aA stealth quest is underway in the Dutch Forest. It’s a tough tick that sits on a blade of grass and waits for the next blood meal. It attaches itself to the exposed leg of an unsuspecting victim, burrows into the skin, and begins feeding. The tick’s sticky, protein-rich saliva turns into a solid cement cone that remains fixed to the skin for several days. This shape-changing liquid is the tick’s bioadhesive.
and many other animals, such as mussels, sandcastle worms, and spiders. bioadhesivebut Siddharth DeshpandeThe biophysicist at Wageningen University and Research found himself stuck with the idea of studying tick glue.1 “Tick adhesive is very unique in that it comes in direct contact with human skin. All other bioadhesives basically stick to rocks and hard substrates, not living substrates.” Deshpande said.
Siddharth Deshpande, a biophysicist at Wageningen University and Research, is interested in studying living systems and how biomolecules self-assemble to form functional structures.
Kseniya Hlinka
However, little was known about the adhesion mechanism of tick saliva. Now, in a new study, Deshpande and his team show how Phase transition of tick saliva proteins Contributes to the formation of cement cones.2 “This is the first report on the physical chemistry behind adhesion,” Deshpande said. These findings show that natural chemistrycould lead to the development of new acaricidal strategies and the synthesis of improved tissue sealants for wound healing.
“It will be very interesting and testing to see how consistently this material overlaps with the behavior of other bioadhesives,” he said. david breslauerHe is a materials scientist and chief technology officer at Bolt Threads, a company that produces bioengineered spider silk, but was not involved in the study.
Tick saliva is rich in glycine-rich protein (GRP). When the animal begins to feed on blood, the expression of GRP in saliva increases, presumably giving the animal strength and insolubility. cement cone.3 Glycine-rich regions can interfere with protein folding and are often found in inherently disordered proteins that do not have a stable three-dimensional structure. These proteins flit between different conformations and establish multiple interactions with neighboring molecules, facilitating the concentration of biomolecules into microscopic droplets. The appearance of such liquid condensates in solutions of biomolecules Liquid-liquid phase separation (LLPS)—As when oil separates from water in solution.4
Deshpande has long been interested in phase separation. When Deshpande discovered GRPs in tick saliva, he immediately thought that solutions of these proteins could phase separate. To test his theory, he focused on a 77-amino acid-long GRP fragment (GRP77) found in hard mites. 26% of this fragment is glycine. tick scapula. AlphaFold predicted that GRP77 would be an ideal candidate for LLPS because it is highly disordered. Deshpande and his colleagues used a simple assay to confirm this.
Phase separation is a concentration-dependent process. A common experimental method to observe this phenomenon is the droplet evaporation assay based on the coffee ring effect. This happens when a drop of coffee falls on the table and evaporates, leaving behind a concentrated dark ring of coffee sediment. Because components in secreted tick saliva also become concentrated through water loss, the researchers tested whether small droplets of an artificially synthesized fluorescent GRP77 solution would exhibit phase separation upon evaporation. About 15 minutes after the researchers placed the droplet on the glass surface, they observed intense fluorescence and the appearance of a rim at the droplet’s boundary. Immediately thereafter, the researchers observed the appearance of numerous micron-sized droplets enriched with GRP77 suspended at the dilute edge of the buffer solution. This is a clear sign of LLPS. Deshpande was overjoyed to see them. “It’s not often that you get what you think you want on your first try,” he said.
Next, Deshpande and colleagues mimicked other LLPS-inducing features of tick saliva, specifically the presence of salt. When phosphate was added to the protein droplets, immediate formation of GRP77 phase-separated condensates was observed.
“We were pretty confident that the proteins would undergo phase separation, but we were in for a big surprise,” Deshpande said. When droplets containing high concentrations of GRP77 were evaporated, a gel-like network, or sometimes a stretched sheet, was visible under the microscope. This looked like an intermediate stage between liquid saliva and solid cement cone.
Researchers are studying a glycine-rich protein (green) in the tick’s saliva to understand how the tick remains attached to the skin for days. A protein solution undergoes phase separation, changing from a liquid to a solid.
Polina Turbina, Wageningen University and Research
To see if they could create a stronger structure, the research team allowed droplets of the protein and salt solution to dry for hours. When Deshpande saw the emergence of stable clusters, he wondered, “We’re seeing condensates, but are they sticky?” As it turned out, the clusters were very sticky and four orders of magnitude more force was required to separate them from the surface compared to the salt-free GRP77 condensate.
Finally, the authors were interested in whether natural saliva also exhibits phase separation. After many trips into the local woods, dragging cloth across the grass, I found enough ticks to collect a usable amount of saliva. Droplet evaporation assays revealed the presence of large amounts of spherical condensates that transformed into fibrous structures upon addition of salt.
These discoveries are the first step toward a variety of potential developments, including anti-mite vaccines and medical adhesives. “Rather than trying to invent bioadhesives, it makes a lot of sense to focus on nature-based solutions,” he said. Romana Santosa marine biologist at the University of Lisbon who studies sea urchin attachment, was not involved in the study. “They’ve been working for animals for so long, so why don’t they work for us?” Santos is also interested in how the mites detach from cement corn and skin. I have it. “Barnacles and mussels also produce cement and live attached to cement for their entire lives. But mites can come off,” she said.
Deshpande now has his sights set on studying the behavior of other GRPs in tick saliva and how they work together to form cement cones. “This really opened up a whole new field of research for me,” he said. “I’m not a tick researcher or a biofouling researcher, and now all of a sudden I am.”
