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Articles by D Yamaguchi
Total Records ( 3 ) for D Yamaguchi
  D Hu , Y Kamiya , K Totani , D Kamiya , N Kawasaki , D Yamaguchi , I Matsuo , N Matsumoto , Y Ito , K Kato and K. Yamamoto

Glucosidase II (GII) is a glycan-processing enzyme that trims two 1,3-linked glucose residues from N-glycan on newly synthesized glycoproteins. Trimming of the first 1,3-linked glucose from Glc2Man9GlcNAc2 (G2M9) is important for a glycoprotein to interact with calnexin/calreticulin (CNX/CRT), and cleavage of the innermost glucose from Glc1Man9GlcNAc2 (G1M9) sets glycoproteins free from the CNX/CRT cycle and allows them to proceed to the Golgi apparatus. GII is a heterodimeric complex consisting of a catalytic subunit (GII) and a tightly associated β subunit (GIIβ) that contains a mannose 6-phosphate receptor homology (MRH) domain. A recent study has suggested a possible involvement of the MRH domain of GIIβ (GIIβ-MRH) in the glucose trimming process via its putative sugar-binding activity. However, it remains unknown whether GIIβ-MRH possesses sugar-binding activity and, if so, what role this activity plays in the function of GII. Here, we demonstrate that human GIIβ-MRH binds to high-mannose-type glycans. Frontal affinity chromatography revealed that GIIβ-MRH binds most strongly to the glycans with the 1,2-linked mannobiose structure. GII with the mutant GIIβ that lost the sugar-binding activity of GIIβ-MRH hydrolyzes p-nitrophenyl--glucopyranoside, but the capacity to remove glucose residues from G1M9 and G2M9 is significantly decreased. Our results clearly demonstrate the capacity of the GIIβ-MRH to bind high-mannose-type glycans and its importance in efficient glucose trimming of N-glycans.

  K Mikami , D Yamaguchi , H Tateno , D Hu , S. Y Qin , N Kawasaki , M Yamada , N Matsumoto , J Hirabayashi , Y Ito and K. Yamamoto

Misfolded glycoproteins are translocated from the endoplasmic reticulum (ER) into the cytoplasm for proteasome-mediated degradation. OS-9 protein is thought to participate in ER-associated glycoprotein degradation (ERAD). The recombinant biotinylated mannose 6-phosphate receptor homology (MRH) domain of human OS-9 (OS-9MRH) together with six kinds of mutated OS-9MRH were prepared and mixed with R-phycoerythrin (PE)-labeled streptavidin to form tetramers (OS-9MRH-SA). The PE-labeled OS-9MRH-SA bound to HeLaS3 cells in a metal ion-independent manner through amino acid residues homologous to those participating in sugar binding of the cation-dependent mannose 6-phosphate receptor, and this binding was greatly increased by swainsonine, deoxymannojirimycin, or kifunensine treatment. N-Acetylglucosaminyltransferase I-deficient Lec1 cells, but not Lec2 or Lec8 cells, were also strongly bound by the tetramer. OS-9MRH-SA binding to the cells was strongly inhibited by Man1,6(Man1,3)Man1,6(Man1,3)Man and Man1,6Man. To further determine the specificity of native ligands for OS-9MRH, frontal affinity chromatography was performed using a wide variety of 92 different oligosaccharides. We found that several N-glycans containing terminal 1,6-linked mannose in the Man1,6(Man1,3)Man1,6(Man1,3)Man structure were good ligands for OS-9MRH, having Ka values of approximately 104 M–1 and that trimming of either an 1,6-linked mannose from the C-arm or an 1,3-linked mannose from the B-arm abrogated binding to OS-9MRH. An immunoprecipitation experiment demonstrated that the 1-antitrypsin variant nullHong Kong, but not wild-type 1-antitrypsin, selectively interacted with OS-9 in the cells in a sugar-dependent manner. These results suggest that trimming of the outermost 1,2-linked mannose on the C-arm is a critical process for misfolded proteins to enter ERAD.

  D Yamaguchi , D Hu , N Matsumoto and K. Yamamoto

XTP3-B is a soluble endoplasmic reticulum (ER)-resident protein containing two mannose-6-phosphate receptor homology (MRH) domains in its sequence. XTP3-B interacts with a membrane-associated ubiquitin ligase complex, and, therefore, is thought to participate in ER-associated degradation (ERAD). In this study, the recombinant human XTP3-B fused with IgG-Fc (XTP3-B-Fc), XTP3-B without an N-terminal MRH domain fused with IgG-Fc (XTP3-B1-Fc), or XTP3-B without a C-terminal MRH domain fused with IgG-Fc (XTP3-B2-Fc) were prepared. XTP3-B-Fc and XTP3-B1-Fc bound to Lec1 cells but not to CHO, Lec2, or Lec8 cells, while XTP3-B2-Fc did not bind to any of these cells. The binding of XTP3-B-Fc and XTP3-B1-Fc to Lec1 cells was abrogated by treatment of the cells with endo-β-N-acetylglucosaminidase H, Man1,6Man or Man1,6(Man1,3)Man1,6(Man1,3)Man, or by substitution of Arg428 or Tyr457 in the C-terminal MRH domain with alanine. Arg428 and Tyr457 are homologous to amino acids that mediate glycan binding by the cation-dependent mannose-6-phosphate receptor. An immunoprecipitation experiment using lysates of cells co-expressing wild-type 1-antitrypsin (AT), 1-antitrypsin variant nullHong Kong (ATNHK), and FLAG-tagged XTP3-B, or its mutants, demonstrated that ATNHK, but not AT, specifically co-precipitated with XTP3-B and XTP3-B1. The glycan-binding-deficient XTP3-B2 did not bind either AT or ATNHK. These results suggest that XTP3-B specifically binds to ATNHK, which is a well-known substrate of ERAD, via a C-terminal MRH domain in a glycan-dependent manner.

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