Giant Bent-Core Mesogens in the Thread Forming Process of Marine Mussels

Abstract

In marine mussels (Mytilus), byssal threads are made in minutes from prefabricated smectic polymer liquid crystals by a process resembling reaction injection molding. The mesogens in these arrays are known to be natural block copolymers with rodlike collagen cores. Using atomic force microscopy, it was shown that these collagenous mesogens are bent-core or banana-shaped in a manner that is consistent with and predictable from their amino acid sequence. The overall bend angle in preCOL-NG in Mytilus galloprovincialis is about 130 degrees. The mesogens have a center-to-center separation of approximately 22 nm and a length of 200 nm. It is evident that the smectic structure of the prefabricated mesophases remains largely intact over 1-3 microm distances in the molded fibers and is presumably locked in place during molding by cross-linking. Like the smectic liquid crystals of many synthetic banana mesogens, the collagenous mesogens of the byssal threads exhibit SmC(2) symmetry with a characteristic tilt of 24.6 degrees. At about 100% extension, this tilt is considerably reduced and the globular end domains are no longer visible presumably because they have been unraveled.

Holdfast heroics: comparing the molecular and mechanical properties ofMytilus californianusbyssal threads

“…This is very reminiscent of the smectic ordering of preCols seen in byssal threads by atomic force microscopy (AFM) (Hassenkam et al, 2004). Bella et al suggest the deletion may provide a 'registration marker' favoring in-register parallel packing rather than the quarter stagger typical of fibrillar collagens (Bella et al, 2006).…”

“…Second, we assume that the molecular packing is similar between species, and that any differences in architecture play a minor role in mechanical differences. Since the overall domain structure of the preCols has been shown to be similar in all species, it is a safe assumption that the preCols of M. californianus maintain a similar smectic alignment as threads of M. galloprovincialis (Hassenkam et al, 2004).…”

“…In addition, the byssus is emerging as an important paradigm for the bioinspired engineering of water-resistant adhesives (Lee et al, 2006), functionally graded polymers (van Hest and Tirrell, 2001;Waite et al, 2004), and injection molding of liquid crystals (Hassenkam et al, 2004). The utility of such paradigms relies on the depth to which structure-function relationships are understood.…”

Mussel adhesion – essential footwork

“…In response to poorly understood signals, rows of granules migrate through narrow elongations of cytoplasm before releasing their contents into conducting tubules that connect with the ventral groove or distal depression of the foot. Thread formation occurs in the ventral groove and resembles injection molding of collagenous liquid crystals (Waite, 1992;Hassenkam et al, 2004), whereas injection molding of the plaque in the distal depression produces a porous solid. During thread formation, byssal proteins are secreted incrementally along a distal to proximal trajectory.…”

Exploring Molecular and Mechanical Gradients in Structural Bioscaffolds

“…Model B does, however, get added support from AFM imaging. Topographical maps based on scanning AFM reveal a lateral uniformity consistent with smectic arrays; more to the point, preCOL-Ds, which are detectable by their multiple bends, appear to follow one another in axial sequence with a C 2 point group symmetry ( Figure 4B) (18). This would seem to rule out model A with alternating preCOL-NG.…”