Towards the understanding of slime formation by the Velvet worm (Onychophora)

What is it about?

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. The secreted slime has many remarkable characteristics: (i) it exhibits high extensibility and tensile strength (ultimate tensile strength of 101.9 +/- 20.1 MPa); (ii) it rapidly phase-separates from a concentrated dope solution into the adhesive slime as soon as it is ejected out of the slime gland; (iii) it is water soluble and (iv) it can reversibly form fibers after being re-dissolved. which draw our attention as a novel biopolymer candidates. Combining transcriptomic and proteomic studies, the full-length sequences of major proteins forming the sticky slime of the velvet worm have been obtained, revealing key characteristics that contribute to slime self-assembly. The presence of beta-sheet domains is predicted and detected in the slime by solid-state NMR. The limited number of cysteine residues detected at both termini of the large molecular weight proteins leads to the formation of large, disulphide-bonded multi-protein complexes. Furthermore, a low complexity sequence region located at the N-terminus of these proteins exhibits liquid-liquid phase separation, which may play a central role during slime biofabrication.

Featured Image

Photo by Demi Kwant on Unsplash

Photo by Demi Kwant on Unsplash

Why is it important?

Our results unveil new molecular insights into the velvet worm slime and its self-assembly mechanisms that provide bioinspired lessons for future synthesis of green biopolymers. While there remain outstanding questions pertaining to the reversible liquid-to-solid transition of the viscous slime into strong adhesive fibers, the complete molecular characterization of all main slime proteins is an important step in this direction and paves the way towards sustainable fabrication of fully recyclable (bio)polymeric materials.