@article{oai:niigata-u.repo.nii.ac.jp:00021390,
 author = {山内, 豊明},
 issue = {6},
 journal = {新潟医学会雑誌, 新潟医学会雑誌},
 month = {Jun},
 note = {A sialidase deficiency has been described in several diseases including mucolipidosis I, cherry-red spot-myoclonus syndrome, galactosialidosis and I-cell disease. Mechanisms of the sialidase deficiency, however, is still unclear due to the extreme difficulty of purification of human sialidase. In order to better undersuand molecular mechanisms of the sialidase deficiency, a purified sialidase has been purified from placenta. On SDS-PAGE analysis, the purified sialidase fraction contains five protein bands with apparent molecular weight of 78kDa, 64kDa, 46kDa, 30kDa and 20kDa. The 64kDa protein is β-galactosidase itself, and the 20kDa and 30kDa proteins are known as protective protein and its precursor protein. To elucidate the function of the 46kDa protein, molecular cloning of cDNA for the 46kDa protein was conducted. Partial amino acid sequences were obtained from tryptic peptides of the 46kDa protein and two oligonucleotide probes were synthesized. On screening of cDNA libraries with the oligonucleotide probes, a full-length cDNA has been isolated. The identity of the cDNAs were confirmed by complete colinearity between the deduced amino acid sequence and chemically determined amino acid sequence of the 46kDa protein. Furthermore, the identity was also confirmed by western blotting analysis of the fusion protein made by E.coli. The full-length cDNA, pcD2-HS1225 codes for 411 amind acids with the first 17 residues representing a putative signal peptide. The predicted amino acid sequence shows striking homology with human α-galactosidase A and yeast α-galactosidase, suggesting that the 46kDa protein is a protein related to α-galactosidase A. An isoenzyme of α-galactosidase A has been identified as α-N-acetylgalactosaminidase (α-galactosidase B). To elucidate the function of the 46kDa protein, the analysis of α-galactosidase and α-N-acetylgalactosaminidase activities of the purified 46kDa protein as well as in COS cells transfected with cDNAs for the 46kDa protein was therefore performed. The purified 46kDa protein did show α-N-acetylgalactosaminidase activity toward p-nitrophenyl-α-N-acetylgalactosaminide as well as α-galactosidase activity toward 4-methylumbelliferyl-α-galactopyranoside. Hydroxylapatite column chromatography confirmed the identity of the 46kDa protein as α-galactosidase B (α-N-acetylgalactosaminidase). COS cells transfected with pcD2-HS1207, pcD2-HS1225 and pcD2-HS1237 showed marked increase of α-N-acetylgalactosaminidase activity as well as α-galactosidase activity. SP-Sephadex column chromatography demonstrated that the expressed α-galactosidase activity behaves as α-galactosidase B, which is in good agreement with previous suggestion that α-galactosidase B is in reality α-N-acetylgalactosaminidase. The COS cells transfected with pcD2-HS1225 also shows α-N-acetylgalactosaminidase activity toward Forssman hapten, asialo-bovine submandibular mucin and asialo-porcine gastric mucin, confirming the previous findings that the α-N-acetylgalactosaminidase has a broad substrate specificity. It was concluded that the 46kDa protein associated with the sialidase fraction, is α-N-acetylgalactosaminidase., Recently a deficiency of the α-N-acetylgalactosaminidase in human has been reported. The patients with the α-N-acetylgalactosaminidase deficiency excrete large amount of amino acid glycosides. To elucidate the mechanisms of urinary excretion of amino acid glycosides, α-N-acetylgalactosaminidase activity toward urinary amino acid glycosides was investigated. The structure of the major amino acid glycosides has been determined to be NeuAcα2-3Galβ1-3Gal NAcα1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-3Galβ1-4GalNAcβ1-6) GalNAcα1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAcα1-Ser(Thr) and NeuAcα2-3Galβ1-3(NeuAcα2-6) GalNAcα1-Thr-Pro. α-GalNAc-Ser(Thr)-DNS, prepared from the NeuAcα2-3Galβ1-3GalNAcαβ1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-3Galβ1-4GalNAcβ1-6) GalNAcα1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-6) GalNAcα1-Ser(Thr) was shown to be hydrolyzed by the α-N-acetylgalactosaminidase expressed in the COS cells transfected with pcD2-HS1225. Amino acid glycosides, NeuAcα2-3Galβ1-3GalNAcα1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-3Galα1-4GalNAcβ1-6)GalNAcα1-Ser(Thr), NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAcα1-Ser(Thr)cannot be cleaved by the α-N-acetylgalactosaminidase. The result suggests that addition of sialic acid and galactose to GalNAcα1-Ser(Thr) might take place after the degradation of GalNAcα1-Ser(Thr) is blocked due to the α-N-acetylgalactosaminidase deficiency.},
 pages = {393--409},
 title = {ヒトα-N-acetylgalactosaminidaseの分子生物学的研究},
 volume = {105},
 year = {1991}
}