【摘要】 从陆地棉纤维cDNA文库中分离出两个β-甘露糖苷酶的cDNA克隆,GhManAl和GhManA2。它们的开放读码框编码长度分别为834个氨基酸和976个氨基酸的多肽序列,这两个多肽C-末端的747个氨基酸残基是完全一致的,而N-末端的序列差异较大。GhManAl和GhManA2均属于糖基水解酶家族2的成员,它们与其它植物来源的该家族中β-甘露糖苷酶之间具有较高的同源性,而与非植物来源的β-甘露糖苷酶之间的同源性较低,但不同蛋白序列中均存在糖基水解酶家族2的酶催化活性所需的两个Glu保守残基。这两个多肽的N-末端均没有信号肽序列,因此可能为胞内酶。从表达特征来看,GhManAl属于组成型表达基因,而GhManA2则为纤维细胞优势表达基因。更多还原

【Abstract】 By using the method of PCR-based cDNA library screening, two β-mannosidase clones, GhManAl and GhManA2, had been isolated. GhManAl had a length of 2 692 bp coding for a polypeptide of 834 amino acids, and GhManA2 was 3 209 bp which encoded a polypeptide of 976 amino acids. GhManAl and GhManA2 shared an identical sequence of 747 amino acids in their carboxyl-terminals, but were distinctly different in their amino-terminaLs (Fig. 1). Both β-mannosidases were members of gly-cosyl hydrolase family 2, which had two conserved glutamine residues in their sequences as the acid-base catalyst and nucleophilic group, respectively. Most surprisingly, the first 93 amino acids in the amino-terminal of GhManAl was highly homologous to the β-barrel domain of ATP synthase α-/β-subunit, but an analogous domain has never been found in the sequence of other non-ATP synthase protein (Fig.2). GhManAl was constitutively expressed in different cotton tissues, and GhManA2 was specifically expressed in fiber cells (Fig.3).更多还原