Hard ticks feed on their host for multiple days. To ensure firm attachment, they secrete a protein-rich saliva that eventually forms a solid cement cone. The underlying mechanism of this liquid-to-solid transition is currently not understood. This study focuses on the phase transitions of a disordered glycine-rich protein (GRP) found in tick saliva. We show that GRP undergoes liquid–liquid phase separation via simple coacervation to form biomolecular condensates in salty environments. Cation–π and π–π interactions mediated by periodically placed arginine and aromatic amino-acid residues are the primary driving forces that promote phase separation. Interestingly, GRP condensates exhibit ageing by undergoing liquid-to-gel transition over time and exhibit adhesive properties, similar to the naturally occurring cement cone. Finally, we provide evidence for protein-rich condensates in natural tick saliva. Our findings provide a starting point to gain further insights into the bioadhesion of ticks, to develop novel tick control strategies, and towards achieving biomedical applications such as tissue sealants.

硬蜱虫以宿主为食数天。为了确保牢固的附着，它们会分泌富含蛋白质的唾液，最终形成一个坚固的水泥锥。这种液态到固态转变的潜在机制目前尚不清楚。本研究侧重于蜱唾液中发现的无序富含甘氨酸的蛋白 （GRP） 的相变。我们表明 GRP 通过简单的凝聚进行液-液相分离，在含盐环境中形成生物分子缩聚物。由周期性放置的精氨酸和芳香族氨基酸残基介导的阳离子-π 和 π-π 相互作用是促进相分离的主要驱动力。有趣的是，GRP 冷凝物会随着时间的推移经历液体到凝胶的转变而老化，并表现出类似于天然存在的水泥锥体的粘合性能。最后，我们提供了天然蜱唾液中富含蛋白质的冷凝物的证据。我们的研究结果为进一步了解蜱虫的生物粘附性、开发新的蜱虫控制策略以及实现组织密封剂等生物医学应用提供了一个起点。