The Role of Redox Chemistry in Mussel Byssus

The mussel byssus is a collection of extra-organismal, acellular, proteinaceous load bearing structures that are radial displayed and utilized by marine mussels to secure themselves to a multitude of substrates. A single byssal thread can be subdivided into the loading bearing thread and adhesive plaque, which provide tensile strength and adhesive strength respectively. Both regions of the byssus face their own unique challenges and have devised independent mechanisms to protect themselves against oxidative stresses. Here we present evidence the mussel utilizes isolated redox compartments to protect 3, 4-dihydroxyphenylalanine (Dopa) from oxidative damage in both the thread and plaque, permitting long lasting mechanical performance of the byssus. The byssus thread is an extremely tough core-shelled fiber that dissipates substantial amounts of energy during tensile loading. The mechanical performance of the shell is critically reliant on Dopa’s ability to form reversible iron-catecholate complexes at pH 8. However, the formation of these coordinate crosslinks is undercut by Dopa’s oxidation to Dopa-quinone, a spontaneous process at seawater conditions. Using a combination of electron and atomic force microscopy we identify a previously undescribed stratum situated between the core and shell. Spectroscopy results indicate this region is rich in thiol and thus will be called the thiol rich layer (TRL). We propose the TRL acts as an electron sink to protect the shell against oxidation. Additionally, indentation type atomic force microscopy reveals the TRL has intermediate mechanical properties which act as a mechanical buffer between the shell and core. The adhesive plaque is also reliant on Dopa. Dopa in the plaque is primarily responsible for strong adhesion but only if protected from oxidation at the adhesive-substratum interface. Dopa oxidation is thermodynamically favorable in seawater yet barely detectable in mature plaques. Experiments were designed to understand how plaques insulate Dopa-containing mfps against oxidation. Spectrometry and confocal fluorescence results indicate seawater sulfate triggers a mfp3 and mfp6 liquid-liquid phase separation (LLPS). Subsequently, cyclic voltammetry of LLPS material demonstrates DOPA’s redox potential is phase dependent. Furthermore, mass spectrometry and redox exchange assays indicate Dopa-containing mfp-3 and mfp-6 in phase-separated droplets remain stable despite rapid oxidation in the equilibrium solution. Taken together, the results suggest that a cohort of oxidation-prone proteins is endowed with phase-dependent redox stability. Moreover, in forming LLPS compartments, Dopa-proteins become reservoirs of chemical energy which can be called upon in the event of oxidative damage

The Thiol-Rich Interlayer in the Shell/Core Architecture of Mussel Byssal Threads.

The mussel byssus thread is an extremely tough core-shelled fiber that dissipates substantial amounts of energy during tensile loading. The mechanical performance of the shell is critically reliant on 3,4-dihydroxyphenylalanine's (Dopa) ability to form reversible iron-catecholate complexes at pH 8. However, the formation of these coordinate cross-links is undercut by Dopa's oxidation to Dopa-quinone, a spontaneous process at seawater conditions. The large mechanical mismatch between the cuticle and the core lends itself to further complications. Despite these challenges, the mussel byssus thread performs its tethering function over long periods of time. Here, we address these two major questions: (1) how does the mussel slow/prevent oxidation in the cuticle, and (2) how is the mechanical mismatch at the core/shell interface mitigated? By combining a number of microscopy and spectroscopy techniques we have discerned a previously undescribed layer. Our results indicate this interlayer is thiol rich and thus will be called the thiol-rich interlayer (TRL). We propose the TRL serves as a long-lasting redox reservoir as well as a mechanical barrier

Impact of Molecular Architecture and Adsorption Density on Adhesion of Mussel-Inspired Surface Primers with Catechol-Cation Synergy.

Marine mussels secrete proteins rich in residues containing catechols and cationic amines that displace hydration layers and adhere to charged surfaces under water via a cooperative binding effect known as catechol-cation synergy. Mussel-inspired adhesives containing paired catechol and cationic functionalities are a promising class of materials for biomedical applications, but few studies address the molecular adhesion mechanism(s) of these materials. To determine whether intramolecular adjacency of these functionalities is necessary for robust adhesion, a suite of siderophore analog surface primers was synthesized with systematic variations in intramolecular spacing between catechol and cationic functionalities. Adhesion measurements conducted with a surface forces apparatus (SFA) allow adhesive failure to be distinguished from cohesive failure and show that the failure mode depends critically on the siderophore analog adsorption density. The adhesion of these molecules to muscovite mica in an aqueous electrolyte solution demonstrates that direct intramolecular adjacency of catechol and cationic functionalities is not necessary for synergistic binding. However, we show that increasing the catechol-cation spacing by incorporating nonbinding domains results in decreased adhesion, which we attribute to a decrease in the density of catechol functionalities. A mechanism for catechol-cation synergy is proposed based on electrostatically driven adsorption and subsequent binding of catechol functionalities. This work should guide the design of new adhesives for binding to charged surfaces in saline environments

Pennsylvania Folklife Vol. 36, No. 4

• The Art of Glass Blowing • Portrait Painting • The Ox Roast • Herbal Soap-Making • Fly-Fishing and Fly-Tying • Chalkware • Silversmithing • Festival Focus • Festival Programs • Coopering • Knife Making • Corn Husk Dolls • Salt Glaze Pottery • Blacksmithing and Iron Working • Bird Carving • Soft Pretzelshttps://digitalcommons.ursinus.edu/pafolklifemag/1116/thumbnail.jp

An Empirical Explanation of the Speed-Distance Effect

Understanding motion perception continues to be the subject of much debate, a central challenge being to account for why the speeds and directions seen accord with neither the physical movements of objects nor their projected movements on the retina. Here we investigate the varied perceptions of speed that occur when stimuli moving across the retina traverse different projected distances (the speed-distance effect). By analyzing a database of moving objects projected onto an image plane we show that this phenomenology can be quantitatively accounted for by the frequency of occurrence of image speeds generated by perspective transformation. These results indicate that speed-distance effects are determined empirically from accumulated past experience with the relationship between image speeds and moving objects

Spatial variations in ambient ultrafine particle concentrations and the risk of incident prostate cancer: A case-control study

Background Diesel exhaust contains large numbers of ultrafine particles (UFPs, <0.1 µm) and is a recognized human carcinogen. However, epidemiological studies have yet to evaluate the relationship between UFPs and cancer incidence. Methods We conducted a case-control study of UFPs and incident prostate cancer in Montreal, Canada. Cases were identified from all main Francophone hospitals in the Montreal area between 2005 and 2009. Population controls were identified from provincial electoral lists of French Montreal residents and frequency-matched to cases using 5-year age gr

The Role of Redox Chemistry in Mussel Byssus

The mussel byssus is a collection of extra-organismal, acellular, proteinaceous load bearing structures that are radial displayed and utilized by marine mussels to secure themselves to a multitude of substrates. A single byssal thread can be subdivided into the loading bearing thread and adhesive plaque, which provide tensile strength and adhesive strength respectively. Both regions of the byssus face their own unique challenges and have devised independent mechanisms to protect themselves against oxidative stresses. Here we present evidence the mussel utilizes isolated redox compartments to protect 3, 4-dihydroxyphenylalanine (Dopa) from oxidative damage in both the thread and plaque, permitting long lasting mechanical performance of the byssus. The byssus thread is an extremely tough core-shelled fiber that dissipates substantial amounts of energy during tensile loading. The mechanical performance of the shell is critically reliant on Dopa’s ability to form reversible iron-catecholate complexes at pH 8. However, the formation of these coordinate crosslinks is undercut by Dopa’s oxidation to Dopa-quinone, a spontaneous process at seawater conditions. Using a combination of electron and atomic force microscopy we identify a previously undescribed stratum situated between the core and shell. Spectroscopy results indicate this region is rich in thiol and thus will be called the thiol rich layer (TRL). We propose the TRL acts as an electron sink to protect the shell against oxidation. Additionally, indentation type atomic force microscopy reveals the TRL has intermediate mechanical properties which act as a mechanical buffer between the shell and core. The adhesive plaque is also reliant on Dopa. Dopa in the plaque is primarily responsible for strong adhesion but only if protected from oxidation at the adhesive-substratum interface. Dopa oxidation is thermodynamically favorable in seawater yet barely detectable in mature plaques. Experiments were designed to understand how plaques insulate Dopa-containing mfps against oxidation. Spectrometry and confocal fluorescence results indicate seawater sulfate triggers a mfp3 and mfp6 liquid-liquid phase separation (LLPS). Subsequently, cyclic voltammetry of LLPS material demonstrates DOPA’s redox potential is phase dependent. Furthermore, mass spectrometry and redox exchange assays indicate Dopa-containing mfp-3 and mfp-6 in phase-separated droplets remain stable despite rapid oxidation in the equilibrium solution. Taken together, the results suggest that a cohort of oxidation-prone proteins is endowed with phase-dependent redox stability. Moreover, in forming LLPS compartments, Dopa-proteins become reservoirs of chemical energy which can be called upon in the event of oxidative damage