Researchers at the University of Toronto have identified a protein from the quagga mussel that can stick to surfaces underwater, even though it lacks a chemical feature long thought to be essential for this kind of adhesion. The protein, called Dbfp7, is the first freshwater mussel adhesive protein to be functionally characterized.  

The finding, published in a recent issue of PNAS, helps explain how some organisms attach themselves in wet environments and could inform the design of future medical glues — such as medical sealants and surgical adhesives — or other materials that need to work reliably in water.

Most studies of underwater adhesion have focused on marine mussels, which use proteins rich in a modified amino acid called 3,4-dihydroxyphenylalanine (DOPA) to bond to surfaces. Freshwater species have been studied less, and whether they rely on the same chemistry has not been clear.

The quagga mussel, an invasive species in the Great Lakes, uses a structure called a byssus to anchor itself in moving water. Until now, the specific proteins at the contact point between this structure and a surface have not been well defined.

“There are multiple examples where nature solves the problem of wet adhesion, with some species from varying environmental conditions evolving different strategies. Studying freshwater bio-adhesives helps us expand the current set of known biological adhesives,” explained Angelico Obille, lead author of the study and a PhD candidate at the Institute of Biomedical Engineering at the University of Toronto.

“DOPA-based adhesives face some limitations because of its susceptibility to oxidize into non-adhesive forms. Insights from freshwater mussel adhesives may help us circumvent the need for DOPA or at least find ways to enhance the efficacy of even small amounts of DOPA.”

To identify the proteins, the team analyzed the material at the interface where the mussel attaches to a surface using quantitative proteomics, allowing them to localize the specific set of proteins directly in contact with surfaces. They found several proteins that were more abundant at this interface, with Dbfp7 standing out because of its size and high expression in the mussel’s foot, the organ that produces the adhesive.

The researchers then purified Dbfp7 and used atomic force microscopy to map the mechanical properties of this protein in water. The tests showed that Dbfp7 could adhere to surfaces in wet conditions, despite containing little to no DOPA. The team compared its performance with other known proteins and found that Dbfp7’s adhesive strength was in the same range as some marine mussel proteins that are used as benchmarks in the field.

“We’re currently investigating the properties of Dbfp7 and other footprint proteins in the overall mechanism of adhesion, such as sequence motifs and structural features that are tailored for freshwater conditions,” said Professor Eli Sone (BME, MSE), the corresponding author of the study.

“Uncovering the adhesion strategies used by these invasive freshwater mussels can lead to improved medical adhesives, as well as anti-fouling technologies.”