Studies on solution structures of a1-antutrypsin derived C-terminal peptide (C36)

• Main Authors: chia-mon Chang, 張家萌
• Other Authors: mei-feng Jeng
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/52288078443960229865

碩士 === 國立成功大學 === 生物科技研究所碩博士班 === 91 === á1-antitrypsin (AAT) is an inhibitor of serine protease in general and its most important target enzyme is neutrophil elastase. AAT, like other serpins, presents a reactive site region as a proteinase accessible loop, thus mimicking an ideal substrate to the target enzyme. Formation of a 1:1 molar complex between serpin and enzyme is accompanied by an irreversible molecular transition of AAT. Following complex formation and hydrolysis of the reactive site peptide bond, a ~ 4 kDa carboxy terminal fragment of the inhibitor is generated (C36). C36 has been pronounced tendency to aggregate and form amyloid fibrils. C36 fibrils morphologically appear very similar to Alzheimer amyloid â fibrils formation. This peptide is involved in many physiological functions: It regulates inflammatory transcription factors in primary human monocytes and activates the production of PPARá, PPARã which will result in atherosclerosis. C36 peptide has been found in atherosclerosclerotic plaques, therefore C36 might play an important role in the pathogenesis of atherosclerosis. á1-antitrypsin may influence amyloid â fibril processing, affecting both promotion and inhibition of fibrillogenesis. Detailed examination of C36 structure will lead us to a better elucidation for the structure determinants regarding its mechanism for amyloid fibril formation and its structure-function relationship. First, circular dichroic spectra of C36 in aqueous solution-2mM SDS/10mM Na2HPO4 and in different membrane-mimicking environment 240mM SDS micelle , 3 mM DPC micelle and 60% TFE at various pH indicate that (i) the content of á-helix structure of C36 in aqueous solution contain 2 mM SDS is increased with decrease of pH. (ii) the content of á-helix structure of C36 in TFE membrane—mimicking environment is higher with increase of pH. (iii) in SDS micelle, C36 contains more â-strand structures than in TFE. (iv) in SDS micelle, the secondary structures of C36 are almost the same when pH below 7.4. C36 forms more â-stranded structure IV at lower pH than at pH > 8. This phenomen is similar to that in physiological condition. Under physiological condition, more â-stranded structure facilitates C36 to form a thinned-out fibrous cap of atherosclerosis plaque . (v) in TFE, C36 facilitates á-helix structure. We prospected the solution structure of C36 in the sodium dodecyl sulphate (SDS) micelle, pH 4.8, by NMR method it exists three â-strands. Unlike other solution structure of amyloid peptide which forms á-helix in SDS micelle, we proposed that threeβstrands protofilaments will then aggregate to form fibrils which result in plaque. These results may suggest that C36 may provide a good model for the investigation of Amyloid fibril formation.