Abstact

We present the crystal structure of an immunoglobulin light-chain-like domain, CTLA-4, as a strand-swapped dimer displaying cis-trans proline isomerisation and native-like hydrogen bonding. We also show that CTLA-4 can form amyloid-like fibres and amorphous deposits explainable by the same strand swapping. Our results suggest a molecular basis for the pathological aggregation of immunoglobulin domains and why amyloid-like fibres are more often composed of homologous rather than heterologous subunits.