Krishnasamy S, Teng A L, Dhand R, Schultz R M, Gross N J
Research Service, Hines Veterans Affairs Hospital, Hines, Illinois 60141, USA.
Am J Physiol. 1998 Nov;275(5):L969-75. doi: 10.1152/ajplung.1998.275.5.L969.
We recently reported the purification and partial amino acid sequence of "surfactant convertase," a 72-kDa glycoprotein involved in the extracellular metabolism of lung surfactant (S. Krishnasamy, N. J. Gross, A. L. Teng, R. M. Schultz, and R. Dhand. Biochem. Biophys. Res. Commun. 235: 180-184, 1997). We report here the isolation of a cDNA clone encoding putative convertase from a mouse lung cDNA library. The cDNA spans a 1,836-bp sequence, with an open reading frame encoding 536 amino acid residues in the mature protein and an 18-amino acid signal peptide at the NH2 terminus. The deduced amino acid sequence matches the four partial amino acid sequences (68 residues) that were previously obtained from the purified protein. The deduced amino acid sequence contains an 18-amino acid residue signal peptide, a serine active site consensus sequence, a histidine consensus sequence, five potential N-linked glycosylation sites, and a COOH-terminal secretory-type sequence His-Thr-Glu-His-Lys. Primer-extension analysis revealed that transcription starts 29 nucleotides upstream from the start codon. Northern blot analysis of RNA isolated from various mouse organs showed that convertase is expressed in lung, kidney, and liver as a 1,800-nucleotide-long transcript. The nucleotide and amino acid sequences of putative convertase are 98% homologous with mouse liver carboxylesterase. It thus may be the first member of the carboxylesterase family (EC 3.1.1.1) to be expressed in lung parenchyma and the first with a known physiological function.
我们最近报道了“表面活性剂转化酶”的纯化及部分氨基酸序列，这是一种参与肺表面活性剂细胞外代谢的72 kDa糖蛋白（S. Krishnasamy、N. J. Gross、A. L. Teng、R. M. Schultz和R. Dhand，《生物化学与生物物理研究通讯》235: 180 - 184, 1997）。我们在此报告从鼠肺cDNA文库中分离出一个编码假定转化酶的cDNA克隆。该cDNA跨度为1836 bp序列，其开放阅读框编码成熟蛋白中的536个氨基酸残基，在NH2末端有一个18个氨基酸的信号肽。推导的氨基酸序列与先前从纯化蛋白中获得的四个部分氨基酸序列（68个残基）相匹配。推导的氨基酸序列包含一个18个氨基酸残基的信号肽、一个丝氨酸活性位点共有序列、一个组氨酸共有序列、五个潜在的N - 连接糖基化位点以及一个COOH末端分泌型序列His - Thr - Glu - His - Lys。引物延伸分析显示转录起始于起始密码子上游29个核苷酸处。对从各种小鼠器官分离的RNA进行的Northern印迹分析表明，转化酶在肺、肾和肝脏中以1800个核苷酸长的转录本形式表达。假定转化酶的核苷酸和氨基酸序列与小鼠肝脏羧酸酯酶的同源性为98%。因此，它可能是羧酸酯酶家族（EC 3.1.1.1）中第一个在肺实质中表达且具有已知生理功能的成员。
