Development of inhibitors as research tools for carbohydrate-processing enzymes

Abstract Carbohydrates, which are present in all domains of life, play important roles in a host of cellular processes. These ubiquitous biomolecules form highly diverse and often complex glycan structures without the aid of a template. The carbohydrate structures are regulated solely by the location and specificity of the enzymes responsible for their synthesis and degradation. These enzymes, glycosyltransferases and glycoside hydrolases, need to be functionally well characterized in order to investigate the structure and function of glycans. The use of enzyme inhibitors, which target a particular enzyme, can significantly aid this understanding, and may also provide insights into therapeutic applications. The present article describes some of the approaches used to design and develop enzyme inhibitors as tools for investigating carbohydrateprocessing enzymes

CRISPR antiphage defence mediated by the cyclic nucleotide-binding membrane protein Csx23

Biotechnology and Biological Sciences Research Council [BB/T004789/1 to M.F.W., T.M.G.]; European Research Council Advanced Grant [101018608 to M.F.W.]; Engineering and Physical Sciences Research Council [EP/X016455/1 to K.A., B.E.B., M.F.W.]; BBSRC equipment grants [BB/R013780/1, BB/T017740/1 to B.E.B.]. Funding for open access charge: University of St Andrews block grant.CRISPR-Cas provides adaptive immunity in prokaryotes. Type III CRISPR systems detect invading RNA and activate the catalytic Cas10 subunit, which generates a range of nucleotide second messengers to signal infection. These molecules bind and activate a diverse range of effector proteins that provide immunity by degrading viral components and/or by disturbing key aspects of cellular metabolism to slow down viral replication. Here, we focus on the uncharacterised effector Csx23, which is widespread in Vibrio cholerae. Csx23 provides immunity against plasmids and phage when expressed in Escherichia coli along with its cognate type III CRISPR system. The Csx23 protein localises in the membrane using an N-terminal transmembrane α-helical domain and has a cytoplasmic C-terminal domain that binds cyclic tetra-adenylate (cA4), activating its defence function. Structural studies reveal a tetrameric structure with a novel fold that binds cA4 specifically. Using pulse EPR, we demonstrate that cA4 binding to the cytoplasmic domain of Csx23 results in a major perturbation of the transmembrane domain, consistent with the opening of a pore and/or disruption of membrane integrity. This work reveals a new class of cyclic nucleotide binding protein and provides key mechanistic detail on a membrane-associated CRISPR effector.Many anti-viral defence systems generate a cyclic nucleotide signal that activates cellular defences in response to infection. Type III CRISPR systems use a specialised polymerase to make cyclic oligoadenylate (cOA) molecules from ATP. These can bind and activate a range of effector proteins that slow down viral replication. In this study, we focussed on the Csx23 effector from the human pathogen Vibrio cholerae – a trans-membrane protein that binds a cOA molecule, leading to anti-viral immunity. Structural studies revealed a new class of nucleotide recognition domain, where cOA binding is transmitted to changes in the trans-membrane domain, most likely resulting in membrane depolarisation. This study highlights the diversity of mechanisms for anti-viral defence via nucleotide signalling.Peer reviewe

Structural snapshots of the reaction coordinate for O-GlcNAc transferase

Visualization of the reaction coordinate undertaken by glycosyltransferases has remained elusive, but is critical for understanding this important class of enzyme. Using substrates and substrate mimics, we describe structural snapshots of all species along the kinetic pathway for human O-GlcNAc transferase, an intracellular enzyme that catalyzes installation of a dynamic post-translational modification. The structures reveal key features of the mechanism and show that substrate participation is important during catalysis

Democratic Legitimacy of Politically Unaccountable Administrative Authorities in Comparative Constitutional Law

Uz temeljna ustavna načela vladavine prava i podjele vlasti, načelo kolektivne i pojedinačne ministarske odgovornosti jamac je demokratskog legitimiteta uprave, koji leži u neprekinutom lancu delegacije i odgovornosti od birača prema parlamentu, od parlamenta do ministra te od ministra kroz sve razine uprave do razine najbliže građanima. U ovom radu razmatra se ustavnopravna osnovanost demokratskog legitimiteta neovisnih regulatornih tijela, s posebnim osvrtom na načelo ministarske odgovornosti. Poredbeno se obrađuju primjeri iz europskih država, gdje neovisnost regulatornih tijela ne zadire u temeljna ustavna načela. Zaključno se nastoji utvrditi u kojoj mjeri formalno utvrđena politička neovisnost jamči takvu neovisnost u materijalnom smislu te se razmatraju neke od najutjecajnijih teorija koje o svrsi osnivanja neovisnih regulatornih tijela nudi politička znanost.In addition to the fundamental constitutional principles of the rule of law and separation of powers, the principle of collective and individual ministerial responsibility is the guarantee of the democratic legitimacy of administration that lies in the unbroken chains of delegation and accountability from voters to Parliament, from Parliament to the minister, and from the minister through all levels of administration, to the level closest to citizens. This paper examines the theoretical constructions of the democratic legitimacy of independent regulatory authorities from the constitutionalist point of view, with particular reference to the principle of ministerial responsibility. It further discusses comparative examples from European countries where the independence of the regulatory authorities does not violate fundamental constitutional principles. In conclusion, this paper seeks to determine the extent to which formally established political independence guarantees such independence in the material sense, bearing in mind some of the most influential theories on the purpose of the establishment of independent regulatory authoritie

Production of α-L-iduronidase in maize for the potential treatment of a human lysosomal storage disease

Lysosomal storage diseases are a class of over 70 rare genetic diseases that are amenable to enzyme replacement therapy. Towards developing a plant-based enzyme replacement therapeutic for the lysosomal storage disease mucopolysaccharidosis I, here we expressed α-L-iduronidase in the endosperm of maize seeds by a previously uncharacterized mRNA-targeting-based mechanism. Immunolocalization, cellular fractionation and in situ RT-PCR demonstrate that the α-L-iduronidase protein and mRNA are targeted to endoplasmic reticulum (ER)-derived protein bodies and to protein body-ER regions, respectively, using regulatory (5′-and 3′-UTR) and signal-peptide coding sequences from the γ-zein gene. The maize α-L-iduronidase exhibits high activity, contains high-mannose N-glycans and is amenable to in vitro phosphorylation. This mRNA-based strategy is of widespread importance as plant N-glycan maturation is controlled and the therapeutic protein is generated in a native form. For our target enzyme, the N-glycan structures are appropriate for downstream processing, a prerequisite for its potential as a therapeutic protein.9 page(s

Advances in understanding glycosyltransferases from a structural perspective

Glycosyltransferases (GTs), the enzymes that catalyse glycosidic bond formation, create a diverse range of saccharides and glycoconjugates in nature. Understanding GTs at the molecular level, through structural and kinetic studies, is important for gaining insights into their function. In addition, this understanding can help identify those enzymes which are involved in diseases, or that could be engineered to synthesize biologically or medically relevant molecules. This review describes how structural data, obtained in the last 3-4 years, have contributed to our understanding of the mechanisms of action and specificity of GTs. Particular highlights include the structure of a bacterial oligosaccharyltransferase, which provides insights into N-linked glycosylation, the structure of the human O-GlcNAc transferase, and the structure of a bacterial integral membrane protein complex that catalyses the synthesis of cellulose, the most abundant organic molecule in the biosphere.Publisher PDFPeer reviewe

Exploitation of carbohydrate processing enzymes in biocatalysis

Exploitation of enzymes in biocatalytic processes provides scope both in the synthesis and degradation of molecules. Enzymes have power not only in their catalytic efficiency, but their chemoselectivity, regioselectivity, and stereoselectivity means the reactions they catalyze are precise and reproducible. Focusing on carbohydrate processing enzymes, this review covers advances in biocatalysis involving carbohydrates over the last 2–3 years. Given the notorious difficulties in the chemical synthesis of carbohydrates, the use of enzymes for synthesis has potential for significant impact in the future. The use of catabolic enzymes in the degradation of biomass, which can be exploited in the production of biofuels to provide a sustainable and greener source of energy, and the synthesis of molecules that have a range of applications including in the pharmaceutical and food industries will be explored.</p

Development of inhibitors as research tools for carbohydrate-processing enzymes

Carbohydrates, which are present in all domains of life, play important roles in a host of cellular processes. These ubiquitous biomolecules form highly diverse and often complex glycan structures without the aid of a template. The carbohydrate structures are regulated solely by the location and specificity of the enzymes responsible for their synthesis and degradation. These enzymes, glycosyltransferases and glycoside hydrolases, need to be functionally well characterized in order to investigate the structure and function of glycans. The use of enzyme inhibitors, which target a particular enzyme, can significantly aid this understanding, and may also provide insights into therapeutic applications. The present article describes some of the approaches used to design and develop enzyme inhibitors as tools for investigating carbohydrate-processing enzymes.</p

Developing inhibitors of glycan processing enzymes as tools for enabling glycobiology

Glycoconjugates are ubiquitous biomolecules found in all kingdoms of life. These diverse structures are metabolically responsive and occur in a cell line-and protein-specific manner, conferring tissue type-specific properties. Glycans have essential roles in diverse processes, including, for example, intercellular signaling, inflammation, protein quality control, glucohomeostasis and cellular adhesion as well as cell differentiation and proliferation. Many mysteries remain in the field, however, and uncovering the physiological roles of various glycans remains a key pursuit. Realizing this aim necessitates the ability to subtly and selectively manipulate the series of different glycoconjugates both in cells and in vivo. Selective small-molecule inhibitors of glycan processing enzymes hold great potential for such manipulation as well as for determining the function of 'orphan' carbohydrate-processing enzymes. In this review, we discuss recent advances and existing inhibitors, the prospects for small-molecule inhibitors and the challenges associated with generating high-quality chemical probes for these families of enzymes. The coordinated efforts of chemists, biochemists and biologists will be crucial for creating and characterizing inhibitors that are useful tools both for advancing a basic understanding of glycobiology in mammals as well as for validating new potential therapeutic targets within this burgeoning field.</p

Mechanism, Structure, and Inhibition of O-GlcNAc Processing Enzymes

The post-translational modification of nucleocytoplasmic proteins with O-linked 2-acetamido-2-deoxy-d-glucopyranose (O-GlcNAc) is a topic of considerable interest and attracts a great deal of research effort. O-GlcNAcylation is a dynamic process which can occur multiple times over the lifetime of a protein, sometimes in a reciprocal relationship with phosphorylation. Several hundred proteins, which are involved in a diverse range of cellular processes, have been identified as being modified with the monosaccharide. The control of the O-GlcNAc modification state on different protein targets appears to be important in the aetiology of a number of diseases, including type II diabetes, neurodegenerative diseases and cancer. Two enzymes are responsible for the addition and removal of the O-GlcNAc modification: uridine diphospho-N-acetylglucosamine:polypeptide β-N-acetylglucosaminyltransferase (OGT) and O-GlcNAcase (OGA), respectively. Over the past decade the volume of information known about these two enzymes has increased significantly. In particular, mechanistic studies of OGA, in conjunction with structural studies of bacterial homologues of OGA have stimulated the design of inhibitors and offered a rationale for the binding of certain potent and selective inhibitors. Mechanistic information about OGT lags a little way behind OGA, but the recent deduction of the structure of an OGT bacterial homologue should now drive these studies forward