The adhesion of mussel foot proteins (Mfps) to a variety of specially engineered mineral and metal oxide surfaces has previously been investigated extensively, but the relevance of these studies to adhesion in biological environments remains unknown. Most solid surfaces exposed to seawater or physiological fluids become fouled by organic conditioning films and biofilms within minutes. Understanding the binding mechanisms of Mfps to organic films with known chemical and physical properties therefore is of considerable theoretical and practical interest. Using selfassembled monolayers (SAMs) on atomically smooth gold substrates and the surface forces apparatus, we explored the forcedistance profiles and adhesion energies of three different Mfps, Mfp-1, Mfp-3, and Mfp-5, on (i) hydrophobic methyl (CH 3 )-and (ii) hydrophilic alcohol (OH)-terminated SAM surfaces between pH 3 and pH 7.5. At acidic pH, all three Mfps adhered strongly to the CH 3 -terminated SAM surfaces via hydrophobic interactions (range of adhesive interaction energy = −4 to −9 mJ/m 2 ) but only weakly to the OH-terminated SAM surfaces through H-bonding (adhesive interaction energy ≤ −0.5 mJ/m 2 ). 3, 4-Dihydroxyphenylalanine (Dopa) residues in Mfps mediate binding to both SAM surface types but do so through different interactions: typical bidentate H-bonding by Dopa is frustrated by the longer spacing of OHSAMs; in contrast, on CH 3 -SAMs, Dopa in synergy with other nonpolar residues partitions to the hydrophobic surface. Asymmetry in the distribution of hydrophobic residues in intrinsically unstructured proteins, the distortion of bond geometry between H-bonding surfaces, and the manipulation of physisorbed binding lifetimes represent important concepts for the design of adhesive and nonfouling surfaces. M arine mussels are experts at wet adhesion, achieving strong and durable attachments to a variety of surfaces in their chemically heterogeneous habitat. Adhesion is mediated by a byssus, which is essentially a bundle of leathery threads that emerge from the living mussel tissue at one end and are tipped by flat adhesive plaques at the other. Byssal plaques consist of a complex array of proteins (mostly mussel foot proteins, Mfps), each of which has a distinct localization and function in the structure, but all share the unusual modified amino acid 3, 4-dihydroxyphenylalanine (Dopa) (Fig. 1).Of the dozen or so known mussel foot proteins, Mfp-1, Mfp-3, and Mfp-5 have been shown to exhibit remarkable binding to mineral surfaces such as mica and TiO 2 (1). The versatility of mussel adhesion to surfaces with wide-ranging chemical and physical properties has inspired much research dedicated to understanding the mechanism of mussel adhesion and to developing biomimetic coatings and adhesives for wide-ranging industrial and biomedical applications, the latter including paints for coronary arteries (2), fetal membrane sealants (3), cell encapsulants (4), bone glues (5), and for securing transplants for diabetics (6).The catecholic moiety of Dopa (Fig. 1) ...

The mussel byssus is a remarkable attachment structure that is formed by injection molding and rapid in-situ hardening of concentrated solutions of proteins enriched in the catecholic amino acid 3,4-dihydroxy-L-phenylalanine (DOPA). Fe3+, found in high concentrations in the byssus, has been speculated to participate in redox reactions with DOPA that lead to protein polymerization, however direct evidence to support this hypothesis has been lacking. Using small molecule catechols, DOPA-containing peptides, and native mussel foot proteins, we report the first direct observation of catechol oxidation and polymerization accompanied by reduction of Fe3+ to Fe2+. In the case of the small molecule catechol, we identified two dominant dimer species and characterized their connectivities by nuclear magnetic resonance (NMR), with the C6-C6 and C5-C6 linked species as the major and minor products, respectively. For the DOPA-containing peptide, we studied the pH dependence of the reaction and demonstrated that catechol polymerization occurs readily at low pH, but is increasingly diminished in favor of metal-catechol coordination interactions at higher pH. Finally, we demonstrate that Fe3+ can induce cross-links in native byssal mussel proteins mefp-1 and mcfp-1 at acidic pH. Based on these findings, we discuss the potential implications to the chemistry of mussel adhesion.

Overexpression of ABI5/ABF binding proteins (AFPs) results in extreme ABA resistance of seeds via multiple mechanisms repressing ABA response, including interactions with histone deacetylases and the co-repressor TOPLESS. Several ABI5/ABF binding proteins (AFPs) inhibit ABA response, resulting in extreme ABA resistance in transgenic Arabidopsis overexpression lines, but their mechanism of action has remained obscure. By analogy to the related Novel Interactor of JAZ (NINJA) protein, it was suggested that the AFPs interact with the co-repressor TOPLESS to inhibit ABA-regulated gene expression. This study shows that the AFPs that inhibit ABA response have intrinsic repressor activity in a heterologous system, which does not depend on the domain involved in the interaction with TOPLESS. This domain is also not essential for repressing ABA response in transgenic plants, but does contribute to stronger ABA resistance. Additional interactions between some AFPs and histone deacetylase subunits were observed in yeast two-hybrid and bimolecular fluorescence assays, consistent with a more direct mechanism of AFP-mediated repression of gene expression. Chemical inhibition of histone deacetylase activity by trichostatin A suppressed AFP effects on a small fraction of the ABI5-regulated genes tested. Collectively, these results suggest that the AFPs participate in multiple mechanisms modulating ABA response, including both TOPLESS-dependent and -independent chromatin modification.