Direct Write Printing of Ultraviolet-Curable Bulk Superhydrophobic Ink Material

Although superhydrophobic surfaces have various promising applications, their fabrication methods are often limited to 2D plane surfaces that are vulnerable to abrasion and have limited adhesion to the substrate. Herein, an ultraviolet (UV) curable ink with bulk superhydrophobicity, consisting of poly(dimethylsiloxane) (PDMS) resins, hydrophobic silica, and solvent (porogen), was successfully developed for UV-assisted direct write printing processing. After UV curing of the ink followed by solvent evaporation, the generated porous structure cooperates with silica particles to form a self-similar and hierarchical structure throughout the bulk material, which can keep its original morphology even after cyclic abrasion (over 1000 times) and thus exhibits durable superhydrophobicity. With this unique ink, UV-assisted direct write printing can not only create 2D superhydrophobic surfaces on various substrates (e.g., paper and wire mesh) but also fabricate self-supporting 3D superhydrophobic objects for various applications such as waterproofing and oil-water separation. The printed objects exhibited a stable superhydrophobicity against liquid corrosion and mechanical damage. In addition, the 3D printing approach can be used to optimize the oil-water separation performance of the superhydrophobic porous materials by tuning the pore size, thus presenting promising applications.

Triubiquitin Probes for Identification of Reader and Eraser Proteins of Branched Polyubiquitin Chains

The important roles played by branched polyubiquitin chains were recently uncovered in proteasomal protein degradation, mitotic regulation, and NF-κB signaling. With the new realization of a wide presence of branched ubiquitin chains in mammalian cells, there is an urgent need of identifying the reader and eraser proteins of the various branched ubiquitin chains. In this work, we report the generation of noncleavable branched triubiquitin probes with combinations of K11-, K48-, and K63-linkages. Through a pulldown approach using the branched triUb probes, we identified human proteins that recognize branched triubiquitin structures including ubiquitin-binding proteins and deubiquitinases (DUBs). Proteomics analysis of the identified proteins enriched by the branched triubiquitin probes points to possible roles of branched ubiquitin chains in cellular processes including DNA damage response, autophagy, and receptor endocytosis. In vitro characterization of several identified UIM-containing proteins demonstrated their binding to branch triubiquitin chains with moderate to high affinities. Availability of this new class of branched triubiquitin probes will enable future investigation into the roles of branched polyubiquitin chains through identification of specific reader and eraser proteins, and the modes of branched ubiquitin chain recognition and processing using biochemical and biophysical methods.

Getting to the Root of Branched Ubiquitin Chains: A Review of Current Methods and Functions

Nearly 20 years since the first branched ubiquitin (Ub) chains were identified by mass spectrometry, our understanding of these chains and their function is still evolving. This is due to the limitations of classical Ub research techniques in identifying these chains and the vast complexity of potential branched chains. Considering only lysine or N-terminal methionine attachment sites, there are already 28 different possible branch points. Taking into account recently discovered ester-linked ubiquitination, branch points of more than two linkage types, and the higher-order chain structures within which branch points exist, the diversity of branched chains is nearly infinite. This review breaks down the complexity of these chains into their general functions, what we know so far about the different linkage combinations, branched chain-optimized methodologies, and the future perspectives of branched chain research.

The chemical biology of ubiquitin

This mini-review will cover the various chemical biology approaches employed to prepare and modulate ubiquitin chains and the ubiquitin-proteasome system. Emphasis will be given to the biochemistry and chemical biology of poly-ubiquitin chain preparation as a tool to elucidate its roles in biological systems as well as the hijacking of the ubiquitin proteasome system using heterobifunctional compounds to induce intracellular ubiquitination.

A modular toolbox to generate complex polymeric ubiquitin architectures using orthogonal sortase enzymes

The post-translational modification of proteins with ubiquitin (Ub) and Ub-like modifiers (Ubls) represents one of the most important regulators in eukaryotic biology. Polymeric Ub/Ubl chains of distinct topologies control the activity, stability, interaction and localization of almost all cellular proteins and elicit a variety of biological outputs. Our ability to characterize the roles of distinct Ub/Ubl topologies and to identify enzymes and receptors that create, recognize and remove these modifications is however hampered by the difficulty to prepare them. Here we introduce a modular toolbox (Ubl-tools) that allows the stepwise assembly of Ub/Ubl chains in a flexible and user-defined manner facilitated by orthogonal sortase enzymes. We demonstrate the universality and applicability of Ubl-tools by generating distinctly linked Ub/Ubl hybrid chains, and investigate their role in DNA damage repair. Importantly, Ubl-tools guarantees straightforward access to target proteins, site-specifically modified with distinct homo- and heterotypic (including branched) Ub chains, providing a powerful approach for studying the functional impact of these complex modifications on cellular processes.

The Jo-In protein welding system is a relevant tool to create CBM-containing plant cell wall degrading enzymes

Irrespective of their biological origin, most proteins are composed of several elementary domains connected by linkers. These domains are either functionally independent units, or part of larger multidomain structures whose functions are defined by their spatial proximity. Carbohydrate-degrading enzymes provide examples of a range of multidomain structures, in which catalytic protein domains are frequently appended to one or more non-catalytic carbohydrate-binding modules which specifically bind to carbohydrate motifs. While the carbohydrate-binding specificity of these modules is clear, their function is not fully elucidated. Herein, an original approach to tackle the study of carbohydrate-binding modules using the Jo-In biomolecular welding protein pair is presented. To provide a proof of concept, recombinant xylanases appended to two different carbohydrate-binding modules have been created and produced. The data reveal the biochemical properties of four xylanase variants and provide the basis for correlating enzyme activity to structural properties and to the nature of the substrate and the ligand specificity of the appended carbohydrate-binding module. It reveals that specific spatial arrangements favour activity on soluble polymeric substrates and that activity on such substrates does not predict the behaviour of multimodular enzymes on insoluble plant cell wall samples. The results highlight that the Jo-In protein welding system is extremely useful to design multimodular enzyme systems, especially to create rigid conformations that decrease the risk of intermodular interference. Further work on Jo-In will target the introduction of varying degrees of flexibility, providing the means to study this property and the way it may influence multimodular enzyme functions.

Emerging functions of branched ubiquitin chains

Ubiquitylation is a critical post-translational modification that controls a wide variety of processes in eukaryotes. Ubiquitin chains of different topologies are specialized for different cellular functions and control the stability, activity, interaction properties, and localization of many different proteins. Recent work has highlighted a role for branched ubiquitin chains in the regulation of cell signaling and protein degradation pathways. Similar to their unbranched counterparts, branched ubiquitin chains are remarkably diverse in terms of their chemical linkages, structures, and the biological information they transmit. In this review, we discuss emerging themes related to the architecture, synthesis, and functions of branched ubiquitin chains. We also describe methodologies that have recently been developed to identify and decode the functions of these branched polymers.

Branched Ubiquitination: Detection Methods, Biological Functions and Chemical Synthesis

Ubiquitination is a versatile posttranslational modification that elicits signaling roles to impact on various cellular processes and disease states. The versatility is a result of the complexity of ubiquitin conjugates, ranging from a single ubiquitin monomer to polymers with different length and linkage types. Recent studies have revealed the abundant existence of branched ubiquitin chains in which one ubiquitin molecule is connected to two or more ubiquitin moieties in the same ubiquitin polymer. Compared to the homotypic ubiquitin chain, the branched chain is recognized or processed differently by readers and erasers of the ubiquitin system, respectively, resulting in a qualitative or quantitative alteration of the functional output. Furthermore, certain types of branched ubiquitination are induced by cellular stresses, implicating their important physiological role in stress adaption. In addition, the current chemical methodologies of solid phase peptide synthesis and expanding genetic code approach have been developed to synthesize different architectures of branched ubiquitin chains. The synthesized branched ubiquitin chains have shown their significance in understanding the topologies and binding partners of the branched chains. Here, we discuss the recent progresses on the detection, functional characterization and synthesis of branched ubiquitin chains as well as the future perspectives of this emerging field.

The Ubiquitin Enigma: Progress in the Detection and Chemical Synthesis of Branched Ubiquitin Chains

Ubiquitin chains with distinct topologies play essential roles in eukaryotic cells. Recently, it was discovered that multiple ubiquitin units can be ligated to more than one lysine residue in the same ubiquitin to form diverse branched ubiquitin chains. Although there is increasing evidence implicating these branched chains in a plethora of biological functions, few mechanistic details have been elucidated. This concept article introduces the function, detection and chemical synthesis of branched ubiquitin chains; and offers some future perspective for this exciting new field.

An E1-Catalyzed Chemoenzymatic Strategy to Isopeptide-N-Ethylated Deubiquitylase-Resistant Ubiquitin Probes

Triazole-based deubiquitylase (DUB)-resistant ubiquitin (Ub) probes have recently emerged as effective tools for the discovery of Ub chain-specific interactors in proteomic studies, but their structural diversity is limited. A new family of DUB-resistant Ub probes is reported based on isopeptide-N-ethylated dimeric or polymeric Ub chains, which can be efficiently prepared by a one-pot, ubiquitin-activating enzyme (E1)-catalyzed condensation reaction of recombinant Ub precursors to give various homotypic and even branched Ub probes at multi-milligram scale. Proteomic studies using label-free quantitative (LFQ) MS indicated that the isopeptide-N-ethylated Ub probes may complement the triazole-based probes in the study of Ub interactome. Our study highlights the utility of modern protein synthetic chemistry to develop structurally and new families of tool molecules needed for proteomic studies.