Kageyama T, Tanabe K, Koiwai O
Department of Biochemistry, Kyoto University, Aichi, Japan.
J Biol Chem. 1990 Oct 5;265(28):17031-8.
In order to clarify the structure and development of rabbit pepsinogens, purification and molecular cloning of these proteins were performed at various developmental stages. Several pepsinogens were isolated, and they were classified as pepsinogens F and M, and into pepsinogen groups I, II, and III. The relative levels and specific activities of the various pepsinogens changed significantly during development. Pepsinogens F and M were present only at the early postnatal stage, and their level was higher than those of other pepsinogens at this stage. Pepsinogens in groups I, II, and III were the predominant zymogens at the late postnatal stage. cDNA clones encoding all of these pepsinogens were obtained, with the exception of pepsinogens I and M, and the nucleotide sequences were determined. Each cDNA contained a leader region (signal peptide), a pro-region (activation segment), and a pepsin region, of 15, 44, and 328 residues, respectively, with the exception of the cDNA for pepsinogen F in which the pro- and pepsin regions were composed of 43 and 330 residues, respectively. Pepsinogens in groups II and III exhibited a high degree of similarity with one another, whereas many substitutions were found in pepsinogen F. A unique substitution in the activation segment of pepsinogen F, namely, Gly----Asp at position 21, was found, which made the structural features of this segment more specific. A phylogenic tree was constructed from the differences in nucleotide sequences and showed clearly that each pepsinogen in groups II and III could be classified as pepsinogen A, a major pepsinogen in mammals. Pepsinogen F diverged significantly from these groups and may be a new type of pepsinogen. Northern analysis revealed that the expression of the gene for pepsinogen F was restricted to the early postnatal stage, and the expression of genes for pepsinogens in groups II and III was detected predominantly at later stages, a result that shows the switching of gene expression from fetal pepsinogen to adult pepsinogens during development.
为了阐明兔胃蛋白酶原的结构和发育过程，在不同发育阶段对这些蛋白质进行了纯化和分子克隆。分离出了几种胃蛋白酶原，并将它们分为F型和M型胃蛋白酶原，以及I、II和III组胃蛋白酶原。在发育过程中，各种胃蛋白酶原的相对水平和比活性发生了显著变化。F型和M型胃蛋白酶原仅在出生后早期存在，且在此阶段其水平高于其他胃蛋白酶原。I、II和III组胃蛋白酶原是出生后晚期的主要酶原。除I型和M型胃蛋白酶原外，获得了编码所有这些胃蛋白酶原的cDNA克隆，并测定了核苷酸序列。每个cDNA分别包含一个由15个、44个和328个残基组成的前导区（信号肽）、前肽区（激活片段）和胃蛋白酶区，不过F型胃蛋白酶原的cDNA中，前肽区和胃蛋白酶区分别由43个和330个残基组成。II组和III组胃蛋白酶原彼此间表现出高度相似性，而在F型胃蛋白酶原中发现了许多取代。在F型胃蛋白酶原的激活片段中发现了一个独特的取代，即在第21位由甘氨酸突变为天冬氨酸，这使得该片段的结构特征更加独特。根据核苷酸序列的差异构建了系统发育树，结果清楚地表明，II组和III组中的每种胃蛋白酶原都可归类为哺乳动物中的主要胃蛋白酶原A。F型胃蛋白酶原与这些组有显著差异，可能是一种新型胃蛋白酶原。Northern分析表明，F型胃蛋白酶原基因的表达仅限于出生后早期，而II组和III组胃蛋白酶原基因的表达主要在后期检测到，这一结果表明在发育过程中基因表达从胎儿胃蛋白酶原向成人胃蛋白酶原发生了转换。
