Proteins Help Organisms Adhere to Wet Surfaces

harvested green mussels lay together in a large pile

Biological Strategy

Green mussel

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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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Attach Temporarily

Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.

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Bivalves

Class Bivalvia (“two-valved”): Clams, mussels, oysters

The bivalve name says it all: these animals are characterized by a two-sided shell that is connected at the hinge with a muscle. The 15,000 species in 90 families have flattened bodies, no head, and generally live a sedentary lifestyle. Instead of having a circular band of teeth like other molluscs, many are filter feeders. They use cilia, or hair-like extensions, to move water into their bodies and pluck out plankton to eat. Consequently, there are no terrestrial bivalves, and only 15% live in freshwater ecosystems. The rest live in marine environments.

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Byssus threads of the green mussel attach to a wet, solid surface due to glycosylated hydroxytryptophan in one of its adhesive proteins.

Some mussels adhere to rocks and other ocean substrates using a that contains an called Dopa (3,4-dihydroxyphenyl-L-alanine). However, the invasive green mussel, Perna viridis, has a more complcated adhesive chemistry based on a protein with an elaborate modification of the amino acid tryptophan.

The stickiness of the green mussel’s foot, especially how it works in wet environments could be mimicked to form new adhesives, including use for teeth, bones, and for repairing ships at sea that have developed cracks.

(adapted from an article at http://www.eurekalert.org/pub_releases/2009-08/uoc–tig082709.php)

Image: Vishal Bhave /

Last Updated August 23, 2016

References

Journal article

Glycosylated Hydroxytryptophan in a Mussel Adhesive Protein from Perna viridis

Journal of Biological Chemistry | 08/07/2009 | H. Zhao, J. Sagert, D. S. Hwang, J. H. Waite

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