Distinct properties of wild-type and the amyloidogenic human cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type.

Abstract

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 alpha-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.

• Authors: M Calero, M Pawlik, C Soto, E M Castaño, E M Sigurdsson, A Kumar, G Gallo, B Frangione, E Levy
• Journal: Journal of neurochemistry (J Neurochem) Vol. 77 Issue 2 Pg. 628-37 (Apr 2001) ISSN: 0022-3042 [Print] England
• PMID: 11299325 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• CST3 protein, human
• Codon
• Cystatin C
• Cystatins
• Nerve Tissue Proteins
• Recombinant Fusion Proteins
• Glutamine
• Leucine

Topics

• Amino Acid Substitution
• Animals
• Cerebral Amyloid Angiopathy (genetics, metabolism)
• Cerebral Hemorrhage (genetics, metabolism)
• Chemical Phenomena
• Chemistry, Physical
• Chickens
• Circular Dichroism
• Codon (genetics)
• Computer Simulation
• Cystatin C
• Cystatins (chemistry, genetics)
• Dimerization
• Glutamine (chemistry)
• Humans
• Leucine (chemistry)
• Microscopy, Electron
• Models, Molecular
• Mutation, Missense
• Nerve Tissue Proteins (chemistry, genetics)
• Protein Conformation
• Protein Folding
• Protein Structure, Secondary
• Recombinant Fusion Proteins (chemistry)
• Species Specificity
• Spectroscopy, Fourier Transform Infrared
• Transfection