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J. Biol. Chem., Vol. 265, Issue 35, 21859-21866, Dec, 1990
AM Wang, DF Bishop and RJ Desnick
Human alpha-N-acetylgalactosaminidase (alpha-GalNAc, E.C. 3.2.1.49), the
lysosomal glycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties
from glycoconjugates, is encoded by a gene localized to chromosome
22q13----qter. The deficient activity of alpha-GalNAc is the enzymatic
defect in Schindler disease, an inherited neuroaxonal dystrophy. To isolate
a full-length cDNA, the enzyme from human lung was purified to homogeneity,
129 non-overlapping amino acids were determined by microsequencing the N
terminus and seven tryptic peptides, and four synthetic oligonucleotide
mixtures were used to screen a human fibroblast cDNA library. A full-length
cDNA, pAGB-3, isolated from a placental lambda gt11 cDNA library, had a
2158-base pair (bp) insert with an open reading frame which predicted an
amino acid sequence that was colinear with all 129 microsequenced residues
of the purified enzyme. The pAGB-3 insert had a 344-bp 5'-untranslated
region, a 1236-bp open reading frame encoding 411 amino acids, a 514-bp
3'-untranslated region, and a 64-bp poly(A) tract. A signal peptide
sequence of 17 amino acids as well as six N-glycosylation sites were
predicted. The pAGB-3 cDNA was subcloned into the p91023(B) mammalian
expression vector and human alpha-GalNAc activity was transiently expressed
in COS-1 cells, demonstrating the functional integrity of the full-length
cDNA. Northern hybridization analysis of mRNA revealed two transcripts of
about 3.6 and 2.2 kilobases (kb), and primer extension studies indicated a
cap site at nucleotide -347 for the 2.2-kb transcript. The 3.6-kb cDNA
(pAGB-35) was isolated; the 3598-bp pAGB-35 insert was identical to that of
the 2.2-kb insert but had additional 5'- and 3'-untranslated sequences
including a second downstream polyadenylation signal at nucleotide
3100-3105. Isolation of a genomic clone, gAGB-1, and sequencing the 2048-bp
region including pAGB-3 revealed a 1754-bp intron between codons 319 and
320, which also was the site of a 70-bp insertion and a45-bp deletion in
other cDNA clones. Notably, the alpha-GalNAc cDNA had remarkable amino acid
homology with the human alpha-galactosidase A (alpha-Gal A) cDNA suggesting
the evolutionary relatedness of these genes. The alpha-GalNAc cDNA had
46.9- 64.7% amino acid identity in sequences (codons 1-319) corresponding
to alpha-Gal A exons 1 through 6, while the comparable exon 7 sequence
(pAGB-3 codons 320-411) had only 15.8% homology with numerous
gaps.(ABSTRACT TRUNCATED AT 400 WORDS)
Human alpha-N-acetylgalactosaminidase-molecular cloning, nucleotide sequence, and expression of a full-length cDNA. Homology with human alpha-galactosidase A suggests evolution from a common ancestral gene
Division of Medical and Molecular Genetics, Mount Sinai School of Medicine, New York, New York 10029.
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