We know geckos cling on to surfaces using their ‘sticky’ feet hairs. Now, a group of Belgian researchers had discovered a protein abundant in starfish “feet” that enhances its stride and tenacity. And more: we could put it to use as well!
The study is published in PNAS this week.
Geckos vs. Starfish: Clinging
Gecko clinging is all about sticking on to dry surfaces. With starfish it’s about moving on watery surfaces, sometimes also facing the water currents. Starfish attach or move themselves with the help of numerous feet, known as “tube feet” that look like micro-versions of elephant feet.
Tube feet help starfish not only to move, but also to horn in to clams and mussels, locate a mate, or for defense. “… Adhesion is a “way of life” in the sea…” write the authors in the paper. But, what the scientists didn’t know was “what is responsible at a molecular scale” for this sticky stride.
Now the scientists give credits to a big protein that resides and works in starfish tube feet.
Tube Feet work like Post-It Notes
A microscopic look at the tube feet “skin” would reveal a stack of specialized cells that store and release adhesives. Elise Hennebert, a post-doctoral scientist at the University of Mons, Belgium, who is also the first author of the paper tells Decoded Science, “the epidermis of the distal part of these organs is specialized for adhesion and encloses adhesive cells which release an adhesive material upon contact with a surface.”
There is a cocktail of proteins in the adhesive material. However, the scientists found that a protein called Sea star footprint protein 1 (Sfp1) is abundant in the mix. Sfp1 acts as a structural scaffold of the “foot print” that is left behind the starfish, as it strides forward – but the adhesion is only temporary.
The marine environment forces those living underwater to stick themselves temporarily or permanently on to surfaces for various reasons, just in order not to wash themselves away in the current.
While barnacles cling permanently on rocks, starfish cannot afford to do so. Hence they evolved to have a temporary adhesion. “Tube feet act like a Post-it” says Hennebert, “[so] they can attach and detach repeatedly from a surface.”
“To date, the permanent adhesives produced by mussels, barnacles and tube worms have been the most investigated. This is the first time that a protein is characterized from a temporary adhesive,” points out Hennebert, the novelty of this study.
Sfp1 at work
Of the many proteins, scientists found that Sfp1 is from a single mRNA, whereon the message for a protein from DNA is transcribed. And they found Sfp1 to be big, having four domains that let them multi-task. Each of these domains takes up a biochemical job inside and outside the adhesive cells in the tube feet.
Click to download and view the researchers’ video of Starfish in a Tank. Video provided by Elise Hennebert, used with permission.
There are sticky sugars called glycocalyx on the tube foot skin. While it remains inside the cells, the Sfp1 is clustered as fragments. Some of the Sfp1 fragments shake hands with the sugars and coat the surface with a thin adhesive film, which makes the starfish stick to the surface. As soon as the starfish firm its feet down, the cells release the Sfp1. On the surface, the Sfp1 stick together as glue.
When the starfish move forward, a group of cells called “deadhesive cells” work in reverse order, and let them leave foot prints. The first adhesive film formed on the surface remains as the footprint.
Bio-mimicry: Sticky Feet For Humans
While we are amused at how starfish stick to and leave off a surface, we are also inspired by them – just like by spider silk and gecko cling. Innovators are at work in developing bio-inspired mimics, or bio-mimetics to be useful in a variety of places.
We could put Sfp1 to use in shipping, dairy industry and medicine, as engineered water-resistant adhesives. Henneberg says, “Because sea star adhesive acts directly underwater, it could be useful in a huge number of applications where glue is needed directly underwater, such as to fix tanks, boats, on teeth, inside the human body, etc.”
Stop Fouling With Sfp1
Fouling is a nuisance for boat owners and in shipping. In the dairy industry, bacteria stick to the inner surfaces of tanks and reactors and foul them. In medicine, bacteria form a film on medical devices or prosthetics and foul them. So, the ability to engineer water-resistant adhesives like Sfp1 could help us in many ways.
Strong Adhesive on Glass
Click to download and view the researchers’ video of Starfish on Glass. This video shows a sea star’s arm strongly attached to the wall of a tank. When we pull the arm, the tube feet are extended and some of them can even break and remain attached to the wall, illustrating the strength of adhesion. Video provided by Elise Hennebert, used with permission.
The scientists found Sfp1 to stick strongly on glass or mica surfaces, but weakly to surfaces like Teflon. And remember, Sfp1 is from a single mRNA. Moreover, the scientists found out that biochemically Sfp1 does not undergo any complicated changes, after production in the cell. These properties of Sfp1 make biotechnologists and engineers happy, since otherwise, these become the usual challenges to develop protein-based products.
Sea Star Proteins for Product Applications
“[We have] to characterize the other sea star proteins, try to produce Sfp1 subunits, and to do adhesion tests and biocompatibility assays on the products,” Hennebert tells Decoded Science. So how soon can we get Sfp1-based products? “Several years, I think. The time between characterizing a protein and obtaining a good product for applications in human life is always long” says Hennebert.