPEI/pDNA. This result indicates that polycations conjugated with antioxidants could be useful in facilitating microalgal transformation.

Gene Delivery Technologies with Applications in Microalgal Genetic Engineering

Microalgae and cyanobacteria are photosynthetic microbes that can be grown with the simple inputs of water, carbon dioxide, (sun)light, and trace elements. Their engineering holds the promise of tailored bio-molecule production using sustainable, environmentally friendly waste carbon inputs. Although algal engineering examples are beginning to show maturity, severe limitations remain in the transformation of multigene expression cassettes into model species and DNA delivery into non-model hosts. This review highlights common and emerging DNA delivery methods used for other organisms that may find future applications in algal engineering.

Development of a pVEC peptide-based ribonucleoprotein (RNP) delivery system for genome editing using CRISPR/Cas9 in Chlamydomonas reinhardtii

Recent technical advances related to the CRISPR/Cas9-based genome editing system have enabled sophisticated genome editing in microalgae. Although the demand for research on genome editing in microalgae has increased over time, methodological research has not been established to date for the delivery of a ribonucleoprotein (Cas9/sgRNA complex) using a cell penetrating peptide into microalgal cell lines. Here, we present a ribonucleoprotein delivery system for Chlamydomonas reinhardtii mediated by the cell penetrating peptide pVEC (LLIILRRRIRKQAHAHSK) which is in a non-covalent form. Using this technically simple method, the ribonucleoprotein was successfully delivered into C. reinhardtii. Gene Maa7 and FKB12 were disrupted, and their distinguishing patterns of Indel mutations were analyzed with the observation of several insertions of sequences not originating from the genome DNA, such as chloroplast DNA, into the expected loci. In addition, the cytotoxicity of Cas9 and the ribonucleoprotein was investigated according to the concentration and time in the algal cells. It was observed that Cas9 alone without the sgRNA induces a more severe cytotoxicity compared to the ribonucleoprotein. Our study will not only contribute to algal cell biology and its genetic engineering for further applications involving various organisms but will also provide a deeper understating of the basic science of the CRISPR/Cas9 system.

Rapid identification of a subset of foodborne bacteria in live-cell assays

The detection and identification of microbial pathogens in meat and fresh produce play an essential role in food safety for reducing foodborne illnesses every year. A new approach based on targeting a specific sequence of the 16S rRNA region for each bacterium is proposed and validated. The probe complex consists of a C60, a conjugated RNA detector which targets a specific 16S rRNA sequence, and a complementary fluorescent reporter. The RNA detectors were designed by integrating NIH nucleotide and Vienna RNA Webservice databases, and their specificities were validated by the RDP database. Probe complexes were synthesized for identifying E. coli K12, E. coli O157: H7, S. enterica, Y. enterocolitica, C. perfringens, and L. monocytogenes. First, under controlled conditions of known bacterial mixtures, the efficiency and crosstalk for identifying the foodborne bacteria were quantified to be above 94% and below 5%, respectively. Second, experiments were designed by inoculating meat products by known numbers of bacteria and measuring the limit of detection. In one experiment, 225 g of autoclaved ground chicken was inoculated with 9 E. coli O157:H7, where 6.8 ± 1.2 bacteria with 95% confidence interval were recovered. Third, by positionally printing probe complexes in microwells, specific microorganisms were identified with only one fluorophore. The proposed protocol is a cell-based system, can identify live bacteria in 15 min, requires no amplification, and has the potential to open new surveillance opportunities.Key points• The identification of foodborne bacteria is enabled in live-cell assays.• The limit of detection for 100 g of fresh chicken breast inoculated with 4 bacteria is 2.7 ± 1.4 with 95% confidence interval.• The identification of five bacteria in a coded microwell chip is enabled with only one fluorophore.

Dual Peptide-Based Gene Delivery System for the Efficient Transfection of Plant Callus Cells

Owing to their diverse functions and tunable physicochemical properties, peptides are promising alternatives to the conventional gene delivery tools that are available for plant systems. However, peptide-mediated gene delivery is limited by low transfection efficiency in plants because of the insufficient cytosolic translocation of DNA cargo. Here, we report a dual peptide-based gene delivery system for the efficient transfection of plant callus cells. This system is based on the combination of an artificial peptide composed of cationic cell-penetrating and hydrophobic endosomal escape domains with a gene carrier peptide composed of amphiphilic cell-penetrating and cationic DNA-binding domains. Cellular internalization and transfection studies revealed that this dual peptide-based system enables more efficient transfection of callus cells than does a carrier peptide alone by enhancing the endocytic uptake and subsequent cytosolic translocation of a carrier peptide/DNA complex. The present strategy will expand the utility of peptide-mediated plant gene delivery for a wide range of applications and basic research.

The rational design of cell-penetrating peptides for application in delivery systems

Cell penetrating peptides (CPPs) play a crucial role in the transportation of bioactive molecules. Although CPPs have been used widely in various delivery systems, further applications of CPPs are hampered by several drawbacks, such as high toxicity, low delivery efficiency, proteolytic instability and poor specificity. To design CPPs with great cell-penetrating ability, physicochemical properties and safety, researchers have tried to develop new methods to overcome the defects of CPPs. Briefly, (1) the side chain of arginine containing the guanidinium group is essential for the facilitation of cellular uptake; (2) the hydrophobic counterion complex around the guanidinium-rich backbone can "coat" the highly cationic structure with lipophilic moieties and act as an activator; (3) the conformation-constrained strategy was pursued to shield the peptide, thereby impeding access of the proteolytic enzyme; (4) targeting strategies can increase cell-type specificity of CPPs. In this review, the above four aspects were discussed in detail.

Genetic transformation of Chlorella vulgaris mediated by HIV-TAT peptide

Scientific interest in microalgal species is growing and, genetic transformation has definitely opened more avenues, in the ongoing research on microphytes. In the present study, we have attempted to transform Chlorella vulgaris by mobilizing double-stranded linear Transfer DNA (T-DNA) comprised of green fluorescent protein (egfp) gene cassette and hygromycin phosphotransferase II (hptII) gene cassette non-covalently bound to TAT peptide, into C. vulgaris cells treated with Triton X-100. The transformed C. vulgaris cells when examined under fluorescent microscope, exhibited green fluorescence in comparison to the untransformed cells. The transformed cells were further screened, and the surviving colonies were sub-cultured, on BG11 medium fortified with Hygromycin. The surviving colonies were confirmed for the presence of integrated T-DNA by Polymerase Chain Reaction with egfp and hptII gene-specific primers. This methodology has potential to substitute the existing tedious transformation methodologies and ease the future studies in microalgae.

A Dual-Function Antibiotic-Transporter Conjugate Exhibits Superior Activity in Sterilizing MRSA Biofilms and Killing Persister Cells

New strategies are urgently needed to target MRSA, a major global health problem and the leading cause of mortality from antibiotic-resistant infections in many countries. Here, we report a general approach to this problem exemplified by the design and synthesis of a vancomycin-d-octaarginine conjugate (V-r8) and investigation of its efficacy in addressing antibiotic-insensitive bacterial populations. V-r8 eradicated MRSA biofilm and persister cells in vitro, outperforming vancomycin by orders of magnitude. It also eliminated 97% of biofilm-associated MRSA in a murine wound infection model and displayed no acute dermal toxicity. This new dual-function conjugate displays enhanced cellular accumulation and membrane perturbation as compared to vancomycin. Based on its rapid and potent activity against biofilm and persister cells, V-r8 is a promising agent against clinical MRSA infections.

Ion and metabolite transport in the chloroplast of algae: lessons from land plants

Chloroplasts are endosymbiotic organelles and play crucial roles in energy supply and metabolism of eukaryotic photosynthetic organisms (algae and land plants). They harbor channels and transporters in the envelope and thylakoid membranes, mediating the exchange of ions and metabolites with the cytosol and the chloroplast stroma and between the different chloroplast subcompartments. In secondarily evolved algae, three or four envelope membranes surround the chloroplast, making more complex the exchange of ions and metabolites. Despite the importance of transport proteins for the optimal functioning of the chloroplast in algae, and that many land plant homologues have been predicted, experimental evidence and molecular characterization are missing in most cases. Here, we provide an overview of the current knowledge about ion and metabolite transport in the chloroplast from algae. The main aspects reviewed are localization and activity of the transport proteins from algae and/or of homologues from other organisms including land plants. Most chloroplast transporters were identified in the green alga Chlamydomonas reinhardtii, reside in the envelope and participate in carbon acquisition and metabolism. Only a few identified algal transporters are located in the thylakoid membrane and play role in ion transport. The presence of genes for putative transporters in green algae, red algae, diatoms, glaucophytes and cryptophytes is discussed, and roles in the chloroplast are suggested. A deep knowledge in this field is required because algae represent a potential source of biomass and valuable metabolites for industry, medicine and agriculture.

Peptide-drug conjugates as effective prodrug strategies for targeted delivery

Peptide-drug conjugates (PDCs) represent an important class of therapeutic agents that combine one or more drug molecules with a short peptide through a biodegradable linker. This prodrug strategy uniquely and specifically exploits the biological activities and self-assembling potential of small-molecule peptides to improve the treatment efficacy of medicinal compounds. We review here the recent progress in the design and synthesis of peptide-drug conjugates in the context of targeted drug delivery and cancer chemotherapy. We analyze carefully the key design features in choosing the peptide sequence and linker chemistry for the drug of interest, as well as the strategies to optimize the conjugate design. We highlight the recent progress in the design and synthesis of self-assembling peptide-drug amphiphiles to construct supramolecular nanomedicine and nanofiber hydrogels for both systemic and topical delivery of active pharmaceutical ingredients.

Vault Nanoparticles: Chemical Modifications for Imaging and Enhanced Delivery

Vault nanoparticles represent promising vehicles for drug and probe delivery. Innately found within human cells, vaults are stable, biocompatible nanocapsules possessing an internal volume that can encapsulate hundreds to thousands of molecules. They can also be targeted. Unlike most nanoparticles, vaults are nonimmunogenic and monodispersed and can be rapidly produced in insect cells. Efforts to create vaults with modified properties have been, to date, almost entirely limited to recombinant bioengineering approaches. Here we report a systematic chemical study of covalent vault modifications, directed at tuning vault properties for research and clinical applications, such as imaging, targeted delivery, and enhanced cellular uptake. As supra-macromolecular structures, vaults contain thousands of derivatizable amino acid side chains. This study is focused on establishing the comparative selectivity and efficiency of chemically modifying vault lysine and cysteine residues, using Michael additions, nucleophilic substitutions, and disulfide exchange reactions. We also report a strategy that converts the more abundant vault lysine residues to readily functionalizable thiol terminated side chains through treatment with 2-iminothiolane (Traut's reagent). These studies provide a method to doubly modify vaults with cell penetrating peptides and imaging agents, allowing for in vitro studies on their enhanced uptake into cells.

PolyMetformin combines carrier and anticancer activities for in vivo siRNA delivery

Metformin, a widely implemented anti-diabetic drug, exhibits potent anticancer efficacies. Herein a polymeric construction of Metformin, PolyMetformin (PolyMet) is successfully synthesized through conjugation of linear polyethylenimine (PEI) with dicyandiamide. The delocalization of cationic charges in the biguanide groups of PolyMet reduces the toxicity of PEI both in vitro and in vivo. Furthermore, the polycationic properties of PolyMet permits capture of siRNA into a core-membrane structured lipid-polycation-hyaluronic acid (LPH) nanoparticle for systemic gene delivery. Advances herein permit LPH-PolyMet nanoparticles to facilitate VEGF siRNA delivery for VEGF knockdown in a human lung cancer xenograft, leading to enhanced tumour suppressive efficacy. Even in the absence of RNAi, LPH-PolyMet nanoparticles act similarly to Metformin and induce antitumour efficacy through activation of the AMPK and inhibition of the mTOR. In essence, PolyMet successfully combines the intrinsic anticancer efficacy of Metformin with the capacity to carry siRNA to enhance the therapeutic activity of an anticancer gene therapy.

Polymyxins Facilitate Entry into Mammalian Cells

Polymyxin and guanidinylated polymyxin effectively deliver large biomolecules and liposomal assemblies into mammalian cells.

Polymyxin B is an antibiotic used against multi-resistant Gram negative infections, despite observed nephrotoxicity. Here we report the synthesis of functionalized derivatives of polymyxin B and its per-guanidinylated derivative in order to further explore the structural requirements necessary to facilitate uptake of the antibiotic into mammalian cells. We also investigate the possibility of using these novel scaffolds as molecular transporters. At nanomolar concentrations, both are capable of delivering large cargo (>300 kDa) into living cells. Their uptake depends exclusively on cell surface heparan sulfate. Mechanistic studies indicate these novel transporters are internalized through caveolae-mediated pathways and confocal microscopy show colocalization with lysosomes. The polymyxin-based transporters demonstrate cytosolic delivery through the delivery of a ribosome-inactivating protein. Furthermore, the natural polymyxin scaffold can be incorporated into liposomes and enhance their intracellular uptake. In addition to demonstrating the ability of the polymyxin scaffold to facilitate internalization into mammalian cells, these observations suggest the potential use of polymyxin and guanidinopolymyxin for intracellular delivery.

Cell-Penetrating, Guanidinium-Rich Oligophosphoesters: Effective and Versatile Molecular Transporters for Drug and Probe Delivery

The design, synthesis, and biological evaluation of a new family of highly effective cell-penetrating molecular transporters, guanidinium-rich oligophosphoesters, are described. These unique transporters are synthesized in two steps, irrespective of oligomer length, by the organocatalytic ring-opening polymerization (OROP) of 5-membered cyclic phospholane monomers followed by oligomer deprotection. Varying the initiating alcohol results in a wide variety of cargo attachment strategies for releasable or nonreleasable transporter applications. Initiation of oligomerization with a fluorescent probe produces, upon deprotection, a transporter-probe conjugate that is shown to readily enter multiple cell lines in a dose-dependent manner. These new transporters are superior in cell uptake to previously studied guanidinium-rich oligocarbonates and oligoarginines, showing over 2-fold higher uptake than the former and 6-fold higher uptake than the latter. Initiation with a protected thiol gives, upon deprotection, thiol-terminated transporters which can be thiol-click conjugated to a variety of probes, drugs and other cargos as exemplified by the conjugation and delivery of the model probe fluorescein-maleimide and the medicinal agent paclitaxel (PTX) into cells. Of particular significance given that drug resistance is a major cause of chemotherapy failure, the PTX-transporter conjugate, designed to evade Pgp export and release free PTX after cell entry, shows efficacy against PTX-resistant ovarian cancer cells. Collectively this study introduces a new and highly effective class of guanidinium-rich cell-penetrating transporters and methodology for their single-step conjugation to drugs and probes, and demonstrates that the resulting drug/probe-conjugates readily enter cells, outperforming previously reported guanidinium-rich oligocarbonates and peptide transporters.

Functionalized Buckyballs for Visualizing Microbial Species in Different States and Environments

To date, in situ visualization of microbial density has remained an open problem. Here, functionalized buckyballs (e.g., C60-pyrrolidine tris acid) are shown to be a versatile platform that allows internalization within a microorganism without either adhering to the cell wall and cell membrane or binding to a matrix substrate such as soil. These molecular probes are validated via multi-scale imaging, to show association with microorganisms via fluorescence microscopy, positive cellular uptake via electron microscopy, and non-specific binding to the substrates through a combination of fluorescence and autoradiography imaging. We also demonstrate that cysteine-functionalized C60-pyrrolidine tris acid can differentiate live and dead microorganisms.

A preorganized β-amino acid bearing a guanidinium side chain and its use in cell-penetrating peptides

A cyclic β-amino acid (APC^Gu) bearing a side-chain guanidinium group has been developed.

Toward the ideal synthesis and molecular function through synthesis-informed design

This Highlight describes factors that contribute to an ideal synthesis, including economies (step, time, atom, solvent, energy) and orientations (target, diversity, safety, function), and the role of synthesis-informed design directed at function in advancing synthesis and its impact on science.

Fifteen years of cell-penetrating, guanidinium-rich molecular transporters: basic science, research tools, and clinical applications

All living systems require biochemical barriers. As a consequence, all drugs, imaging agents, and probes have targets that are either on, in, or inside of these barriers. Fifteen years ago, we initiated research directed at more fully understanding these barriers and at developing tools and strategies for breaching them that could be of use in basic research, imaging, diagnostics, and medicine. At the outset of this research and now to a lesser extent, the "rules" for drug design biased the selection of drug candidates mainly to those with an intermediate and narrow log P. At the same time, it was becoming increasingly apparent that Nature had long ago developed clever strategies to circumvent these "rules." In 1988, for example, independent reports documented the otherwise uncommon passage of a protein (HIV-Tat) across a membrane. A subsequent study implicated a highly basic domain in this protein (Tat49-57) in its cellular entry. This conspicuously contradictory behavior of a polar, highly charged peptide passing through a nonpolar membrane set the stage for learning how Nature had gotten around the current "rules" of transport. As elaborated in our studies and discussed in this Account, the key strategy used in Nature rests in part on the ability of a molecule to change its properties as a function of microenvironment; such molecules need to be polarity chameleons, polar in a polar milieu and relatively nonpolar in a nonpolar environment. Because this research originated in part with the protein Tat and its basic peptide domain, Tat49-57, the field focused heavily on peptides, even limiting its nomenclature to names such as "cell-penetrating peptides," "cell-permeating peptides," "protein transduction domains," and "membrane translocating peptides." Starting in 1997, through a systematic reverse engineering approach, we established that the ability of Tat49-57 to enter cells is not a function of its peptide backbone, but rather a function of the number and spatial array of its guanidinium groups. These function-oriented studies enabled us and others to design more effective peptidic agents and to think beyond the confines of peptidic systems to new and even more effective nonpeptidic agents. Because the function of passage across a cell membrane is not limited to or even best achieved with the peptide backbone, we referred to these agents by their shared function, "cell-penetrating molecular transporters." The scope of this molecular approach to breaching biochemical barriers has expanded remarkably in the past 15 years: enabling or enhancing the delivery of a wide range of cargos into cells and across other biochemical barriers, creating new tools for research, imaging, and diagnostics, and introducing new therapies into clinical trials.

A role for the membrane in regulating Chlamydomonas flagellar length

Flagellar assembly requires coordination between the assembly of axonemal proteins and the assembly of the flagellar membrane and membrane proteins. Fully grown steady-state Chlamydomonas flagella release flagellar vesicles from their tips and failure to resupply membrane should affect flagellar length. To study vesicle release, plasma and flagellar membrane surface proteins were vectorially pulse-labeled and flagella and vesicles were analyzed for biotinylated proteins. Based on the quantity of biotinylated proteins in purified vesicles, steady-state flagella appeared to shed a minimum of 16% of their surface membrane per hour, equivalent to a complete flagellar membrane being released every 6 hrs or less. Brefeldin-A destroyed Chlamydomonas Golgi, inhibited the secretory pathway, inhibited flagellar regeneration, and induced full-length flagella to disassemble within 6 hrs, consistent with flagellar disassembly being induced by a failure to resupply membrane. In contrast to membrane lipids, a pool of biotinylatable membrane proteins was identified that was sufficient to resupply flagella as they released vesicles for 6 hrs in the absence of protein synthesis and to support one and nearly two regenerations of flagella following amputation. These studies reveal the importance of the secretory pathway to assemble and maintain full-length flagella.