A sulfilimine bond identified in collagen IV

1,2-Difunctionalization of Aryne with Sulfenamide and Organohalide: Mild and Metal-Free Access to S-(o-Halo)aryl Sulfilimine

A mild and metal-free approach has been developed for 1,2-difunctionalization of aryne using sulfenamides as a nucleophile and a halogen source (CX4) as an electrophile to synthesize S-(o-halo)aryl sulfilimines. The late-stage functionalizations of halide handles via Suzuki-Miyaura and Buchwald-Hartwig reactions exhibit the synthetic utilities of the products. The chemoselectivity, regioselectivity, rapidity, and use of economical CCl4 are the advantages of this protocol.

Syntheses of Sulfilimines by Iron-Catalyzed Iminations of Sulfides with 2,2,2-Trichloroethyl Sulfamate

N-protected sulfilimines are prepared by imination of sulfides with a combination of 2,2,2-trichloroethyl sulfamate (H2NTces), (diacetoxyiodo)benzene (PIDA), and a catalytic amount of iron triflate. The reaction proceeds at room temperature, and after only 3 h a wide range of acyclic and cyclic NTces-sulfilimines with various functional groups and (hetero)aryl substituents can be obtained. By subsequent oxidation followed by deprotection, the products are converted into NH-sulfoximines.

Polymerizing Laminins in Development, Health and Disease

Polymerizing laminins are multi-domain basement membrane (BM) glycoproteins that self-assemble into cell-anchored planar lattices to establish the initial BM scaffold. Nidogens, collagen-IV and proteoglycans then bind to the scaffold at different domain loci to create a mature BM. The LN domains of adjacent laminins bind to each other to form a polymer node, while the LG domains attach to cytoskeletal-anchoring integrins and dystroglycan, as well as to sulfatides and heparan sulfates. The polymer node, the repeating unit of the polymer scaffold, is organized into a near-symmetrical triskelion. The structure, recently solved by cryo-electron microscopy in combination with AlphaFold2 modelling and biochemical studies, reveals how the LN surface residues interact with each other and how mutations cause failures of self-assembly in an emerging group of diseases, the LN-lamininopathies, that include LAMA2-related dystrophy and Pierson syndrome.

Copper-Catalyzed Sulfur Alkylation of Sulfenamides with N-Sulfonylhydrazones

Sulfilimines are valuable compounds in both organic synthesis and pharmaceuticals. In this study, we present a copper-catalyzed sulfur alkylation of sulfenamides with N-sulfonylhydrazones. In contrast to prior findings, hydrazones derived from aldehydes act as donor-type carbene precursors, effectively engaging in coupling with sulfenamides via a copper catalyst, demonstrating exclusive S selectivity. The utility of the protocol was highlighted in the rapid access to a wide range of sulfoximine derivatives.

Assessing Heterogeneity in the N-Telopeptides of Type I Collagen by Mass Spectrometry

Collagen cross-links created by the lysyl oxidase and lysyl hydroxylase families of enzymes are a significant contributing factor to the biomechanical strength and rigidity of tissues, which in turn influence cell signaling and ultimately cell phenotype. In the clinic, the proteolytically liberated N-terminal cross-linked peptide of collagen I (NTX) is used as a biomarker of bone and connective tissue turnover, which is altered in several disease processes. Despite the clinical utility of these collagen breakdown products, the majority of the cross-linked peptide species have not been identified in proteomic datasets. Here we evaluate several parameters for the preparation and identification of these peptides from the collagen I-rich Achilles tendon. Our refined approach involving chemical digestion for protein solubilization coupled with mass spectrometry allows for the identification of the NTX cross-links in a range of modification states. Based on the specificity of the enzymatic cross-linking reaction we utilized follow-up variable modification searches to facilitate identification with a wider range of analytical workflows. We then applied a spectral library approach to identify differences in collagen cross-links in bovine pulmonary hypertension. The presented method offers unique opportunities to understand extracellular matrix remodeling events in development, aging, wound healing, and fibrotic disease that modulate collagen architecture through lysyl-hydroxylase and lysyl-oxidase enzymes.

Diphenylphosphinylhydroxylamine (DPPH) Affords Late-Stage S-imination to access free-NH Sulfilimines and Sulfoximines

Sulfilimines, as potential aza-isosteres of sulfoxides, are valued as building blocks, auxiliaries, ligands, bioconjugation handles, and as precursors to versatile S(VI) scaffolds including sulfoximines and sulfondiimines. Here, we report a thioether imination methodology that exploits O-(diphenylphosphinyl)hydroxyl amine (DPPH). Under mild, metal-free, and biomolecule-compatible conditions, DPPH enables late-stage S-imination on peptides, natural products, and a clinically trialled drug, and shows both excellent chemoselectivity and broad functional group tolerance. This methodological report is extended to an efficient and high-yielding one-pot reaction for accessing free-NH sulfoximines with diverse substrates including ones of potential clinical importance. In the presence of a rhodium catalyst, sulfoxides are S-iminated in higher yields to afford free-NH sulfoximines. S-imination was validated on an oxidatively delicate amatoxin to give sulfilimine and sulfoximine congeners. Interestingly, these new sulfilimine and sulfoximine-amatoxins show cytotoxicity. This method is further extended to create sulfilimine and sulfoximine-Fulvestrant and buthionine analogues.

Copper-Catalyzed Sulfimidation in Aqueous Media: a Fast, Chemoselective and Biomolecule-Compatible Reaction

Performing transition metal-catalyzed reactions in cells and living systems has equipped scientists with a toolbox to study biological processes and release drugs on demand. Thus far, an impressive scope of reactions has been performed in these settings, but many are yet to be introduced. Nitrene transfer presents a rather unexplored new-to-nature reaction. The reaction products are frequently encountered motifs in pharmaceuticals, presenting opportunities for the controlled, intracellular synthesis of drugs. Hence, we explored the transition metal-catalyzed sulfimidation reaction in water for future in vivo application. Two Cu(I) complexes containing trispyrazolylborate ligands (Tpx ) were selected, and the catalytic system was evaluated with the aid of three fitness factors. The excellent nitrene transfer reactivity and high chemoselectivity of the catalysts, coupled with good biomolecule compatibility, successfully enabled the sulfimidation of thioethers in aqueous media. We envision that this copper-catalyzed sulfimidation reaction could be an interesting starting point to unlock the potential of nitrene transfer catalysis in vivo.

Decarboxylative Radical Sulfilimination via Photoredox, Copper, and Brønsted Base Catalysis

Sulfilimines, the aza-variants of sulfoxides, are key structural motifs in natural products, pharmaceuticals, and agrochemicals; and sulfilimine synthesis is therefore important in organic chemistry. However, methods for radical sulfilimination remain elusive, and as a result, the structural diversity of currently available sulfilimines is limited. Herein, we report the first protocol for decarboxylative radical sulfilimination reactions between sulfenamides and N-hydroxyphthalimide esters of primary, secondary, and tertiary alkyl carboxylic acids, which were achieved via a combination of photoredox, copper, and Brønsted base catalysis. This novel protocol provided a wide variety of sulfilimines, in addition to serving as an efficient route for the synthesis of S-alkyl/S-aryl homocysteine sulfilimines and S-(4-methylphenyl) homocysteine sulfoximine. Moreover, it could be used for late-stage introduction of a sulfilimine group into structurally complex molecules, thereby avoiding the need to preserve labile organosulfur moieties through multistep synthetic sequences. A mechanism involving photocatalytic substrate transformation and copper-mediated C(sp3 )-S bond formation is proposed.

Mask and Release Strategy-Enabled Diversity-Oriented Synthesis for DNA-Encoded Library

An ideal DNA-encoded library (DEL) selection requires the library to consist of diverse core skeletons and cover chemical space as much as possible. However, the lack of efficient on-DNA synthetic approaches toward core skeletons has greatly restricted the diversity of DEL. To mitigate this issue, this work disclosed a "Mask & Release" strategy to streamline the challenging on-DNA core skeleton synthesis. N-phenoxyacetamide is used as a masked phenol and versatile directing group to mediate diversified DNA-compatible C-H functionalization, introducing the 1st-dimensional diversity at a defined site, and simultaneously releasing the phenol functionality, which can facilitate the introduction of the 2nd diversity. This work not only provides a set of efficient syntheses toward DNA-conjugated drug-like core skeletons such as ortho-alkenyl/sulfiliminyl/cyclopropyl phenol, benzofuran, dihydrobenzofuran but also provides a paradigm for on-DNA core skeleton synthetic method development.

Sulfilimine bond formation in collagen IV

The collagen IV network plays a crucial role in providing structural support and mechanical integrity to the basement membrane and surrounding tissues. A key aspect of this network is the formation of intra- and inter-collagen fibril crosslinks. One particular crosslink, an inter-residue sulfilimine bond, has been found, so far, to be unique to collagen IV. More specifically, these crosslinks are primarily formed between methionine and lysine or hydroxylysine residues and can occur within a single collagen fibril or between different collagen fibrils. Due to its significance as the major crosslink in the collagen IV network, the sulfilimine bond plays critical roles in tissue development and various human diseases. While the proposed reaction mechanism for sulfilimine bond formation is supported by experimental evidence, the precise nature of this bond remained uncertain until computational studies were conducted. The process involves the reaction of hypohalous acids (e.g., HOBr, HOCl), produced by a peroxidasin enzyme in the basement membrane, with the sidechain sulfur of methionine or sidechain nitrogen of lysine/hydroxylysine residues in collagen IV, to form halosulfonium or haloamine intermediates, respectively. The halosulfonium/haloamine then reacts with the sidechain amine/sulfide of the lysine (or hydroxylysine) or methionine respectively, eventually resulting in the formation of the sulfilimine (MetSNLys/Hyl) crosslink. The sulfilimine product formed not only plays a crucial role in physiological processes but also finds applications in various industrial and pharmaceutical contexts. In this review, we provide a comprehensive summary of existing studies, including our own research, aimed at understanding the reaction mechanism, protonation states, characteristic nature, and dynamic behavior of the sulfilimine bond in collagen IV. The goal is to offer readers an overview of this critically important biochemical bond.

Peroxidasin is required for full viability in development and for maintenance of tissue mechanics in adults

Basement membranes are thin strong sheets of extracellular matrix. They provide mechanical and biochemical support to epithelia, muscles, nerves, and blood vessels, among other tissues. The mechanical properties of basement membranes are conferred in part by Collagen IV (Col4), an abundant protein of basement membranes that forms an extensive two-dimensional network through head-to-head and tail-to-tail interactions. After the Col4 network is assembled into a basement membrane, it is crosslinked by the matrix-resident enzyme Peroxidasin to form a large covalent polymer. Peroxidasin and Col4 crosslinking are highly conserved throughout the animal kingdom, indicating they are important, but homozygous mutant mice have mild phenotypes. To explore the role of Peroxidasin, we analyzed mutants in Drosophila, including a new CRISPR-generated catalytic null, and found that homozygotes were mostly lethal with 13 % viable escapers. Mouse mutants also show semi-lethality, with Mendelian analysis demonstrating ∼50 % lethality and ∼50 % escapers. Despite the strong mutations, the homozygous fly and mouse escapers had low but detectable levels of Col4 crosslinking, indicating the existence of inefficient alternative crosslinking mechanisms, probably responsible for the viable escapers. Fly mutant phenotypes are consistent with decreased basement membrane stiffness. Interestingly, we found that even after basement membranes are assembled and crosslinked in wild-type animals, continuing Peroxidasin activity is required in adults to maintain tissue stiffness over time. These results suggest that Peroxidasin crosslinking may be more important than previously appreciated.

Mechanism of peroxidasin inactivation in hyperglycemia: Heme damage by reactive oxygen species

Diabetic complications present a serious health problem. Functional damage to proteins due to post-translational modifications by glycoxidation reactions is a known factor contributing to pathology. Extracellular proteins are especially vulnerable to diabetic damage because robust antioxidant defenses are lacking outside the cell. We investigated glucose-induced inactivation of peroxidasin (PXDN), a heme protein catalyzing sulfilimine crosslinking of collagen IV that reinforce the basement membranes (BM). Experiments using physiological diabetic glucose levels were carried out to exclude several potential mechanisms of PXDN inactivation i.e., direct adduction of glucose, reactive carbonyl damage, steric hindrance, and osmotic stress. Further experiments established that PXDN activity was inhibited via heme degradation by reactive oxygen species. Activity of another extracellular heme protein, myeloperoxidase, was unaffected by glucose because its heme was resistant to glucose-induced oxidative degradation. Our findings point to specific mechanisms which may compromise BM structure and stability in diabetes and suggest potential modes of protection.

Collagen IV of basement membranes: IV. Adaptive mechanism of collagen IV scaffold assembly in Drosophila

Collagen IV is an essential structural protein in all metazoans. It provides a scaffold for the assembly of basement membranes, a specialized form of extracellular matrix, which anchors and signals cells and provides microscale tensile strength. Defective scaffolds cause basement membrane destabilization and tissue dysfunction. Scaffolds are composed of α-chains that coassemble into triple-helical protomers of distinct chain compositions, which in turn oligomerize into supramolecular scaffolds. Chloride ions mediate the oligomerization via NC1 trimeric domains, forming an NC1 hexamer at the protomer-protomer interface. The chloride concentration-"chloride pressure"-on the outside of cells is a primordial innovation that drives the assembly and dynamic stabilization of collagen IV scaffolds. However, a Cl-independent mechanism is operative in Ctenophora, Ecdysozoa, and Rotifera, which suggests evolutionary adaptations to environmental or tissue conditions. An understanding of these exceptions, such as the example of Drosophila, could shed light on the fundamentals of how NC1 trimers direct the oligomerization of protomers into scaffolds. Here, we investigated the NC1 assembly of Drosophila. We solved the crystal structure of the NC1 hexamer, determined the chain composition of protomers, and found that Drosophila adapted an evolutionarily unique mechanism of scaffold assembly that requires divalent cations. By studying the Drosophila case we highlighted the mechanistic role of chloride pressure for maintaining functionality of the NC1 domain in humans. Moreover, we discovered that the NC1 trimers encode information for homing protomers to distant tissue locations, providing clues for the development of protein replacement therapy for collagen IV genetic diseases.

Identification of brominated proteins in renal extracellular matrix: Potential interactions with peroxidasin

Peroxidasin (PXDN) is an extracellular peroxidase, which generates hypobromous acid to form sulfilimine cross-links within collagen IV networks. We have previously demonstrated that mouse and human renal basement membranes (BM) are enriched in bromine due to PXDN-dependent post-translational bromination of protein tyrosine residues. The goal of the present study was identification of specific brominated sites within renal BM. A comprehensive analysis of brominated proteome of mouse glomerular matrix had been performed using liquid chromatography-tandem mass spectrometry. We found that out of over 200 identified proteins, only three were detectably brominated, each containing a single distinct brominated tyrosine site i.e., Tyr-1485 in collagen IV α2 chain, Tyr-292 in TINAGL1 and Tyr-664 in nidogen-2. To explain this highly selective bromination, we proposed that these proteins interact with PXDN within the glomerular matrix. Experiments using purified proteins demonstrated that both TINAGL1 and nidogen-2 can compete with PXDN for binding to collagen IV and that TINAGL1 can directly interact with PXDN. We propose that a protein complex, including PXDN, TINAGL1, nidogen-2 and collagen IV, may exist in renal BM.

Collagen IV of basement membranes: III. Chloride pressure is a primordial innovation that drives and maintains the assembly of scaffolds

Collagen IV scaffold is a primordial innovation enabling the assembly of a fundamental architectural unit of epithelial tissues-a basement membrane attached to polarized cells. A family of six α-chains (α1 to α6) coassemble into three distinct protomers that form supramolecular scaffolds, noted as collagen IVα121, collagen IVα345, and collagen IVα121-α556. Chloride ions play a pivotal role in scaffold assembly, based on studies of NC1 hexamers from mammalian tissues. First, Cl- activates a molecular switch within trimeric NC1 domains that initiates protomer oligomerization, forming an NC1 hexamer between adjoining protomers. Second, Cl- stabilizes the hexamer structure. Whether this Cl--dependent mechanism is of fundamental importance in animal evolution is unknown. Here, we developed a simple in vitro method of SDS-PAGE to determine the role of solution Cl- in hexamer stability. Hexamers were characterized from 34 animal species across 15 major phyla, including the basal Cnidarian and Ctenophora phyla. We found that solution Cl- stabilized the quaternary hexamer structure across all phyla except Ctenophora, Ecdysozoa, and Rotifera. Further analysis of hexamers from peroxidasin knockout mice, a model for decreasing hexamer crosslinks, showed that solution Cl- also stabilized the hexamer surface conformation. The presence of sufficient chloride concentration in solution or "chloride pressure" dynamically maintains the native form of the hexamer. Collectively, our findings revealed that chloride pressure on the outside of cells is a primordial innovation that drives and maintains the quaternary and conformational structure of NC1 hexamers of collagen IV scaffolds.

The role of peroxidasin in solid cancer progression

Peroxidasin is a heme-containing peroxidase enzyme that plays a vital role in the cross-linking of collagen IV molecules in basement membranes. Collagen IV cross-links are essential for providing structure and mechanical stability throughout tissue development, homeostasis, and wound healing. During cancer progression, the basement membrane is degraded, and proteins typically found in the basement membrane, including peroxidasin and collagen IV, can be found spread throughout the tumour microenvironment where they interact with cancer cells and alter cell behaviour. Whilst peroxidasin is reported to be up-regulated in a number of different cancers, the role that it plays in disease progression and metastasis has only recently begun to be studied. This review highlights the current literature exploring the known roles of peroxidasin in normal tissues and cancer progression, regulators of peroxidasin expression, and the reported relationships between peroxidasin expression and patient outcome in cancer.

Selective S-Arylation of Sulfenamides with Arynes: Access to Sulfilimines

Sulfilimines, the aza analogues of sulfoxides, are of increasing interest in medicinal and agrochemical research programs. However, the development of efficient routes for their synthesis has remained relatively unexplored. In this study, we report a transition metal-free, selective S-arylation reaction between sulfenamides and arynes, enabling the facile preparation of structurally diverse sulfilimines under mild and redox-neutral conditions in good yields. The application value of our method was further demonstrated by scale-up synthesis, downstream derivatization, and robustness screen.

Synthesis of Sulfilimines via Multicomponent Reaction of Arynes, Sulfamides, and Thiosulfonates

In this work, a facile and efficient method for the synthesis of sulfilimines through multicomponent reaction of arynes, sulfamides, and thiosulfonates was developed. A variety of structurally diverse substrates and functional groups were very compatible in the reaction, giving the corresponding sulfilimines in good to high yields. This protocol could be conducted on a gram scale, and the product was easily converted to sulfide and sulfoximine. Mechanism studies revealed that sulfenamide generated in situ is the key intermediate for the reaction.

Analysis of Drosophila and mouse mutants reveals that Peroxidasin is required for tissue mechanics and full viability

Basement membranes are thin strong sheets of extracellular matrix. They provide mechanical and biochemical support to epithelia, muscles, nerves, and blood vessels, among other tissues. The mechanical properties of basement membranes are conferred in part by Collagen IV (Col4), an abundant protein of basement membrane that forms an extensive two-dimensional network through head-to-head and tail-to-tail interactions. After the Col4 network is assembled into a basement membrane, it is crosslinked by the matrix-resident enzyme Peroxidasin to form a large covalent polymer. Peroxidasin and Col4 crosslinking are highly conserved, indicating they are essential, but homozygous mutant mice have mild phenotypes. To explore the role of Peroxidasin, we analyzed mutants in Drosophila, including a newly generated catalytic null, and found that homozygotes were mostly lethal with 13% viable escapers. A Mendelian analysis of mouse mutants shows a similar pattern, with homozygotes displaying ~50% lethality and ~50% escapers. Despite the strong mutations, the homozygous escapers had low but detectable levels of Col4 crosslinking, indicating that inefficient alternative mechanisms exist and that are probably responsible for the viable escapers. Further, fly mutants have phenotypes consistent with a decrease in stiffness. Interestingly, we found that even after adult basement membranes are assembled and crosslinked, Peroxidasin is still required to maintain stiffness. These results suggest that Peroxidasin crosslinking may be more important than previously appreciated.

Synthesis of Sulfilimines via Aryne and Cyclohexyne Intermediates

An efficient and metal-free approach for the synthesis of sulfilimines from sulfenamides with aryne and cyclohexyne precursors has been developed. The reaction proceeds through unusual S-C bond formation, which offers a novel and practical entry to access a wide range of sulfilimines in moderate to good yields with excellent chemoselectivity. Moreover, this protocol is amenable to gram-scale synthesis and is applicable to the transformation of the products into useful sulfoximines.

Identification of unique α4 chain structure and conserved antiangiogenic activity of α3NC1 type IV collagen in zebrafish

BACKGROUND

Type IV collagen is an abundant component of basement membranes in all multicellular species and is essential for the extracellular scaffold supporting tissue architecture and function. Lower organisms typically have two type IV collagen genes, encoding α1 and α2 chains, in contrast with the six genes in humans, encoding α1-α6 chains. The α chains assemble into trimeric protomers, the building blocks of the type IV collagen network. The detailed evolutionary conservation of type IV collagen network remains to be studied.

RESULTS

We report on the molecular evolution of type IV collagen genes. The zebrafish α4 non-collagenous (NC1) domain, in contrast with its human ortholog, contains an additional cysteine residue and lacks the M93 and K211 residues involved in sulfilimine bond formation between adjacent protomers. This may alter α4 chain interactions with other α chains, as supported by temporal and anatomic expression patterns of collagen IV chains during the zebrafish development. Despite the divergence between zebrafish and human α3 NC1 domain (endogenous angiogenesis inhibitor, Tumstatin), the zebrafish α3 NC1 domain exhibits conserved antiangiogenic activity in human endothelial cells.

CONCLUSIONS

Our work supports type IV collagen is largely conserved between zebrafish and humans, with a possible difference involving the α4 chain.

Metal-Free Chemoselective S-Arylation of Sulfenamides To Access Sulfilimines

A novel and efficient S-arylation of sulfenamides with diaryliodonium salts for the synthesis of sulfilimines is developed. The reaction proceeds smoothly under transition-metal-free and air conditions, giving rapid access to sulfilimines in good to excellent yields via selective S-C bond formation. This protocol is scalable and exhibits a broad substrate scope, good functional group tolerance, and excellent chemoselectivity.

Base-Promoted S-Arylation of Sulfenamides for the Synthesis of Sulfilimines

Sulfilimines are key intermediates to common motifs in medicines and agrochemicals. Typically, this class of compounds are prepared by imidation of thioethers, transition-metal-catalyzed or base-promoted sulfur alkylation and transition-metal-catalyzed sulfur arylation. Here, we report a practical and efficient base-mediated sulfur arylation reaction for the preparation of sulfilimines. A wide range of N-acyl and N-aryl sulfenamides react with various diaryliodonium salts smoothly to afford the sulfilimines in high yields with excellent chemoselectivities.

Computational Insights into the Formation and Structure of S-N Containing Cyclic Peptides

Cyclic peptides are known to have biologically important roles and may also be applicable to the pharmaceutical and other industries. Furthermore, thiols and amines, which are found throughout biological systems, can react to form S-N bonds and to date, ∼100 biomolecules containing such a bond have been identified. However, while there are in principle numerous S-N containing peptide-derived rings possible, only a few are presently known to occur in biochemical systems. Density functional theory-based calculations have been used to consider the formation and structure of S-N containing cyclic peptides from systematic series of linear peptides in which a cysteinyl has first been oxidized to a sulfenic or sulfonic acid. In addition, the possible effect of the cysteine's vicinal residue on the free energy of formation has also been considered. In general, when the cysteine is first oxidized to a sulfenic acid, only the formation of smaller S-N containing rings is calculated to be exergonic in aqueous solution. In contrast, when the cysteine is first oxidized to a sulfonic acid, the formation of all rings considered (with one exception) is calculated to be endergonic in aqueous solution. The nature of vicinal residue can influence ring formation through stabilizing or destabilizing intramolecular interactions.

Late chronic local inflammation, synaptic alterations, vascular remodeling and arteriovenous malformations in the brains of male rats exposed to repetitive low-level blast overpressures

In the course of military operations in modern war theaters, blast exposures are associated with the development of a variety of mental health disorders associated with a post-traumatic stress disorder-related features, including anxiety, impulsivity, insomnia, suicidality, depression, and cognitive decline. Several lines of evidence indicate that acute and chronic cerebral vascular alterations are involved in the development of these blast-induced neuropsychiatric changes. In the present study, we investigated late occurring neuropathological events associated with cerebrovascular alterations in a rat model of repetitive low-level blast-exposures (3 × 74.5 kPa). The observed events included hippocampal hypoperfusion associated with late-onset inflammation, vascular extracellular matrix degeneration, synaptic structural changes and neuronal loss. We also demonstrate that arteriovenous malformations in exposed animals are a direct consequence of blast-induced tissue tears. Overall, our results further identify the cerebral vasculature as a main target for blast-induced damage and support the urgent need to develop early therapeutic approaches for the prevention of blast-induced late-onset neurovascular degenerative processes.

Redox-Neutral Strategy for Sulfilimines Synthesis via S-Arylation of Sulfenamides

In this investigation, an unprecedented transition-metal-free and redox-neutral synthesis of sulfilimines was realized through the S-arylation of readily obtainable sulfenamides employing diaryliodonium salts. The pivotal step encompassed the resonance between bivalent nitrogen-centered anions, engendered postdeprotonation of sulfenamides under alkaline conditions, and sulfinimidoyl anions. The experimental outcomes demonstrate that sulfinimidoyl anionic species function as efficacious nucleophilic reagents, affording sulfilimines with notable to exceptional yields and superlative chemoselectivity, all executed within a transition-metal-free protocol and under exceptionally mild conditions.

Synthesis of Sulfilimines Enabled by Copper-Catalyzed S-Arylation of Sulfenamides

Herein, an unprecedented synthetic route to sulfilimines via a copper-catalyzed Chan-Lam-type coupling of sulfenamides is presented. A key to success in this novel transformation is the chemoselective S-arylation of S(II) sulfenamides to form S(IV) sulfilimines, overriding the competitive, and more thermodynamically favored, C-N bond formation that does not require a change in the sulfur oxidation state. Computations reveal that the selectivity arises from a selective transmetallation event where bidentate sulfenamide coordination through the sulfur and oxygen atoms favors the S-arylation pathway. The mild and environmentally benign catalytic conditions enable broad functional group compatibility, allowing a variety of diaryl or alkyl aryl sulfilimines to be efficiently prepared. The Chan-Lam coupling procedure could also tolerate alkenylboronic acids as coupling partners to afford alkenyl aryl sulfilimines, a class of scaffolds that cannot be directly synthesized via conventional imination strategies. The benzoyl-protecting groups could be conveniently removed from the product, which, in turn, could be readily transformed into several S(IV) and S(VI) derivatives.

Synthesis of Sulfilimines via Selective S-C Bond Formation in Water

Sulfilimines are valuable compounds both in organic synthesis and in pharmaceuticals. Here we developed a mild and simplified method for preparation of sulfilimines via selective S-C bond formation rather than traditional S-N bond formation. The method is both attractive and useful for the following reasons: it uses a readily available alkylation reagent such alkyl bromide or alkyl iodide, it uses water as solvent, it is easy to perform, and it is convenient for late-stage diversification of drugs.

Protein-Based Biological Materials: Molecular Design and Artificial Production

Polymeric materials produced from fossil fuels have been intimately linked to the development of industrial activities in the 20th century and, consequently, to the transformation of our way of living. While this has brought many benefits, the fabrication and disposal of these materials is bringing enormous sustainable challenges. Thus, materials that are produced in a more sustainable fashion and whose degradation products are harmless to the environment are urgently needed. Natural biopolymers─which can compete with and sometimes surpass the performance of synthetic polymers─provide a great source of inspiration. They are made of natural chemicals, under benign environmental conditions, and their degradation products are harmless. Before these materials can be synthetically replicated, it is essential to elucidate their chemical design and biofabrication. For protein-based materials, this means obtaining the complete sequences of the proteinaceous building blocks, a task that historically took decades of research. Thus, we start this review with a historical perspective on early efforts to obtain the primary sequences of load-bearing proteins, followed by the latest developments in sequencing and proteomic technologies that have greatly accelerated sequencing of extracellular proteins. Next, four main classes of protein materials are presented, namely fibrous materials, bioelastomers exhibiting high reversible deformability, hard bulk materials, and biological adhesives. In each class, we focus on the design at the primary and secondary structure levels and discuss their interplays with the mechanical response. We finally discuss earlier and the latest research to artificially produce protein-based materials using biotechnology and synthetic biology, including current developments by start-up companies to scale-up the production of proteinaceous materials in an economically viable manner.

Advances in organic fluorescent probes for bromide ions, hypobromous acid and related eosinophil peroxidase-A review

Elemental bromine is among the essential elements for human health. In living organisms, bromide (Br^-) and hydrogen peroxide (H₂O₂) can be catalyzed by eosinophil peroxidase (EPO) to generate a reactive oxygen species (ROS), hypobromous acid (HOBr), which exhibits properties similar to those of hypochlorous acid (HOCl). Moreover, HOBr possesses strong oxidative and antibacterial properties, which are believed to play an important role in the neutrophil host defense system. However, overexpression or misexpression of HOBr can cause organismal and tissue damage, which is closely related to the development of various diseases. Therefore, an increasing number of studies has demonstrated physiological associations with the conversion of Br^- to HOBr. With the development of fluorescence imaging technology, developing fluorescent probes with novel structures and high selectivity to detect changes in Br^-, HOBr, and the related enzyme EPO levels in organisms has become very important. This paper summarizes Br^-, HOBr, and EPO fluorescent probes reported in recent years, including the design principles, mechanisms, optical properties, and bioapplications. Finally, the application prospects and challenges are also discussed.

Asymmetric Synthesis of Chiral Sulfimides through the O-Alkylation of Enantioenriched Sulfinamides and Addition of Carbon Nucleophiles

Chiral sulfimides, the aza-analogues of sulfoxides, are valuable compounds in organic synthesis and medicinal chemistry. Herein, we report an efficient method for preparing chiral sulfimides from easily available enantioenriched sulfinamides. The key step of this method is a stereospecific oxygen-selective alkylation of enantioenriched sulfinamides, which is accomplished by using isopropyl iodide, K₂ CO₃ , and DMPU. The resulting chiral sulfinimidate esters are transformed to chiral sulfimides by the nucleophilic addition of the Grignard reagents under simple conditions. This transformation enables access to the enantioenriched diaryl or dialkyl sulfimides bearing two similar carbon substituents, which are difficult to synthesize by previous methods.

Molecular Dynamics Investigation on the Effects of Protonation and Lysyl Hydroxylation on Sulfilimine Cross-links in Collagen IV

Collagen IV networks are an essential component of basement membranes that are important for their structural integrity and thus that of an organism's tissues. Improper functioning of these networks has been associated with several diseases. Cross-links, such as sulfilimine bonds interconnecting NC1 domains, are critical for forming and mechanically stabilizing these collagen IV networks. More specifically, the sulfilimine cross-links form between methionine (Met93) and lysine/hydroxylsine (Lys211/Hyl211) residues of NC1 domains. Therefore, the dynamic nature of the sulfilimine bond in collagen IV is crucial for network formation. To understand the dynamic nature of a neutral and protonated sulfilimine bond in collagen IV, we performed molecular dynamics (MD) simulations on four sulfilimine cross-linked systems (i.e., _Met93S-N_Lys211, _Met93S-NH_Lys211 ⁺, _Met93S-N_Hyl211, and _Met93S-NH_Hyl211 ⁺) of collagen IV. The MD results showed that the neutral _Met93S-N_Lys211 system has the smallest protein backbone and showed the cross-linked residues' RMSD value. The conformational change analyses showed that the conformations of the sulfilimine cross-linked residues take on a U-shape for the _Met93S-N_Hyl211 and _Met93S-HN_Hyl211 ⁺ systems, whereas the conformations of the sulfilimine cross-linked residues are more open for the _Met93S-N_Lys211, and _Met93S-NH_Lys211 ⁺ systems. Protonation is a crucial biochemical process to stabilize the protein structure or the biological cross-links. Furthermore, the protonation of the sulfilimine bond could potentially influence hydrogen bond interaction with near amino acid residues, and according to water distribution analyses, the sulfilimine bond can potentially exist in one or more protonation states.

Sulfilimines as Transformable and Retainable Directing Groups in Rhodium-Catalyzed ortho-C-H Bond Functionalization

Shown herein is the first time that the sulfilimine is utilized as a directing group for Rh(III)-catalyzed C-H activation/annulation with intermolecular and intramolecular alkyne compounds. Sulfilimine serves as a transformable directing group, an internal oxidant, in the annulation with an alkyne moiety via N-S bond cleavage. Notably, the retention of sulfilimine as a directing group is also achieved in the Rh(III)-catalyzed ortho-alkynylation with alkyne bromides.

Pathogenicity of missense variants affecting the collagen IV α5 carboxy non-collagenous domain in X-linked Alport syndrome

X-linked Alport syndrome is a genetic kidney disease caused by pathogenic COL4A5 variants, but little is known of the consequences of missense variants affecting the NC1 domain of the corresponding collagen IV α5 chain. This study examined these variants in a normal (gnomAD) and other databases (LOVD, Clin Var and 100,000 Genomes Project) to determine their pathogenicity and clinical significance. Males with Cys substitutions in the collagen IV α5 NC1 domain reported in LOVD (n = 25) were examined for typical Alport features, including age at kidney failure. All NC1 variants in LOVD (n = 86) were then assessed for structural damage using an online computational tool, Missense3D. Variants in the ClinVar, gnomAD and 100,000 Genomes Project databases were also examined for structural effects. Predicted damage associated with NC1 substitutions was then correlated with the level of conservation of the affected residues. Cys substitutions in males were associated with the typical features of X-linked Alport syndrome, with a median age at kidney failure of 31 years. NC1 substitutions predicted to cause structural damage were overrepresented in LOVD (p < 0.001), and those affecting Cys residues or 'buried' Gly residues were more common than expected (both p < 0.001). Most NC1 substitutions in gnomAD (88%) were predicted to be structurally-neutral. Substitutions affecting conserved residues resulted in more structural damage than those affecting non-conserved residues (p < 0.001). Many pathogenic missense variants affecting the collagen IV α5 NC1 domain have their effect through molecular structural damage and 3D modelling is a useful tool in their assessment.

Class III Peroxidases PRX01, PRX44, and PRX73 Control Root Hair Growth in Arabidopsis thaliana

Root hair cells are important sensors of soil conditions. They grow towards and absorb water-soluble nutrients. This fast and oscillatory growth is mediated by continuous remodeling of the cell wall. Root hair cell walls contain polysaccharides and hydroxyproline-rich glycoproteins, including extensins (EXTs). Class-III peroxidases (PRXs) are secreted into the apoplastic space and are thought to trigger either cell wall loosening or polymerization of cell wall components, such as Tyr-mediated assembly of EXT networks (EXT-PRXs). The precise role of these EXT-PRXs is unknown. Using genetic, biochemical, and modeling approaches, we identified and characterized three root-hair-specific putative EXT-PRXs, PRX01, PRX44, and PRX73. prx01,44,73 triple mutation and PRX44 and PRX73 overexpression had opposite effects on root hair growth, peroxidase activity, and ROS production, with a clear impact on cell wall thickness. We use an EXT fluorescent reporter with contrasting levels of cell wall insolubilization in prx01,44,73 and PRX44-overexpressing background plants. In this study, we propose that PRX01, PRX44, and PRX73 control EXT-mediated cell wall properties during polar expansion of root hair cells.

Air pollution particles hijack peroxidasin to disrupt immunosurveillance and promote lung cancer

Although fine particulate matter (FPM) in air pollutants and tobacco smoke is recognized as a strong carcinogen and global threat to public health, its biological mechanism for inducing lung cancer remains unclear. Here, by investigating FPM's bioactivities in lung carcinoma mice models, we discover that these particles promote lung tumor progression by inducing aberrant thickening of tissue matrix and hampering migration of antitumor immunocytes. Upon inhalation into lung tissue, these FPM particles abundantly adsorb peroxidasin (PXDN) - an enzyme mediating type IV collagen (Col IV) crosslinking - onto their surface. The adsorbed PXDN exerts abnormally high activity to crosslink Col IV via increasing the formation of sulfilimine bonds at the NC1 domain, leading to an overly dense matrix in the lung tissue. This disordered structure decreases the mobility of cytotoxic CD8+ T lymphocytes into the lung and consequently impairs the local immune surveillance, enabling the flourishing of nascent tumor cells. Meanwhile, inhibiting the activity of PXDN abolishes the tumor-promoting effect of FPM, indicating the key impact of aberrant PXDN activity on the tumorigenic process. In summary, our finding elucidates a new mechanism for FPM-induced lung tumorigenesis and identifies PXDN as a potential target for treatment or prevention of the FPM-relevant biological risks.

Computational insights into the formation and nature of the sulfilimine bond in collagen-IV

Collagen IV is essential component of basement membrane in the tissues. It provides proper cellular structure by the formation of sulfilimine bond (S Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N) between methionine and lysine or hydroxylysine (cross-links) residues which can be formed with or without post-translational modification. The sulfilimine bond has critical roles in tissue development and human diseases. Peroxidasin, a basement membrane peroxidase, generates reactive halogen species including hypobromous (HOBr) acid and hypochlorous (HOCl) acid which help to form halosulfonium or haloamine. The sulfilamine bond can be formed either by the formation of halosulfonium or by the formation of halomine. The aim of the study is the investigation of the formation of sulfilimine bond and its nature in collagen IV using multi-scale approach that included MD, QM-cluster, systematic series of small models, and NBO analysis. These results suggest that sulfilimine bond can be formed either via brominated/chlorinated halosulfonium or haloamine pathway. The results of systematic series of small model indicate that the formation of sulfilimine complex from halosulfonium happens through the formation of positively charged halosulfonated sulfilimine complex. It also suggests that the formation of sulfilimine complex from haloamine occurs through the formation of positively charged sulfilimine complex where the S and N bond forms and halogen goes off at the same time. Furthermore, the NBO analysis suggest the S and N bond is strongly polarized toward nitrogen in both single protonated and neutral system, N^δ− ← S^δ+ and also indicate the existence of a coordinate covalent (i.e. dative) bond.

The proposed mechanisms for formation of the sulfilimine bond in collagen IV, and effects of protonation on the nature and properties of the bond have been computationally examined.

Selective covalent capture of collagen triple helices with a minimal protecting group strategy

A minimal protecting group strategy is developed to allow selective covalent capture of collagen-like triple helices. This allows stabilization of this critical fold while preserving charge–pair interactions critical for biological applications.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Alport Syndrome: A Primer for Clinicians

Alport syndrome is a genetic and hereditary disease, caused by mutations in the type IV collagen genes COL4A3, COL4A4 and COL4A5, that affects the glomerular basement membrane of the kidney. It is a rare disease with an underestimated prevalence. Genetic analysis of population cohorts has revealed that it is the second most common inherited kidney disease after polycystic kidney disease. Renal involvement is the main manifestation, although it may have associated extrarenal manifestations such as hearing loss or ocular problems. The degree of expression of the disease changes according to the gene affected and other factors, known or yet to be known. The pathophysiology is not yet fully understood, although some receptors, pathways or molecules are known to be linked to the disease. There is also no specific treatment for Alport syndrome; the most commonly used are renin–angiotensin–aldosterone system inhibitors. In recent years, diagnosis has come a long way, thanks to advances in DNA sequencing technologies such as next-generation sequencing (NGS). Further research at the genetic and molecular levels in the future will complete the partial vision of the pathophysiological mechanism that we have, and will allow us to better understand what is happening and how to solve it.

Sequence-dependent mechanics of collagen reflect its structural and functional organization

Extracellular matrix mechanics influence diverse cellular functions, yet surprisingly little is known about the mechanical properties of their constituent collagen proteins. In particular, network-forming collagen IV, an integral component of basement membranes, has been far less studied than fibril-forming collagens. A key feature of collagen IV is the presence of interruptions in the triple-helix-defining (Gly-X-Y) sequence along its collagenous domain. Here, we used atomic force microscopy to determine the impact of sequence heterogeneity on the local flexibility of collagen IV and of the fibril-forming collagen III. Our extracted flexibility profile of collagen IV reveals that it possesses highly heterogeneous mechanics, ranging from semiflexible regions as found for fibril-forming collagens to a lengthy region of high flexibility toward its N-terminus. A simple model in which flexibility is dictated only by the presence of interruptions fit the extracted profile reasonably well, providing insight into the alignment of chains and demonstrating that interruptions, particularly when coinciding in multiple chains, significantly enhance local flexibility. To a lesser extent, sequence variations within the triple helix lead to variable flexibility, as seen along the continuously triple-helical collagen III. We found this fibril-forming collagen to possess a high-flexibility region around its matrix-metalloprotease binding site, suggesting a unique mechanical fingerprint of this region that is key for matrix remodeling. Surprisingly, proline content did not correlate with local flexibility in either collagen type. We also found that physiologically relevant changes in pH and chloride concentration did not alter the flexibility of collagen IV, indicating such environmental changes are unlikely to control its compaction during secretion. Although extracellular chloride ions play a role in triggering collagen IV network formation, they do not appear to modulate the structure of its collagenous domain.

How Mechanical Forces Change the Human Endometrium during the Menstrual Cycle in Preparation for Embryo Implantation

The human endometrium is characterized by exceptional plasticity, as evidenced by rapid growth and differentiation during the menstrual cycle and fast tissue remodeling during early pregnancy. Past work has rarely addressed the role of cellular mechanics in these processes. It is becoming increasingly clear that sensing and responding to mechanical forces are as significant for cell behavior as biochemical signaling. Here, we provide an overview of experimental evidence and concepts that illustrate how mechanical forces influence endometrial cell behavior during the hormone-driven menstrual cycle and prepare the endometrium for embryo implantation. Given the fundamental species differences during implantation, we restrict the review to the human situation. Novel technologies and devices such as 3D multifrequency magnetic resonance elastography, atomic force microscopy, organ-on-a-chip microfluidic systems, stem-cell-derived organoid formation, and complex 3D co-culture systems have propelled the understanding how endometrial receptivity and blastocyst implantation are regulated in the human uterus. Accumulating evidence has shown that junctional adhesion, cytoskeletal rearrangement, and extracellular matrix stiffness affect the local force balance that regulates endometrial differentiation and blastocyst invasion. A focus of this review is on the hormonal regulation of endometrial epithelial cell mechanics. We discuss potential implications for embryo implantation.

Consensus statement on standards and guidelines for the molecular diagnostics of Alport syndrome: refining the ACMG criteria

The recent Chandos House meeting of the Alport Variant Collaborative extended the indications for screening for pathogenic variants in the COL4A5, COL4A3 and COL4A4 genes beyond the classical Alport phenotype (haematuria, renal failure; family history of haematuria or renal failure) to include persistent proteinuria, steroid-resistant nephrotic syndrome, focal and segmental glomerulosclerosis (FSGS), familial IgA glomerulonephritis and end-stage kidney failure without an obvious cause. The meeting refined the ACMG criteria for variant assessment for the Alport genes (COL4A3-5). It identified 'mutational hotspots' (PM1) in the collagen IV α5, α3 and α4 chains including position 1 Glycine residues in the Gly-X-Y repeats in the intermediate collagenous domains; and Cysteine residues in the carboxy non-collagenous domain (PP3). It considered that 'well-established' functional assays (PS3, BS3) were still mainly research tools but sequencing and minigene assays were commonly used to confirm splicing variants. It was not possible to define the Minor Allele Frequency (MAF) threshold above which variants were considered Benign (BA1, BS1), because of the different modes of inheritances of Alport syndrome, and the occurrence of hypomorphic variants (often Glycine adjacent to a non-collagenous interruption) and local founder effects. Heterozygous COL4A3 and COL4A4 variants were common 'incidental' findings also present in normal reference databases. The recognition and interpretation of hypomorphic variants in the COL4A3-COL4A5 genes remains a challenge.

New insights into the mechanisms of age-related protein-protein crosslinking in the human lens

Although protein crosslinking is often linked with aging as well as some age-related diseases, very few molecular details are available on the nature of the amino acids involved, or mechanisms that are responsible for crosslinking. Recent research has shown that several amino acids are able to generate reactive intermediates that ultimately lead to covalent crosslinking through multiple non-enzymatic mechanisms. This information has been derived from proteomic investigations on aged human lenses and the mechanisms of crosslinking, in each case, have been elucidated using model peptides. Residues involved in spontaneous protein-protein crosslinking include aspartic acid, asparagine, cysteine, lysine, phosphoserine, phosphothreonine, glutamic acid and glutamine. It has become clear, therefore, that several amino acids can act as potential sites for crosslinking in the long-lived proteins that are present in aged individuals. Moreover, the lens has been an invaluable model tissue and source of crosslinked proteins from which to determine crosslinking mechanisms that may lead to crosslinking in other human tissues.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Collagen IV differentially regulates planarian stem cell potency and lineage progression

Comprehensive assessment of matrisome genes identified collagen IV as one of the many extracellular matrix (ECM) proteins regulating the stem cell pool in planarian tissue homeostasis and regeneration. While collagen IV has been shown to be involved in stem cell biology, our finding links it to pluripotent stem cells in vivo, including self-renewal and differentiation into tissue-specific progenitors. We show a link between the ECM niches in the parenchyma/gut region and EGF/neuregulin-secreting neurons, thus providing mechanistic insight into interactions between cell niches. The conservation of basement membranes between planarian and mammalian gut niches suggests a similar interplay may exist in the mammalian systems, worthy of further investigation.

The extracellular matrix (ECM) provides a precise physical and molecular environment for cell maintenance, self-renewal, and differentiation in the stem cell niche. However, the nature and organization of the ECM niche is not well understood. The adult freshwater planarian Schmidtea mediterranea maintains a large population of multipotent stem cells (neoblasts), presenting an ideal model to study the role of the ECM niche in stem cell regulation. Here we tested the function of 165 planarian homologs of ECM and ECM-related genes in neoblast regulation. We identified the collagen gene family as one with differential effects in promoting or suppressing proliferation of neoblasts. col4-1, encoding a type IV collagen α-chain, had the strongest effect. RNA interference (RNAi) of col4-1 impaired tissue maintenance and regeneration, causing tissue regression. Finally, we provide evidence for an interaction between type IV collagen, the discoidin domain receptor, and neuregulin-7 (NRG-7), which constitutes a mechanism to regulate the balance of symmetric and asymmetric division of neoblasts via the NRG-7/EGFR pathway.

In vitro generation of peri-islet basement membrane-like structures

The peri-islet extracellular matrix (ECM) is a key component of the microenvironmental niche surrounding pancreatic islets of Langerhans. The cell anchorage and signaling provided by the peri-islet ECM is critical for optimum beta cell glucose responsiveness, but islets lose this important native ECM when isolated for transplantation or in vitro studies. Here, we established a method to construct a peri-islet ECM on the surfaces of isolated rat and human islets by the co-assembly from solution of laminin, nidogen and collagen IV proteins. Successful deposition of contiguous peri-islet ECM networks was confirmed by immunofluorescence, western blot, and transmission electron microscopy. The ECM coatings were disrupted when assembly occurred in Ca²⁺/Mg²⁺-free conditions. As laminin network polymerization is divalent cation dependent, our data are consistent with receptor-driven ordered ECM network formation rather than passive protein adsorption. To further illustrate the utility of ECM coatings, we employed stem cell derived beta-like cell clusters (sBCs) as a renewable source of functional beta cells for cell replacement therapy. We observe that sBC pseudo-islets lack an endogenous peri-islet ECM, but successfully applied our approach to construct a de novo ECM coating on the surfaces of sBCs.

Collagen IVα345 dysfunction in glomerular basement membrane diseases. II. Crystal structure of the α345 hexamer

Our recent work identified a genetic variant of the α345 hexamer of the collagen IV scaffold that is present in patients with glomerular basement membrane diseases, Goodpasture’s disease (GP) and Alport syndrome (AS), and phenocopies of AS in knock-in mice. To understand the context of this “Zurich” variant, an 8-amino acid appendage, we developed a construct of the WT α345 hexamer using the single-chain NC1 trimer technology, which allowed us to solve a crystal structure of this key connection module. The α345 hexamer structure revealed a ring of 12 chloride ions at the trimer–trimer interface, analogous to the collagen α121 hexamer, and the location of the 170 AS variants. The hexamer surface is marked by multiple pores and crevices that are potentially accessible to small molecules. Loop-crevice-loop features constitute bioactive sites, where pathogenic pathways converge that are linked to AS and GP, and, potentially, diabetic nephropathy. In Pedchenko et al., we demonstrate that these sites exhibit conformational plasticity, a dynamic property underlying assembly of bioactive sites and hexamer dysfunction. The α345 hexamer structure is a platform to decipher how variants cause AS and how hypoepitopes can be triggered, causing GP. Furthermore, the bioactive sites, along with the pores and crevices on the hexamer surface, are prospective targets for therapeutic interventions.

Collagen IVα345 dysfunction in glomerular basement membrane diseases. III. A functional framework for α345 hexamer assembly

We identified a genetic variant, an 8-residue appendage, of the α345 hexamer of collagen IV present in patients with glomerular basement membrane diseases, Goodpasture’s disease and Alport syndrome, and determined the long-awaited crystal structure of the hexamer. We sought to elucidate how variants cause glomerular basement membrane disease by exploring the mechanism of the hexamer assembly. Chloride ions induced in vitro hexamer assembly in a composition-specific manner in the presence of equimolar concentrations of α3, α4, and α5 NC1 monomers. Chloride ions, together with sulfilimine crosslinks, stabilized the assembled hexamer. Furthermore, the chloride ion–dependent assembly revealed the conformational plasticity of the loop-crevice-loop bioactive sites, a critical property underlying bioactivity and pathogenesis. We explored the native mechanism by expressing recombinant α345 miniprotomers in the cell culture and characterizing the expressed proteins. Our findings revealed NC1-directed trimerization, forming protomers inside the cell; hexamerization, forming scaffolds outside the cell; and a Cl gradient–signaled hexamerization. This assembly detail, along with a crystal structure, provides a framework for understanding hexamer dysfunction. Restoration of the native conformation of bioactive sites and α345 hexamer replacement are prospective approaches to therapeutic intervention.