Lysosomal mannosidases

Golgi a-l)-mannosidase II lysosomal mannosidase glycoprotein A-linked oligosaccharide processing [toxic, neurotoxic effects mimic hereditary lysosomal storage disease mannosidosis] (3-D-Glucuronidase cx-1-iduronidase Glucosidase... 

Based on its primary sequence, mannosidase II is a member of the class II mannosidase family (CAZy glycohydrolase family 38, which includes also the lysosomal mannosidase involved in glycoprotein catabolism). Like the lysosomal enzyme, mannosidase II is inhibited by swain-sonine [62], thus this reagent can be used to block the formation of complex A-glycans. The... 

The lysosomal mannosidase has been purified from a munber of species [130, 156-160] and the subunit molecular weights vary significantly between species. The human enzyme can be separated into two forms by ion exchange chromatography, termed A and B, but significant evidence indicates that the two enzymes are differently modified versions of the same gene product [156]. Pulse-chase studies have indicated that the initial translation product of the human gene is a 110 kDa pre-... 

Synthesis of ( )-Swmnsonine ( )-Swainsonine is an indoUzidine alkaloid that is isolated from the fungus Rhizoctonia leguminicola and later it was found in the AustraUan plant Swainsona canescens It is famous for its lysosomal mannosidase inhibiting activity. ( )-Swainso-nine is also well known for its antineoplastic activity as it is... 

Swainsonine (1) is of great biochemical interest since it is a potent and specific inhibitor of both lysosomal a-mannosidase and mannosidase II, which are involved in the cellular degradation of polysaccharides and in the processing of asparagine-linked glycoproteins, respectively [1]. 

Genetic mannosidosis has been described in man, Angus cattle and Murray Gray cattle, and is characterized by a deficiency of a-mannosidase leading to storage of excess mannose-rich oligosaccharides in lysosomes. Pathologically, there is vacuolation of reticuloendothelial cells in the liver and lymph nodes, pancreatic exocrine cells, and neurons. Affected cattle are ataxic, uncoordinated, fail to thrive, and die in the first year of life. 

Investigation of the inhibitory effects on glycosidases has been carried out for the hydroxylated pyrrolidines [65] and piperidines [73]. Among the pyrrolidines prepared only the l,4-dideoxy-l,4-imino-L-allitol (23) (Scheme 7) and its C-5 isomer showed any remarkable effects. They inhibited lysosomal a-manno-sidase rather than the processing a-mannosidases I and II [65], and their specificity is in accord with the structural requirements of azafuranose analogues of mannose for inhibiting mammalian a-o-mannosidases [80]. 

In mouse liver and kidney and in rat liver, a-D-mannosidase activity appeared to be equally distributed between the two cytoplasmic-granule fractions. With mouse spleen and cancer tissue, a considerable proportion of the enzyme was found free in the cytoplasm. Rat spleen, on the other hand, lacked this cytoplasmic fraction. Inasmuch as the enzyme within the cytoplasmic granules was not fully active in a sucrose homogenate until the membranes had been disintegrated, a-D-mannosidase conforms to the definition of a lysosomal hydrolase. 

The theory has been advanced that there exists in the cell a particulate structure somewhat smaller than the mitochondrion, the lyso-some, that contains certain autolytic enzymes in a latent situation. The lysosome theory55,56 is very largely based upon measurements made in sucrose homogenates of rodent liver. Although the results for a-D-mannosidase in this tissue (see Table IV) are not incompatible with the theory, the results for other tissues do not always conform to it. In particular, the contrast between mouse and rat spleen argues against a universal single particle to which a-D-mannosidase is confined. Apart from the results quoted in Table IV, not much work has been done on the intracellular location of a-D-mannosidase. 

Since mannosido.se results from a genetically derrved absence of lysosomal a-mannosidase that leads to an accumulation of mannose-rich oligosaccharides, the effects of swainsonine (1) on this enzyme were investigated. The alkaloid, which bears a structural resemblance to the open-chain form of D-man nose (2), was in fact shown to be a reversible inhibitor of lysosomal a-mannosidase.8... 

A detailed spectroscopic study has shown that swainsonine, from Swainsona canescens (Benth.) A. Lee, is 8a/3-indolizidine-la,2a,8 3-triol (1), and the structure and relative configuration have been confirmed by X-ray crystallography.1 Swainsonine is a potent inhibitor of a-mannosidase, and in animals it produces an accumulation of mannose-rich oligosaccharides in the lysosomal system of cells, leading to organ dysfunction and clinical disease.1... 

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