Hoefsloot L H, Hoogeveen-Westerveld M, Kroos M A, van Beeumen J, Reuser A J, Oostra B A
Department of Cell Biology and Genetics, Erasmus University, Rotterdam, The Netherlands.
EMBO J. 1988 Jun;7(6):1697-704. doi: 10.1002/j.1460-2075.1988.tb02998.x.
Lysosomal alpha-glucosidase (acid maltase) is essential for degradation of glycogen in lysosomes. Enzyme deficiency results in glycogenosis type II. The amino acid sequence of the entire enzyme was derived from the nucleotide sequence of cloned cDNA. The cDNA comprises 3636 nt, and hybridizes with a messenger RNA of approximately 3.6 kb, which is absent in fibroblasts of two patients with glycogenosis type II. The encoded protein has a molecular mass of 104.645 kd and starts with a signal peptide. Sites of proteolytic processing are established by identification of N-terminal amino acid sequences of the 110-kd precursor, and the 76-kd and 70-kd mature forms of the enzyme encoded by the cDNA. Interestingly, both amino-terminal and carboxy-terminal processing occurs. Sites of sugar-chain attachment are proposed. A remarkable homology is observed between this soluble lysosomal alpha-glucosidase and the membrane-bound intestinal brush border sucrase-isomaltase enzyme complex. It is proposed that these enzymes are derived from the same ancestral gene. Around the putative active site of sucrase and isomaltase, 10 out of 13 amino acids are identical to the corresponding amino acids of lysosomal alpha-glucosidase. This strongly suggests that the aspartic acid residue at this position is essential for catalytic function of lysosomal alpha-glucosidase.
溶酶体α-葡萄糖苷酶（酸性麦芽糖酶）对于溶酶体中糖原的降解至关重要。酶缺乏会导致II型糖原贮积病。整个酶的氨基酸序列由克隆的cDNA的核苷酸序列推导而来。该cDNA包含3636个核苷酸，与约3.6kb的信使RNA杂交，而在两名II型糖原贮积病患者的成纤维细胞中不存在这种信使RNA。编码的蛋白质分子量为104.645kd，起始于一个信号肽。通过鉴定110kd前体以及由cDNA编码的该酶的76kd和70kd成熟形式的N端氨基酸序列，确定了蛋白水解加工位点。有趣的是，氨基端和羧基端都发生了加工。提出了糖链连接位点。在这种可溶性溶酶体α-葡萄糖苷酶与膜结合的肠刷状缘蔗糖酶-异麦芽糖酶复合物之间观察到显著的同源性。有人提出这些酶源自同一个祖先基因。在蔗糖酶和异麦芽糖酶的假定活性位点周围，13个氨基酸中有10个与溶酶体α-葡萄糖苷酶的相应氨基酸相同。这有力地表明该位置的天冬氨酸残基对于溶酶体α-葡萄糖苷酶的催化功能至关重要。
