Figure 4: Self-assembly mechanism of resilin proteins.

(a) Model of chain folding, fibrillar structure formation and physical stress for exon I. (1) Possible chain folding intra- and inter-molecular schemes. (2) Fibril assembly with larger-chain hydrophilic blocks in contact with the surrounding aqueous solution. (3) The assembly process upon heating and alignment of fibrils and interactions promoted by physical stress. To fully understand the nanostructure changes in the thermal transitions, the surface morphology of exon I was observed in AFM phase images and by SEM before (4) and right after (5) thermal treatments. The black scale bar is 200 nm and the white is 30 nm. (b) Model of chain folding, micelle and globule formation and physical stress for exon III. (1) Possible chain folding intra- and inter-molecular schemes. (2) Micelle and globule assembly driven by hydrophilic-hydrophobic multiblock co-polymers with a larger hydrophobic block at the middle of the chain, resulting in the formation of the hydrophobic core of irregular sized globular proteins. (3) The assembly process upon heating and alignment of globules with ordered, water-excluding, core-containing micelles. The surface morphology of exon III peptides were also observed in AFM phase images and by SEM before (4) and right after (5) thermal treatments. The black scale bar is 200 nm, the white is 30 nm and the green is 5.5 nm. (c) Proposed model of resilin elasticity in the process of energy input and release. (1) Possible chain folding intra- and inter-molecular schemes. (2) Structure assembly and relaxed network driven by hydrophilic–hydrophobic–hydrophilic polymers to form water-swollen structures with irregular sized micelles crosslinked by fibrils. (3) The assembly process upon heating and tighter elastic network after energy input. The surface morphology of full-length resilin was observed in the AFM phase images and by SEM before (4) and right after (5) thermal treatments. The black scale bar is 200 nm and the white is 30 nm.