Mussel byssus

Resilin and elastin have relatively high extensibility and resilience, but as compared to the collagen and the silks, the proteins sacrifice stiffness (elastic modulus) and strength (see Table 2). Collagen and dragUne sflk are much stiffer materials, but lack the extensibility that is characteristic of the rubber-like proteins. On the other hand, the mussel byssus fibers and the viscid silk have the extensibility of resilin and elastin, but lack the resilience [208]. 

T.J. Deming, Mussel byssus and biomolecular materials, Curr. 

A closer look at the system, however, does pique curiosity. The initial pH within the chamber is not 7 but 2-3, and the reactions are non-equilibrium, often irreversible, and involve other intermediates that can become important end products. The acidic pH represents a problem in that thiolates, not thiols, are the operative reductants, thus cannot reduce at pH values below their typical i.e. 8-9. This is resolved by proteins, including mfp-6, by sequence specific effects such as flanking cationic groups that reduce the Cys pK, e.g. redox active Cys-59 in DsB-A has a p Tg of 3.5. Several Cys residues in mfp-6 are acidic, but specific p Tg values have yet to be measured. The non-equilibrium, irreversible nature of the oxidation reactions is a particular problem with Dopa and other catechols. Indeed, the chemical fate of catechols in mussel byssus is highly dependent on their location. In the cuticle, the fate of Dopa appears to be tris catecholato-Fe complexes in the thread and plaque core, Dopa forms covalent cross-links after oxidation to quinones, whereas at the plaque-substratum interface, it is some combination of metal chelates and reduced H-bonded Dopa on metal oxide surfaces. The reducing capacity of mfp-6 plays a role in maximizing the latter and is astonishingly sustained, i.e. >21 days. ... 

Haningtrai MJ, Gupta HS, Fratzl P, Waite JH (2009) Collagen insulated from tensile damage by dmnains that unfold reversibly in situ X-ray investigation of mechanical yield and damage repair in the mussel byssus. J Struct Biol 167 47-54... 

Waite JH, Qin XX, Coyne KJ (1998) The peculiar collagens of mussel byssus. Matrix Biol 17 93-106... 

Carrington E, Gosline JM (2004) Mechanical design of mussel byssus load cycle and strain rate dependence. Am Malacol Bull 18 135-142... 

Deming, T.J. (1999) Mussel byssus and biomolecular materials. Curr. Opin. Chem. Biol., 3,100-105. 

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