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Distinct properties of wild‐type and the amyloidogenic human cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type
Author(s) -
Calero Miguel,
Pawlik Monika,
Soto Claudio,
Castaño Eduardo M.,
Sigurdsson Einar M.,
Kumar Asok,
Gallo Gloria,
Frangione Blas,
Levy Efrat
Publication year - 2001
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2001.00256.x
Subject(s) - cystatin , cystatin c , chemistry , amyloidosis , biochemistry , wild type , fibrillogenesis , proteolysis , tryptophan , microbiology and biotechnology , circular dichroism , amino acid , biology , mutant , gene , in vitro , enzyme , medicine , renal function
Variant human cystatin C (L68Q) is an amyloidogenic protein. It deposits in the cerebral vasculature of Icelandic patients with cerebral amyloid angiopathy, leading to stroke. Wild‐type and variant cystatin C are cysteine proteinase inhibitors which form concentration dependent inactive dimers; however, variant cystatin C dimerizes at lower concentrations and has an increased susceptibility to a serine protease. We studied the effect of the L68Q amino acid substitution on cystatin C properties, utilizing full length cystatin C purified in mild conditions from media of cells stably transfected with either the wild‐type or variant cystatin C genes. The variant cystatin C forms fibrils in vitro detectable by electron microscopy in conditions in which the wild‐type protein forms amorphous aggregates. We also show by circular dichroism, steady‐state fluorescence and Fourier‐transformed infrared spectroscopy that the amino acid substitution modifies cystatin C structure by destabilizing α‐helical structures and exposing the tryptophan residue to a more polar environment, yielding a more unfolded molecule. These spectral changes demonstrate that variant cystatin C has a three‐dimensional structure different from that of the wild‐type protein. The structural differences between variant and wild‐type cystatin C account for the susceptibility of the variant protein to unfolding, proteolysis and fibrillogenesis.