Limited Proteolysis Reveals That Amyloids from the 3D Domain-Swapping Cystatin B Have a Non-Native β-Sheet Topology

Limited Proteolysis Reveals That Amyloids from the 3D Domain-Swapping Cystatin B Have a... 3D domain-swapping proteins form multimers by unfolding and then sharing of secondary structure elements, often with native-like interactions. Runaway domain swapping is proposed as a mechanism for folded proteins to form amyloid fibres, with examples including serpins and cystatins. Cystatin C amyloids cause a hereditary form of cerebral amyloid angiopathy whilst cystatin B aggregates are found in cases of Unverricht-Lundborg Syndrome, a progressive form of myoclonic epilepsy. Under conditions that favour fibrillisation, cystatins populate stable 3D domain-swapped dimers both in vitro and in vivo that represent intermediates on route to the formation of fibrils. Previous work on cystatin B amyloid fibrils revealed that the α-helical region of the protein becomes disordered and identified the conservation of a continuous 20-residue elongated β-strand (residues 39–58), the latter being a salient feature of the dimeric 3D domain-swapped structure. Here we apply limited proteolysis to cystatin B amyloid fibrils and show that not only the α-helical N-terminal of the protein (residues 1–35) but also the C-terminal of the protein (residues 80–98) can be removed without disturbing the underlying fibril structure. This observation is incompatible with previous models of cystatin amyloid fibrils where the β-sheet is assumed to retain its native antiparallel arrangement. We conclude that our data favour a more generic, at least partially parallel, arrangement for cystatin β-sheet structure in mature amyloids and propose a model that remains consistent with available data for amyloids from either cystatin B or cystatin C. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Molecular Biology Elsevier

Limited Proteolysis Reveals That Amyloids from the 3D Domain-Swapping Cystatin B Have a Non-Native β-Sheet Topology

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Publisher
Elsevier
Copyright
Copyright © 2015 Elsevier Ltd
ISSN
0022-2836
D.O.I.
10.1016/j.jmb.2015.05.014
Publisher site
See Article on Publisher Site

Abstract

3D domain-swapping proteins form multimers by unfolding and then sharing of secondary structure elements, often with native-like interactions. Runaway domain swapping is proposed as a mechanism for folded proteins to form amyloid fibres, with examples including serpins and cystatins. Cystatin C amyloids cause a hereditary form of cerebral amyloid angiopathy whilst cystatin B aggregates are found in cases of Unverricht-Lundborg Syndrome, a progressive form of myoclonic epilepsy. Under conditions that favour fibrillisation, cystatins populate stable 3D domain-swapped dimers both in vitro and in vivo that represent intermediates on route to the formation of fibrils. Previous work on cystatin B amyloid fibrils revealed that the α-helical region of the protein becomes disordered and identified the conservation of a continuous 20-residue elongated β-strand (residues 39–58), the latter being a salient feature of the dimeric 3D domain-swapped structure. Here we apply limited proteolysis to cystatin B amyloid fibrils and show that not only the α-helical N-terminal of the protein (residues 1–35) but also the C-terminal of the protein (residues 80–98) can be removed without disturbing the underlying fibril structure. This observation is incompatible with previous models of cystatin amyloid fibrils where the β-sheet is assumed to retain its native antiparallel arrangement. We conclude that our data favour a more generic, at least partially parallel, arrangement for cystatin β-sheet structure in mature amyloids and propose a model that remains consistent with available data for amyloids from either cystatin B or cystatin C.

Journal

Journal of Molecular BiologyElsevier

Published: Jul 31, 2015

References

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