The liquid-to-solid transition of FUS is promoted by the condensate surface

A wide range of macromolecules can undergo phase separation, forming biomolecular condensates in living cells. These membraneless organelles are typically highly dynamic, formed reversibly, and carry out essential functions in biological systems. Crucially, however, a further liquid-to-solid transition of the condensates can lead to irreversible pathological aggregation and cellular dysfunction associated with the onset and development of neurodegenerative diseases. Despite the importance of this liquid-to-solid transition of proteins, the mechanism by which it is initiated in normally functional condensates is unknown. Here we show, by measuring the changes in structure, dynamics, and mechanics in time and space, that single-component FUS condensates do not uniformly convert to a solid gel, but rather that liquid and gel phases coexist simultaneously within the same condensate, resulting in highly inhomogeneous structures. Furthermore, our results show that this transition originates at the interface between the condensate and the dilute continuous phase, and once initiated, the gelation process propagates toward the center of the condensate. To probe such spatially inhomogeneous rheology during condensate aging, we use a combination of established micropipette aspiration experiments together with two optical techniques, spatial dynamic mapping and reflective confocal dynamic speckle microscopy. These results reveal the importance of the spatiotemporal dimension of the liquid-to-solid transition and highlight the interface of biomolecular condensates as a critical element in driving pathological protein aggregation.

Glutamate helps unmask the differences in driving forces for phase separation versus clustering of FET family proteins in sub-saturated solutions

Multivalent proteins undergo coupled segregative and associative phase transitions. Phase separation, a segregative transition, is driven by macromolecular solubility, and this leads to coexisting phases above system-specific saturation concentrations. Percolation is a continuous transition that is driven by multivalent associations among cohesive motifs. Contributions from percolation are highlighted by the formation of heterogeneous distributions of clusters in sub-saturated solutions, as was recently reported for Fused in sarcoma (FUS) and FET family proteins. Here, we show that clustering and phase separation are defined by a separation of length- and energy-scales. This is unmasked when glutamate is the primary solution anion. Glutamate is preferentially excluded from protein sites, and this enhances molecular associations. Differences between glutamate and chloride are manifest at ultra-low protein concentrations. These differences are amplified as concentrations increase, and they saturate as the micron-scale is approached. Therefore, condensate formation in supersaturated solutions and clustering in sub-saturated are governed by distinct energy and length scales. Glutamate, unlike chloride, is the dominant intracellular anion, and the separation of scales, which is masked in chloride, is unmasked in glutamate. Our work highlights how components of cellular milieus and sequence-encoded interactions contribute to amplifying distinct contributions from associative versus segregative phase transitions.

Theoretical and Data-Driven Approaches for Biomolecular Condensates

Biomolecular condensation processes are increasingly recognized as a fundamental mechanism that living cells use to organize biomolecules in time and space. These processes can lead to the formation of membraneless organelles that enable cells to perform distinct biochemical processes in controlled local environments, thereby supplying them with an additional degree of spatial control relative to that achieved by membrane-bound organelles. This fundamental importance of biomolecular condensation has motivated a quest to discover and understand the molecular mechanisms and determinants that drive and control this process. Within this molecular viewpoint, computational methods can provide a unique angle to studying biomolecular condensation processes by contributing the resolution and scale that are challenging to reach with experimental techniques alone. In this Review, we focus on three types of dry-lab approaches: theoretical methods, physics-driven simulations and data-driven machine learning methods. We review recent progress in using these tools for probing biomolecular condensation across all three fields and outline the key advantages and limitations of each of the approaches. We further discuss some of the key outstanding challenges that we foresee the community addressing next in order to develop a more complete picture of the molecular driving forces behind biomolecular condensation processes and their biological roles in health and disease.

Positional influence on cellular transcriptional identity revealed through spatially segmented single-cell transcriptomics

Single-cell RNA sequencing (scRNA-seq) is a powerful technique for describing cell states. Identifying the spatial arrangement of these states in tissues remains challenging, with the existing methods requiring niche methodologies and expertise. Here, we describe segmentation by exogenous perfusion (SEEP), a rapid and integrated method to link surface proximity and environment accessibility to transcriptional identity within three-dimensional (3D) disease models. The method utilizes the steady-state diffusion kinetics of a fluorescent dye to establish a gradient along the radial axis of disease models. Classification of sample layers based on dye accessibility enables dissociated and sorted cells to be characterized by transcriptomic and regional identities. Using SEEP, we analyze spheroid, organoid, and in vivo tumor models of high-grade serous ovarian cancer (HGSOC). The results validate long-standing beliefs about the relationship between cell state and position while revealing new concepts regarding how spatially unique microenvironments influence the identity of individual cells within tumors.

Formation of Protein Nanoparticles in Microdroplet Flow Reactors

Nanoparticles are increasingly being used for biological applications, such as drug delivery and gene transfection. Different biological and bioinspired building blocks have been used for generating such particles, including lipids and synthetic polymers. Proteins are an attractive class of material for such applications due to their excellent biocompatibility, low immunogenicity, and self-assembly characteristics. Stable, controllable, and homogeneous formation of protein nanoparticles, which is key to successfully delivering cargo intracellularly, has been challenging to achieve using conventional methods. In order to address this issue, we employed droplet microfluidics and utilized the characteristic of rapid and continuous mixing within microdroplets in order to produce highly monodisperse protein nanoparticles. We exploit the naturally occurring vortex flows within microdroplets to prevent nanoparticle aggregation following nucleation, resulting in systematic control over the particle size and monodispersity. Through combination of simulation and experiment, we find that the internal vortex velocity within microdroplets determines the uniformity of the protein nanoparticles, and by varying parameters such as protein concentration and flow rates, we are able to finely tune nanoparticle dimensional properties. Finally, we show that our nanoparticles are highly biocompatible with HEK-293 cells, and through confocal microscopy, we determine that the nanoparticles fully enter into the cell with almost all cells containing them. Due to the high throughput of the method of production and the level of control afforded, we believe that the approach described in this study for generating monodisperse protein-based nanoparticles has the potential for intracellular drug delivery or for gene transfection in the future.

Formation of amyloid loops in brain tissues is controlled by the flexibility of protofibril chains

Neurodegenerative diseases, such as Alzheimer's disease (AD), are associated with protein misfolding and aggregation into amyloid fibrils. Increasing evidence suggests that soluble, low-molecular-weight aggregates play a key role in disease-associated toxicity. Within this population of aggregates, closed-loop pore-like structures have been observed for a variety of amyloid systems, and their presence in brain tissues is associated with high levels of neuropathology. However, their mechanism of formation and relationship with mature fibrils have largely remained challenging to elucidate. Here, we use atomic force microscopy and statistical theory of biopolymers to characterize amyloid ring structures derived from the brains of AD patients. We analyze the bending fluctuations of protofibrils and show that the process of loop formation is governed by the mechanical properties of their chains. We conclude that ex vivo protofibril chains possess greater flexibility than that imparted by hydrogen-bonded networks characteristic of mature amyloid fibrils, such that they are able to form end-to-end connections. These results explain the diversity in the structures formed from protein aggregation and shed light on the links between early forms of flexible ring-forming aggregates and their role in disease.

Microfluidic antibody affinity profiling of alloantibody-HLA interactions in human serum

Antibody profiling is a fundamental component of understanding the humoral response in a wide range of disease areas. Most currently used approaches operate by capturing antibodies onto functionalised surfaces. Such measurements of surface binding are governed by an overall antibody titre, while the two fundamental molecular parameters, antibody affinity and antibody concentration, are challenging to determine individually from such approaches. Here, by applying microfluidic diffusional sizing (MDS), we show how we can overcome this challenge and demonstrate reliable quantification of alloantibody binding affinity and concentration of alloantibodies binding to Human Leukocyte Antigens (HLA), an extensively used clinical biomarker in organ transplantation, both in buffer and in crude human serum. Capitalising on the ability to vary both serum and HLA concentrations during MDS, we show that both affinity and concentration of HLA-specific antibodies can be determined directly in serum when neither of these parameters is known. Finally, we provide proof of principle in clinical transplant patient sera that our assay enables differentiation of alloantibody reactivity against HLA proteins of highly similar structure, providing information not attainable through currently available techniques. These results outline a path towards detection and in-depth profiling of humoral immunity and may enable further insights into the clinical relevance of antibody reactivity in clinical transplantation and beyond.

Surface patches induce nonspecific binding and phase separation of antibodies

Nonspecific interactions are a key challenge in the successful development of therapeutic antibodies. The tendency for nonspecific binding of antibodies is often difficult to reduce by rational design, and instead, it is necessary to rely on comprehensive screening campaigns. To address this issue, we performed a systematic analysis of the impact of surface patch properties on antibody nonspecificity using a designer antibody library as a model system and single-stranded DNA as a nonspecificity ligand. Using an in-solution microfluidic approach, we find that the antibodies tested bind to single-stranded DNA with affinities as high as KD = 1 µM. We show that DNA binding is driven primarily by a hydrophobic patch in the complementarity-determining regions. By quantifying the surface patches across the library, the nonspecific binding affinity is shown to correlate with a trade-off between the hydrophobic and total charged patch areas. Moreover, we show that a change in formulation conditions at low ionic strengths leads to DNA-induced antibody phase separation as a manifestation of nonspecific binding at low micromolar antibody concentrations. We highlight that phase separation is driven by a cooperative electrostatic network assembly mechanism of antibodies with DNA, which correlates with a balance between positive and negative charged patches. Importantly, our study demonstrates that both nonspecific binding and phase separation are controlled by the size of the surface patches. Taken together, these findings highlight the importance of surface patches and their role in conferring antibody nonspecificity and its macroscopic manifestation in phase separation.

ANXA11 biomolecular condensates facilitate protein-lipid phase coupling on lysosomal membranes

Phase transitions of cellular proteins and lipids play a key role in governing the organisation and coordination of intracellular biology. The frequent juxtaposition of proteinaceous biomolecular condensates to cellular membranes raises the intriguing prospect that phase transitions in proteins and lipids could be co-regulated. Here we investigate this possibility in the ribonucleoprotein (RNP) granule-ANXA11-lysosome ensemble, where ANXA11 tethers RNP granule condensates to lysosomal membranes to enable their co-trafficking. We show that changes to the protein phase state within this system, driven by the low complexity ANXA11 N-terminus, induce a coupled phase state change in the lipids of the underlying membrane. We identify the ANXA11 interacting proteins ALG2 and CALC as potent regulators of ANXA11-based phase coupling and demonstrate their influence on the nanomechanical properties of the ANXA11-lysosome ensemble and its capacity to engage RNP granules. The phenomenon of protein-lipid phase coupling we observe within this system offers an important template to understand the numerous other examples across the cell whereby biomolecular condensates closely juxtapose cell membranes.

GRAPHICAL ABSTRACT

Protocol to determine antibody affinity and concentration in complex solutions using microfluidic antibody affinity profiling

Conventional methods of measuring affinity are limited by artificial immobilization, large sample volumes, and homogeneous solutions. This protocol describes microfluidic antibody affinity profiling on complex human samples in solution to obtain a fingerprint reflecting both affinity and active concentration of the target protein. To illustrate the protocol, we analyze the antibody response in SARS-CoV-2 omicron-naïve samples against different SARS-CoV-2 variants of concern. However, the protocol and the technology are amenable to a broad spectrum of biomedical questions. For complete details on the use and execution of this protocol, please refer to Emmenegger et al. (2022),1 Schneider et al. (2022),2 and Fiedler et al. (2022).3.

Multidimensional Protein Solubility Optimization with an Ultrahigh-Throughput Microfluidic Platform

Protein-based biologics are highly suitable for drug development as they exhibit low toxicity and high specificity for their targets. However, for therapeutic applications, biologics must often be formulated to elevated concentrations, making insufficient solubility a critical bottleneck in the drug development pipeline. Here, we report an ultrahigh-throughput microfluidic platform for protein solubility screening. In comparison with previous methods, this microfluidic platform can make, incubate, and measure samples in a few minutes, uses just 20 μg of protein (>10-fold improvement), and yields 10,000 data points (1000-fold improvement). This allows quantitative comparison of formulation excipients, such as sodium chloride, polysorbate, histidine, arginine, and sucrose. Additionally, we can measure how solubility is affected by the combinatorial effect of multiple additives, find a suitable pH for the formulation, and measure the impact of mutations on solubility, thus enabling the screening of large libraries. By reducing material and time costs, this approach makes detailed multidimensional solubility optimization experiments possible, streamlining drug development and increasing our understanding of biotherapeutic solubility and the effects of excipients.

Kinetic Analysis Reveals the Role of Secondary Nucleation in Regenerated Silk Fibroin Self-Assembly

Silk proteins obtained from the Bombyx mori silkworm have been extensively studied due to their remarkable mechanical properties. One of the major structural components of this complex material is silk fibroin, which can be isolated and processed further in vitro to form artificial functional materials. Due to the excellent biocompatibility and rich self-assembly behavior, there has been sustained interest in such materials formed through the assembly of regenerated silk fibroin feedstocks. The molecular mechanisms by which the soluble regenerated fibroin molecules self-assemble into protein nanofibrils remain, however, largely unknown. Here, we use the framework of chemical kinetics to connect macroscopic measurements of regenerated silk fibroin self-assembly to the underlying microscopic mechanisms. Our results reveal that the aggregation of regenerated silk fibroin is dominated by a nonclassical secondary nucleation processes, where the formation of new fibrils is catalyzed by the existing aggregates in an autocatalytic manner. Such secondary nucleation pathways were originally discovered in the context of polymerization of disease-associated proteins, but the present results demonstrate that this pathway can also occur in functional assembly. Furthermore, our results show that shear flow induces the formation of nuclei, which subsequently accelerate the process of aggregation through an autocatalytic amplification driven by the secondary nucleation pathway. Taken together, these results allow us to identify the parameters governing the kinetics of regenerated silk fibroin self-assembly and expand our current understanding of the spinning of bioinspired protein-based fibers, which have a wide range of applications in materials science.

Single-Molecule Sizing through Nanocavity Confinement

An approach relying on nanocavity confinement is developed in this paper for the sizing of nanoscale particles and single biomolecules in solution. The approach, termed nanocavity diffusional sizing (NDS), measures particle residence times within nanofluidic cavities to determine their hydrodynamic radii. Using theoretical modeling and simulations, we show that the residence time of particles within nanocavities above a critical time scale depends on the diffusion coefficient of the particle, which allows the estimation of the particle's size. We demonstrate this approach experimentally through the measurement of particle residence times within nanofluidic cavities using single-molecule confocal microscopy. Our data show that the residence times scale linearly with the sizes of nanoscale colloids, protein aggregates, and single DNA oligonucleotides. NDS thus constitutes a new single molecule optofluidic approach that allows rapid and quantitative sizing of nanoscale particles for potential applications in nanobiotechnology, biophysics, and clinical diagnostics.

Selenium Silk Nanostructured Films with Antifungal and Antibacterial Activity

The rapid emergence of drug-resistant bacteria and fungi poses a threat for healthcare worldwide. The development of novel effective small molecule therapeutic strategies in this space has remained challenging. Therefore, one orthogonal approach is to explore biomaterials with physical modes of action that have the potential to generate antimicrobial activity and, in some cases, even prevent antimicrobial resistance. Here, to this effect, we describe an approach for forming silk-based films that contain embedded selenium nanoparticles. We show that these materials exhibit both antibacterial and antifungal properties while crucially also remaining highly biocompatible and noncytotoxic toward mammalian cells. By incorporating the nanoparticles into silk films, the protein scaffold acts in a 2-fold manner; it protects the mammalian cells from the cytotoxic effects of the bare nanoparticles, while also providing a template for bacterial and fungal eradication. A range of hybrid inorganic/organic films were produced and an optimum concentration was found, which allowed for both high bacterial and fungal death while also exhibiting low mammalian cell cytotoxicity. Such films can thus pave the way for next-generation antimicrobial materials for applications such as wound healing and as agents against topical infections, with the added benefit that bacteria and fungi are unlikely to develop antimicrobial resistance to these hybrid materials.

Spatially non-uniform condensates emerge from dynamically arrested phase separation

The formation of biomolecular condensates through phase separation from proteins and nucleic acids is emerging as a spatial organisational principle used broadly by living cells. Many such biomolecular condensates are not, however, homogeneous fluids, but possess an internal structure consisting of distinct sub-compartments with different compositions. Notably, condensates can contain compartments that are depleted in the biopolymers that make up the condensate. Here, we show that such double-emulsion condensates emerge via dynamically arrested phase transitions. The combination of a change in composition coupled with a slow response to this change can lead to the nucleation of biopolymer-poor droplets within the polymer-rich condensate phase. Our findings demonstrate that condensates with a complex internal architecture can arise from kinetic, rather than purely thermodynamic driving forces, and provide more generally an avenue to understand and control the internal structure of condensates in vitro and in vivo.

Direct digital sensing of protein biomarkers in solution

The detection of proteins is of central importance to biomolecular analysis and diagnostics. Typical immunosensing assays rely on surface-capture of target molecules, but this constraint can limit specificity, sensitivity, and the ability to obtain information beyond simple concentration measurements. Here we present a surface-free, single-molecule microfluidic sensing platform for direct digital protein biomarker detection in solution, termed digital immunosensor assay (DigitISA). DigitISA is based on microchip electrophoretic separation combined with single-molecule detection and enables absolute number/concentration quantification of proteins in a single, solution-phase step. Applying DigitISA to a range of targets including amyloid aggregates, exosomes, and biomolecular condensates, we demonstrate that the assay provides information beyond stoichiometric interactions, and enables characterization of immunochemistry, binding affinity, and protein biomarker abundance. Taken together, our results suggest a experimental paradigm for the sensing of protein biomarkers, which enables analyses of targets that are challenging to address using conventional immunosensing approaches.

Bioprinting microporous functional living materials from protein-based core-shell microgels

Living materials bring together material science and biology to allow the engineering and augmenting of living systems with novel functionalities. Bioprinting promises accurate control over the formation of such complex materials through programmable deposition of cells in soft materials, but current approaches had limited success in fine-tuning cell microenvironments while generating robust macroscopic morphologies. Here, we address this challenge through the use of core-shell microgel ink to decouple cell microenvironments from the structural shell for further processing. Cells are microfluidically immobilized in the viscous core that can promote the formation of both microbial populations and mammalian cellular spheroids, followed by interparticle annealing to give covalently stabilized functional scaffolds with controlled microporosity. The results show that the core-shell strategy mitigates cell leakage while affording a favorable environment for cell culture. Furthermore, we demonstrate that different microbial consortia can be printed into scaffolds for a range of applications. By compartmentalizing microbial consortia in separate microgels, the collective bioprocessing capability of the scaffold is significantly enhanced, shedding light on strategies to augment living materials with bioprocessing capabilities.

Perphenazine-Macrocycle Conjugates Rapidly Sequester the Aβ42 Monomer and Prevent Formation of Toxic Oligomers and Amyloid

Alzheimer's disease is imposing a growing social and economic burden worldwide, and effective therapies are urgently required. One possible approach to modulation of the disease outcome is to use small molecules to limit the conversion of monomeric amyloid (Aβ42) to cytotoxic amyloid oligomers and fibrils. We have synthesized modulators of amyloid assembly that are unlike others studied to date: these compounds act primarily by sequestering the Aβ42 monomer. We provide kinetic and nuclear magnetic resonance data showing that these perphenazine conjugates divert the Aβ42 monomer into amorphous aggregates that are not cytotoxic. Rapid monomer sequestration by the compounds reduces fibril assembly, even in the presence of pre-formed fibrillar seeds. The compounds are therefore also able to disrupt monomer-dependent secondary nucleation, the autocatalytic process that generates the majority of toxic oligomers. The inhibitors have a modular design that is easily varied, aiding future exploration and use of these tools to probe the impact of distinct Aβ42 species populated during amyloid assembly.

The Chromatin Regulator HMGA1a Undergoes Phase Separation in the Nucleus

The protein high mobility group A1 (HMGA1) is an important regulator of chromatin organization and function. However, the mechanisms by which it exerts its biological function are not fully understood. Here, we report that the HMGA isoform, HMGA1a, nucleates into foci that display liquid-like properties in the nucleus, and that the protein readily undergoes phase separation to form liquid condensates in vitro. By bringing together machine-leaning modelling, cellular and biophysical experiments and multiscale simulations, we demonstrate that phase separation of HMGA1a is promoted by protein-DNA interactions, and has the potential to be modulated by post-transcriptional effects such as phosphorylation. We further show that the intrinsically disordered C-terminal tail of HMGA1a significantly contributes to its phase separation through electrostatic interactions via AT hooks 2 and 3. Our work sheds light on HMGA1 phase separation as an emergent biophysical factor in regulating chromatin structure.

Structure-Based Discovery of Small-Molecule Inhibitors of the Autocatalytic Proliferation of α-Synuclein Aggregates

The presence of amyloid fibrils of α-synuclein is closely associated with Parkinson's disease and related synucleinopathies. It is still very challenging, however, to systematically discover small molecules that prevent the formation of these aberrant aggregates. Here, we describe a structure-based approach to identify small molecules that specifically inhibit the surface-catalyzed secondary nucleation step in the aggregation of α-synuclein by binding to the surface of the amyloid fibrils. The resulting small molecules are screened using a range of kinetic and thermodynamic assays for their ability to bind α-synuclein fibrils and prevent the further generation of α-synuclein oligomers. This study demonstrates that the combination of structure-based and kinetic-based drug discovery methods can lead to the identification of small molecules that selectively inhibit the autocatalytic proliferation of α-synuclein aggregates.

A Kinetic Map of the Influence of Biomimetic Lipid Model Membranes on Aβ42 Aggregation

The aggregation of the amyloid β (Aβ) peptide is one of the molecular hallmarks of Alzheimer's disease (AD). Although Aβ deposits have mostly been observed extracellularly, various studies have also reported the presence of intracellular Aβ assemblies. Because these intracellular Aβ aggregates might play a role in the onset and progression of AD, it is important to investigate their possible origins at different locations of the cell along the secretory pathway of the amyloid precursor protein, from which Aβ is derived by proteolytic cleavage. Senile plaques found in AD are largely composed of the 42-residue form of Aβ (Aβ₄₂). Intracellularly, Aβ₄₂ is produced in the endoplasmatic reticulum (ER) and Golgi apparatus. Since lipid bilayers have been shown to promote the aggregation of Aβ, in this study, we measure the effects of the lipid membrane composition on the in vitro aggregation kinetics of Aβ₄₂. By using large unilamellar vesicles to model cellular membranes at different locations, including the inner and outer leaflets of the plasma membrane, late endosomes, the ER, and the Golgi apparatus, we show that Aβ₄₂ aggregation is inhibited by the ER and Golgi model membranes. These results provide a preliminary map of the possible effects of the membrane composition in different cellular locations on Aβ aggregation and suggest the presence of an evolutionary optimization of the lipid composition to prevent the intracellular aggregation of Aβ.

Microfluidics for multiscale studies of biomolecular condensates

Membraneless organelles formed through condensation of biomolecules in living cells have become the focus of sustained efforts to elucidate their mechanisms of formation and function. These condensates perform a range of vital functions in cells and are closely connected to key processes in functional and aberrant biology. Since these systems occupy a size scale intermediate between single proteins and conventional protein complexes on the one hand, and cellular length scales on the other hand, they have proved challenging to probe using conventional approaches from either protein science or cell biology. Additionally, condensate can form, solidify and perform functions on various time-scales. From a physical point of view, biomolecular condensates are colloidal soft matter systems, and microfluidic approaches, which originated in soft condensed matter research, have successfully been used to study biomolecular condensates. This review explores how microfluidics have aided condensate research into the thermodynamics, kinetics and other properties of condensates, by offering high-throughput and novel experimental setups.

Serological fingerprints link antiviral activity of therapeutic antibodies to affinity and concentration

The effectiveness of therapeutic monoclonal antibodies (mAbs) against variants of the SARS-CoV-2 virus is highly variable. As target recognition of mAbs relies on tight binding affinity, we assessed the affinities of five therapeutic mAbs to the receptor binding domain (RBD) of wild type (A), Delta (B.1.617.2), and Omicron BA.1 SARS-CoV-2 (B.1.1.529.1) spike using microfluidic diffusional sizing (MDS). Four therapeutic mAbs showed strongly reduced affinity to Omicron BA.1 RBD, whereas one (sotrovimab) was less impacted. These affinity reductions correlate with reduced antiviral activities suggesting that affinity could serve as a rapid indicator for activity before time-consuming virus neutralization assays are performed. We also compared the same mAbs to serological fingerprints (affinity and concentration) obtained by MDS of antibodies in sera of 65 convalescent individuals. The affinities of the therapeutic mAbs to wild type and Delta RBD were similar to the serum antibody response, indicating high antiviral activities. For Omicron BA.1 RBD, only sotrovimab retained affinities within the range of the serum antibody response, in agreement with high antiviral activity. These results suggest that serological fingerprints provide a route to evaluating affinity and antiviral activity of mAb drugs and could guide the development of new therapeutics.

Characterization of full-length p53 aggregates and their kinetics of formation

Mutations in the TP53 gene are common in cancer with the R248Q missense mutation conferring an increased propensity to aggregate. Previous p53 aggregation studies showed that, at micromolar concentrations, protein unfolding to produce aggregation-prone species is the rate-determining step. Here we show that, at physiological concentrations, aggregation kinetics of insect cell-derived full-length wild-type p53 and p53R248Q are determined by a nucleation-growth model, rather than formation of aggregation-prone monomeric species. Self-seeding, but not cross-seeding, increases aggregation rate, confirming the aggregation process as rate determining. p53R248Q displays enhanced aggregation propensity due to decreased solubility and increased aggregation rate, forming greater numbers of larger amorphous aggregates that disrupt lipid bilayers and invokes an inflammatory response. These results suggest that p53 aggregation can occur under physiological conditions, a rate enhanced by R248Q mutation, and that aggregates formed can cause membrane damage and inflammation that may influence tumorigenesis.