Escherichia coli heat-labile enterotoxin. Nucleotide sequence of the A subunit gene.
Escherichia coli heat-labile enterotoxin. Nucleotide sequence of the A subunit gene.
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发表时间：
1982-05
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通讯作者：
E. Spicer;J. A. Noble
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作者：
E. Spicer;J. A. Noble
本文报道了大肠杆菌不耐热肠毒素LT A亚单位的基因全序列，并从其DNA序列推导出LT A亚单位的氨基酸序列。LT A亚基以甲硫氨酸开始，以亮氨酸结束，并且包含254个氨基酸。LT A的计算分子量为29，673。霍乱毒素A亚单位（CTA）已被证明在结构和功能上与LT A亚单位相关。LTA的一级结构与CTA的已知部分氨基酸序列的比较表明，这两种多肽在其整个序列中具有相当大的同源性。NH 2-末端区域表现出最高程度的同源性（91%），而COOH-末端区域，包含每个毒素中唯一的胱氨酸残基是不太保守的（约52%）。在LTA和CTA的COOH-末端区域中同源残基的比对表明LTA的蛋白水解切割的可能位点在Arg残基188之后。所得A2多肽将为46个氨基酸长，将含有单个半胱氨酸残基，并且具有Mr = 5261。elt A核苷酸序列进一步预测LT A蛋白以前体形式合成，在其NH 2末端具有18个氨基酸的信号序列。
We report the complete DNA sequence of the Escherichia coli elt A gene, which codes for the A subunit of the heat-labile enterotoxin, LT. The amino acid sequence of the LT A subunit has been deduced from the DNA sequence of elt A. The LT A subunit starts with methionine, ends with leucine, and comprises 254 amino acids. The computed molecular weight of LT A is 29,673. The A subunit of cholera toxin (CT A) has been shown to be structurally and functionally related to the LT A subunit. Comparison of the primary structure of LT A with the known partial amino acid sequence of CT A indicates that the 2 polypeptides share considerable homology throughout their sequences. The NH2-terminal regions exhibit the highest degree of homology (91%), while the COOH-terminal region, containing the sole cystine residue in each toxin is less conserved (approximately 52%). Alignment of homologous residues in the COOH-terminal regions of LT A and CT A indicates that a likely site for proteolytic cleavage of LT A is after Arg residue 188. The resulting A2 polypeptide would be 46 amino acids long, would contain a single cysteine residue, and have Mr = 5261. The elt A nucleotide sequence further predicts that the LT A protein is synthesized in a precursor form, possessing an 18-amino acid signal sequence at its NH2 terminus.