A new class of proteinaceous biomaterial with unprecedented properties in unicellular eukaryotes

Biomaterials fundamentally reshape material use, providing superior properties and sustainable alternatives relevant to medicine, textiles, and high-tech applications. Research mainly focuses on animal-derived proteinaceous biomaterials, which remain challenging to reproduce while retaining their remarkable properties. We discovered that the shells of tintinnid ciliates, a group of planktonic unicellular eukaryotes, are composed of self-assembling structural proteins. The shells form in water, are structurally diverse, and show exceptional resistance against high temperatures and the strongest chemicals. Combining single-cell transcriptomics and mass-spectrometry of the shells, we identified the amino acid sequences of the shell-forming proteins. They are exceptionally rich in aromatic residues and possess a unique architecture with flexible, unfolded segments connecting highly stable beta-sheets. This easily accessible system promises new aspects to advance current biomaterial design.