Phase-separating peptides for direct cytosolic delivery and redox-activated release of macromolecular therapeutics

The emerging roles of liquid-liquid phase separation in tumor immunity

Recent advancements in tumor immunotherapy, particularly PD-1 targeted therapy, have shown significant promise, marking major progress in tumor treatment approaches. Despite this, the development of resistance to therapy and mechanisms of immune evasion by tumors pose considerable obstacles to the broad application of immunotherapy. This necessitates a deeper exploration of complex immune signaling pathways integral to tumor immunity. This review aims to critically analyze the role of liquid-liquid phase separation (LLPS) within tumor immunity, specifically its impact on immune signaling pathways and its potential to foster the development of novel cancer therapies. LLPS, a biophysical process newly recognized for its ability to spontaneously segregate and organize biomacromolecules into liquid-like condensates through weak multivalent interactions, offers a novel perspective on the formation of signaling clusters and the functionality of immune molecules. The review delves into the micromolecular mechanisms behind the creation of signaling condensates via LLPS and reviews recent progress in adjusting signaling pathways pertinent to tumor immunity, including the T cell receptor (TCR), B cell receptor (BCR), immune checkpoints, and innate immune pathways such as the cGAS-STING pathway, stress granules, and the ADP-heptose-ALPK1 signaling axis. Furthermore, it considers the prospects of utilizing LLPS to generate groundbreaking cancer therapies capable of navigating past current treatment barriers. Through an extensive examination of LLPS's impact on tumor immunity, the review seeks to highlight novel therapeutic strategies and address the challenges and future directions in this rapidly evolving field.

The role of phase separation in RNA modification: both cause and effect

Phase separation is a critical mechanism for partitioning cellular functions by specific aggregation of biological macromolecules. Recent studies have found that phase separation is widely contributed in various biological functions, particularly in RNA related processes. Over 170 different post-transcriptional modifications occur in RNA, which is considered to be one of the most important physiological and pathogenic epigenetic mechanisms. Here, we discuss the role of phase separation in regulating RNA modification processing to ensure orderly RNA metabolism and function. Enzymes responsible for RNA modification undergo compartmentalization, enabling them to traffic client RNAs and amplify modifying efficacy. Meanwhile, altered RNA affects the formation, dissolution, and biophysical properties of phase separation conversely. These findings deeper our understanding of the interplay between phase separation and RNAs that governs a wide range of cellular processes. Finally, we concluded pathological roles of phase separation in RNA modification towards clinical applications and outlined perspectives to research RNA modification through the lens of phase separation.

A Gd(III)-labelled self-assembling peptide as a potential pH-responsive MRI contrast agent

A marine-derived peptide labelled with a Gd(III)-chelate was found to self-assemble depending on the solution pH, accompanied by changes in T1-relaxivity (r1) values when in the dispersed or self-assembled form. Such pH-responsive behavior can be advantageous in the development of macromolecular magnetic resonance imaging (MRI) contrast agents which monitor the tissue physiology.

Recent advances in engineering synthetic biomolecular condensates

Biomolecular condensates are intriguing entities found within living cells. These structures possess the ability to selectively concentrate specific components through phase separation, thereby playing a crucial role in the spatiotemporal regulation of a wide range of cellular processes and metabolic activities. To date, extensive studies have been dedicated to unraveling the intricate connections between molecular features, physical properties, and cellular functions of condensates. This collective effort has paved the way for deliberate engineering of tailor-made condensates with specific applications. In this review, we comprehensively examine the underpinnings governing condensate formation. Next, we summarize the material states of condensates and delve into the design of synthetic intrinsically disordered proteins with tunable phase behaviors and physical properties. Subsequently, we review the diverse biological functions demonstrated by synthetic biomolecular condensates, encompassing gene regulation, cellular behaviors, modulation of biochemical reactions, and manipulation of endogenous protein activities. Lastly, we discuss future challenges and opportunities in constructing synthetic condensates with tunable physical properties and customized cellular functions, which may shed light on the development of new types of sophisticated condensate systems with distinct functions applicable to various scenarios.

Peptide-Based Biomimetic Condensates via Liquid-Liquid Phase Separation as Biomedical Delivery Vehicles

Biomolecular condensates are dynamic liquid droplets through intracellular liquid-liquid phase separation that function as membraneless organelles, which are highly involved in various complex cellular processes and functions. Artificial analogs formed via similar pathways that can be integrated with biological complexity and advanced functions have received tremendous research interest in the field of synthetic biology. The coacervate droplet-based compartments can partition and concentrate a wide range of solutes, which are regarded as attractive candidates for mimicking phase-separation behaviors and biophysical features of biomolecular condensates. The use of peptide-based materials as phase-separating components has advantages such as the diversity of amino acid residues and customized sequence design, which allows for programming their phase-separation behaviors and the physicochemical properties of the resulting compartments. In this Perspective, we highlight the recent advancements in the design and construction of biomimicry condensates from synthetic peptides relevant to intracellular phase-separating protein, with specific reference to their molecular design, self-assembly via phase separation, and biorelated applications, to envisage the use of peptide-based droplets as emerging biomedical delivery vehicles.

Trehalose-based coacervates for local bioactive protein delivery to the central nervous system

Therapeutic outcomes of local biomolecule delivery to the central nervous system (CNS) using bulk biomaterials are limited by inadequate drug loading, neuropil disruption, and severe foreign body responses. Effective CNS delivery requires addressing these issues and developing well-tolerated, highly-loaded carriers that are dispersible within local neural parenchyma. Here, we synthesized biodegradable trehalose-based polyelectrolyte oligomers using facile A2:B3:AR thiol-ene Michael addition reactions that form complex coacervates upon mixing of oppositely charged oligomers. Coacervates permit high concentration loading and controlled release of bioactive growth factors, enzymes, and antibodies, with modular formulation parameters that confer tunable release kinetics. Coacervates are cytocompatible with cultured neural cells in vitro and can be formulated to either direct intracellular protein delivery or sequester media containing proteins and remain extracellular. Coacervates serve as effective vehicles for precisely delivering biomolecules, including bioactive neurotrophins, to the mouse striatum following intraparenchymal injection. These results support the use of trehalose-based coacervates as part of therapeutic protein delivery strategies for CNS disorders.

Cellular Uptake of Phase-Separating Peptide Coacervates

Peptide coacervates self-assembling via liquid-liquid phase separation are appealing intracellular delivery vehicles of macromolecular therapeutics (proteins, DNA, mRNA) owing to their non-cytotoxicity, high encapsulation capacity, and efficient cellular uptake. However, the mechanisms by which these viscoelastic droplets cross the cellular membranes remain unknown. Here, using multimodal imaging, data analytics, and biochemical inhibition assays, identify the key steps by which droplets enter the cell. find that the uptake follows a non-canonical pathway and instead integrates essential features of macropinocytosis and phagocytosis, namely active remodeling of the actin cytoskeleton and appearance of filopodia-like protrusions. Experiments using giant unilamellar vesicles show that the coacervates attach to the bounding membrane in a charge- and cholesterol-dependent manner but do not breach the lipid bilayer barrier. Cell uptake in the presence of small molecule inhibitors - interfering with actin and tubulin polymerization - confirm the active role of cytoskeleton remodeling, most prominently evident in electron microscopy imaging. These findings suggest a peculiar internalization mechanism for viscoelastic, glassy coacervate droplets combining features of non-specific uptake of fluids by macropinocytosis and particulate uptake of phagocytosis. The broad implications of this study will enable to enhance the efficacy and utility of coacervate-based strategies for intracellular delivery of macromolecular therapeutics.

Polyphenol-stabilized coacervates for enzyme-triggered drug delivery

Stability issues in membrane-free coacervates have been addressed with coating strategies, but these approaches often compromise the permeability of the coacervate. Here we report a facile approach to maintain both stability and permeability using tannic acid and then demonstrate the value of this approach in enzyme-triggered drug release. First, we develop size-tunable coacervates via self-assembly of heparin glycosaminoglycan with tyrosine and arginine-based peptides. A thrombin-recognition site within the peptide building block results in heparin release upon thrombin proteolysis. Notably, polyphenols are integrated within the nano-coacervates to improve stability in biofluids. Phenolic crosslinking at the liquid-liquid interface enables nano-coacervates to maintain exceptional structural integrity across various environments. We discover a pivotal polyphenol threshold for preserving enzymatic activity alongside enhanced stability. The disassembly rate of the nano-coacervates increases as a function of thrombin activity, thus preventing a coagulation cascade. This polyphenol-based approach not only improves stability but also opens the way for applications in biomedicine, protease sensing, and bio-responsive drug delivery.

Unraveling mechanisms of protein encapsulation and release in coacervates via molecular dynamics and machine learning

Coacervates play a pivotal role in protein-based drug delivery research, yet their drug encapsulation and release mechanisms remain poorly understood. Here, we utilized the Martini model to investigate bovine serum albumin (BSA) protein encapsulation and release within polylysine/polyglutamate (PLys/PGlu) coacervates. Our findings emphasize the importance of ingredient addition sequence in coacervate formation and encapsulation rates, attributed to preference contact between oppositely charged proteins and poly(amino acid)s. Notably, coacervates composed of β-sheet poly(amino acid)s demonstrate greater BSA encapsulation efficiency due to their reduced entropy and flexibility. Furthermore, we examined the pH responsiveness of coacervates, shedding light on the dissolution process driven by Coulomb forces. By leveraging machine learning algorithms to analyze simulation results, our research advances the understanding of coacervate-based drug delivery systems, with the ultimate goal of optimizing therapeutic outcomes.

Intracellular delivery strategies using membrane-interacting peptides and proteins

While the cellular cytosol and organelles contain attractive targets for disease treatments, it remains a challenge to deliver therapeutic biomacromolecules to these sites. This is due to the selective permeability of the plasma and endosomal membranes, especially for large and hydrophilic therapeutic cargos such as proteins and nucleic acids. In response, many different delivery systems and molecules have been devised to help therapeutics cross these barriers to reach cytosolic targets. Among them are peptide and protein-based systems, which have several advantages over other natural and synthetic materials including their ability to interact with cell membranes. In this review, we will describe recent advances and current challenges of peptide and protein strategies that leverage cell membrane association and modulation to enable cytosolic delivery of biomacromolecule cargo. The approaches covered here include peptides and proteins derived from or inspired by natural sequences as well as those designed de novo for delivery function.

Targeted Reprogramming of Pathogenic Fibroblast Genes at the 3'-Untranslated Regions by DNA Nanorobots for Periodontitis

Periodontitis, with its persistent nature, causes significant distress for most sufferers. Current treatments, such as mechanical cleaning and surgery, often fail to fully address the underlying overactivation of fibroblasts that drives this degradation. Targeting the post-transcriptional regulation of fibroblasts, particularly at the 3'-untranslated regions (3'UTR) of pathogenic genes, offers a therapeutic strategy for periodontitis. Herein, we developed a DNA nanorobot for this purpose. This system uses a dynamic DNA nanoframework to incorporate therapeutic microRNAs through molecular recognition and covalent bonds, facilitated by DNA monomers modified with disulfide bonds. The assembled-DNA nanoframework is encapsulated in a cell membrane embedded with a fibroblast-targeting peptide. By analyzing the 3'UTR regions of pathogenic fibroblast genes FOSB and JUND, we identified the therapeutic microRNA as miR-1-3p and integrated it into this system. As expected, the DNA nanorobot delivered the internal components to fibroblasts by the targeting peptide and outer membrane that responsively releases miR-1-3p under intracellular glutathione. It resulted in a precise reduction of mRNA and suppression of protein function in pathogenic genes, effectively reprogramming fibroblast behavior. Our results confirm that this approach not only mitigates the inflammation but also promotes tissue regeneration in periodontal models, offering a promising therapeutic avenue for periodontitis.

Lung-specific supramolecular nanoparticles for efficient delivery of therapeutic proteins and genome editing nucleases

Protein therapeutics play a critical role in treating a large variety of diseases, ranging from infections to genetic disorders. However, their delivery to target tissues beyond the liver, such as the lungs, remains a great challenge. Here, we report a universally applicable strategy for lung-targeted protein delivery by engineering Lung-Specific Supramolecular Nanoparticles (LSNPs). These nanoparticles are designed through the hierarchical self-assembly of metal-organic polyhedra (MOP), featuring a customized surface chemistry that enables protein encapsulation and specific lung affinity after intravenous administration. Our design of LSNPs not only addresses the hurdles of cell membrane impermeability of protein and nonspecific tissue distribution of protein delivery, but also shows exceptional versatility in delivering various proteins, including those vital for anti-inflammatory and CRISPR-based genome editing to the lung, and across multiple animal species, including mice, rabbits, and dogs. Notably, the delivery of antimicrobial proteins using LSNPs effectively alleviates acute bacterial pneumonia, demonstrating a significant therapeutic potential. Our strategy not only surmounts the obstacles of tissue-specific protein delivery but also paves the way for targeted treatments in genetic disorders and combating antibiotic resistance, offering a versatile solution for precision protein therapy.

Hydrogen Bonding-Driven Self-Coacervation of Nonionic Homopolymers for Stimuli-Triggered Therapeutic Release

Inspired by the unique functionalities of biomolecular membraneless organelles (MLOs) formed via liquid-liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs) and nucleic acids, a great deal of effort has been devoted to devising phase-separated artificial subcellular dynamic compartments. These endeavors aim to unravel the molecular mechanism underlying the formation and intracellular delivery of susceptible macromolecular therapeutics. We report herein pyroglutamic acid (PGA)-based well-defined homopolymers featuring stimuli-tunable reversible self-coacervation ability. The polymer exhibits an upper critical solution temperature (UCST) transition in aqueous solutions and has the propensity to undergo cooling-induced LLPS, producing micrometer-sized liquid droplets. This phase separation phenomenon could be modulated by various factors, including polymer concentration, chain length, solution pH, and types and concentrations of different additives. These micrometer droplets are thermally reversible and encapsulate a wide variety of cargoes, including small hydrophobic fluorescent molecules, hydrophilic anticancer drugs, and fluorophore-labeled macromolecular proteins (bovine serum albumin and lysozyme). The payloads were released by exploiting the thermo/pH-mediated disassembly behavior of the coacervates, preserving the bioactivity of the sensitive therapeutics. This environmentally responsive, simple yet versatile artificial MLO model system will provide insights into the biomolecular nonionic condensates and pave the way for the de novo design of dynamic biomolecule depots.

Colon Targeting pH-Responsive Coacervate Microdroplets for Treatment of Ulcerative Colitis

Ulcerative colitis (UC), an immune-mediated chronic inflammatory disease, drastically impacts patients' quality of life and increases their risk of colorectal cancer worldwide. However, effective oral targeted delivery and retention of drugs in colonic lesions are still great challenges in the treatment of UC. Coacervate microdroplets, formed by liquid-liquid phase separation, are recently explored in drug delivery as the simplicity in fabrication, spontaneous enrichment on small molecules and biological macromolecules, and high drug loading capacity. Herein, in this study, a biocompatible diethylaminoethyl-dextran hydrochloride/sodium polyphenylene sulfonate coacervates, coated with eudragit S100 to improve the stability and colon targeting ability, named EU-Coac, is developed. Emodin, an active ingredient in traditional Chinese herbs proven to alleviate UC symptoms, is loaded in EU-Coac (EMO@EU-Coac) showing good stability in gastric acid and pepsin and pH-responsive release behavior. After oral administration, EMO@EU-Coac can effectively target and retain in the colon, displaying good therapeutic effects on UC treatment through attenuating inflammation and oxidative stress response, repairing colonic epithelia, as well as regulating intestinal flora balance. In short, this study provides a novel and facile coacervate microdroplet delivery system for UC treatment.

Finding ways into the cytosol: Peptide-mediated approaches for delivering proteins into cells

The delivery of functional proteins, including antibodies, into cells opens up many opportunities to regulate cellular events, with significant implications for studies in chemical biology and therapeutics. The inside of cells is isolated from the outside by the cell membrane. The hydrophilic nature of proteins prevents direct permeation of proteins through the cell membrane by passive diffusion. Therefore, delivery routes using endocytic uptake followed by endosomal escape have been explored. Alternatively, delivery concepts using transient permeabilization of cell membranes or effective promotion of endocytic uptake and endosomal escape using modified membrane-lytic peptides have been reported in recent years. Non-canonical protein delivery concepts, such as the use of liquid droplets or coacervates, have also been proposed. This review highlights some of the topics in peptide-mediated intracellular protein delivery.

Reversing MET-Mediated Resistance in Oncogene-Driven NSCLC by MET-Activated Wnt Condensative Prodrug

The amplification of MET is a major cause of acquired resistance to targeted therapy in EGFR-mutant non-small-cell lung cancer (NSCLC), only to be temporarily restrained by the partial efficacy of MET inhibitors. This study reveals that the MET inhibitor has unexpectedly limited efficacy due to amplified MET triggering a strong positive feedback loop in the Wnt/β-catenin signaling pathway, allowing optimal functionality even when the MET pathway is suppressed again. To test this conjecture and specifically target the Wnt/β-catenin pathway, a cleverly designed Wnt condensative pro drug called WntSI is developed using reversible supramolecular self-assembly driven by liquidliquid phase separation (LLPS). This process involves a MET/pH-responsive peptide (Tyr-Pep) and a potent Wnt inhibitor known as CA. Upon recognition and phosphorylation of Tyr-Pep by over expressed MET in cells, it disrupts LLPS propensity and facilitates the disintegration of WntSI. Consequently,this enables it to suppress the carcinogenic effect mediated by β-catenin,effectively overcoming acquired resistance to EGFR-TKIs caused by MET amplification in both cell line-derived and patient-derived tumor xenograft (PDX) mouse models while maintaining exceptional biosecurity. This effective strategy not only suppresses the Wnt/β-catenin signaling pathway selectively, but also serves as an innovative example for pro-drug development through biologically responsive LLPS.

Phase Separation Enhanced PROTAC for Highly Efficient Protein Degradation

Biomacromolecular condensates formed via phase separation establish compartments for the enrichment of specific compositions, which is also used as a biological tool to enhance molecule condensation, thereby increasing the efficiency of biological processes. Proteolysis-targeting chimeras (PROTACs) have been developed as powerful tools for targeted protein degradation in cells, offering a promising approach for therapies for different diseases. Herein, we introduce an intrinsically disordered region in the PROTAC (denoted PSETAC), which led to the formation of droplets of target proteins in the cells and increased degradation efficiency compared with PROTAC without phase separation. Further, using a nucleus targeting intrinsically disordered domain, the PSETAC was able to target and degrade nuclear-located proteins. Finally, we demonstrated intracellular delivery of PSETAC using lipid nanoparticle-encapsulated mRNA (mRNA-LNP) for the degradation of the endogenous target protein. This study established the PSETAC mRNA-LNP method as a potentially translatable, safe therapeutic strategy for the development of clinical applications based on PROTAC.

Tyrosine - a structural glue for hierarchical protein assembly

Protein self-assembly, guided by the interplay of sequence- and environment-dependent liquid-liquid phase separation (LLPS), constitutes a fundamental process in the assembly of numerous intrinsically disordered proteins. Heuristic examination of these proteins has underscored the role of tyrosine residues, evident in their conservation and pivotal involvement in initiating LLPS and subsequent liquid-solid phase transitions (LSPT). The development of tyrosine-templated constructs, designed to mimic their natural counterparts, emerges as a promising strategy for creating adaptive, self-assembling systems with diverse applications. This review explores the central role of tyrosine in orchestrating protein self-assembly, delving into key interactions and examining its potential in innovative applications, including responsive biomaterials and bioengineering.

Recent advances in design and application of synthetic membraneless organelles

Membraneless organelles (MLOs) formed by liquid-liquid phase separation (LLPS) have been extensively studied due to their spatiotemporal control of biochemical and cellular processes in living cells. These findings have provided valuable insights into the physicochemical principles underlying the formation and functionalization of biomolecular condensates, which paves the way for the development of versatile phase-separating systems capable of addressing a variety of application scenarios. Here, we highlight the potential of constructing synthetic MLOs with programmable and functional properties. Notably, we organize how these synthetic membraneless compartments have been capitalized to manipulate enzymatic activities and metabolic reactions. The aim of this review is to inspire readerships to deeply comprehend the widespread roles of synthetic MLOs in the regulation enzymatic reactions and control of metabolic processes, and to encourage the rational design of controllable and functional membraneless compartments for a broad range of bioengineering applications.

Iron-Confined CRISPR/Cas9-Ribonucleoprotein Delivery System for Redox-Responsive Gene Editing

Clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (Cas9) is a promising gene editing tool to treat diseases at the genetic level. Nonetheless, the challenge of the safe and efficient delivery of CRISPR/Cas9 to host cells constrains its clinical applicability. In the current study, a facile, redox-responsive CRISPR/Cas9-Ribonucleoprotein (RNP) delivery system by combining iron-coordinated aggregation with liposomes (Fe-RNP@L) is reported. The Fe-RNP is formed by the coordination of Fe3+ with amino and carboxyl groups of Cas9, which modifies the lipophilicity and surface charge of RNP and alters cellular uptake from primary endocytosis to endocytosis and cholesterol-dependent membrane fusion. RNP can be rapidly and reversibly released from Fe-RNP in response to glutathione without loss of structural integrity and enzymatic activity. In addition, iron coordination also improves the stability of RNP and substantially mitigates cytotoxicity. This construct enabled highly efficient cytoplasmic/nuclear delivery (≈90%) and gene-editing efficiency (≈70%) even at low concentrations. The high payload content, high editing efficiency, good stability, low immunogenicity, and ease of production and storage, highlight its potential for diverse genome editing and clinical applications.

Spatiotemporal Regulation of Cell Fate in Living Systems Using Photoactivatable Artificial DNA Membraneless Organelles

Coacervates formed by liquid-liquid phase separation emerge as important biomimetic models for studying the dynamic behaviors of membraneless organelles and synchronously motivating the creation of smart architectures with the regulation of cell fate. Despite continuous progress, it remains challenging to balance the trade-offs among structural stability, versatility, and molecular communication for regulation of cell fate and systemic investigation in a complex physiological system. Herein, we present a self-stabilizing and fastener-bound gain-of-function methodology to create a new type of synthetic DNA membraneless organelle (MO) with high stability and controlled bioactivity on the basis of DNA coacervates. Specifically, long single-strand DNA generated by rolling circle amplification (RCA) is selected as the scaffold that assembles into membraneless coacervates via phase separation. Intriguingly, the as-formed DNA MO can recruit RCA byproducts and other components to achieve self-stabilization, nanoscale condensation, and function encoding. As a proof of concept, photoactivatable DNA MO is constructed and successfully employed for time-dependent accumulation and spatiotemporal management of cancer in a mouse model. This study offers new, important insights into synthetic membraneless organelles for the basic understanding and manipulation of important life processes.

Tuning interfacial fluidity and colloidal stability of membranized coacervate protocells

The cell membrane not only serves as the boundary between the cell's interior and the external environment but also plays a crucial role in regulating fundamental cellular behaviours. Interfacial membranization of membraneless coacervates, formed through liquid-liquid phase separation (LLPS), represents a reliable approach to constructing hierarchical cell-like entities known as protocells. In this study, we demonstrate the capability to modulate the interfacial membrane fluidity and thickness of dextran-bound coacervate protocells by adjusting the molecular weight of dextran or utilizing dextranase-catalyzed hydrolysis. This modulation allows for rational control over colloidal stability, interfacial molecular transport and cell-protocell interactions. Our work opens a new avenue for surface engineering of coacervate protocells, enabling the establishment of cell-mimicking structures and behaviours.

Elucidation of Spatial Cooperativity in Chemo-Immunotherapy by a Sequential Dual-pH-Responsive Drug Delivery System

Combining immune checkpoint blockade with chemotherapy through nanotechnology is promising in terms of safety and efficacy. However, the distinct subcellular distribution of each ingredient's action site makes it challenging to acquire an optimal synergism. Herein, a dual-pH responsive hybrid polymeric micelle system, HNP(αPDL16.9, Dox5.3), is constructed as a proof-of-concept for the spatial cooperativity in chemo-immunotherapy. HNP retains the inherent pH-transition of each polymer, with stepwise disassembly under discrete pH thresholds. Within weakly acidic extracellular tumor environment, αPDL1 is first released to block the checkpoint on cell membranes. The remaining intact Doxorubicin-loaded micelle NP(Dox)5.3 displays significant tropism toward tumor cells and releases Dox upon lysosomal pH for efficient tumor immunogenic cell death without immune toxicity. This sequential-released pattern boosts DC activation and primes CD8+ T cells, leading to enhanced therapeutic performance than single agent or an inverse-ordered combination in multiple murine tumor models. Using HNP, the indispensable role of conventional type 1 DC (cDC1) is identified in chemo-immunotherapy. A co-signature of cDC1 and CD8 correlates with cancer patient survival after neoadjuvant Pembrolizumab plus chemotherapy in clinic. This study highlights spatial cooperativity of chemo- and immuno-agents in immunoregulation and provides insights into the rational design of drug combination for future nanotherapeutics development.

Light-triggered AND logic tetrapeptide dynamic covalent assembly

We demonstrate light-triggered dynamic covalent assembly of a linear short tetrapeptide containing two terminal cysteine residues in an AND logic manner. A photobase generator is introduced to accomplish light-mediated pH regulation to increase the reduction potential of thiols in the tetrapeptide, which activates its oxidative polymerization through disulfide bonds. Interestingly, it is elucidated that under light irradiation, mere co-existence of photobase generator and the oxidizing agent permits the polymerization performance of this tetrapeptide. Hence, a light-triggered AND logic dynamic covalent assembly of a tetrapeptide is achieved. Further, upon redox response, the reversible aggregation and disaggregation can be transformed for numerous times due to the dynamic covalent feature of disulfide bond. As a comparison, no assembly occurs for a short peptide containing one terminal cysteine residue under the same stimuli condition. This work offers a new approach to remotely control programmable molecular assembly of short linear peptides based on dynamic covalent bond, holding great potential in wide bioapplications.

Develop Targeted Protein Drug Carriers through a High-Throughput Screening Platform and Rational Design

Protein-based drugs offer advantages, such as high specificity, low toxicity, and minimal side effects compared to small molecule drugs. However, delivery of proteins to target tissues or cells remains challenging due to the instability, diverse structures, charges, and molecular weights of proteins. Polymers have emerged as a leading choice for designing effective protein delivery systems, but identifying a suitable polymer for a given protein is complicated by the complexity of both proteins and polymers. To address this challenge, a fluorescence-based high-throughput screening platform called ProMatch to efficiently collect data on protein-polymer interactions, followed by in vivo and in vitro experiments with rational design is developed. Using this approach to streamline polymer selection for targeted protein delivery, candidate polymers from commercially available options are identified and a polyhexamethylene biguanide (PHMB)-based system for delivering proteins to white adipose tissue as a treatment for obesity is developed. A branched polyethylenimine (bPEI)-based system for neuron-specific protein delivery to stimulate optic nerve regeneration is also developed. The high-throughput screening methodology expedites identification of promising polymer candidates for tissue-specific protein delivery systems, thereby providing a platform to develop innovative protein-based therapeutics.

Wireless sequential dual light delivery for programmed PDT in vivo

Using photodynamic therapy (PDT) to treat deep-seated cancers is limited due to inefficient delivery of photosensitizers and low tissue penetration of light. Polymeric nanocarriers are widely used for photosensitizer delivery, while the self-quenching of the encapsulated photosensitizers would impair the PDT efficacy. Furthermore, the generated short-lived reactive oxygen spieces (ROS) can hardly diffuse out of nanocarriers, resulting in low PDT efficacy. Therefore, a smart nanocarrier system which can be degraded by light, followed by photosensitizer activation can potentially overcome these limitations and enhance the PDT efficacy. A light-sensitive polymer nanocarrier encapsulating photosensitizer (RB-M) was synthesized. An implantable wireless dual wavelength microLED device which delivers the two light wavelengths sequentially was developed to programmatically control the release and activation of the loaded photosensitizer. Two transmitter coils with matching resonant frequencies allow activation of the connected LEDs to emit different wavelengths independently. Optimal irradiation time, dose, and RB-M concentration were determined using an agent-based digital simulation method. In vitro and in vivo validation experiments in an orthotopic rat liver hepatocellular carcinoma disease model confirmed that the nanocarrier rupture and sequential low dose light irradiation strategy resulted in successful PDT at reduced photosensitizer and irradiation dose, which is a clinically significant event that enhances treatment safety.

Controlled Supramolecular Polymerization via Bioinspired, Liquid-Liquid Phase Separation of Monomers

Dynamic supramolecular assemblies, driven by noncovalent interactions, pervade the biological realm. In the synthetic domain, their counterparts, supramolecular polymers, endowed with remarkable self-repair and adaptive traits, are often realized through bioinspired designs. Recently, controlled supramolecular polymerization strategies have emerged, drawing inspiration from protein self-assembly. A burgeoning area of research involves mimicking the liquid-liquid phase separation (LLPS) observed in proteins to create coacervate droplets and recognizing their significance in cellular organization and diverse functions. Herein, we introduce a novel perspective on synthetic coacervates, extending beyond their established role in synthetic biology as dynamic, membraneless phases to enable structural control in synthetic supramolecular polymers. Drawing parallels with the cooperative growth of amyloid fibrils through LLPS, we present metastable coacervate droplets as dormant monomer phases for controlled supramolecular polymerization. This is achieved via a π-conjugated monomer design that combines structural characteristics for both coacervation through its terminal ionic groups and one-dimensional growth via a π-conjugated core. This design leads to a unique temporal LLPS, resulting in a metastable coacervate phase, which subsequently undergoes one-dimensional growth via nucleation within the droplets. In-depth spectroscopic and microscopic characterization provides insights into the temporal evolution of disordered and ordered phases. Furthermore, to modulate the kinetics of liquid-to-solid transformation and to achieve precise control over the structural characteristics of the resulting supramolecular polymers, we invoke seeding in the droplets, showcasing living growth characteristics. Our work thus opens up new avenues in the exciting field of supramolecular polymerization, offering general design principles and controlled synthesis of precision self-assembled structures in confined environments.

Self-assembly of peptides in living cells for disease theranostics

The past few decades have witnessed substantial progress in biomedical materials for addressing health concerns and improving disease therapeutic and diagnostic efficacy. Conventional biomedical materials are typically created through an ex vivo approach and are usually utilized under physiological environments via transfer from preparative media. This transfer potentially gives rise to challenges for the efficient preservation of the bioactivity and implementation of theranostic goals on site. To overcome these issues, the in situ synthesis of biomedical materials on site has attracted great attention in the past few years. Peptides, which exhibit remarkable biocompability and reliable noncovalent interactions, can be tailored via tunable assembly to precisely create biomedical materials. In this review, we summarize the progress in the self-assembly of peptides in living cells for disease diagnosis and therapy. After a brief introduction to the basic design principles of peptide assembly systems in living cells, the applications of peptide assemblies for bioimaging and disease treatment are highlighted. The challenges in the field of peptide self-assembly in living cells and the prospects for novel peptide assembly systems towards next-generation biomaterials are also discussed, which will hopefully help elucidate the great potential of peptide assembly in living cells for future healthcare applications.

Reversible Assembly of Proteins and Phenolic Polymers for Intracellular Protein Delivery with Serum Stability

The design of intracellular delivery systems for protein drugs remains a challenge due to limited delivery efficacy and serum stability. Herein, we propose a reversible assembly strategy to assemble cargo proteins and phenolic polymers into stable nanoparticles for this purpose using a heterobifunctional adaptor (2-formylbenzeneboronic acid). The adaptor is easily decorated on cargo proteins via iminoboronate chemistry and further conjugates with catechol-bearing polymers to form nanoparticles via boronate diester linkages. The nanoparticles exhibit excellent serum stability in culture media but rapidly release the cargo proteins triggered by lysosomal acidity and GSH after endocytosis. In a proof-of-concept animal model, the strategy successfully transports superoxide dismutase to retina via intravitreal injection and efficiently ameliorates the oxidative stress and cellular damage in the retina induced by ischemia-reperfusion (I/R) with minimal adverse effects. The reversible assembly strategy represents a robust and efficient method to develop serum-stable systems for the intracellular delivery of biomacromolecules.

Probing the surface charge of condensates using microelectrophoresis

Biomolecular condensates play an important role in cellular organization. Coacervates are commonly used models that mimic the physicochemical properties of biomolecular condensates. The surface of condensates plays a key role in governing molecular exchange between condensates, accumulation of species at the interface, and the stability of condensates against coalescence. However, most important surface properties, including the surface charge and zeta potential, remain poorly characterized and understood. The zeta potential of coacervates is often measured using laser doppler electrophoresis, which assumes a size-independent electrophoretic mobility. Here, we show that this assumption is incorrect for liquid-like condensates and present an alternative method to study the electrophoretic mobility of coacervates and in vitro condensate models by microelectrophoresis and single-particle tracking. Coacervates have a size-dependent electrophoretic mobility, originating from their fluid nature, from which a well-defined zeta potential is calculated. Interestingly, microelectrophoresis measurements reveal that polylysine chains are enriched at the surface of polylysine/polyaspartic acid complex coacervates, which causes the negatively charged protein ɑ-synuclein to adsorb and accumulate at the interface. Addition of ATP inverts the surface charge, displaces ɑ-synuclein from the surface and may help to suppress its interface-catalyzed aggregation. Together, these findings show how condensate surface charge can be measured and altered, making this microelectrophoresis platform combined with automated single-particle tracking a promising characterization technique for both biomolecular condensates and coacervate protocells.

Liquid-liquid phase separation-inspired design of biomaterials

Liquid-liquid phase separation (LLPS) is a crucial biological process that governs biomolecular condensation, assembly, and functionality within phase-separated aqueous environments. This phenomenon serves as a source of inspiration for the creation of artificial designs in both structured and functional biomaterials, presenting novel strategies for manipulating the structures of functional protein aggregates in a wide range of biomedical applications. This mini review summarizes my past research endeavors, offering a panoramic overview of LLPS-inspired biomaterials utilized in the design of structured materials, the development of cell mimetics, and the advancement of intelligent biomaterials.

Overcoming Endosomal Escape Barriers in Gene Drug Delivery Using De Novo Designed pH-Responsive Peptides

A major challenge in using nanocarriers for intracellular drug delivery is their restricted capacity to escape from endosomes into the cytosol. Here, we significantly enhance the drug delivery efficiency by accurately predicting and regulating the transition pH (pH0) of peptides to modulate their endosomal escape capability. Moreover, by inverting the chirality of the peptide carriers, we could further enhance their ability to deliver nucleic acid drugs as well as antitumor drugs. The resulting peptide carriers exhibit versatility in transfecting various cell types with a high efficiency of up to 90% by using siRNA, pDNA, and mRNA. In vivo antitumor experiments demonstrate a tumor growth inhibition of 83.4% using the peptide. This research offers a potent method for the rapid development of peptide vectors with exceptional transfection efficiencies for diverse pathophysiological indications.

Self-assembly of stabilized droplets from liquid-liquid phase separation for higher-order structures and functions

Dynamic microscale droplets produced by liquid-liquid phase separation (LLPS) have emerged as appealing biomaterials due to their remarkable features. However, the instability of droplets limits the construction of population-level structures with collective behaviors. Here we first provide a brief background of droplets in the context of materials properties. Subsequently, we discuss current strategies for stabilizing droplets including physical separation and chemical modulation. We also discuss the recent development of LLPS droplets for various applications such as synthetic cells and biomedical materials. Finally, we give insights on how stabilized droplets can self-assemble into higher-order structures displaying coordinated functions to fully exploit their potentials in bottom-up synthetic biology and biomedical applications.

Liquid Droplet-Mediated Formulation of Lipid Nanoparticles Encapsulating Immunoglobulin G for Cytosolic Delivery

Antibodies are promising biopharmaceuticals that offer new therapeutic options for diseases. Since antibodies are membrane impermeable, approaches that allow immunoglobulin Gs (IgGs) to access intracellular therapeutic targets would open new horizons in antibody therapies. Lipid nanoparticles (LNPs) are among the classes of vectors that deliver biopharmaceuticals into cells. Using liquid droplets formed by IgG and polyglutamate, we report here a unique approach to forming LNPs containing IgG via liquid droplets formed in the presence of polyglutamic acid (polyE). The addition of polyE promoted the formation of smaller LNPs with cationic lipids than in its absence, and the formed LNPs were much more efficient in cytosolic IgG delivery and targeting of cellular proteins. This approach also allows for the encapsulation of intact IgG without the need for chemical or sequence modification. The intracellularly delivered IgG retained its target binding ability, as demonstrated by labeling of nuclear pore complex and HRas-GFP and inhibition of antiapoptotic cell death by phosphorylated Akt protein in live cells.

Dual stimuli-responsive and sustained drug delivery NanoSensoGel formulation for prevention of cisplatin-induced ototoxicity

Cisplatin (CisPt)-induced ototoxicity (CIO) is delineated as a consequence of CisPt-induced intracellular generation of reactive oxygen species (ROS) which can be circumvented by Bucillamine (BUC; an antioxidant drug with sulfhydryl groups) and Diltiazem (DLT, L-type calcium channel blocker). However, its effective accumulation in the Organ of Corti and cell cytoplasm is desired. Therefore, a biocompatible BUC- and DLT-nanoparticles (NPs)-impregnated dual stimuli-responsive formulation (NanoSensoGel) presented here with ROS- and thermo-responsive properties for the sustained and receptive delivery of drugs. The ROS-responsive polypropylene sulfide- methyl polyethylene glycol-2000 (PPS-mPEG2000) polymer was rationally designed, synthesized, and characterized to fabricate BUC- and DLT-loaded PPS-mPEG2000-NPs (BUC- and DLT-NPs). The fabricated BUC- and DLT-NPs showed efficient cellular uptake, intracellular delivery, ROS responsiveness, and cytoprotective effect which was characterized using cellular internalization, intracellular ROS, mitochondrial superoxide, and Caspase 3/7 assays on the House Ear Institute-Organ of Corti-1 (HEI-OC1) cells. The composite NanoSensoGel (i.e., ROS-responsive BUC- and DLT-NPs suspended in the thermo-responsive hydrogel) present in a sol state at room temperature and turned to gel above 33°C, which could be essential for retaining the formulation at the target site for long-term release. The NanoSensoGel showed sustained release of BUC and DLT following Fickian release diffusion kinetics. Overall, a novel NanoSensoGel formulation developed in this study has demonstrated its great potential in delivering therapeutics in the inner ear for prophylactic treatment of CIO, and associated hearing loss.

From structural design to delivery: mRNA therapeutics for cancer immunotherapy

mRNA therapeutics have emerged as powerful tools for cancer immunotherapy in accordance with their superiority in expressing all sequence-known proteins in vivo. In particular, with a small dosage of delivered mRNA, antigen-presenting cells (APCs) can synthesize mutant neo-antigens and multi-antigens and present epitopes to T lymphocytes to elicit antitumor effects. In addition, expressing receptors like chimeric antigen receptor (CAR), T-cell receptor (TCR), CD134, and immune-modulating factors including cytokines, interferons, and antibodies in specific cells can enhance immunological response against tumors. With the maturation of in vitro transcription (IVT) technology, large-scale and pure mRNA encoding specific proteins can be synthesized quickly. However, the clinical translation of mRNA-based anticancer strategies is restricted by delivering mRNA into target organs or cells and the inadequate endosomal escape efficiency of mRNA. Recently, there have been some advances in mRNA-based cancer immunotherapy, which can be roughly classified as modifications of the mRNA structure and the development of delivery systems, especially the lipid nanoparticle platforms. In this review, the latest strategies for overcoming the limitations of mRNA-based cancer immunotherapies and the recent advances in delivering mRNA into specific organs and cells are summarized. Challenges and opportunities for clinical applications of mRNA-based cancer immunotherapy are also discussed.

Probing the hierarchical dynamics of DNA-sperm nuclear transition protein complexes through fuzzy interaction and mesoscale condensation

Nuclear transition protein TNP1 is a crucial player mediating histone-protamine exchange in condensing spermatids. A unique combination of intrinsic disorder and multivalent properties turns TNP1 into an ideal agent for orchestrating the formation of versatile TNP-DNA assemblies. Despite its significance, the physicochemical property and the molecular mechanism followed by TNP1 for histone replacement and DNA condensation are still poorly understood. This study reports the first-time in vitro expression and purification of human TNP1 and investigates the hierarchical dynamics of TNP1-DNA interaction using a combination of computational simulations, biochemical assays, fluorescence imaging, and atomic force microscopy. We explored three crucial facets of TNP1-DNA interactions. Initially, we delve into the molecular binding process that entails fuzzy interactions between TNP1 and DNA at the atomistic scale. Subsequently, we analyze how TNP1 binding affects the electrostatic and mechanical characteristics of DNA and influences its morphology. Finally, we study the biomolecular condensation of TNP1-DNA when subjected to high concentrations. The findings of our study set the foundation for comprehending the potential involvement of TNP1 in histone replacement and DNA condensation in spermatogenesis.

Topochemistry for Difficult Peptide-Polymer Synthesis: Single-Crystal-to-Single-Crystal Synthesis of an Isoleucine-Based Polymer, a Hydrophobic Coating Material

Polymers of hydrophobic amino acids are predicted to be potential coating materials for the creation of hydrophobic surfaces. The oligopeptides of hydrophobic amino acids are called "difficult peptides"; as the name suggests, it is difficult to synthesize them by conventional methods. We circumvented this synthetic challenge by adopting topochemical azide-alkyne cycloaddition (TAAC) polymerization of a hydrophobic dipeptide monomer. We designed an Ile-based dipeptide, decorated with azide and alkyne, which arrange in the crystal in a head-to-tail fashion with the azide and alkyne of the adjacent molecules in a ready-to-react orientation. The monomer, on mild heating of its crystals, undergoes regiospecific TAAC polymerization to yield a 1,4-disubstituted-triazole-linked polymer in a single-crystal-to-single-crystal fashion. The solid obtained after evaporation of the monomer solution also maintained crystallinity and underwent regiospecific topochemical polymerization as in the case of crystals. This topochemical polymerization could be studied using different techniques such as FTIR, NMR, DSC, GPC, MALDI, PXRD, and SCXRD. Since the polymer is insoluble in common solvents and hence difficult to coat surfaces, the monomer was first sprayed and evaporated on various surfaces and polymerized on the surface. Such polymer-coated surfaces exhibited water contact angles of up to 134°, showing that this Ile-derived polymer is very hydrophobic and can potentially be used as a coating material for various applications.

Fluorinated Lipid Nanoparticles for Enhancing mRNA Delivery Efficiency

Lipid nanoparticles (LNPs), a nonviral nucleic acid delivery system, have shown vast potential for vaccine development and disease treatment. LNPs assist mRNA to cross physiological barriers such as cell membranes and endosomes/lysosomes, promoting the intracellular presentation of mRNA. However, the endosome escape efficiency and biosafety of currently commercialized LNPs are still unsatisfactory, resulting in underutilization of mRNA. Herein, we report that fluorinated modification of the 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol)-2000 (PEG-DSPE), termed as FPD, in the LNPs can improve the delivery efficiency of mRNA. FPD accounts for only 1.5% of lipids in LNPs but could mediate a 5-fold and nearly 2-fold enhancement of mRNA expression efficiency in B16F10 tumor cells and primary dendritic cells, respectively. Mechanism studies reveal that FPD promotes the cellular internalization of LNPs as well as endosome escape. In vivo studies substantiate that FPD can augment overall mRNA expression at least 3-fold, either by intravenous or intraperitoneal injection, compared to LNPs prepared with nonfluorinated PEG-lipids at a relatively low mRNA dose. Besides, with the introduction of FPD, mRNA expression in the spleen augmented compared to that of the DMG-PEG commercial formulations. Benefiting from a prudent dosage of fluorine, the fluorinated LNPs display favorable biosafety profiles at cellular and zoological levels.

High-Throughput Screening of Surface Engineered Cyanine Nanodots for Active Transport of Therapeutic Antibodies into Solid Tumor

The successful delivery of therapeutic biomacromolecules into solid tumor holds great challenge due to their high resistance to penetrate through the complex tumor microenvironments. Here, active-transporting nanoparticles are harnessed to efficiently deliver biomacromolecular drugs into solid tumors through cell transcytosis. A series of molecularly precise cyanine 5-cored polylysine G5 dendrimers (Cy5 nanodots) with different peripheral amino acids (G5-AA) is prepared. The capability of these positively charged nanodots to induce cell endocytosis, exocytosis, and transcytosis is evaluated via fluorescence-based high-throughput screen. The optimized nanodots (G5-R) are conjugated with αPD-L1 (a therapeutic monoclonal antibody binding to programmed-death ligand 1) (αPD-L1-G5-R) to demonstrate the nanoparticle-mediated tumor active transport. The αPD-L1-G5-R can greatly enhance the tumor-penetration capability through adsorption-mediated transcytosis (AMT). The effectiveness of αPD-L1-G5-R is tested in treating mice bearing partially resected CT26 tumors, mimicking the local immunotherapy of residual tumors post-surgery in clinic. The αPD-L1-G5-R embedded in fibrin gel can efficiently mediate tumor cell transcytosis, and deliver αPD-L1 throughout the tumor, thereby enhancing immune checkpoint blockade, reducing tumor recurrence, and significantly prolonging the survival time. The active-transporting nanodots are promising platforms for efficient tumor delivery of therapeutic biomacromolecules.

E3MPH16: An efficient endosomolytic peptide for intracellular protein delivery

To facilitate the introduction of proteins, such as antibodies, into cells, a variety of delivery peptides have been engineered. These peptides are typically highly cationic and somewhat hydrophobic, enabling cytosolic protein delivery at the cost of causing cell damage by rupturing membranes. This balance between delivery effectiveness and cytotoxicity presents obstacles for their real-world use. To tackle this problem, we designed a new endosome-disruptive cytosolic delivery peptide, E3MPH16, inspired by mastoparan X (MP). E3MPH16 was engineered to incorporate three Glu (E3) and 16 His (H16) residues at the N- and C-termini of MP, respectively. The negative charges of E3 substantially mitigate the cell-surface damage induced by MP. The H16 segment is known to enhance cell-surface adsorption and endocytic uptake of the associated molecules. With these modifications, E3MPH16 was successfully trapped within endosomes. The acidification of endosomes is expected to protonate the side chains of E3 and H16, enabling E3MPH16 to rupture endosomal membranes. As a result, nearly 100% of cells achieved cytosolic delivery of a model biomacromolecule, Alexa Fluor 488-labeled dextran (10 kDa), via endosomal escape by co-incubation with E3MPH16. The delivery process also suggested the involvement of macropinocytosis and caveolae-mediated endocytosis. With the assistance of E3MPH16, Cre recombinase and anti-Ras-IgG delivered into HEK293 cells and HT1080 cells enabled gene recombination and inhibited cell proliferation, respectively. The potential for in vivo application of this intracellular delivery method was further validated by topically injecting the green fluorescent protein fused with a nuclear localization signal (NLS-GFP) along with E3MPH16 into Colon-26 tumor xenografts in mice.

Sequestration within peptide coacervates improves the fluorescence intensity, kinetics, and limits of detection of dye-based DNA biosensors

Peptide-based liquid-liquid phase separated domains, or coacervates, are a biomaterial gaining new interest due to their exciting potential in fields ranging from biosensing to drug delivery. In this study, we demonstrate that coacervates provide a simple and biocompatible medium to improve nucleic acid biosensors through the sequestration of both the biosensor and target strands within the coacervate, thereby increasing their local concentration. Using the well-established polyarginine (R9) - ATP coacervate system and an energy transfer-based DNA molecular beacon we observed three key improvements: i) a greater than 20-fold reduction of the limit of detection within coacervates when compared to control buffer solutions; ii) an increase in the kinetics, equilibrium was reached more than 4-times faster in coacervates; and iii) enhancement in the dye fluorescent quantum yields within the coacervates, resulting in greater signal-to-noise. The observed benefits translate into coacervates greatly improving bioassay functionality.

Organ/Cell-Selective Intracellular Delivery of Biologics via N-Acetylated Galactosamine-Functionalized Polydisulfide Conjugates

Biologics, including proteins and antisense oligonucleotides (ASOs), face significant challenges when it comes to achieving intracellular delivery within specific organs or cells through systemic administrations. In this study, we present a novel approach for delivering proteins and ASOs to liver cells, both in vitro and in vivo, using conjugates that tether N-acetylated galactosamine (GalNAc)-functionalized, cell-penetrating polydisulfides (PDSs). The method involves the thiol-bearing cargo-mediated ring-opening polymerization of GalNAc-functionalized lipoamide monomers through the so-called aggregation-induced polymerization, leading to the formation of site-specific protein/ASO-PDS conjugates with narrow dispersity. The hepatocyte-selective intracellular delivery of the conjugates arises from a combination of factors, including first GalNAc binding with ASGPR receptors on liver cells, leading to cell immobilization, and the subsequent thiol-disulfide exchange occurring on the cell surface, promoting internalization. Our findings emphasize the critical role of the close proximity of the PDS backbone to the cell surface, as it governs the success of thiol-disulfide exchange and, consequently, cell penetration. These conjugates hold tremendous potential in overcoming the various biological barriers encountered during systemic and cell-specific delivery of biomacromolecular cargos, opening up new avenues for the diagnosis and treatment of a range of liver-targeting diseases.

Design of functional intrinsically disordered proteins

Many proteins do not fold into a fixed three-dimensional structure, but rather function in a highly disordered state. These intrinsically disordered proteins pose a unique challenge to protein engineering and design: How can proteins be designed de novo if not by tailoring their structure? Here, we will review the nascent field of design of intrinsically disordered proteins with focus on applications in biotechnology and medicine. The design goals should not necessarily be the same as for de novo design of folded proteins as disordered proteins have unique functional strengths and limitations. We focus on functions where intrinsically disordered proteins are uniquely suited including disordered linkers, desiccation chaperones, sensors of the chemical environment, delivery of pharmaceuticals, and constituents of biomolecular condensates. Design of functional intrinsically disordered proteins relies on a combination of computational tools and heuristics gleaned from sequence-function studies. There are few cases where intrinsically disordered proteins have made it into industrial applications. However, we argue that disordered proteins can perform many roles currently performed by organic polymers, and that these proteins might be more designable due to their modularity.

Intracellular Protein Delivery: Approaches, Challenges, and Clinical Applications

Protein biologics are powerful therapeutic agents with diverse inhibitory and enzymatic functions. However, their clinical use has been limited to extracellular applications due to their inability to cross plasma membranes. Overcoming this physiological barrier would unlock the potential of protein drugs for the treatment of many intractable diseases. In this review, we highlight progress made toward achieving cytosolic delivery of recombinant proteins. We start by first considering intracellular protein delivery as a drug modality compared to existing Food and Drug Administration-approved drug modalities. Then, we summarize strategies that have been reported to achieve protein internalization. These techniques can be broadly classified into 3 categories: physical methods, direct protein engineering, and nanocarrier-mediated delivery. Finally, we highlight existing challenges for cytosolic protein delivery and offer an outlook for future advances.

Particle Engineering via Supramolecular Assembly of Macroscopic Hydrophobic Building Blocks

Tailoring the hydrophobicity of supramolecular assembly building blocks enables the fabrication of well-defined functional materials. However, the selection of building blocks used in the assembly of metal-phenolic networks (MPNs), an emerging supramolecular assembly platform for particle engineering, has been essentially limited to hydrophilic molecules. Herein, we synthesized and applied biscatechol-functionalized hydrophobic polymers (poly(methyl acrylate) (PMA) and poly(butyl acrylate) (PBA)) as building blocks to engineer MPN particle systems (particles and capsules). Our method allowed control over the shell thickness (e.g., between 10 and 21 nm), stiffness (e.g., from 10 to 126 mN m-1 ), and permeability (e.g., 28-72 % capsules were permeable to 500 kDa fluorescein isothiocyanate-dextran) of the MPN capsules by selection of the hydrophobic polymer building blocks (PMA or PBA) and by controlling the polymer concentration in the MPN assembly solution (0.25-2.0 mM) without additional/engineered assembly processes. Molecular dynamics simulations provided insights into the structural states of the hydrophobic building blocks during assembly and mechanism of film formation. Furthermore, the hydrophobic MPNs facilitated the preparation of fluorescent-labeled and bioactive capsules through postfunctionalization and also particle-cell association engineering by controlling the hydrophobicity of the building blocks. Engineering MPN particle systems via building block hydrophobicity is expected to expand their use.

Tuning the viscoelastic properties of peptide coacervates by single amino acid mutations and salt kosmotropicity

Coacervation, or liquid-liquid phase separation (LLPS) of biomacromolecules, is increasingly recognized to play an important role both intracellularly and in the extracellular space. Central questions that remain to be addressed are the links between the material properties of coacervates (condensates) and both the primary and the secondary structures of their constitutive building blocks. Short LLPS-prone peptides, such as GY23 variants explored in this study, are ideal model systems to investigate these links because simple sequence modifications and the chemical environment strongly affect the viscoelastic properties of coacervates. Herein, a systematic investigation of the structure/property relationships of peptide coacervates was conducted using GY23 variants, combining biophysical characterization (plate rheology and surface force apparatus, SFA) with secondary structure investigations by infrared (IR) and circular dichroism (CD) spectroscopy. Mutating specific residues into either more hydrophobic or more hydrophilic residues strongly regulates the viscoelastic properties of GY23 coacervates. Furthermore, the ionic strength and kosmotropic characteristics (Hofmeister series) of the buffer in which LLPS is induced also significantly impact the properties of formed coacervates. Structural investigations by CD and IR indicate a direct correlation between variations in properties induced by endogenous (peptide sequence) or exogenous (ionic strength, kosmotropic characteristics, aging) factors and the β-sheet content within coacervates. These findings provide valuable insights to rationally design short peptide coacervates with programmable materials properties that are increasingly used in biomedical applications.

Bioinspired Squid Peptides─A Tale of Curiosity-Driven Research Leading to Unforeseen Biomedical Applications

The molecular design of many peptide-based materials originates from structural proteins identified in living organisms. Prominent examples that have garnered broad interdisciplinary research interest (chemistry, materials science, bioengineering, etc.) include elastin, silk, or mussel adhesive proteins. The critical first steps in this type of research are to identify a convenient model system of interest followed by sequencing the prevailing proteins from which these biological structures are assembled. In our laboratory, the main model systems for many years have been the hard biotools of cephalopods, particularly their parrot-like tough beak and their sucker ring teeth (SRT) embedded within the sucker cuptions that line the interior surfaces of their arms and tentacles. Unlike the majority of biological hard tissues, these structures are devoid of biominerals and consist of protein/polysaccharide biomolecular composites (the beak) or, in the case of SRT, are entirely made of proteins that are assembled by supramolecular interactions.In this Account, we chronicle our journey into the discovery of these intriguing biological materials. We initially focus on their excellent mechanical robustness followed by the identification and sequencing of the structural proteins from which they are built, using the latest "omics" techniques including next-generation sequencing and high-throughput proteomics. A common feature of these proteins is their modular architecture at the molecular level consisting of short peptide repeats. We describe the molecular design of these peptide building blocks, highlighting the consensus motifs identified to play a key role in biofabrication and in regulating the mechanical properties of the macroscopic biological material. Structure/property relationships unveiled through advanced spectroscopic and scattering techniques, including Raman, infrared, circular dichroism, and NMR spectroscopies as well as wide-angle and small-angle X-ray scattering, are also discussed.We then present recent developments in exploiting the discovered molecular designs to engineer peptides and their conjugates for promising biomedical applications. One example includes short peptide hydrogels that self-assemble entirely under aqueous conditions and simultaneously encapsulate large macromolecules during the gelation process. A second example involves peptide coacervate microdroplets produced by liquid-liquid phase separation. These microdroplets are capable of recruiting and delivering large macromolecular therapeutics (genes, mRNA, proteins, peptides, CRISPR/Cas 9 modalities, etc.) into mammalian cells, which introduces exciting prospects in cancer, gene, and immune therapies.This Account also serves as a testament to how curiosity-driven explorations, which may lack an obvious practical goal initially, can lead to discoveries with unexpected and promising translational potential.

Dipeptide coacervates as artificial membraneless organelles for bioorthogonal catalysis

Artificial organelles can manipulate cellular functions and introduce non-biological processes into cells. Coacervate droplets have emerged as a close analog of membraneless cellular organelles. Their biomimetic properties, such as molecular crowding and selective partitioning, make them promising components for designing cell-like materials. However, their use as artificial organelles has been limited by their complex molecular structure, limited control over internal microenvironment properties, and inherent colloidal instability. Here we report the design of dipeptide coacervates that exhibit enhanced stability, biocompatibility, and a hydrophobic microenvironment. The hydrophobic character facilitates the encapsulation of hydrophobic species, including transition metal-based catalysts, enhancing their efficiency in aqueous environments. Dipeptide coacervates carrying a metal-based catalyst are incorporated as active artificial organelles in cells and trigger an internal non-biological chemical reaction. The development of coacervates with a hydrophobic microenvironment opens an alternative avenue in the field of biomimetic materials with applications in catalysis and synthetic biology.

Biofunctional coacervate-based artificial protocells with membrane-like and cytoplasm-like structures for the treatment of persistent hyperuricemia

Coacervate droplets formed by liquid-liquid phase separation have attracted considerable attention due to their ability to enrich biomacromolecules while preserving their bioactivities. However, there are challenges to develop coacervate droplets as delivery vesicles for therapeutics resulting from the lack of physiological stability and inherent lack of membranes in coacervate droplets. Herein, polylysine-polynucleotide complex coacervate droplets with favorable physiological stability are formulated to efficiently and facilely concentrate small molecules, biomacromolecules and nanoparticles without organic solvents. To improve the biocompatibility, the PEGylated phospholipid membrane is further coated on the surface of the coacervate droplets to prepare coacervate-based artificial protocells (ArtPC) with membrane-like and cytoplasm-like structures. The ArtPC can confine the cyclic catalytic system of uricase and catalase inside to degrade uric acid and deplete the toxicity of H2O2. This biofunctional ArtPC effectively reduces blood uric acid levels and prevents renal injuries in mice with persistent hyperuricemia. The ArtPC-based therapy can bridge the disciplines of synthetic biology, pharmaceutics and therapeutics.