Blaxter M L, Vanfleteren J R, Xia J, Moens L
Department of Biology, Imperial College of Science, London, United Kingdom.
J Biol Chem. 1994 Dec 2;269(48):30181-6.
Globin was purified from the body wall of adults of the parasitic nematode Ascaris suum. Internal peptide fragments were sequenced and cDNAs encoding a polypeptide of 154 amino acids isolated by polymerase chain reaction. The polypeptide lacks a signal sequence, identifying it as a cytosolic myoglobin-like species. The native protein is a dimer. The predicted amino acid sequence shares several unusual substitutions with other nematode globins. Like the abundant pseudocoelomic A. suum hemoglobin it has a Tyr at B10 and a Gln at E7, substitutions thought to be determinants of high affinity. However, the 10-fold lower oxygen affinity of body wall globin suggests that in this molecule Tyr(B10) does not form an additional hydrogen bond with the heme bound oxygen. Evolutionary analysis of the nematode globins suggests that the monodomain myoglobin-like molecules and the two-domain hemoglobin-like molecules diverged about 500 million years ago, well before the divergence of the ascarid genera Ascaris and Pseudoterranova. The absence of introns in the A. suum myoglobin, in contrast to other nematode globin genes, is consistent with the hypothesis that during evolution intron elimination was the predominant event.
从寄生线虫猪蛔虫成虫的体壁中纯化出珠蛋白。对内部肽片段进行测序，并通过聚合酶链反应分离出编码154个氨基酸的多肽的cDNA。该多肽缺乏信号序列，确定其为胞质肌红蛋白样物质。天然蛋白为二聚体。预测的氨基酸序列与其他线虫珠蛋白有几个不同寻常的取代。与丰富的假体腔猪蛔虫血红蛋白一样，它在B10位有一个酪氨酸，在E7位有一个谷氨酰胺，这些取代被认为是高亲和力的决定因素。然而，体壁珠蛋白的氧亲和力低10倍，这表明在该分子中，酪氨酸（B10）与血红素结合的氧不形成额外的氢键。对线虫珠蛋白的进化分析表明，单结构域肌红蛋白样分子和双结构域血红蛋白样分子大约在5亿年前分化，早于蛔科属蛔虫和假新蛔属的分化。与其他线虫珠蛋白基因不同，猪蛔虫肌红蛋白中没有内含子，这与进化过程中内含子消除是主要事件的假设一致。
