Human mannosidosis--the enzyme defect

Amount and properties of uptake forms in preparations of alpha-mannosidase from pig kidney

alpha-Mannosidase (alpha-D-mannoside mannohydrolase, EC 3.2.1.24) from pig kidney has been shown to exist in multiple forms differing in their capability to be endocytosed by alpha-mannosidase deficient cultured cells. A method is presented to evaluate the amount of "uptake" forms in different preparations of the enzyme. Preparations with different rates of uptake were shown to contain different amount of "uptake" forms and "non-uptake" forms. The content of "uptake" forms in a preparation was identical with that of enzyme molecules bearing a phosphorylated carbohydrate group necessary for the recognition by cell surface receptors.

Punctate lenticular opacities in type II mannosidosis

Ocular examination in four siblings with Type II mannosidosis revealed scattered punctate opacities in the entire lens. No such lenticular opacities were described in 28 previously reported patients, 17 presumed Type II and 11 Type I. Complete ocular examination with particular attention to opacities in the lens and cornea may provide additional phenotypic data for identification of genetic variants with amnnosidosis.

Measurement of the alpha-mannosidase activities in human plasma by a differential assay

A differential assay based on their difference in thermal stability has been used to measure the acidic and true intermediate alpha-mannosidases in the plasma of cntrols and individuals homozygous or heterozygous for mannosidosis. The intermediate activity was found to be independent of age, sex or mannosidosis genotype. The acidic alpha-mannosidase did not vary significantly with age or between sexes for groups of the same age. The concentrations of acidic and intermediate alpha-mannosidase showed a positive correlation for adults but not for children. The ratio of acidic to true intermediate alpha-mannosidase might therefore be a useful secondary test for the detection of adult heterozygotes for mannosidosis.

Mannosidosis. Clinical and biochemical study

The clinical, radiological, and biochemical features of 2 male children with mannosidosis are described. Superficially they appeared to suffer from Hurler's syndrome, but the facies, eye signs, radiological and cytological features were atypical. Excess urinary oligosaccharides were found by thin-layer chromatography. The diagnosis was confirmed by determining the acidic alpha-mannosidase activity of leucocytes and cultured skin fibroblasts. Prenatal diagnosis is possible from cultured amniotic cells.

Expression of alpha-D-mannosidase in man-hamster somatic cell hybrids

Two types of alpha-D-mannosidase isozymes are present in human white blood cells, human diploid fibroblasts, and HeLa cells. One of these (the S isozyme) constitutes the major alpha-D-mannosidase of the human cells, has a pH optimum of 4.4, and is associated with lysosomes. The other (the F isozyme) is most active at pH 6, is acid labile, and is located in the soluble portion of the cytoplasm. The expression of human lysosomal alpha-D-mannosidase was examined in man-hamster hybrid clones, and was found to be concordant with that of phosphohexose isomerase in 54 of 55 primary clones. A locus specifying human lysosomal alpha-D-mannosidase has therfore been assigned to chromosome 19.

A serological investigation into the acidic alpha-D-mannosidase in normal Angus cattle and in a calf with mannosidosis

Antiserum was raised in a rabbit against bovine kidney acidic alpha-mannosidase that had been purified 570-fold by affinity chromatography on concanavalin A--Sepharose and Sepharose 4B-xi-aminohexanoylmannosylamine. The antiserum precipitated the acidic but not the neutral alpha-mannosidase in normal calf tissues. Human acidic alpha-mannosidase cross-reacted partially with the antiserum, emphasizing the close structural resemblance between the enzyme in the two species. The residual acidic alpha-mannosidase in the tissues of a calf with mannosidosis was also precipitated by the antiserum, the same volume of antiserum being required to precipitate a unit of alpha-mannosidase activity from the normal and pathological tissues. The concentration of cross-reacting material detected by antibody-consumption experiments in the organs of the calf with mannosidosis appeared to be proportional to the concentration of the residual acidic alpha-mannosidase. It is suggested that the residual acidic alpha-mannosidase in mannosidosis accounts for the cross-reacting material detected and that it is unlikely that enzymically inactive but cross-reacting material is present. The residual acidic alpha-mannosidase could be a decreased concentration of the normal gene product or an altered enzyme with a decreased specific enzymic activity and a correspondingly decreased antigenicity.

A gene apparently determining the extent of sialylation of lysosomal alpha-mannosidase in mouse liver

Organ-specific electrophoretic heterogeneity of lysosomal alpha-mannosidase has been observed within individual strains of inbred mice. Polymorphism between C57BL/6J and CBA/J for liver lysosomal alpha-mannosidase is determined by a single genetic locus on chromosome 5 and appears to be the result of differences in sialylation of the lysosomal enzyme. Two different patterns of expression of development of the liver electrophoretic forms have been observed.

Clinical manifestations of mannosidosis--a longitudinal study

Mannosidosis is a partially defined disorder of glycoprotein metabolism; less than 20 cases have been reported in the literature. In this work, a longitudinal study of five new patients is presented in an attempt to delineate the phenotype and clinical course of this unusual storage disease. The data on our patients and those in the literature indicate that people with mannosidosis appear normal at birth and that their typical phenotype develops by two years of age. This is characterized by a distinctive coarse facies and dysostosis multiplex. Although recurrent infections, hearing loss and mental retardation occur, the course in this storage disorder generally is stable and is compatible with adult life. The diagnosis is confirmed by the presence of a deficiency in alpha-D-mannosidase activity in leukocytes or fibroblasts, by the presence of vacuolated lymphocytes in peripheral blood and foam cells in bone marrow, and an increased excretion of mannose-rich oligosaccharides in urine.

Uptake of iodinated human kidney alpha-D-mannosidase by rat liver- Association with membrane elements and stability in vivo and in vitro

1. Human kidney alpha-D-mannosidase (form A) was labelled with 125I to a specific radio-activity of approx. 2250muCi/mg of protein, essentially without loss of enzymic activity. The enzymic activity and radioactivity of the iodinated material also co-migrated in gel filtration and gel electrophoresis. 2. The binding of 125I-labelled mannosidase in vitro to particulate material in liver and kidney homogenates was of the other of 2 pg/mg of particulate material in liver and kidney homogenates was of the order of 2pg/mg of particulate protein withing 16h at 37 degrees C, and essentially zero in intervals of up to 60 min. The degradation in vitro of labelled exogenous mannosidase was of the order of 10-20pg/ 16th per mg of protein in postnuclear supernatant, and it was saturated entirely within 1h at 37 degrees C. 3. The binding of labelled mannosidase in vivo to particulate elements of liver homogenates 60 min after intravenous injection was at least 10 times higher in terms of specific radioactivity than the highest value attainable in vitro. Virtually all exogenous enzyme bound to liver particulate material could be recovered in macromolecular form after disruption of membranes by detergents. 4. The radioactive enzyme bound to liver particulate material could be detached almost completely by shearing, repeated freezing and thawing, and exposure to strong detergents under conditions that do not eliminate rough-endoplasmic-membrane structure. It could bot be released, however, by high salt concentration (0.5M-KC1) or by exposure to weak detergents such as Tween 80. The particle-bound enzyme should thus be associated with plasma membranes and lysosome-like elements. 5. Of the rat tissues studied, only liver could approach, within 60 min after the injection, the concentration of exogenous mannosidase found in the blood serum. The activity per g tissue weight fell progressively from liver (60% of serum value) to kidney (16% of serum value), lung (8% of serum vlaue), spleen (6% of serum value) and brain (0.9% of serum value). Most of the radioactive enzyme found in tissues other than liver appeared to be present in a free form, whereas in liver more than 50% of the labelled enzyme was associated with membrane elements.

A lysosomal storage disorder of the epidermis characterized by a deficiency of alpha-mannosidase and an accumulation of mannose-rich materials

Laboratory investigation of a patient diagnosed as ichthyosiform erythroderma bullosa revealed the following abnormalities: (1) alpha- and beta-galactosidases were elevated in the lesion. (2) alpha-mannosidase activity was extremely low both in the lesion and in relatively normal epidermis. (3) The mannose:glucose ratio of water-soluble hexose-containing material in the scales was very high. (4) Membrane-limited vacuoles, apparently enlarged secondary lysosomes, were observed. We conclude that this patients is the first documented example of a lysosomal storage disease in which overt clinical lesions are confined to the epidermis.

Neutral alpha-mannosidase activity in human serum

Two types of alpha-mannosidase (alpha-D-mannoside mannohydrolase, EC 3.2.1.24) with neutral pH optima exist in serum. The activity with an optimum between pH 6.0 and 6.4 is similar to alpha-mannosidase C, described earlier in tissues. The second activity, with a pH optimum between pH 5.2 and 5.8 is the dominant form in serum. These two forms can be differentiated from each other by gel-filtration, chromatography on DEAE-cellulose or chromatography on Concanavalin-A Sepharose. Using the chromatographic techniques, the serum type neutral activity co-elutes with the acidic forms of the enzyme. However, these two forms can be easily distinguished by effect of pH, heating or inhibition by the substrate methyl-alpha-D-mannopyranoside. The presence of the serum type alpha-mannosidase activity is discussed with respect to mannosidosis, a lysosomal storage disease.

Ocular findings in mannosidosis

Three patients with typical features of mannosidosis and deficiency of alpha-mannosidase activity, who were examined ophthalmologically, had similar lenticular opacities. Corneal opacities were absent. Chamber angle and striking ophthalmoscopic anomalies occurred in two young patients who had normal electroretinograms. Two patients had strabismus. Conjunctival biopsy specimens morphologically confirmed the lysosomal nature of this disorder.

Molecular forms and activities of glycosidases in cultures of amniotic-fluid cells

Ion-exchange chromatography of gel filtration demonstrated the presence of different molecular forms of nine lysosomal enzymes in cultured amniotic-fluid cells. The patterns of molecular forms were similar to those known from skin fibroblasts and liver tissue. During cultivation total enzyme activities fluctuated with the number of passages, without any consistent trend of increase or decrease, and without correlation to the dominating cell type in the culture.

Storage of mannose-containing material in cultured human mannosidosis cells and metabolic correction by pig kidney alpha-mannosidase

Skin fibroblasts from healthy individuals and a mannosidosis patient were cultured in the presence of [2-3H] mannose and the cell homogenates were fractionated by trichloroacetic acid precipitation into a precipitable and a non-precipitable portion. In uptake as well as in chase experiments the precipitable fractions show no significant difference in their content of radioactivity, while an increased level of radioactivity is found in the non-precipitable fraction of mannosidosis cells. This higher radioactivity content is due to a higher mannose content and is caused by a slower degradation of this fraction. The differences between the metabolisms of the two cell lines can be expressed by the ratio of radioactivity in the non-precipitable and the precipitable fractions. This value is about three times higher for mannosidosis than for control cells. Pig kidney alpha-mannosidase is taken up by both cell lines and is able to correct the impaired degradation of the non-precipitable material in mannosidosis cells, as shown by the normalization of the above defined ratio of radioactivity for this cell type.

Characterization of human liver alpha-D-mannosidase purified by affinity chromatography

Human liver acidic alpha-D-mannosidase was purified 1400-fold by a relatively short procedure incorporating chromatography on concanavalin A-Sepharose and affinity chromatography on Sepharose 4B-epsilon-aminohexanoylmannosylamine. In contrast with the acidic enzymic activity the neutral alpha-mannosidase did not bind to the concanavalin A-Sepharose so the two types of alpha-mannosidase could be separated at an early stage in the purification. The only significant glycosidase contaminant after affinity chromatography on the mannosylamine ligand was alpha-L-fucosidase, which was selectively removed by affinity chromatography on the corresponding fucosylamine ligand. The final preparation was free of other glycosidase activities. The pI of the purified enzyme was increased from 6.0 to 6.45 on treatment with neuraminidase. Although the pI and the mol.wt. (220 000) suggested that alpha-mannosidase A had been purified selectively, ion-exchange chromatography on DEAE-cellulose indicated that the preparation consisted predominantly of alpha-mannosidase B. This discrepancy is discussed in relation to the basis of the multiple forms of human alpha-mannosidase. The purified enzyme completely removed the alpha-linked non-reducing terminal mannose from a trisaccharide isolated from the urine of a patient with mannosidosis. A comparison of the activity of the pure enzyme towards the natural substrate and synthetic substrates suggests that the same enzymic activity is responsible for hydrolysing all the substrates. These results validate the use of synthetic substrates for determining the mannosidosis genotype. They are also further evidence that mannosidosis is a lysosomal storage disease resulting from a deficiency of acidic alpha-mannosidase.

Immunological characterization of human liver alpha-D-mannosidase

Antiserum was raised against purified human liver alpha-D-mannosidase B. It precipitated alpha-mannosidases A and B from solution, demonstrating the close structural resemblance of these 2 forms of acidic alpha-mannosidase activity. A continuous enzymically active precipitin line with no spurs was obtained when alpha-mannosidase A and B were placed in adjacent wells on Ouchterlony double-diffusion plates. The antiserum precipitated acidic but not neutral alpha-mannosidase from an extract of human liver, confirming that the acidic and neutral activities are not closely related. Acidic activity was also precipitated from extracts of human brain, kidney and leucocytes by the antiserum. However, it did not cross-react with bovine acidic alpha-mannosidase activity or with the activity in human plasma that has an optimum pH of 5.5. The two acidic forms of human liver alpha-mannosidase, A and B, are immunologically identical but distinct from neutral alpha-mannosidase and that activity with an optimum pH of 5.5.

Specificity studies on alpha-mannosidases using oligosaccharides from mannosidosis urine as substrates

Oligosaccharides containing terminal non-reducing alpha(1 leads to 2)-, alpha(1 leads to 3)-, and alpha(1 leads to 6)-linked mannose residues, isolated from human and bovine mannosidosis urines were used as substrates to test the specificities of acidic alpha-mannosidases isolated from human and bovine liver. The enzymes released all the alpha-linked mannose residues from each oligosaccharide and were most effective on the smallest substrate. Enzyme A in each case was less active on the oligosaccharides than alpha-mannosidase B2, even though the apparent Km value for the substrates was the same with each enzyme. The human acidic alpha-mannosidases were also found to be more active on substrates isolated from human rather than bovine mannosidosis urine. Human alpha-mannosidase C, which has a neutral pH optimum when assayed with a synthetic substrate, did not hydrolyse any of the oligosaccharides at neutral pH, but was found to be active at an acidic pH.

A urinary pentasaccharide in bovine mannosidosis

Abnormally high amounts of low molecular weight mannose-rich carbohydrate material were found in the urine of an Angus calf with mannosidosis. At least five oligosaccharide fractions were detected by paper chromatography. The most abundant compound was purified by gel chromatography, zone electrophoresis, and two consecutive preparative paper chromatographic steps. The yield was 10 mg/liter of urine. From structural studies including nuclear magnetic resonance spectroscopy, optical rotation, sugar analysis, methylation analysis, and partial enzymatic degradation the following structure was deduced: alpha-D-Manp-(1 leads to 6)-beta-D-Manp-(1 leads to 4)-beta-D-GlcNAcp-(1 leads to 4)-beta-D-GlcNAcp-(1 leads to 4)-D-GlcNAc. This oligosaccharide is distinct from all the oligosaccharides previously described which are excreted by patients with mannosidosis.

The relationship between different forms of human alpha-mannosidase

The tissue distribution and some properties of human alpha-mannosidase (alpha-D-mannoside mannohydrolase EC 3.2.1.24) have been studied. The acidic forms of the enzyme were fairly stable, whereas the neutral forms easily lost enzymic activity. The acidic forms were sensitive to neuraminidase but the neutral forms were unaffected. The experiments indicate that the acidic components are closely related to each other, differing only in sialic acid content and possibly conformation. The neutral forms of the enzyme are probably quite different from the acidic forms both in structure and cellular function.

Mannosidosis: deficiency of a specific alpha-mannosidase component in cultured fibroblasts

Evidence is prisented which shows that the enzymatic defect in mannosidosis, the deficiency of alpha-mannosidase, is expressed in cultured skin fibroblasts from patients with mannosidosis. Additionally, by Cellogel electrophoresis, the enzyme can be separated into two major components (a heat stable component missing in mannosidosis fibroblasts with a pH optimum of 3.6-4.0 and a heat labile component present in mannosidosis fibroblasts with a pH optimum of 5.6-6.0). The specific activity and electrophoresis of alpha-mannosidase from cultured amniotic fluid cells are also shown to be similar to cultured skin fibroblasts.

Separation and properties of human brain hexosaminidase C

Hexosaminidase C was separated from human brain supernatant by immunoadsorption of the A and B forms on to a column of immobilized antibody followed by preparative starch-block electrophoresis. There were some differences in the properties of hexosaminidase C preparations after each of these stages, shown by comparison of their heat-inactivation characteristics and filtration through Bio-Gel P-200. The C form prepared by both separation steps had properties which differed markedly from those of the A and B isoenzymes; its molecular weight was much larger, greater than 200000, it had optimum activity between pH6 and 7 and could not be successfully eluted from DEAE-cellulose, even with high salt concentrations, or from Sephadex G-200. These results seem to support the proposal that the C form is under a separate genetic control from the others.

Mannosidosis in Angus cattle. The enzymic defect

Normal calf alpha-mannosidase activity exists in at least three forms separable by chromatography on DEAE-cellulose and by starch-gel electrophoresis. Two components, A and B, have optimum activity between pH3.75 and 4.75, but component C has an optimum of pH6.6. Components A and B are virtually absent from the tissues of a calf with mannosidosis and the residual activity is due to component C. The acidic and neutral forms of alpha-mannosidase differ in their molecular weights and sensitivity to EDTA, Zn(2+), Co(2+) and Mn(2+). An acidic alpha-mannosidase component (pH optimum 4.0) accounts for most of the activity in normal plasma but it is absent from the plasma of a calf with mannosidosis. Although the acidic alpha-mannosidase component is probably related to tissue components A and B, it can be distinguished from them by ion-exchange chromatography and gel filtration. The optimum pH of the low residual activity in the plasma from a calf with mannosidosis is pH5.5-5.75. The results support the hypothesis that Angus-cattle mannosidosis is a storage disease caused by a deficiency of lysosomal acidic alpha-mannosidase activity.