Abstrakt

Forisomes are giant self-assembling mechanoproteins that undergo reversiblestructural changes in response to Ca2+and various other stimuli. Artificial for-isomes assembled from the monomer MtSEO-F1 can be used as smart bioma-terials, but the molecular basis of their functionality is not understood. Todetermine the role of protein polymerization in forisome activity, we tested theCa2+association of MtSEO-F1 dimers (the basic polymerization unit) by circu-lar dichroism spectroscopy and microscale thermophoresis. We found that sol-uble MtSEO-F1 dimers neither associate with Ca2+nor undergo structuralchanges. However, polarization modulation infrared reflection absorptionspectroscopy revealed that aggregated MtSEO-F1 dimers and fully-assembledforisomes associate with Ca2+, allowing the hydration of poorly-hydrated pro-tein areas. A change in the signal profile of complete forisomes indicated thatCa2+interacts with negatively-charged regions in the protein complexes thatonly become available during aggregation. We conclude that aggregation isrequired to establish the Ca2+response of forisome polymers.