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 at <8 mM hydrochloric acid that is not correlated to protein protonation, while sodium chloride over the same range of concentrations does not cause aggregation. We measure the structures present on the protein and aggregate lengthscales in these solutions using both optical and 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.