ALPHA(1)-ANTITRYPSIN MMALTON (PHE(52)-DELETED) FORMS LOOP-SHEET POLYMERS IN-VIVO - EVIDENCE FOR THE C-SHEET MECHANISM OF POLYMERIZATION

被引:133
作者
LOMAS, DA
ELLIOTT, PR
SIDHAR, SK
FOREMAN, RC
FINCH, JT
COX, DW
WHISSTOCK, JC
CARRELL, RW
机构
[1] MRC CTR, MOLEC BIOL LAB, CAMBRIDGE CB2 2QH, ENGLAND
[2] UNIV SOUTHAMPTON, DEPT PHYSIOL & PHARMACOL, SOUTHAMPTON SO9 3TU, HANTS, ENGLAND
[3] HOSP SICK CHILDREN, DEPT PEDIAT, TORONTO, ON M5G 1X8, CANADA
[4] HOSP SICK CHILDREN, DEPT GENET, TORONTO, ON M5G 1X8, CANADA
基金
英国惠康基金;
关键词
D O I
10.1074/jbc.270.28.16864
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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.
引用
收藏
页码:16864 / 16870
页数:7
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