Human
cystatin C (HCC)
amyloid angiopathy (HCCAA) is characterized by tissue deposition of
amyloid fibrils in blood vessels, which can lead to recurrent
hemorrhagic stroke. Wild-type HCC forms part of the
amyloid deposits in brain arteries of elderly people with
amyloid angiopathy. A point mutation causing a
glutamine to a
leucine substitution at residue 68 in the HCC
polypeptide chain greatly increases the amyloidogenic propensity of HCC and causes a more severe
cerebral hemorrhage and premature death in young adults. In this study, we used molecular dynamics simulations to assess the importance of
disulfide bridge formation upon the stability of
chicken cystatin and how this may influence the propensity for
amyloid formation. We found that
disulfide bridge formation between Cys95 and Cys115 in human
cystatin played a critical role in overall protein stability. Importantly, Cys95-Cys115 influenced
cystatin structure in regions of the
protein that play key roles in the protein-folding transitions that occur, which enable
amyloid fibril formation. We hypothesized that correct
disulfide bridge formation is a critical step in stabilizing
cystatin toward its native conformation. Disrupting Cys95-Cys115
disulfide bridge formation within
cystatin appears to significantly enhance the amyloidogenic properties of this
protein. In addition, by combining in silico studies with our previous experimental results on Eps1, a
molecular chaperone of the PDI family, we proposed that age-related HCCAA, may possess a different pathogenic mechanism compared with its amyloidogenic counterpart, the early onset amyloidogenic
cystatin-related CAA.