Substrate specificity of human liver neutral α-mannosidase

The digestion of radiolabelled natural oligosaccharide substrates by human liver neutral alpha-mannosidase has been studied by h.p.l.c. and h.p.t.l.c. The high-mannose oligosaccharides Man9GlcNAc and Man8GlcNAc are hydrolysed by the enzyme by two distinct non-random routes to a common product of composition Man6GlcNAc, which is then slowly converted into a unique Man5GlcNAc oligosaccharide, Man alpha(1----2)Man alpha(1----2)Man alpha(1----3)[Man alpha (1----6)] Man beta(1----4)GlcNAc. These pathways are different from the processing and lysosomal catabolic pathways for these structures. In particular, the alpha(1----2)-linked mannose residues attached to the core alpha(1----3)-linked mannose residue are resistant to hydrolysis. The key processing intermediate, Man alpha(1----3)[Man alpha(1----6)]Man alpha(1----6)[Man alpha(1----3)] Man beta(1----4)GlcNAc, is not produced in the digestion of high-mannose glycans by the neutral alpha-mannosidase, but it is hydrolysed by the enzyme by a non-random route to Man beta(1----4)GlcNAc via the core structure Man alpha(1----3)[Man alpha(1----6)]Man beta(1----4)GlcNAc. In contrast with its ready hydrolysis by lysosomal alpha-mannosidase, the core alpha(1----3)-mannosidic linkage is quite resistant to hydrolysis by neutral alpha-mannosidase. The precise specificity of neutral alpha-mannosidase towards high-mannose oligosaccharides suggests that it has a role in the modification of such structures in the cytosol.

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The substrate-specificity of human lysosomal α-d-mannosidase in relation to genetic α-mannosidosis

Biochemical Journal ◽

10.1042/bj2770743 ◽

1991 ◽

Vol 277 (3) ◽

pp. 743-751 ◽

Cited By ~ 33

Author(s):

S al Daher ◽

R de Gasperi ◽

P Daniel ◽

N Hall ◽

C D Warren ◽

...

Keyword(s):

Substrate Specificity ◽

Active Site ◽

Human Liver ◽

Catabolic Pathway ◽

Before And After ◽

Storage Products ◽

High Mannose ◽

Relative Abundances

The specificity of human liver lysosomal alpha-mannosidase (EC 3.2.1.24) towards a series of oligosaccharide substrates derived from high-mannose, complex and hybrid asparagine-linked glycans and from the storage products in alpha-mannosidosis was investigated. The enzyme hydrolyses all alpha(1-2)-, alpha(1-3)- and alpha(1-6)-mannosidic linkages in these glycans without a requirement for added Zn2+, albeit at different rates. A major finding of this study is that all the substrates are hydrolysed by non-random pathways. These pathways were established by determining the structures of intermediates in the digestion mixtures by a combination of h.p.t.l.c. and h.p.l.c. before and after acetolysis. The catabolic pathway for a particular substrate appears to be determined by its structure, raising the possibility that degradation occurs by an uninterrupted sequence of steps within one active site. The structures of the digestion intermediates are compared with the published structures of the storage products in mannosidosis and of intact asparagine-linked glycans. Most but not all of the digestion intermediates derived from high-mannose glycans have structures found in intact asparagine-linked glycans of human glycoproteins or among the storage products in the urine of patients with mannosidosis. However, the relative abundances of these structures suggests that the catabolic pathway is not the same as the processing pathway. In contrast, the intermediates formed from the digestion of oligosaccharides derived from hybrid and complex N-glycans are completely different from any processing intermediates and also from the oligosaccharides of composition Man2-4GlcNAc that account for 80-90% of the storage products in alpha-mannosidosis. It is postulated that the structures of these major storage products arise from the action of an exo/endo-alpha(1-6)-mannosidase on the partially catabolized oligomannosides that accumulate in the absence of the main lysosomal alpha-mannosidase.

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Appropriate aglycone modification significantly expands the glycan substrate acceptability of α1,6-fucosyltransferase (FUT8)

Biochemical Journal ◽

10.1042/bcj20210138 ◽

2021 ◽

Author(s):

Roushu Zhang ◽

Qiang Yang ◽

Bhargavi M Boruah ◽

Guanghui Zong ◽

Chao Li ◽

...

Keyword(s):

Substrate Specificity ◽

Turnover Rate ◽

Human Neutrophils ◽

Complex Type ◽

The Core ◽

Km Value ◽

High Mannose ◽

Overall Efficiency ◽

Core Fucosylation ◽

Lysosomal Proteins

The α1,6-fucosyltransferase, FUT8, is the sole enzyme catalyzing the core-fucosylation of N-glycoproteins in mammalian systems. Previous studies using free N-glycans as acceptor substrates indicated that a terminal β1,2-GlcNAc moiety on the Man-α1,3-Man arm of N-glycan substrates is required for efficient FUT8-catalyzed core-fucosylation. In contrast, we recently demonstrated that, in a proper protein context, FUT8 could also fucosylate Man5GlcNAc2 without a GlcNAc at the non-reducing end. We describe here a further study of the substrate specificity of FUT8 using a range of N-glycans containing different aglycones. We found that FUT8 could fucosylate most of high-mannose and complex-type N-glycans, including highly branched N-glycans from chicken ovalbumin, when the aglycone moiety is modified with a 9-fluorenylmethyloxycarbonyl (Fmoc) moiety or in a suitable peptide/protein context, even if they lack the terminal GlcNAc moiety on the Man-α1,3-Man arm. FUT8 could also fucosylate paucimannose structures when they are on glycoprotein substrates. Such core-fucosylated paucimannosylation is a prominent feature of lysosomal proteins of human neutrophils and several types of cancers. We also found that sialylation of N-glycans significantly reduced their activity as substrate of FUT8. Kinetic analysis demonstrated that Fmoc aglycone modification could either improve the turnover rate or decrease the Km value depending on the nature of the substrates, thus significantly enhancing the overall efficiency of FUT8 catalyzed fucosylation. Our results indicate that an appropriate aglycone context of N-glycans could significantly broaden the acceptor substrate specificity of FUT8 beyond what has previously been thought.

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Indexicality of Grammar: The Case of Japanese Transgender Speakers

The Oxford Handbook of Language and Sexuality ◽

10.1093/oxfordhb/9780190212926.013.16 ◽

2019 ◽

Author(s):

Hideko Abe

Keyword(s):

Gender Identity ◽

Gender Identity Disorder ◽

Grammatical Gender ◽

Core Structure ◽

Subject Positions ◽

Transgender Identity ◽

The Core ◽

History Of ◽

History Of Scholarship ◽

Grammatical Structures

This article discusses how the intersection of grammatical gender and social gender, entwined in the core structure of language, can be analyzed to understand the dynamic status of selfhood. After reviewing a history of scholarship that demonstrates this claim, the discussion analyzes the language practices of transgender individuals in Japan, where transgender identity is currently understood in terms of sei-dōitsusei-shōgai (gender identity disorder). Based on fieldwork conducted between 2011 and 2017, the analysis reveals how individuals identifying with sei-dōitsusei-shōgai negotiate subject positions by manipulating the specific indexical meanings attached to grammatical structures.

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Solvent-free and efficient synthesis of bicyclic 2-pyridone derivatives for endoplasmic reticulum imaging

Organic Chemistry Frontiers ◽

10.1039/d1qo00350j ◽

2021 ◽

Author(s):

Xiaoyun Ran ◽

Qian Zhou ◽

Jin Zhang ◽

Shanqiang Wang ◽

Gui Wang ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Citric Acid ◽

Core Structure ◽

Solvent Free ◽

Efficient Synthesis ◽

The Core ◽

Catalyst Free ◽

Synthesis Approach ◽

Ethylenediamine Derivatives

Started from citric acid (CA) and ethylenediamine derivatives, a solvent-free, catalyst-free and highly yield synthesis approach for bicyclic 2-pyridones was presented. Continuing to modify the core structure, a series of...

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