ALPHA(1)-ANTITRYPSIN MMALTON (PHE(52)-DELETED) FORMS LOOP-SHEET POLYMERS IN-VIVO - EVIDENCE FOR THE C-SHEET MECHANISM OF POLYMERIZATION
ALPHA(1)-ANTITRYPSIN MMALTON (PHE(52)-DELETED) FORMS LOOP-SHEET POLYMERS IN-VIVO - EVIDENCE FOR THE C-SHEET MECHANISM OF POLYMERIZATION
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DOI：
10.1074/jbc.270.28.16864
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发表时间：
1995-07-14
影响因子：
4.8
通讯作者：
CARRELL, RW
中科院分区：
文献类型：
--
作者：
LOMAS, DA;ELLIOTT, PR;CARRELL, RW
α(1)-抗胰蛋白酶的Z （Glu(342) -> Lys）和Siiyama （Ser(53) -> Phe）缺陷变体通过环-片聚合导致肝细胞内质网中的蛋白质保留，其中一个分子的反应中心环插入另一个分子的β -褶片。我们在这里表明，与相同的肝包涵体相关的抗胰蛋白酶mmalton （Phe(52)-deleted）也在爪蟾卵母细胞加工的内糖苷酶h敏感阶段保留，并在体内自发形成聚合物。这些聚合物是从Mmalton/QO （null）博尔顿杂合子的血浆中获得的，比其他抗胰蛋白酶聚合物短得多，并且包含一个反应性中心环切割物种。从血浆中也分离到抗胰蛋白酶单体突变体。在横向尿素梯度凝胶电泳上，单体组分具有正常的展开转变，在体外形成聚合物比M更容易，但比Z更容易，抗胰蛋白酶。a- β片比Z抗胰蛋白酶更容易容纳反应性中心环肽，而Z抗胰蛋白酶则比天然M抗胰蛋白酶更不容易接受。抗胰蛋白酶Mmalton中A片的非接受构象对动力学参数、sds稳定配合物的形成、S到R的转变以及潜在构象的形成影响不大。与抗凝血酶变体Rouen VI相关的短链聚合物的类似发现的结果比较（Bruce， D., Perry， D., Borg， J.-Y.）。卡雷尔，r.w.，沃德尔，m.r.（1994）。Invest. 94, 2265-2274)表明聚合反应的机理比先前提出的更为复杂。Z， Siiyama和Mmalton突变有利于抗胰蛋白酶分子的构象变化，使其成为天然形式和潜伏形式之间的中间形式。这将涉及到反应性环在a片中的部分过插入，并伴有1C链的位移和随后的环- c片聚合。
The Z (Glu(342) --> Lys) and Siiyama (Ser(53) --> Phe) deficiency variants of alpha(1)-antitrypsin result in the retention of protein in the endoplasmic reticulum of the hepatocyte by loop-sheet polymerization in which the reactive center loop of one molecule is inserted into a beta-pleated sheet of a second. We show here that antitrypsin Mmal-ton (Phe(52)-deleted), which is associated with the same liver inclusions, is also retained at an endoglycosidase H-sensitive stage of processing in the Xenopus oocyte and spontaneously forms polymers in vivo. These polymers, obtained from the plasma of an Mmalton/QO (null) bolton heterozygote, were much shorter than other antitrypsin polymers and contained a reactive center loop-cleaved species. Monomeric mutant antitrypsin was also isolated from the plasma. The monomeric component had a normal unfolding transition on transverse urea gradient gel electrophoresis and formed polymers in vitro more readily than M, but less readily than Z, antitrypsin, The A beta-sheet accommodated a reactive center loop peptide much less readily than Z antitrypsin, which in turn was less receptive than native M antitrypsin. The nonreceptive conformation of the A sheet in antitrypsin Mmalton had little effect on kinetic parameters, the formation of SDS-stable complexes, the S to R transition, and the formation of the latent conformation.Comparison of the results with similar findings of short chain polymers associated with the antithrombin variant Rouen VI (Bruce, D., Perry, D., Borg, J.-Y., Carrell, R. W., and Wardell, M. R. (1994) J. Clin. Invest. 94, 2265-2274) suggests that polymerization is more complicated than the mechanism proposed earlier. The Z, Siiyama, and Mmalton mutations favor a conformational change in the antitrypsin molecule to an intermediate between the native and latent forms. This would involve a partial overinsertion of the reactive loop into the A sheet with displacement of strand 1C and consequent loop-C sheet polymerization.