Dopa (3,4-dihydroxyphenylalanine) is recognized as a key chemical signature of mussel adhesion and has been adopted into diverse synthetic polymer systems. Dopa’s notorious susceptibility to oxidation, however, poses significant challenges to the practical translation of mussel adhesion. Using a Surface Forces Apparatus to investigate the adhesion of Mfp3 (mussel foot protein 3) slow, a hydrophobic protein variant of the Mfp3 family in the plaque, we have discovered a subtle molecular strategy correlated with hydrophobicity that appears to compensate for Dopa instability. At pH 3, where Dopa is stable, Mfp3 slow like Mfp3 fast adhesion to mica is directly proportional to the mol% of Dopa present in the protein. At pH 5.5 and 7.5, however, loss of adhesion in Mfp3 slow was less than half that occurring in Mfp3 fast, purportedly because Dopa in Mfp3 slow is less prone to oxidation. Indeed, cyclic voltammetry showed that the oxidation potential of Dopa in Mfp3 slow is significantly higher than in Mfp3 fast at pH 7.5. A much greater difference between the two variants was revealed in the interaction energy of two symmetric Mfp3 slow films (Ead = −3 mJ/m2). This energy corresponds to the energy of protein cohesion which is notable for its reversibility and pH-independence. Exploitation of aromatic hydrophobic sequences to protect Dopa against oxidation as well as to mediate hydrophobic and H-bonding interactions between proteins provides new insights for developing effective artificial underwater adhesives.

Contrary to conventional wisdom, mineralization is not the only strategy evolved for the formation of hard, stiff materials. Indeed, the sclerotized mouthparts of marine invertebrates exhibit Young's modulus and hardness approaching 10 and 1 GPa, respectively, with little to no help from mineralization. Based on biochemical analyses, three of these mouthparts, the jaws of glycerid and nereid polychaetes and a squid beak, reveal a largely organic composition dominated by glycine- and histidine-rich proteins. Despite the well-known metal ion binding by the imidazole side-chain of histidine and the suggestion that this interaction provides mechanical support in nereid jaws, there is at present no universal molecular explanation for the relationship of histidine to mechanical properties in these sclerotized structures.

survival measures might produce inferior biomaterials; (2) during an abrupt and extreme environmental stress, one or more factors (e.g. waves and acidic run-off) might combine to briefly undermine the performance of materials in service, or (3) during a sustained change in the environment that is not physiologically stressful, the quality of normal biomaterials might deteriorate (Fig.1). To date, it remains unknown whether the first, second, third, or some combination of the three represents the most realistic perturbation of biomaterials serving an individual or community.Of the many different properties exhibited by extra-organismic biomaterials in the extended organism, many research groups including ours have focused on those with mechanical or load bearing properties. These are necessary in biomaterials that function in, for example, support, shelter, feeding, prey capture and adhesion. This review is about structure-function relationships in the load-bearing biomaterials of extended organisms and the hypothesis that the functional performance of biomaterials is linked to structures that are perturbed by a changing environment. The proposition is somewhat rhetorical because the toolkits to properly test it are incomplete and few are suited to field ecology. Notwithstanding this, the overview will briefly survey old and new techniques for studying structures and mechanical properties in marine biomaterials, survey how different test conditions affect structure and function in byssal threads, and speculate on what these studies might contribute to ecomechanics. Approaches to structure-function analysisA major goal in experimental biology is discovering relationships between structure and function. This goal is equally relevant to studying biomaterials, except that mechanical properties are used as proxies for function. It is understood that the measured mechanical properties may only be one of many in a multifunctional material. The conventional wisdom in materials science is that structure determines properties; thus, altering structure is likely to alter Accepted 31 May 2011 Summary Most marine organisms make functional biomolecular materials that extend to varying degrees ʻbeyond their skinsʼ. These materials are very diverse and include shells, spines, frustules, tubes, mucus trails, egg capsules and byssal threads, to mention a few. Because they are devoid of cells, these materials lack the dynamic maintenance afforded intra-organismic tissues and thus are usually assumed to be inherently more durable than their internalized counterparts. Recent advances in nanomechanics and submicron spectroscopic imaging have enabled the characterization of structure-property relationships in a variety of extraorganismic materials and provided important new insights about their adaptive functions and stability. Some structure-property relationships in byssal threads are described to show how available analytical methods can reveal hitherto unappreciated interdependences between these materials and their prevailing che...

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