Fig. 2: Highly extensible fibers made by recombinant Sbp5-2 analog proteins.

a Schematic illustration of the spatial distribution of different proteins in scallop byssus. In the thread region, Sbp5-2 has been identified as the highest enriched protein (37.36%), among seven proteins. b Amino acid sequence of Sbp5-2 showing 14 highly identical flanking domains. Each TRM contains 2 Cys (C) (displayed in shade of orange), and several negative charged Asp (D) and/or Glu (E) (displayed in green font). rTRM7 was constructed rationally by fusing gene sequence of TRM8−14 marked in red dotted box. c The amino acid components of rTRM7 is compared with that of Sbp5-2. Amino acids composition and proportion of rTRM7 are both like that of Sbp5-2. Positively charged amino acids are shown in blue, negatively charged amino acids in green, and cysteine in orange. d Schematic illustration of fabricating rTRM7 fiber by drawing process. Freshly purified rTRM7 protein is firstly lyophilized and dissolved in HFIP at 200 mg/mL. Then, rTRM7 HFIP solution is casted into a film formed on CaCl₂ buffer surface. Finally, rTRM7 fiber is picked up from solution surface by using forceps. e Photographs of rTRM7 film (left) and fiber (right) in drawing process corresponding to d. f SEM image of microscopic sectional view of rTRM7 fiber. g X-ray fiber diffraction pattern of rTRM7 fiber. rTRM7 fiber shows the same pattern of cross-β strand as scallop byssal thread, in which the meridional reflection is ~4.67 Å and the equatorial reflection is ~9.27 Å.