The Internal Structure of the Velvet Worm Projectile Slime: A Small‐Angle Scattering Study

Abstract

For prey capture and defense, velvet worms eject an adhesive slime which has been established as a model system for recyclable complex liquids. Triggered by mechanical agitation, the liquid bio‐adhesive rapidly transitions into solid fibers. In order to understand this mechanoresponsive behavior, here, the nanostructural organization of slime components are studied using small‐angle scattering with neutrons and X‐rays. The scattering intensities are successfully described with a three‐component model accounting for proteins of two dominant molecular weight fractions and nanoscale globules. In contrast to the previous assumption that high molecular weight proteins—the presumed building blocks of the fiber core—are contained in the nanoglobules, it is found that the majority of slime proteins exist freely in solution. Only less than 10% of the slime proteins are contained in the nanoglobules, necessitating a reassessment of their function in fiber formation. Comparing scattering data of slime re‐hydrated with light and heavy water reveals that the majority of lipids in slime are contained in the nanoglobules with homogeneous distribution. Vibrating mechanical impact under exclusion of air neither leads to formation of fibers nor alters the bulk structure of slime significantly, suggesting that interfacial phenomena and directional shearing are required for fiber formation.

Phosphonated glycans as post-translational modifications of proteins in velvet worm slime

“…Biochemical analysis of slime from several species has been performed, revealing a primarily proteinaceous composition with components of different sizes. Mid-molecularweight (MMW) proteins together with small quantities of lipids (<1 %) were proposed to form nanoscale condensed liquid nanodroplets 4 , while low molecular weight (LMW) proteins may act as antimicrobial components 5 . However, several high molecular weight (HMW) proteins were shown to be the major structural component of slime fibers 3,[5][6][7][8][9] .…”

Peculiar Phosphonate Modifications of Velvet Worm Slime Revealed by Advanced Nuclear Magnetic Resonance and Mass Spectrometry

“…Previous biochemical analyses from several onychophoran species have revealed a primarily proteinaceous composition with components of different sizes. 4−6 Mid-molecular-weight (MMW) proteins and small quantities of lipids (<1%) were proposed to form condensed nanodroplets, 4 while lowmolecular-weight (LMW) proteins are proposed to act as antimicrobial components. 6 However, several high-molecularweight (HMW) proteins were shown to be the major structural component of slime fibers.…”

“…rowelli slime. 4,10 Deeper structural analysis of the 2-AEP moieties was performed by MAS-DNP and HCD-MS/MS. MAS-DNP provides enhanced sensitivity (Figure 3a and Figure S8), enabling detection and identification of carbon signals in endogenous abundance, and determination of proximity between carbon and phosphorus atoms by monitoring the magnetization transfer from 31 P to 13 C during cross-polarization (CP); as duration increases, carbons further from the phosphorus atom gradually appear on the spectra (Figure 3a, b).…”

“…According to previous SDS-PAGE analyses, this includes HMW monomers/complexes (232–429/478–634 kDa) or MMW (110 kDa) proteins in Eu. rowelli slime. , …”

“…Previous biochemical analyses from several onychophoran species have revealed a primarily proteinaceous composition with components of different sizes. − Mid-molecular-weight (MMW) proteins and small quantities of lipids (<1%) were proposed to form condensed nanodroplets, while low-molecular-weight (LMW) proteins are proposed to act as antimicrobial components . However, several high-molecular-weight (HMW) proteins were shown to be the major structural component of slime fibers. − Based on positive phosphostaining and elemental analysis of the HMW proteins from the Peripatopsidae species Euperipatoides rowelli , as well as the high content of divalent cations (Mg 2+ , Ca 2+ ), phosphate-mediated electrostatic interactions were hypothesized to drive reversible fiber formation. , However, the prediction of phosphorylated amino acids in Eu. rowelli slime was solely based on bioinformatics analyses, and never experimentally confirmed .…”