title: Fibrillogenic oligomers of human cystatin C are formed by propagated domain swapping.
abstract: Cystatin C and the prion protein have been shown to form dimers via three-dimensional domain swapping, and this process has also been hypothesized to be involved in amyloidogenesis. Production of oligomers of other amyloidogenic proteins has been reported to precede fibril formation, suggesting oligomers as intermediates in fibrillogenesis. A variant of cystatin C, with a Leu68-->Gln substitution, is highly amyloidogenic, and carriers of this mutation suffer from massive cerebral amyloidosis leading to brain hemorrhage and death in early adulthood. This work describes doughnut-shaped oligomers formed by wild type and L68Q cystatin C upon incubation of the monomeric proteins. Purified oligomers of cystatin C are shown to fibrillize faster and at a lower concentration than the monomeric protein, indicating a role of the oligomers as fibril-assembly intermediates. Moreover, the present work demonstrates that three-dimensional domain swapping is involved in the formation of the oligomers, because variants of monomeric cystatin C, stabilized against three-dimensional domain swapping by engineered disulfide bonds, do not produce oligomers upon incubation under non-reducing conditions. Redox experiments using wild type and stabilized cystatin C strongly suggest that the oligomers, and thus probably the fibrils as well, are formed by propagated domain swapping rather than by assembly of domain-swapped cystatin C dimers.
authors.affiliation: Department of Clinical Chemistry, Lund University Hospital, S-221 85 Lund, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Wahlbom
authors.affiliation: Department of Clinical Chemistry, Lund University Hospital, S-221 85 Lund, Sweden.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Clinical Chemistry, Lund University Hospital, S-221 85 Lund, Sweden.
authors.forename: Veronica
authors.initials: V
authors.lastname: Lindström
authors.affiliation: Department of Clinical Sciences, Lund University, S-223 62 Lund, Sweden.
authors.forename: Eric
authors.initials: E
authors.lastname: Carlemalm
authors.affiliation: Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University and Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Grunwaldzka 6, PL-60-780 Poznan, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Jaskolski
authors.affiliation: Department of Clinical Chemistry, Lund University Hospital, S-221 85 Lund, Sweden. Electronic address: anders.grubb@med.lu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Grubb
mesh_terms: D000682:Amyloid / Q000737:chemistry; D000818:Animals; D002645:Chickens; D055316:Cystatin C; D015891:Cystatins / Q000737:chemistry*; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D005973:Glutamine / Q000737:chemistry; D006801:Humans; D007930:Leucine / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011328:Prions / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D000682:Amyloid; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D011328:Prions; D005973:Glutamine; D007930:Leucine