Tough Coating Proteins: Subtle Sequence Variation Modulates Cohesion

Abstract

Mussel foot protein-1 (mfp-1) is an essential constituent of the protective cuticle covering all exposed portions of the byssus (plaque and the thread) that marine mussels use to attach to intertidal rocks. The reversible complexation of Fe3+ by the 3,4-dihydroxyphenylalanine (Dopa) side chains in mfp-1 in Mytilus californianus cuticle is responsible for its high extensibility (120%) as well as its stiffness (2 GPa) due to the formation of sacrificial bonds that help to dissipate energy and avoid accumulation of stresses in the material. We have investigated the interactions between Fe3+ and mfp-1 from two mussel species, M. californianus (Mc) and M. edulis (Me), using both surface sensitive and solution phase techniques. Our results show that although mfp-1 homologues from both species bind Fe3+, mfp-1 (Mc) contains Dopa with two distinct Fe3+-binding tendencies and prefers to form intramolecular complexes with Fe3+. In contrast, mfp-1 (Me) is better adapted to intermolecular Fe3+ binding by Dopa. Addition of Fe3+ did not significantly increase the cohesion energy between the mfp-1 (Mc) films at pH 5.5. However, iron appears to stabilize the cohesive bridging of mfp-1 (Mc) films at the physiologically relevant pH of 7.5, where most other mfps lose their ability to adhere reversibly. Understanding the molecular mechanisms underpinning the capacity of M. californianus cuticle to withstand twice the strain of M. edulis cuticle is important for engineering of tunable strain tolerant composite coatings for biomedical applications.

Peptide Length and Dopa Determine Iron‐Mediated Cohesion of Mussel Foot Proteins

“…Recent results suggest that the starting concentration of solutions used for bulk deposition plays a crucial role in determining the adhesive and cohesive properties of a protein film. [8] Hence, the disparity in the results could also be attributed to the lower protein deposition concentrations (20 µg/ml compared with 50 µg/ml in this work) used in the earlier work.…”

“…This is contrary to the commonly observed property of ferric ions to chelate Dopa containing protein films across surfaces as shown in our rmfp-1 films experiments and previously seen in natural mussel foot protein films. [8, 13] Perhaps the Dopa needed to coordinate and form Fe 3+ -mediated bridges between the films is unavailable by virtue of interacting with the mica surface through various interactions as shown in Fig. 1 B .…”

“…It should be noted that the protein deposition concentration was set at 50 µg/ml as previously optimized for mfp1 for achieving maximum cohesive interactions. [8] During the protein adsorption, the discs were kept in a saturated Petri dish to minimize evaporation of the water from the surfaces. The discs were then mounted in the SFA in one of two configurations.…”

“…[8] The interaction between Fe 3+ and mfp-1 using surface sensitive and solution phase techniques showed that the mfp-1 homologs bind Fe 3+ differently: mfp-1 ( Mc ) Dopa groups interact with Fe 3+ to form intramolecular complexes, whereas mfp-1 ( Me ) Dopa groups form intermolecular complexes. [8] Similarly, the adhesive and cohesive contributions of residues other than Dopa in other mfps are the topic of recent studies [8–9] and will be discussed later.…”

Microphase Behavior and Enhanced Wet-Cohesion of Synthetic Copolyampholytes Inspired by a Mussel Foot Protein

“…This oxidation stability could be due to hydrophobic or electrophilic shielding of the Dopa moieties as proposed for mfp-3s. 9 This study emphasizes the importance of the balance between electrostatic and hydrophobic interactions for coacervation and wet-adhesion in addition to catecholic interactions, e.g., oxidative cross-linking, 17,18 metal coordination, 19,20 and intermolecular hydrogen bonding. 21 The mfp-3s-mimetic copolyampholyte has potential as a high performance wet adhesive/coating with its very strong wet-cohesion (∼8.8, ∼2.4, and ∼1.6 times greater than mfp-3s, 9 mfp-5, 15 the most adhesive natural protein, and the recently engineered mfp-amyloid protein, 22 respectively) and stable coacervation.…”