Coacervation of Interfacial Adhesive Proteins for Initial Mussel Adhesion to a Wet Surface

Abstract

Coacervation of mussel adhesive proteins (MAPs) is proposed as a potential strategy that mussels may use during secretion due to their high concentration density, lack of dispersion into seawater, and low interfacial tension. Particularly, coacervations of interfacial MAPs, foot protein type‐3 fast variant (fp‐3F) and type‐5 (fp‐5), are important in the initial mussel adhesion process due to the relationship between the easy secretion/surface wetting properties of the coacervate and primer‐like surface adhesive role of interfacial MAPs, which directly contact the marine surface. To the best of the authors' knowledge, this is the first report on coacervate formation of major recombinant interfacial MAPs with high charge densities and the highest 3,4‐dihydroxyphenylalanine (Dopa) contents. Specifically, salt‐induced coacervation of fp‐3F is observed at low pH values corresponding to the acidified environment of the distal depression during mussel secretion. In addition, it shows enthalpy driven upper critical solution temperature behavior, possibly relying on bridging interactions between like‐charged cationic fp‐3Fs including salt‐bridge and cation–π/π–π interactions in the presence of specific counterions, supported by Raman spectroscopy. It is believed that this study has broadened the scope of the understanding of coacervation of MAPs and may provide new insight for responsive biomaterial design.

Bioinspired and Mechanically Strong Fibers Based on Engineered Non‐Spider Chimeric Proteins

“…Consequently, most of the recombinant protein fibers exhibit weak mechanical properties compared to natural spider silks. Aside from spider silks, there are many structural proteins with excellent mechanical properties in nature, such as mussel byssus, bagworm silks, sandcastle worm glue, and squid ring teeth, amongst others. The different sequences and structures of those proteins offer many options for the creation of mechanically strong protein fibers.…”

Phase-dependent redox insulation in mussel adhesion

“…The formation of adhesive plaques by mussels (Mytilus californianus) involves a cohort of mostly disordered proteins known as mussel foot proteins (mfps) (8). Several mfps exhibit liquid-liquid phase separation (LLPS) (7,(9)(10)(11) triggered by specific chemical cues in the ambient seawater. Adaptive advantages of coacervation include fluid adhesive protein concentrates, shear thinning to facilitate fluid transport, and low interfacial energy for spontaneous spreading underwater (4,9,12,13).…”

Label‐Free Quantitative Analysis of Coacervates via 3D Phase Imaging

“…[ 10,12,20,21,58 ] For example, mussel‐foot proteins use a form of coacervate with a high protein concentration and low interfacial tension to transport high‐concentration functional proteins without dispersion in seawater, thereby subsequently forming adhesive plaques. [ 59–61 ] Examining how concentrated the protein is within coacervates and how it affects the properties of the coacervates could contribute toward understanding how organisms use LLPS to form extracellular biomaterials. For intracellular phase separation, it has been suggested as a mechanism to maintain the biomolecule level of cells, [ 30–32 ] wherein fluctuations in the biomolecule concentration occur owing to gene expression and chemical reactions.…”