Goldstein L A, Heath E C
J Biol Chem. 1984 Jul 25;259(14):9212-7.
The biosynthesis of rat haptoglobin, a hetrotetrameric glycoprotein (alpha 2 beta 2), requires the post-translational cleavage of its glycosylated primary translation product (prohaptoglobin) into alpha- and beta-subunits (Hanley, J. M., Haugen, T. H., and Heath, E. C. (1983) J. Biol. Chem. 258, 7858-7869). To elucidate the site(s) at which proteolytic cleavage occurs in prohaptoglobin, we have isolated a recombinant plasmid whose cDNA insert encodes for the carboxyl terminus of the alpha-subunit, the alpha beta-subunit junction, and the beta-subunit region, and also the entire 3'-untranslated region (142 base pairs) and poly(A) tail (55 base pairs) of the mRNA. A single arginine residue was found at the alpha beta-subunit junction region -Val-Gln-Arg-Ile-Ile-Gly-Gly-of prohaptoglobin. The sequence homology of this region with serine protease precursors suggests that post-translational processing of prohaptoglobin involves cleavage of the Arg-Ile bond and extraction of the Arg residue. The rat beta-subunit shows a high degree (approximately 80%) of sequence homology with its human counterpart although it possesses only two of the four N-glycosylation sites present in human haptoglobin beta-subunit.
大鼠触珠蛋白（一种异四聚体糖蛋白，α2β2）的生物合成需要将其糖基化的初级翻译产物（触珠蛋白原）进行翻译后切割，形成α亚基和β亚基（Hanley, J. M., Haugen, T. H., and Heath, E. C. (1983) J. Biol. Chem. 258, 7858 - 7869）。为了阐明触珠蛋白原中蛋白水解切割发生的位点，我们分离了一个重组质粒，其cDNA插入片段编码α亚基的羧基末端、αβ亚基连接区、β亚基区域，以及mRNA的整个3'非翻译区（142个碱基对）和聚腺苷酸尾（55个碱基对）。在触珠蛋白原的αβ亚基连接区 -Val-Gln-Arg-Ile-Ile-Gly-Gly- 发现了一个精氨酸残基。该区域与丝氨酸蛋白酶前体的序列同源性表明，触珠蛋白原的翻译后加工涉及Arg-Ile键的切割和Arg残基的去除。大鼠β亚基与其人类对应物具有高度（约80%）的序列同源性，尽管它仅拥有人类触珠蛋白β亚基中四个N-糖基化位点中的两个。
