Gupta R P, Hook G E
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Biochem Biophys Res Commun. 1988 May 31;153(1):470-8. doi: 10.1016/s0006-291x(88)81248-8.
The major secretory product of Clara cells is a low molecular weight protein (CCSP) whose extracellular function, at this time, is not known. The primary translation product of its mRNA is a protein with molecular weight approximately 1 kD greater than that of the native secreted protein (6.0 kD). The primary translation product is not detected in incubated lung tissue, only the secretory protein is found. The primary translation product is trypsin sensitive whereas the secretory protein is not. Cell free translation of the mRNA in the presence of microsomes results in cleavage of the signal peptide and the appearance of the lower molecular weight trypsin-resistant secretory protein. These data indicate that the low molecular weight Clara cell secretory protein is synthesized as a larger, trypsin sensitive, protein. Passage of the protein into the cisternae of the endoplasmic reticulum results in loss of the signal peptide and alterations to the tertiary structure of the protein rendering it trypsin insensitive.
克拉拉细胞的主要分泌产物是一种低分子量蛋白质（克拉拉细胞分泌蛋白，CCSP），目前其细胞外功能尚不清楚。其mRNA的初级翻译产物是一种分子量比天然分泌蛋白（6.0 kD）大约1 kD的蛋白质。在孵育的肺组织中未检测到初级翻译产物，仅发现了分泌蛋白。初级翻译产物对胰蛋白酶敏感，而分泌蛋白则不敏感。在微粒体存在的情况下对mRNA进行无细胞翻译会导致信号肽的切割以及出现较低分子量的抗胰蛋白酶分泌蛋白。这些数据表明，低分子量的克拉拉细胞分泌蛋白是以一种更大的、对胰蛋白酶敏感的蛋白质形式合成的。该蛋白质进入内质网池后会导致信号肽的丢失以及蛋白质三级结构的改变，使其对胰蛋白酶不敏感。
