Wang A M, Desnick R J
Division of Medical and Molecular Genetics, Mount Sinai School of Medicine, New York, New York 10029.
Genomics. 1991 May;10(1):133-42. doi: 10.1016/0888-7543(91)90493-x.
Human alpha-N-acetylgalactosaminidase (alpha-GalNAc; EC 3.2.1.49), the lysosomal glycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties in glycoconjugates, is encoded by a gene localized to chromosome 22q13----qter. The deficient activity of this enzyme results in Schindler disease, an autosomal recessive disorder characterized by the increased urinary excretion of glycopeptides and oligosaccharides containing alpha-N-acetylgalactosaminyl moieties. Recently, the 3.6-kb full-length alpha-GalNAc cDNA sequence was isolated and found to have remarkable nucleotide and predicted amino acid homology (55.8 and 46.9%, respectively) with the human alpha-galactosidase A (alpha-Gal A) cDNA. To investigate the possible evolutionary relatedness of the two glycosidases, the alpha-GalNAc chromosomal gene was isolated and characterized. Screening of a human genomic DNA cosmid library resulted in the identification of a clone, gAGB-1, with an approximately 35-kb insert that contained the entire alpha-GalNAc gene. A single approximately 15-kb EcoRI fragment of gAGB-1, which contained the complete 3.6-kb cDNA sequence, was digested and the subcloned fragments were sequenced in both orientations. The 13,709-bp alpha-GalNAc gene had nine exons ranging from 95 to 2028 bp and intronic sequences of 304 to 2684 bp. All exon/intron junctions conformed to the GT/AG consensus rule. Analysis of 1.4 kb of 5' flanking sequence revealed three Sp1 and two CAAT-like promoter elements. This region was GC-rich (56%), but no HTF island was identified. The gene contained six Alu-repetitive elements, all in the reverse orientation. Comparison of the structural organization of the alpha-GalNAc and the alpha-Gal A genes revealed that all six alpha-Gal A introns were identically positioned in the homologous alpha-GalNAc exonic sequence. Two additional introns, 1 and 8, were identfied in the alpha-GalNAc gene. The predicted amino acid sequences of alpha-GalNAc exons 2 through 7 and those of corresponding alpha-Gal A exons 1 through 6 were 46.2 to 62.7% identical. In contrast, there was little, if any, similarity between the deduced amino acid sequences of alpha-Gal A exon 7 and alpha-GalNAc exons 8 and 9. The remarkable amino acid identity and the identical exonic interruption by six introns of the alpha-GalNAc and alpha-Gal A genes suggest that this region in both genes is evolutionarily related and arose through duplication and divergence from a common ancestral gene.
人α-N-乙酰半乳糖胺酶（α-GalNAc；EC 3.2.1.49）是一种溶酶体糖水解酶，可裂解糖缀合物中的α-N-乙酰半乳糖胺基部分，由定位于22q13----qter染色体的一个基因编码。该酶活性缺乏导致辛德勒病，这是一种常染色体隐性疾病，其特征是尿中含α-N-乙酰半乳糖胺基部分的糖肽和寡糖排泄增加。最近，分离出了3.6 kb的全长α-GalNAc cDNA序列，发现它与人类α-半乳糖苷酶A（α-Gal A）cDNA具有显著的核苷酸和预测氨基酸同源性（分别为55.8%和46.9%）。为了研究这两种糖苷酶可能的进化相关性，对α-GalNAc染色体基因进行了分离和鉴定。筛选人类基因组DNA黏粒文库后，鉴定出一个克隆gAGB-1，其插入片段约35 kb，包含整个α-GalNAc基因。对gAGB-1的一个约15 kb的EcoRI片段进行消化，该片段包含完整的3.6 kb cDNA序列，并对亚克隆片段进行双向测序。13709 bp的α-GalNAc基因有9个外显子，长度从95到2028 bp不等，内含子序列长度为304到2684 bp。所有外显子/内含子连接均符合GT/AG共有规则。对1.4 kb的5'侧翼序列分析揭示了3个Sp1和2个类CAAT启动子元件。该区域富含GC（56%），但未鉴定出HTF岛。该基因包含6个Alu重复元件，均为反向排列。比较α-GalNAc和α-Gal A基因的结构组织发现，所有6个α-Gal A内含子在同源α-GalNAc外显子序列中的位置相同。在α-GalNAc基因中还鉴定出另外两个内含子，即内含子1和内含子8。α-GalNAc外显子2至7的预测氨基酸序列与相应的α-Gal A外显子1至6的预测氨基酸序列的同一性为46.2%至62.7%。相比之下，α-Gal A外显子7与α-GalNAc外显子8和9的推导氨基酸序列之间几乎没有相似性（如果有的话）。α-GalNAc和α-Gal A基因显著的氨基酸同一性以及6个内含子对二者外显子相同的中断表明，这两个基因的该区域在进化上相关，是通过从一个共同祖先基因的复制和分化产生的。
