Characterization of a Human Core-specific Lysosomal α1,6-Mannosidase Involved in N-Glycan Catabolism

Park, Chaeho; Li, Meng; Stanton, Leslie H.; Collins, R.; Mast, Steven W.; Yi, Xiaobing; Strachan, Heather; Moremen, Kelley W.

doi:10.1074/jbc.m508930200

Cited by 42 publications

(34 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2-4), demonstrating that MX is the only enzyme able to compensate for the absence of the MII step in N-glycan processing in vivo. These observations are consistent with the absence of any other genes closely related to either Man2a1 (MII) or Man2a2 (MX) within the Class 2 (glycosylhydrolase family 38) ␣-mannosidases (21) in human or mouse genome databases (22). These data also exclude a role for the Co 2ϩ -stimulated broad-specificity ␣-mannosidase activity previously termed ␣-mannosidase III (13) in N-glycan biosynthesis.…”

Section: Discussionsupporting

confidence: 77%

Essential and mutually compensatory roles of α-mannosidase II and α-mannosidase IIx in N -glycan processing in vivo in mice

Akama

Nakagawa

Wong

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

Many proteins synthesized through the secretory pathway receive posttranslational modifications, including N-glycosylation. ␣-Mannosidase II (MII) is a key enzyme converting precursor high-mannose-type N-glycans to matured complex-type structures. Previous studies showed that MII-null mice synthesize complextype N-glycans, indicating the presence of an alternative pathway. Because ␣-mannosidase IIx (MX) is a candidate enzyme for this pathway, we asked whether MX functions in N-glycan processing by generating MII͞MX double-null mice. Some double-nulls died between embryonic days 15.5 and 18.5, but most survived until shortly after birth and died of respiratory failure, which represents a more severe phenotype than that seen in single-nulls for either gene. Structural analysis of N-glycans revealed that double-nulls completely lack complex-type N-glycans, demonstrating a critical role for at least one of these enzymes for effective N-glycan processing. Recombinant mouse MX and MII showed identical substrate specificities toward N-glycan substrates, suggesting that MX is an isozyme of MII. Thus, either MII or MX can biochemically compensate for the deficiency of the other in vivo, and either of two is required for late embryonic and early postnatal development.gene knockout ͉ mutation N -glycosylation is the major form of posttranslational modification of newly synthesized proteins through the secretory pathway. The major biosynthetic steps for N-glycans in vertebrates have been established (1, 2). A key conversion of highmannose to complex-type oligosaccharides occurs in the medial Golgi, where GlcNAc-transferase I (GlcNAc-TI) adds a GlcNAc residue to form a hybrid-type N-glycan, GlcNAc 1 Man 5 GlcNAc 2 (3). Golgi ␣-mannosidase II (MII) then removes two mannosyl residues to form GlcNAc 1 Man 3 GlcNAc 2 (4, 5), which is further modified by GlcNAc-transferase II (GlcNAc-TII) (6) to form GlcNAc 2 Man 3 GlcNAc 2 , the precursor of complex-type Nglycans.When the gene encoding GlcNAc-TI was disrupted in mouse, GlcNAc-TI-null embryos died between embryonic day 9 (E9) and E10 because of defects in morphogenic processes, including the establishment of left-right asymmetry, vascularization, and neural tube formation (7,8). The observation that GlcNAc-TInull embryos could synthesize only high-mannose-type Nglycans demonstrates that high-mannose-type N-glycans by themselves cannot support embryonic development beyond E9-E10 in the mouse. On the other hand, mice lacking GlcNAc-TII were born and synthesized hybrid-type N-glycans, implying that hybrid-type N-glycans can support embryogenesis (9). However, GlcNAc-TII-null mice showed severe gastrointestinal, hematopoietic, osteogenic, and neuronal dysfunction, with phenotypes similar to those seen in human congenital disorders of glycosylation IIa (10, 11). This evidence indicates that hybrid-type N-glycans are not sufficient to maintain normal postnatal development in the mouse and in humans (12).Although MII catalyzes the step after GlcNAc-TI and before GlcNAc-TII (1, 2), MII-n...

show abstract

Section: Discussionsupporting

confidence: 77%

Essential and mutually compensatory roles of α-mannosidase II and α-mannosidase IIx in N -glycan processing in vivo in mice

Akama

Nakagawa

Wong

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The expanded active site cleft and limited sequence conservation is consistent with the substrate specificity of LM, which cleaves all of the ␣-linked mannose residues from high-mannose oligosaccharides, whereas GMII only cleaves the terminal ␣1,3-and ␣1,6-linked residues from GnMan 5 Gn 2 (2,25).…”

Section: Resultsmentioning

confidence: 73%

Golgi α-mannosidase II cleaves two sugars sequentially in the same catalytic site

Shah

Kuntz

Rose

2008

Proc. Natl. Acad. Sci. U.S.A.

101

View full text Add to dashboard Cite

Golgi ␣-mannosidase II (GMII) is a key glycosyl hydrolase in the N-linked glycosylation pathway. It catalyzes the removal of two different mannosyl linkages of GlcNAcMan 5GlcNAc2, which is the committed step in complex N-glycan synthesis. Inhibition of this enzyme has shown promise in certain cancers in both laboratory and clinical settings. Here we present the high-resolution crystal structure of a nucleophile mutant of Drosophila melanogaster GMII (dGMII) bound to its natural oligosaccharide substrate and an oligosaccharide precursor as well as the structure of the unliganded mutant. These structures allow us to identify three sugar-binding subsites within the larger active site cleft. Our results allow for the formulation of the complete catalytic process of dGMII, which involves a specific order of bond cleavage, and a major substrate rearrangement in the active site. This process is likely conserved for all GMII enzymes-but not in the structurally related lysosomal mannosidase-and will form the basis for the design of specific inhibitors against GMII.cancer therapy ͉ enzyme mechanism ͉ N-glycosylation pathway ͉ x-ray crystallography ͉ glycoside hydrolase

show abstract

“…The predominant occurrence of Man3GlcNAc2 oligosaccharides on native cathepsin B in mice with ␣-mannosidosis suggests a preset order of cleavage with the ␣1,3-linkage by LAMAN prior to the ␣1,6-linkage catalyzed by the core-specific ␣1,6-mannosidase (MAN2B2). Furthermore, it had been demonstrated before that during Nglycan degradation MAN2B2 is dependent on the release of the oligosaccharide from the asparaginyl residue by the activity of the glycosylasparaginase and chitobiase (36). Taken together, we suggest a model for LAMAN function (Fig.…”

Section: Discussionmentioning

confidence: 68%

“…Additionally, a second lysosomal mannosidase (MAN2B2) specific for the core ␣1,6 branch was characterized and found to be dependent on the prior enzymatic activity of lysosomal glycosylasparaginase or chitobiase, releasing Man3GlcNAc2 and Man3GlcNAc oligosaccharides, respectively (21,36). The cooperation of this novel core-specific ␣1,6-mannosidase with chitobiase is also reflected by their similar tissue-specific expression patterns in humans and rodents and their simultaneous absence in cattle and cats (2,14).…”

mentioning

confidence: 99%

Impaired Lysosomal Trimming of N-Linked Oligosaccharides Leads to Hyperglycosylation of Native Lysosomal Proteins in Mice with α-Mannosidosis

Damme

Morelle

Schmidt

et al. 2010

Molecular and Cellular Biology

View full text Add to dashboard Cite

␣-Mannosidosis is caused by the genetic defect of the lysosomal ␣-D-mannosidase (LAMAN), which is involved in the breakdown of free ␣-linked mannose-containing oligosaccharides originating from glycoproteins with N-linked glycans, and thus manifests itself in an extensive storage of mannose-containing oligosaccharides. Here we demonstrate in a model of mice with ␣-mannosidosis that native lysosomal proteins exhibit elongated N-linked oligosaccharides as shown by two-dimensional difference gel electrophoresis, deglycosylation assays, and mass spectrometry. The analysis of cathepsin B-derived oligosaccharides revealed a hypermannosylation of glycoproteins in mice with ␣-mannosidosis as indicated by the predominance of extended Man3GlcNAc2 oligosaccharides. Treatment with recombinant human ␣-mannosidase partially corrected the hyperglycosylation of lysosomal proteins in vivo and in vitro. These data clearly demonstrate that LAMAN is involved not only in the lysosomal catabolism of free oligosaccharides but also in the trimming of asparaginelinked oligosaccharides on native lysosomal proteins.The lysosomal ␣-D-mannosidase (LAMAN; EC 3.2.1.24) belongs to the group of at least seven lysosomal exoglycosidases which sequentially degrade oligosaccharides derived from glycoproteins (2, 31). These glycoproteins enter the lysosomal compartment by either endocytic pathways (extracellular and plasma membrane proteins) or autophagic processes (intracellular proteins). In addition, free oligosaccharides originating from lipid-linked oligosaccharides in the endoplasmic reticulum and from glycoproteins by the endoplasmic reticulumassociated protein degradation (ERAD) pathway are transported into the lysosome, where these oligosaccharides are subsequently degraded (9, 45). Inside the lysosome, the degradation of the glycoproteins is described as a bidirectional process in which on the one hand the polypeptide is hydrolyzed by a cohort of lysosomal endo-and exoproteases with partially overlapping specificities like cathepsins and other peptidases 40,52). On the other hand, the sugar moiety is stepwise hydrolyzed into its monosaccharides by exoglycosidases. The precise order of the bidirectional breakdown of glycoproteins is unclear, although assumptions can be made based on the analysis of the storage products of the different glycoproteinoses (31). Therefore, it is assumed that an efficient degradation of the oligosaccharide chain is highly dependent on the cleavage of the protein-oligosaccharide linkage by the glycosylasparaginase (2, 31). In contrast, the proteolysis of the polypeptide backbone is mainly unaffected by intact oligosaccharide structures on the glycoproteins (1).LAMAN has a broad substrate specificity, cleaving nonreducing terminal ␣1,2-, ␣1,3-, and ␣1,6-mannosyl linkages found in complex-type, hybrid-type, and high-mannose-type asparagine-linked glycans (30, 60). Additionally, a second lysosomal mannosidase (MAN2B2) specific for the core ␣1,6 branch was characterized and found to be dependent on the prior enzymati...

show abstract

Characterization of a Human Core-specific Lysosomal α1,6-Mannosidase Involved in N-Glycan Catabolism

Cited by 42 publications

References 57 publications

Essential and mutually compensatory roles of α-mannosidase II and α-mannosidase IIx in N -glycan processing in vivo in mice

Essential and mutually compensatory roles of α-mannosidase II and α-mannosidase IIx in N -glycan processing in vivo in mice

Golgi α-mannosidase II cleaves two sugars sequentially in the same catalytic site

Impaired Lysosomal Trimming of N-Linked Oligosaccharides Leads to Hyperglycosylation of Native Lysosomal Proteins in Mice with α-Mannosidosis

Contact Info

Product

Resources

About