A natural ionic liquid: low molecular mass compounds of aggregate glue droplets on spider orb webs

TL;DR

This study reveals that spider orb web aggregate glue contains a natural ionic liquid, hydrated choline dihydrogen phosphate, which influences glycoprotein modification and maintains protein stability, offering insights into natural adhesion mechanisms.

Contribution

It identifies a natural ionic liquid in spider glue and demonstrates its role in glycoprotein modification and protein stability, providing a new perspective on biological adhesion materials.

Findings

Aggregate glue contains hydrated choline dihydrogen phosphate.

The ionic liquid concentration affects glycoprotein modification.

Proteins remain stable and functional in the ionic liquid.

Abstract

The aggregate glue of spider orb web is an excellent natural adhesive. Orb-weaver spiders use micron-scale aggregate glue droplets to retain prey in the capture spiral silks of their orb web. In aggregate glue droplets, highly glycosylated and phosphorylated proteins dissolve in low molecular mass compounds. The aggregate glue droplets show a heterogeneous structural distribution after attaching to the substrate. Although components of the aggregate glue droplets have been well analyzed and determined in past studies, visualization of the spatial distribution of their chemical components before and after their attachment is the key to exploring their adhesion mechanisms. Here, we investigated the distribution of low molecular mass compounds and glycoproteins in aggregate glue droplets using the in situ measurement methods and visualized the role of specific low molecular mass compounds in promoting glycoprotein modification in the aggregate glue. The results of the analysis suggest that the constituents of aggregate glue droplets include at least one ionic liquid: hydrated choline dihydrogen phosphate, while the modification of glycoproteins in aggregate glue depends on the concentration of this ionic liquid. This natural ionic liquid does not affect the fluorescence activity of fluorescent proteins, indicating that proteins of aggregate glue droplets can be dissolved well and maintain the stability of their higher-order structures in that ionic liquid. As a natural ionic liquid, aggregate glue droplets from the spider orb webs may be an excellent ionic liquid material model.