Strong reversible Fe ³⁺ -mediated bridging between dopa-containing protein films in water

Abstract

Metal-containing polymer networks are widespread in biology, particularly for load-bearing exoskeletal biomaterials. Mytilus byssal cuticle is an especially interesting case containing moderate levels of Fe 3þ and cuticle protein-mussel foot protein-1 (mfp-1), which has a peculiar combination of high hardness and high extensibility. Mfp-1, containing 13 mol % of dopa (3, 4-dihydroxyphenylalanine) side-chains, is highly positively charged polyelectrolyte (pI ∼ 10) and didn't show any cohesive tendencies in previous surface forces apparatus (SFA) studies. Here, we show that Fe 3þ ions can mediate unusually strong interactions between the positively charged proteins. Using an SFA, Fe 3þ was observed to impart robust bridging (W ad ≈ 4.3 mJ∕m 2 ) between two noninteracting mfp-1 films in aqueous buffer approaching the ionic strength of seawater. The Fe 3þ bridging between the mfp-1-coated surfaces is fully reversible in water, increasing with contact time and iron concentration up to 10 μM; at 100 μM, Fe 3þ bridging adhesion is abolished. Bridging is apparently due to the formation of multivalent dopa-iron complexes. Similar Fe-mediated bridging (W ad ≈ 5.7 mJ∕m 2 ) by a smaller recombinant dopa-containing analogue indicates that bridging is largely independent of molecular weight and posttranslational modifications other than dopa. The results suggest that dopa-metal interactions may provide an energetic new paradigm for engineering strong, self-healing interactions between polymers under water.byssus | metal coordination | tris-catecholato-iron (III) complex M etallopolymers are increasingly viewed as a transformative platform for the next generation of materials. This platform is related in part to their capacity for multifunctionality, but also to their wide and adjustable range of electronic, photonic, and magnetic properties (1). The load-bearing properties of metallopolymers are equally important but have received less attention with few exceptions (2). This oversight needs to be rectified given how widespread metal-containing polymer networks are in biology, particularly for load-bearing exoskeletal biomaterials (3, 4). The byssal cuticle of mussels in the genus Mytilus is an especially interesting case study because of its peculiar combination of hardness (100-150 MPa) and extensibility (>70% strain) (5). Mytilus byssal cuticle contains moderate levels of Fe 3þ and a single protein-mussel foot protein-1 (mfp-1) (6). Mfp-1 has a mass of about 108 kDa in Mytilus edulis (7) and consists largely of tan-

Understanding Mechanisms of Asphaltene Adsorption from Organic Solvent on Mica

“…The SFA is an ideal technique for exploring the adsorption kinetics and interactions between the adsorbed asphaltene layers. 14,[36][37][38][39]41,42 During the force measurements, if the surface separation D is much smaller than local radius of curvature R, the surface interaction of the crossed-cylinder configuration in SFA is equivalent to that between a sphere of the same radius and a flat surface. 36 The surface separation and deformation is monitored in real time and in situ by Multiple Beam Interferometry (MBI) using Fringes of Equal Chromatic Order (FECO).…”

“…14,30 Recently, Adams published a comprehensive review on the chemical and physical nature of asphaltenes and corresponding characteristics of asphaltene adsorption. 37 The above research provided valuable information on stabilization mechanisms and adsorption kinetics of asphaltenes.…”

“…[36][37][38][39] SFA is one of the most powerful techniques for the research objective of this study. The force-distance curves or so-called force profiles obtained from SFA measurements could provide important information on build-up kinetics of adsorbed layers via accurate and absolute film thickness measurement, and properties of adsorbed layers such as asphaltene-asphaltene interfacial energy and molecular conformation changes of the adsorbed asphaltene layers through the force measurement.…”

Three intrinsically unstructured mussel adhesive proteins, mfp‐1, mfp‐2, and mfp‐3: Analysis by circular dichroism

“…Recruitment of the atomic force microscope, nanoindentation, and the surface force apparatus (SFA) has contributed much to understanding the physical and mechanical properties of mussel byssus and byssal proteins particularly the mfps. [5][6][7][8][9] However, structural studies at different length scales have been hampered by considerable challenges, including a menagerie of peculiar post-translational modifications, mfp sequence polymorphism, 2,10 the inability to crystallize any of the mfps, difficulty of purifying mg quantities, and the instability of mfps in solution. 11 This has lead to a variety of experimental approximations, which may or may not be biologically relevant.…”

“…Mfp-1 (from Mytilus californianus) is the only protein known to be present in the byssal cuticle remarkable for its combination of high stiffness and high extensibility. 6 Mfp-1 has a mass between 88 and 92 kDa, a basic isoelectric point (8)(9)(10), and 60 or more tandem repeats of a decapeptide sequence (PKISYO*OTY*K in which Y* is 3,4-dihydroxyphenyl-L-alanine (Dopa), O is trans-4-hydroxproline, and O* denotes trans-2,3-cis-3,4-dihydroxyproline (diHyp). 15 Mfp-2 (from M. edulis) is an abundant protein in the plaques ($25% of adhesive plaque by dry weight) with a mass of 45 kDa and consists of 11 tandem repeats of a 40-res long epidermal growth factor (EGF) motif.…”