Selective Oxidation of N-Glycolylneuraminic Acid Using an Engineered Galactose Oxidase Variant

Sialylation Shields Glycoproteins from Oxidative Stress: Mechanistic Insights into Sialic Acid Oxidation and Structural Stability

Sialylation, a crucial yet labile protein modification, is increasingly recognized for its role in modulating protein structure, function, and stability. While the impact of oxidative stress on protein integrity is well-established, the protective role of sialylation against such damage remains poorly understood. This study employs a microscale low-temperature plasma device to generate a controlled, deep radical oxidation environment mimicking cellular oxidative stress. By subjecting free sialic acids (Neu5Ac and Neu5Gc) to time-resolved deep radical exposure, high-resolution mass spectrometry, and high-fidelity density functional theory calculations, we establish an unprecedented oxidation pathway, revealing unique stepwise side chain oxidation prior to ring opening. Comprehensive radical oxidation maps comprising over 100 oxidative intermediates provide a molecular basis for the higher propensity of Neu5Gc over Neu5Ac in resisting radical oxidation. Further, using human transferrin as a model glycoprotein, we demonstrate the protective role of sialylation against oxidative unfolding. Through a combination of site mapping, enzymatic treatments, and all-ion unfolding ion mobility-mass spectrometry, we identify specific protein sialylation patterns and structural motifs that are crucial for maintaining structural stability under oxidative stress. Our findings provide unprecedented insights into the intricate interplay between sialylation and oxidative stress, highlighting the importance of sialylation in stabilizing protein conformations under various oxidative stresses.

Carbohydrate-active enzyme (CAZyme) discovery and engineering via (Ultra)high-throughput screening

Carbohydrate-active enzymes (CAZymes) constitute a diverse set of enzymes that catalyze the assembly, degradation, and modification of carbohydrates. These enzymes have been fashioned into potent, selective catalysts by millennia of evolution, and yet are also highly adaptable and readily evolved in the laboratory. To identify and engineer CAZymes for different purposes, (ultra)high-throughput screening campaigns have been frequently utilized with great success. This review provides an overview of the different approaches taken in screening for CAZymes and how mechanistic understandings of CAZymes can enable new approaches to screening. Within, we also cover how cutting-edge techniques such as microfluidics, advances in computational approaches and synthetic biology, as well as novel assay designs are leading the field towards more informative and effective screening approaches.

Highly Sensitive Labeling, Clickable Functionalization, and Glycoengineering of the MUC1 Neighboring System

This study introduces a novel wash-type affinity-primed proximity labeling (WAPL) strategy for labeling and surface engineering of the MUC1 protein neighboring system. The strategy entails the utilization of peroxidase in conjunction with a MUC1-selective aptamer, facilitating targeted binding to MUC1 and inducing covalent labeling of the protein neighboring system. This study reveals a novel finding that the WAPL strategy demonstrates superior labeling efficiency in comparison to nonwash-type affinity-primed proximity labeling, marking the first instance of such observations. The WAPL strategy provides signal amplification by converting a single recognition event into multiple covalent labeling events, thereby improving the detection sensitivity for subtle changes in MUC1. The WAPL platform employs two levels of labeling upgrades, modifying the biotin handles of the conventional labeling substrate, biotin-phenol. The first level involves a range of clickable molecules, facilitating dibenzoazacyclooctynylation, alkynylation, and trans-cyclooctenylation of the protein neighboring system. The second level utilizes lactose as a post-translational modification model, enabling rapid and reliable glycoengineering of the MUC1 neighboring system while remaining compatible with cell-based assays. The implementation of the WAPL strategy in protein neighboring systems has resulted in the establishment of a versatile platform that can effectively facilitate diverse monitoring and regulation techniques. This platform offers valuable insights into the regulation of relevant signaling pathways and promotes the advancement of novel therapeutic approaches, thereby bringing substantial implications for human health.

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Recombinant mucin biotechnology and engineering

Mucins represent a largely untapped class of polymeric building block for biomaterials, therapeutics, and other biotechnology. Because the mucin polymer backbone is genetically encoded, sequence-specific mucins with defined physical and biochemical properties can be fabricated using recombinant technologies. The pendent O-glycans of mucins are increasingly implicated in immunomodulation, suppression of pathogen virulence, and other biochemical activities. Recent advances in engineered cell production systems are enabling the scalable synthesis of recombinant mucins with precisely tuned glycan side chains, offering exciting possibilities to tune the biological functionality of mucin-based products. New metabolic and chemoenzymatic strategies enable further tuning and functionalization of mucin O-glycans, opening new possibilities to expand the chemical diversity and functionality of mucin building blocks. In this review, we discuss these advances, and the opportunities for engineered mucins in biomedical applications ranging from in vitro models to therapeutics.

Biocatalytic Approaches to Building Blocks for Enzymatic and Chemical Glycan Synthesis

While the field of biocatalysis has bloomed over the past 20-30 years, advances in the understanding and improvement of carbohydrate-active enzymes, in particular, the sugar nucleotides involved in glycan building block biosynthesis, have progressed relatively more slowly. This perspective highlights the need for further insight into substrate promiscuity and the use of biocatalysis fundamentals (rational design, directed evolution, immobilization) to expand substrate scopes toward such carbohydrate building block syntheses and/or to improve enzyme stability, kinetics, or turnover. Further, it explores the growing premise of using biocatalysis to provide simple, cost-effective access to stereochemically defined carbohydrate materials, which can undergo late-stage chemical functionalization or automated glycan synthesis/polymerization.

Copper radical oxidases: galactose oxidase, glyoxal oxidase, and beyond!

The copper radical oxidases (CROs) are an evolutionary and functionally diverse group of enzymes established by the historically significant galactose 6-oxidase and glyoxal oxidase from fungi. Inducted in 2013, CROs now constitute Auxiliary Activity Family 5 (AA5) in the Carbohydrate-Active Enzymes (CAZy) classification. CROs catalyse the two-electron oxidation of their substrates using oxygen as the final electron acceptor and are particularly distinguished by a cross-linked tyrosine-cysteine co-factor that is integral to radical stabilization. Recently, there has been a significant increase in the biochemically and structurally characterized CROs, which has revealed an expanded natural diversity of catalytic activities in the family. This review provides a brief historical introduction to CRO biochemistry and structural biology as a foundation for an update on current advances in CRO enzymology, biotechnology, and biology across kingdoms of life.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

A promiscuous glycosyltransferase generates poly-β-1,4-glucan derivatives that facilitate mass spectrometry-based detection of cellulolytic enzymes

Promiscuous activity of a glycosyltransferase was exploited to polymerise glucose from UDP-glucose via the generation of β-1,4-glycosidic linkages. The biocatalyst was incorporated into biocatalytic cascades and chemo-enzymatic strategies to synthesise cello-oligosaccharides with tailored functionalities on a scale suitable for employment in mass spectrometry-based assays. The resulting glycan structures enabled reporting of the activity and selectivity of celluloltic enzymes.

Two Fusarium copper radical oxidases with high activity on aryl alcohols

BACKGROUND

Biomass valorization has been suggested as a sustainable alternative to petroleum-based energy and commodities. In this context, the copper radical oxidases (CROs) from Auxiliary Activity Family 5/Subfamily 2 (AA5_2) are attractive biocatalysts for the selective oxidation of primary alcohols to aldehydes. Originally defined by the archetypal galactose 6-oxidase from Fusarium graminearum, fungal AA5_2 members have recently been shown to comprise a wide range of specificities for aromatic, aliphatic and furan-based alcohols. This suggests a broader substrate scope of native CROs for applications. However, only 10% of the annotated AA5_2 members have been characterized to date.

RESULTS

Here, we define two homologues from the filamentous fungi Fusarium graminearum and F. oxysporum as predominant aryl alcohol oxidases (AAOs) through recombinant production in Pichia pastoris, detailed kinetic characterization, and enzyme product analysis. Despite possessing generally similar active-site architectures to the archetypal FgrGalOx, FgrAAO and FoxAAO have weak activity on carbohydrates, but instead efficiently oxidize specific aryl alcohols. Notably, both FgrAAO and FoxAAO oxidize hydroxymethyl furfural (HMF) directly to 5-formyl-2-furoic acid (FFCA), and desymmetrize the bioproduct glycerol to the uncommon L-isomer of glyceraldehyde.

CONCLUSIONS

This work expands understanding of the catalytic diversity of CRO from AA5_2 to include unique representatives from Fusarium species that depart from the well-known galactose 6-oxidase activity of this family. Detailed enzymological analysis highlights the potential biotechnological applications of these orthologs in the production of renewable plastic polymer precursors and other chemicals.

Chemical reporters to study mammalian O-glycosylation

Glycans play essential roles in a range of cellular processes and have been shown to contribute to various pathologies. The diversity and dynamic nature of glycan structures and the complexities of glycan biosynthetic pathways make it challenging to study the roles of specific glycans in normal cellular function and disease. Chemical reporters have emerged as powerful tools to characterise glycan structures and monitor dynamic changes in glycan levels in a native context. A variety of tags can be introduced onto specific monosaccharides via the chemical modification of endogenous glycan structures or by metabolic or enzymatic incorporation of unnatural monosaccharides into cellular glycans. These chemical reporter strategies offer unique opportunities to study and manipulate glycan functions in living cells or whole organisms. In this review, we discuss recent advances in metabolic oligosaccharide engineering and chemoenzymatic glycan labelling, focusing on their application to the study of mammalian O-linked glycans. We describe current barriers to achieving glycan labelling specificity and highlight innovations that have started to pave the way to overcome these challenges.

Enzyme promiscuity of carbohydrate active enzymes and their applications in biocatalysis

The application of biocatalysis for the synthesis of glycans and glycoconjugates is a well-established and successful strategy, both for small and large scale synthesis. Compared to chemical synthesis, is has the advantage of high selectivity, but biocatalysis had been largely limited to natural glycans both in terms of reactivity and substrates. This review describes recent advances in exploiting enzyme promiscuity to expand the range of substrates and reactions that carbohydrate active enzymes (CAZymes) can catalyse. The main focus is on formation and hydrolysis of glycosidic linkages, including sugar kinases, reactions that are central to glycobiotechnology. In addition, biocatalysts that generate sugar analogues and modify carbohydrates, such as oxidases, transaminases and acylases are reviewed. As carbohydrate active enzymes become more accessible and protein engineering strategies become faster, the application of biocatalysis in the generation of a wide range of glycoconjugates, beyond natural structures is expected to expand.

An Enzymatic N-Acylation Step Enables the Biocatalytic Synthesis of Unnatural Sialosides

Chitin is one of the most abundant and cheaply available biopolymers in Nature. Chitin has become a valuable starting material for many biotechnological products through manipulation of its N-acetyl functionality, which can be cleaved under mild conditions using the enzyme family of de-N-acetylases. However, the chemoselective enzymatic re-acylation of glucosamine derivatives, which can introduce new stable functionalities into chitin derivatives, is much less explored. Herein we describe an acylase (CmCDA from Cyclobacterium marinum) that catalyzes the N-acylation of glycosamine with a range of carboxylic acids under physiological reaction conditions. This biocatalyst closes an important gap in allowing the conversion of chitin into complex glycosides, such as C5-modified sialosides, through the use of highly selective enzyme cascades.