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Articles by K Akasaka Manya
Total Records ( 2 ) for K Akasaka Manya
  K Akasaka Manya , H Manya , Y Sakurai , B. S Wojczyk , Y Saito , N Taniguchi , S Murayama and S. L Spitalnik
 

Alteration of glycoprotein glycans often changes various properties of the target glycoprotein and contributes to a wide variety of diseases. Here, we focused on the N-glycans of amyloid precursor protein whose cleaved fragment, β-amyloid, is thought to cause much of the pathology of Alzheimer's disease (AD). We previously determined the N-glycan structures of normal and mutant amyloid precursor proteins (the Swedish type and the London type). In comparison with normal amyloid precursor protein, mutant amyloid precursor proteins had higher contents of bisecting GlcNAc residues. Because N-acetylglucosaminyltransferase III (GnT-III) is the glycosyltransferase responsible for synthesizing a bisecting GlcNAc residue, the current report measured GnT-III mRNA expression levels in the brains of AD patients. Interestingly, GnT-III mRNA expression was increased in AD brains. Furthermore, β-amyloid treatment increased GnT-III mRNA expression in Neuro2a mouse neuroblastoma cells. We then examined the influence of bisecting GlcNAc on the production of β-amyloid. Both β-amyloid 40 and β-amyloid 42 were significantly decreased in GnT-III-transfected cells. When secretase activities were analyzed in GnT-III transfectant cells, -secretase activity was increased. Taken together, these results suggest that upregulation of GnT-III in AD brains may represent an adaptive response to protect them from additional β-amyloid production.

  H Manya , K Akasaka Manya , A Nakajima , M Kawakita and T. Endo
 

The complex of protein O-mannosyltransferase 1 (POMT1) and POMT2 catalyzes the initial step of O-mannosyl glycan biosynthesis. The mutations in either POMT1 or POMT2 can lead to Walker–Warburg syndrome, a congenital muscular dystrophy with abnormal neuronal migration. Here, we used three algorithms for predicting transmembrane helices to construct the secondary structural models of human POMT1 and POMT2. In these models, POMT1 and POMT2 have seven- and nine-transmembrane helices and contain four and five potential N-glycosylation sites, respectively. To determine whether these sites are actually glycosylated, we prepared mutant proteins that were defective in each site by site-directed mutagenesis. Three of the POMT1 sites and all of the POMT2 sites were found to be N-glycosylated, suggesting that these sites face the luminal side of the endoplasmic reticulum. Mutation of any single site did not significantly affect POMT activity, but mutations of all N-glycosylation sites of either POMT1 or POMT2 caused a loss of POMT activity. The loss of activity appeared to be due to the decreased hydrophilicity. These results suggest that the N-glycosylation of POMT1 and POMT2 is required for maintaining the conformation as well as the activity of the POMT1-POMT2 complex.

 
 
 
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