Acid-induced assembly of a reconstituted silk protein system

Silk cocoons are reconstituted into an aqueous suspension, and protein stability is investigated by comparing the protein's response to hydrochloric acid and sodium chloride. Aggregation occurs for systems mixed with hydrochloric acid, while sodium chloride over the same range of concentrations does not cause aggregation. We measure the structures present on the protein and aggregate length scales in these solutions using both optical and small-angle neutron scattering, while mass spectrometry techniques shed light on a possible mechanism for aggregate formation. We find that the introduction of acid modulates the aggregate size and pervaded volume of the protein, an effect that is not observed with salt.