How do ticks stick? Linking tick adhesion to protein phase transitions

Bioadhesives are sticky materials used by a wide variety of organisms for different purposes such as attachment, building, and defense. The range of species producing adhesives is diverse and many of them use protein-based glues: mussels attach via proteinaceous threads, and velvet worms eject slime to entangle their prey. While some of these bioadhesives have been studied in detail, knowledge on adhesive mechanisms of many others is significantly lacking. One of the unexplored and unique bioadhesives is produced by ticks, a widespread ectoparasite of public health and economic importance.

Hard ticks feed on their mammalian hosts over multiple days. To ensure firm attachment, they secrete a protein-rich saliva to eventually form a solid bioadhesive, also known as the cement cone. The underlying mechanism of this liquid-to-solid transition is currently not understood. In this interdisciplinary collaboration between Wageningen University (EmBioSys Lab led by Siddharth Deshpande) and Maastricht University (Ingrid Dijkgaaf’s lab), the researchers explored the physical chemistry origins of the tick bioadhesive. They looked at the phase transitions of disordered glycine-rich proteins (GRPs), a protein family abundant in tick saliva. By chemically synthesizing a GRP identified in the cement cone, they conducted microscopy studies to show that it undergoes liquid-liquid phase separation via cation–and –interactions, formed condensates exhibit ageing and undergo liquid-to-gel transition over time, and the material is strongly adhesive in nature.

This study opens numerous exciting possibilities for future research in understanding cement cone formation, but also for biotechnological applications such as developing novel tick control strategies, and towards biomedical applications such as tissue sealants.

Read more: Ganar et al. “Phase separation and ageing of glycine-rich protein from tick adhesive” Nature Chemistry (2024).

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News articles:

WUR Resource (Ticks get stuck in)

The Scientist (What makes a tick stick?)

Chemistryworld (Protein cement is the trick to how ticks stick)