Multiple Component Glue Aids Underwater Adhesion

barnacles are seen attached to a seashell against a piece of wood near the sea

Biological Strategy

AskNature Team

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Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Chemically Assemble Polymers

We might think that complex polymers are the result of human industrial ingenuity, but nature cornered the market on polymers billions of years earlier. Examples of biopolymers are proteins, carbohydrates, and genetic material. In contrast to human industrial processes, within a cell, ribosomes covalently bond amino acids together to form proteins.

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Attach Permanently

A living system can conserve energy by attaching permanently to a particular site because it can take advantage of resources that come its way, rather than expending energy to move to resources. A permanent attachment, intended to last the lifetime of the living system, creates special challenges. For example, physical mechanisms, such as the anchor that holds a marine algae to the ocean’s bottom, must be able to withstand forces that can pull it off its substrate. Chemical mechanisms, such as a barnacle’s glue, must avoid both physical and chemical breakdown, such as being dissolved by water.

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Crustaceans

Subphylum Crustacea (“crust”): Crabs, barnacles, shrimp, pillbugs

Some crustaceans, like pillpugs and woodlice, live on land, but most are found in the ocean. Their heads are distinctive among the arthropods: they have two pairs of antennae and three pairs of feeding appendages that help them hold and crunch food. Crustaceans also have a unique larval stage called the nauplius (named after the son of Poseidon) which has three pairs of legs and one eye. Most crustaceans are in class Malacostraca, which contains a wide range of species that live in mostly marine environments, like krill, lobster, and mantis shrimp.

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The proteinaceous cement substance produced by barnacles allows tenacious underwater attachment due to cooperation of four cement proteins.

“Barnacles have the capability for tenacious underwater adhesion to the surfaces by a proteinaceous cement substance. Three major s had been identified in a previous study and this study adds a fourth. It is suggested that each cement protein fulfills a distinct and specific role in underwater adhesion, and that firm barnacle adhesion is achieved cooperatively by these cement proteins. Understanding the specific role of each cement protein will help to provide a better understanding of barnacle settlement and of synthetic mimics, including underwater adhesives.” (Courtesy of the Guild)

“Enzymes and biochemical mechanisms essential to survival are under extreme
selective pressure and are highly conserved through evolutionary time. We
applied this evolutionary concept to barnacle cement polymerization, a process
critical to barnacle fitness that involves aggregation and cross-linking of
proteins. The biochemical mechanisms of cement polymerization remain largely
unknown. We hypothesized that this process is biochemically similar to blood
clotting, a critical physiological response that is also based on aggregation
and cross-linking of proteins. Like key elements of vertebrate and
invertebrate blood clotting, barnacle cement polymerization was shown to
involve proteolytic activation of enzymes and structural precursors,
transglutaminase cross-linking and assembly of fibrous proteins. Proteolytic
activation of structural proteins maximizes the potential for bonding
interactions with other proteins and with the surface. Transglutaminase
cross-linking reinforces cement integrity. Remarkably, epitopes and sequences
homologous to bovine trypsin and human transglutaminase were identified in
barnacle cement with tandem mass spectrometry and/or western blotting. Akin to
blood clotting, the s generated during proteolytic activation
functioned as signal molecules, linking a molecular level event (protein
aggregation) to a behavioral response (barnacle larval settlement). Our
results draw attention to a highly conserved protein polymerization mechanism
and shed light on a long-standing biochemical puzzle. We suggest that barnacle
cement polymerization is a specialized form of wound healing. The
polymerization mechanism common between barnacle cement and blood may be a
theme for many marine animal glues.” (Dickinson et al. 2009:3499)

Last Updated September 14, 2016

References

Journal article

Novel barnacle underwater adhesive protein is a charged amino acid-rich protein constituted by a Cys-rich repetitive sequence

Biochem. J. | 10/08/2015 | Kei KAMINO

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Reference

Journal article

Barnacle cement: a polymerization model based on evolutionary concepts

Journal of Experimental Biology | 16/10/2009 | G. H. Dickinson, I. E. Vega, K. J. Wahl, B. Orihuela, V. Beyley, E. N. Rodriguez, R. K. Everett, J. Bonaventura, D. Rittschof

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