Complete sequences of the velvet worm slime proteins reveal that slime formation is enabled by disulfide bonds and intrinsically disordered regions

The slime of velvet worms (Onychophora) is a strong and fully biodegradable protein material, which upon ejection undergoes a fast liquid-to-solid transition to ensnare prey. However, the molecular mechanisms of slime self-assembly are still not well understood, notably because the primary structures of slime proteins are yet unknown. Combining transcriptomic and proteomic studies, we have obtained the complete primary sequences of slime proteins and identified key features for slime self-assembly. The high molecular weight slime proteins contain Cys residues at the N- and C-termini that mediate the formation of multi-protein complexes via disulfide bonding. Low complexity domains in the N-termini were also identified and their propensity for liquid-liquid phase separation established, which may play a central role for slime biofabrication. Using solid-state nuclear magnetic resonance, rigid and flexible domains of the slime proteins were mapped to specific peptide domains. The complete sequencing of major slime proteins is an important step towards sustainable fabrication of polymers inspired by the velvet worm slime.