Lysosomal and microsomal beta-glucuronidase of monkey brain. Differential elution characteristics from con A-sepharose and neutral sugar composition

Elution of tightly bound solutes from concanavalin A Sepharose. Factors affecting the desorption of cottonmouth venom glycoproteins

Some glycoproteins bind so tightly to concanavalin A Sepharose that common desorption techniques are ineffective, so a systematic exploration of factors affecting desorption of cottonmouth venom glycoproteins was undertaken. Glycoprotein desorption is greatly improved by introducing up to four pauses of 5-10 min duration into the elution step. Eluent concentrations above 250 mM methylglucoside or 500 mM methyl-mannoside reduced glycoprotein desorption. Eluent NaCl diminished glycoprotein desorption. Most venom glycoproteins desorb more readily as pH diminishes from 6.0 to 4.0, but phosphodiesterase shows the opposite pattern. Eluents recommended by the supplier for desorbing solutes or for column cleaning were ineffectual.

Mycobacterium leprae binds to a 25-kDa phosphorylated glycoprotein of human peripheral nerve

Mycobacterium leprae, the causative agent of leprosy, specifically invades and destroys the peripheral nerve, which results in the main clinical manifestation of the disease. Little is known about the bacteria-nerve protein interaction. We show in the present work that M leprae binds to a 25 kDa glycoprotein from human peripheral nerve. This protein is phosphorylatable and it binds to lectins which have alpha-mannose specificity. This M leprae-protein interaction could be of importance in the pathogenesis of leprosy.

Human fibroblasts prefer mannose over glucose as a source of mannose for N-glycosylation. Evidence for the functional importance of transported mannose

Mannose in N-linked oligosaccharides is assumed to be derived primarily from glucose through phosphomannose isomerase (PMI). The discovery of mammalian mannose-specific transporters that function at physiological concentrations suggested that mannose might directly contribute to oligosaccharide synthesis. To determine the relative contribution of glucose and mannose, human fibroblasts were labeled with either [2-3H]mannose or [1,5,6-3H]glucose at the same specific activity, and the N-linked chains were released by PNGase F digestion. Most of the trichloroacetic acid-precipitable [3H]mannose label was released by this digestion, but only about 10% of the trichloroacetic acid-precipitable material was released from cells labeled with [1,5,6-3H]glucose. Both sugars labeled a similar array of oligosaccharides, and acid hydrolysis of these chains showed that [2-3H]mannose contributed 65-75% of the [3H]mannose in cells labeled for 1 h, despite the 100-fold higher concentration of exogenous glucose. Mannose consumption and [2-3H]mannose utilization were within the range of rates expected for mannose transport via the mannose-specific transporter. About 7-14% of the [2-3H]mannose is used for glycosylation, while the rest (86-93%) is catabolized to 3H2O via PMI. Increasing the exogenous mannose concentration beyond mannose transporter saturation results in the conversion of >99% of [2-3H]mannose into 3H2O. Long term labeling of cells with [2-3H]mannose showed that the specific activity of mannose in glycoproteins reached 77% of the specific activity of [2-3H]mannose added to the medium. These results show that when fibroblasts are provided with physiological concentrations of mannose, they use the mannose-specific transporter to supply the majority of mannose needed for glycoprotein synthesis. PMI may normally be used to catabolize excess mannose rather than to primarily supply Man-6-P for glycoprotein synthesis.

Plant endogenous beta-glucuronidase activity: how to avoid interference with the use of the E. coli beta-glucuronidase as a reporter gene in transgenic plants

We have detected a plant beta-glucuronidase activity, present in several tissues and organs of plant species belonging to different families. The fluorimetric beta-glucuronidase assay was used to partially characterize this activity in post-ribosomal supernatants of tobacco leaves. The tobacco activity is very stable at low temperatures, but quickly inactivated above 45 degrees C. It is relatively resistant to proteases and insensitive to -SH group reagents and to ionic conditions. It does not require, nor is it inhibited by, divalent cations. Although these properties are shared by the Escherichia coli beta-glucuronidase, the two activities can be distinguished by: (i) their different sensitivity to the specific inhibitor saccharic acid-1,4-lactone; (ii) their different thermal stability (iii) their different pH optima (5.0 for the plant activity and close to neutral for the bacterial enzyme). Therefore, under appropriate experimental conditions, it should be possible to assay the E. coli beta-glucuronidase in transgenic plants without interference from the endogenous plant activity.

Inhibition by lysosomal enzymes and mannose-6-phosphate of the phosphorylation of the lysosomal enzyme binding receptor protein from monkey brain

The lysosomal enzymes beta-glucuronidase and alpha-L-fucosidase and mannose-6-phosphate inhibited the phosphorylation of the lysosomal enzyme binding receptor protein prepared from monkey brain. Inhibition of both serine and tyrosine phosphorylation was observed. A non-lysosomal glycoprotein enzyme butyrylcholinesterase, mannose or glucose did not inhibit phosphorylation. Tyrosine phosphorylation of histone by the receptor protein was also inhibited by the lysosomal enzymes and mannose-6-phosphate.

Phosphorylation of the lysosomal enzyme binding receptor protein from monkey brain and evidence for a tyrosine kinase activity associated with it

The lysosomal enzyme binding receptor protein prepared from monkey brain by phosphomannan-Sepharose affinity chromatography could undergo phosphorylation in the presence of [gamma-32P] ATP. The phosphorylated receptor protein appeared as a single radioactive band on polyacrylamide gel electrophoresis under nondenaturing conditions. Upon SDS-gel electrophoresis two radioactive bands, one corresponding to a high molecular weight (Mr greater than 116,000) component and another corresponding to Mr 45,000 were seen. Phosphoamino acid analysis showed that the receptor protein was phosphorylated on serine and tyrosine residues. The receptor protein could also phosphorylate histone on tyrosine residues exclusively. The phosphorylated receptor protein bound lysosomal enzymes to a lesser extent as compared to the non-phosphorylated receptor protein.

Structural analysis of the carbohydrate chains of beta-N-acetylhexosaminidases from bovine brain

The oligosaccharide structures of bovine brain beta-N-acetylhexosaminidases A and B (EC 3.2.1.30) were studied at the glycopeptide level by employing 500 MHz 1H-n.m.r. spectroscopy and methylation analysis involving g.l.c.-m.s. More than 90% of the chains were found to be of the oligomannoside type, containing, on average, five to six mannose residues. Biantennary N-acetyl-lactosamine-type chains terminated in N-acetylneuraminic acid were found to comprise the remaining 5-10% of the total carbohydrate. The isoenzyme forms A and B do not differ from each other in the structure of their carbohydrate moiety, but do deviate in carbohydrate content and, in consequence, in the number of carbohydrate chains per molecule.

Two forms of acid alpha-D-mannosidase in monkey brain: evidence for the co-existence of high mannose and complex oligosaccharides in one form

Lysosomal alpha-D-mannosidase of monkey brain existed in two forms. One form of mannosidase was bound to the Ricinus communis agglutinin120 (RCA1)-Sepharose and could be specifically eluted with lactose. The other form did not bind to the RCA1-Sepharose. Both forms of mannosidase could bind to a similar extent to the immobilized brain lysosomal receptor protein. Both the forms were purified to apparent homogeneity. Neutral sugar analysis by GLC showed the presence of glucose, mannose and galactose in the RCA1-Sepharose bindable mannosidase and glucose and mannose in the non-bindable mannosidase. Several other brain lysosomal hydrolases did not bind to the RCA1-Sepharose. The results suggested the existence of only high mannose oligosaccharides in the RCA1 non-bindable mannosidase and both high mannose and complex oligosaccharides in the bindable mannosidase.

A binding protein for lysosomal enzymes isolated from brain by phosphomannan-sepharose chromatography

We have isolated from monkey (Macaca radiata) brain lysosomal fraction by phosphomannan-Sepharose chromatography a protein that binds four different lysosomal enzymes, beta-hexosaminidase, beta-glucuronidase, alpha-L-fucosidase and arylsulfatase. The isolated protein which appeared in an aggregated homogeneous form on gel electrophoresis under non-denaturing conditions at both pH 8.3 and pH 5.0 was found to be heterogeneous on SDS-gel electrophoresis with molecular weights less than 67,000. Binding was partly abolished by periodate treatment or by alkaline phosphatase treatment of the lysosomal enzymes. Binding was completely abolished by pronase digestion of the binding protein. Of the different sugars tested for inhibition of binding, mannose-6-phosphate was most effective followed by mannose and N-acetyl glucosamine while glucose and fucose were ineffective.