| Summary: | 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.
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