Altered isoenzyme patterns of liver alpha-L-fucosidase in cystic fibrosis

Terminal glycosylation in cystic fibrosis

Cystic fibrosis (CF) is a common genetic disease for which the gene was identified within the last decade. Pulmonary disease predominates in this ultimately fatal disease and current therapy only slows the progression. CF transmembrane regulator (CFTR), the gene product, is an integral membrane glycoprotein that normally functions as a chloride channel in epithelial cells. The most common mutation, deltaF508, results in mislocalization and altered glycosylation of CFTR. Altered fucosylation and sialylation are hallmarks of both membrane and secreted glycoproteins in CF and the focus here is on these investigations. Oligosaccharides from CF membrane glycoproteins have the Lewis x, selectin ligand in terminal positions. In addition, two major bacterial pathogens in CF, Pseudomonas aeruginosa and Haemophilus influenzae, have binding proteins, which recognize fucose in alpha1,3 linkage and asialoglycoconjugates. We speculate that the altered terminal glycosylation of airway epithelial glycoproteins in CF contributes to the chronic infection and robust inflammatory response in the CF lung. Understanding the effects of mutant CFTR on glycosylation may provide further insight into the regulation of glycoconjugate processing as well as therapy for CF.

Colorimetric assay for free and bound L-fucose

A novel, rapid, and reliable colorimetric method for measuring L-fucose has been developed. This method utilizes NADH formed from the interaction of L-fucose with fucose dehydrogenase and NAD to generate color in a reaction involving CuSO4 and neocuproine. NADH reduces Cu2+ to Cu1+ and the latter interacts with neocuproine to yield a complex with a maximal absorption at 455 nm. The reaction of NADH with copper-neocuproine is immediate and under the conditions of the assay the color formed remains stable for at least 2 h. When the assay is used to determine levels of L-fucose, the absorbance is found to be linearly proportional to exogenously added fucose concentrations from 16 to 179 nmol with resulting molar extinction coefficient of 13,660. Using this procedure, L-fucose released by acid hydrolysis from porcine submaxillary mucin, and by alpha-L-fucosidase from p-nitrophenyl-alpha-L-fucopyranoside, was quantitated.

Lack of proteolytic processing of alpha-L-fucosidase in human skin fibroblasts

Acid hydrolases are synthesized as precursors that undergo several posttranslational modifications including proteolytic processing to a smaller mature enzyme. The amount of proteolytic processing varies for different acid hydrolases, and many details of the intracellular pathways are not known. The processing of alpha-L-fucosidase was distinguished from that of other acid hydrolases reported when studied in systematic pulse-chase labeling experiments. Only one form of alpha-L-fucosidase, Mr 56,000-57,000, was demonstrated intra- and extracellularly. Under the same conditions, N-acetyl-beta-D-glucosaminidase was shown to be processed with several forms, as previously reported by Hasilik and Neufeld (1980a). To obtain these results, human skin fibroblasts were labeled metabolically with L-[3H]leucine for periods of 20 min to 8 hr with varying periods of chase from 1 to 96 hr with nonradioactive L-leucine. alpha-L-Fucosidase was immunoprecipitated by a polyclonal antibody from material extracted from cells and ammonium sulfate precipitated medium and was examined by polyacrylamide gel electrophoresis under denaturing conditions. N-Acetyl-beta-D-glucosaminidase was examined with similar procedures and served as a control for the methods. Tunicamycin treatment of the cells was used to show that glycosylation did not obscure proteolytic processing because, again, only one form of the intra- and extracellular enzyme was observed, although of smaller size, Mr 52,000-53,000. In addition, separation of the cells into prelysosomal and lysosomal fractions showed only one form of the enzyme. It is concluded that alpha-L-fucosidase does not undergo proteolytic processing in human skin fibroblasts in the usual manner described for other acid hydrolases.

Cobalamin R binder as a possible model molecule for glycoprotein study in cystic fibrosis

The isoprotein pattern of semi-purified R binder (an acidic glycoprotein which binds cobalamin) from saliva and sera of 8 cystic fibrosis patients was compared to that of R binder from samples of 5 healthy children. In cases of cystic fibrosis, the mean isoelectric point of salivary R binder was increased from 3.78 up to 4.34 and its microheterogeneity was reduced. These significant physicochemical modifications were not observed with R binder from cystic fibrosis sera and they did not correlate with the beta-galactosidase, alpha-mannosidase, alpha-L-fucosidase nor neuraminidase activity of saliva. We propose the R binder as a model molecule to study the glycoprotein metabolism in cystic fibrosis since it contains 30-40% carbohydrate, is easily complexed with cyano[57Co]cobalamin and is present in most tissues and fluids of the human organism.

alpha-L-Fucosidase in cystic fibrosis: analysis of skin fibroblasts and liver

The lysosomal enzyme alpha-L-fucosidase has been examined by thin layer gel and column isoelectric focusing in skin fibroblasts and liver from patients with cystic fibrosis and controls. All three common phenotypes of the enzyme were observed in both control and CF fibroblasts. When individuals of the same alpha-L-fucosidase phenotype were compared, no major differences between the isozyme profiles of cystic fibrosis patients and controls were detected in either fibroblasts or liver tissue.

Acid hydrolases in sera and plasma from patients with cystic fibrosis

The enzyme activities of alpha-fucosidase (pH 4.0 and pH 5.5), alpha-galactosidase, beta-galactosidase, alpha-glucosidase (pH 4.5 and pH 6.0), beta-glucosidase, beta-glucuronidase, beta-hexosaminidase, and alpha-mannosidase (pH 4.5 and pH 5.5) were investigated in sera from cystic fibrosis (CF) patients. Several of these activities were significantly increased in sera from patients compared to age-matched control children. CF-patients in a more advanced stage of the disease had a tendency to higher values of some of these hydrolases than those in better condition. No new isoenzymes of these hydrolases were found. Only minor differences could be detected in the pH-profiles of alpha-mannosidase and acid phosphatase from age-matched normal controls, heterozygotes and homozygotes for CF. With our technique, alpha-mannosidase and acid phosphatase showed the same thermostability in CF-patients. CF-heterozygotes and age-matched controls, except at 56 degrees C, when the activity of acid-phosphatase in the plasma from adult CF-heterozygotes decreased more than that from adult controls

Susceptibility to neuraminidase of alpha-L-fucosidase and N-acetyl-beta-D-glucosaminidase of cystic fibrosis, I-cell and neuraminidase-deficient fibroblasts

Intracellular alpha-L-fucosidase and hexosaminidase showed similar isoelectro-focusing patterns in control, cystic fibrosis and neuraminidase-deficient fibroblasts and were unaffected by neuraminidase treatment. An I-cell strain excreted these two enzymes at 3-4 times the rate of the three other cell types. I-cell and neuraminidase-deficient cells excreted more of the electronegative forms of these enzymes than control and cystic fibrosis cells. Extracellular hexosaminidase A and B were both sensitive to neuraminidase for the four cell types. Extracellular alpha-L-fucosidase consisted of a pH 6.1 form insensitive to neuraminidase and other forms that were sensitive and changed to a pI 7.0-7.1 form. Cystic fibrosis extracellular alpha-L-fucosidase and hexosaminidase behaved as for control fibroblasts.

Cystic fibrosis serum alpha-l-fucosidase: confirmation of normal activity levels and normal kinetic and isoelectric focusing properties

Comparable alpha-L-fucosidase activity was found for normal and cystic fibrosis sera, 7.8 +/- 3.3 and 9.8 +/- 4.7 nmol/min/ml, respectively. Isoelectric focusing of normal and cystic fibrosis sera alpha-L-fucosidase revealed similar isoelectric profiles with most activity between isoelectric points of 4.7--5.4. Kinetic analysis of normal and cystic fibrosis sera alpha-L-fucosidase revealed identical apparent Michaelis constants for the 4-methylumbelliferyl substrate (51 +/- 6 mumol/l and 50 +/- 8 mumol/l, respectively), similar pH optima curves (both have broad optima between pH 4.8 and 6.5) and identical thermostability curves at three different preincubation temperatures (37 degrees, 45 degrees and 55 degrees C).

Glycosidases in serum of cystic fibrosis patients

In a study of eight glycosidases in serum samples from 72 cystic fibrosis patients, 85 cystic fibrosis parents and 34 healthy and diseased controls, significant elevations of mean alpha-glucosidase levels were found in cystic fibrosis patients. All other glycosidases did not show any significant change. Mean alpha-glucosidase levels in obligate heterozygotes were the same as in control individuals. Moreover, alpha-glucosidase levels in cystic fibrosis patients correlated with the degree of clinical impairment as measured by the Schwachman score.

Primary amniotic fluid cell, skin fibroblast and liver alpha-L-fucosidase and its relation to cystic fibrosis

Cultured skin fibroblast and primary amniotic fluid cell alpha-L-fucosidase had a double optimum of pH 5.0 and 6.0. Alpha-L-fucosidase was largely bound as a single peak to DEAE-cellulose at pH 6.6. Sucrose density isoelectric focusing revealed up to seven components with pI values of 4.9, 5.2, 5.4, 5.8, 6.1, 6.5 and 7.1 with their apparent KM values (77--500 mumol/l) being higher than that (57 mumol/l) of the unfocused enzyme. Liver, skin fibroblast and amniotic fluid cell alpha-L-fucosidase was separated into two peaks by gel filtration. Peak one was more active and stable at low pH and more thermostable at 50 degrees C than peak two, while both peaks had an apparent KM of 52 mumol/l. Apart from the different proportions of the peaks separated by gel filtration, the results for the three tissues were similar. The properties of alpha-L-fucosidase studied were similar for control and cystic fibrosis liver or skin fibroblasts.

Abnormal distribution of alpha-L-fucosidase in cystic fibrosis: decreased activity in serum

The activity of alpha-L-fucosidase is decreased in the serum of cystic fibrosis patients when compared to age-matched controls. This result, combined with the elevated activity in skin fibroblasts, supports the concept of an abnormal intracellular and extracellular distribution of alpha-L-fucosidase in cystic fibrosis.

Secretion of beta-N-acetylglucosaminidase isoenzymes by cultured cystic fibrosis fibroblasts

Secretion of the lysosomal enzyme beta-N-acetylglucosaminidase (EC 3.2.1.30) by normal and cystic fibrosis fibroblasts has been compared. In contrast to an earlier report, no differences were found in either the rate of secretion, or in the molecular forms of the enzyme secreted by normal fibroblast cultures and cultures initiated from patients with cystic fibrosis. The B isoenzyme of beta-N-acetylglucosaminidase from cystic fibrosis fibroblasts was converted to a more negatively charged form during preincubation for 3 h at pH 5.0 and 37 degrees C. The enzyme from normal fibroblasts was unaffected by this treatment.

Lysosomal hydrolases in cystic fibrosis livers

The specific activity of several lysosomal hydrolases in normal and cystic fibrosis (CF) livers has been investigated. Neuraminidase activity with respect to two natural substrates (fetuin and bovine submaxillary mucin) is normal in CF livers. No significant differences were found between CF and normal livers in 4-methylumbelliferyl-alpha-D-mannosidase specific activities determined at three different pH values (4.3, 5.65 and 6.5) corresponding to lysosomal, golgi and cytosolic components of the enzyme, respectively. The specific activities of p-nitrophenyl-beta-D-mannosidase and 4-methylumbelliferyl-beta-N-acetylglucosaminidase were also both similar in CF and normal livers.

Purification and characterization of altered cystic fibrosis liver alpha-L-fucosidase

alpha-L-Fucosidase (E.C.3.2.4.51) from two cystic fibrosis livers has been purified and characterized. Purification was accomplished by an affinity chromatographic procedure previously used for normal liver alpha-L-fucosidase. Characterization of the two cystic fibrosis alpha-L-fucosidases indicated that they were very similar to normal liver alpha-L-fucosidase with regard to pH optima profiles, Michaelis constants (Km's), subunit structure and antigenicity. However, gas liquid chromatographic analysis revealed altered carbohydrate compositions for both the cystic fibrosis alpha-L-fucosidases. The three major sugars found in normal purified liver alpha-L-fucosidase (mannose, N-acetylglucosamine and sialic acid) were reduced in the cystic fibrosis alpha-L-fucosidases, on average, to 51%, 44% and 32%, respectively, of their normal amounts.

Cystic fibrosis liver sialyltransferase

The activity of sialytransferase with regard to the glycoprotein substrates asialofetuin and asialo-ovine submaxillary mucin was determined in normal, pathological control, and cystic fibrosis liver homogenates. Cystic fibrosis and pathological livers have about 40% of the average normal specific activity for sialytransferase. Several properties of cystic fibrosis sialytransferase were investigated and compared to those of the normal liver enzyme (Alhadeff et al. 1977). The pH optima curves were similar, but cystic fibrosis sialyltransferase appears to be more thermolabile than the normal liver enzyme. Isoelectric focusing studies revealed that the three most basic forms of sialyltransferase which are found in normal livers are deficient or absent in most cystic fibrosis liver. The data suggest that altered glycoprotein-sialyltransferases may be present in cystic fibrosis livers, probably a secondary effect due to general liver pathology.