Diatom Adhesive Mucilage Contains Distinct Supramolecular Assemblies of a Single Modular Protein

Abstract

A previous study used atomic force microscopy saw-tooth retraction curves to characterize the adhesive mucilage pads of the diatom Toxarium undulatum. The major mucilage component consisted of adhesive nanofibers (ANFs) made up of modular proteins arranged into cohesive units, each containing a set number of modular proteins aligned in parallel. This study shows that T. undulatum adhesive mucilage is a biocomposite containing four additional adhesive components, including single modular proteins that are likely to be the structural units from which the ANFs are assembled. Two further distinct supramolecular assemblies were observed to coexist with ANFs (ANFs II and III), along with a continuum of single modular proteins through oligomers made up of varying numbers of modular proteins arranged in parallel. All components of the adhesive biocomposite produce a characteristic force spectrum with the same interpeak distance (35.3 +/- 0.3 (mean +/- SE) nm), suggesting they are derived from discrete supramolecular assemblies of the same modular protein, but they are distinguishable from one another based on the rupture force, persistence length, and interpeak force measured from their saw-tooth curves.

Atomic force microscopy of the morphology and mechanical behaviour of barnacle cyprid footprint proteins at the nanoscale

“…Footprint nanofibrils underwent bond reformation when allowed to relax as the tip moved towards the surface. In the next force-separation curve, the rupturing of sacrificial bonds was again observed, suggesting that footprint protein(s) possesses 'self-healing' ability, similar to that reported in titin, silk, diatom adhesives and other proteins (Rief et al 1997a;Becker et al 2003;Dugdale et al 2005Dugdale et al , 2006a. The footprint appearance observed in figure 2 supported the hypothesis that the fibrils are composed of complex and interconnected smaller macromolecular subunits.…”

“…Consequently, many naturally occurring bioadhesives are unusually tough by synthetic adhesive standards (Groshong 2007). In fact, sacrificial bonds are abundant in nature and can be found in many biomaterials such as bone (Smith et al 1999;Fantner et al 2005), spider silk (Becker et al 2003), natural adhesives from algae (Callow et al 2000;Mostaert et al 2006;Mostaert & Jarvis 2007), diatom mucilage (Higgins et al 2003;Dugdale et al 2005Dugdale et al , 2006a and adult barnacle cement (Sun et al 2004). In this paper, the morphology and nanomechanical properties of cyprid footprints were investigated with AFM.…”

On the remarkable mechanostability of scaffoldins and the mechanical clamp motif

“…In the green fluorescent protein (16) the high-force peaks observed when pulling from nonterminal amino acids (548 pN at a pulling speed about one order-of-magnitude faster) can be assumed to be a pure epiphenomenon (i.e., with no physiological relevance) because this protein is not thought to be subjected to mechanical stress. In the adhesive nanofibers (likely proteinaceous) from the extracellular matrix of a fouling diatom, forces of 135-872 pN were reported (at double the pulling speed) (17). Nevertheless, in these experiments the high forces observed are interpreted as being derived from oligomers of parallel molecules in register that are pulled simultaneously.…”

Towards a nanomechanical basis for temporary adhesion in barnacle cyprids ( Semibalanus balanoides )

“…Figure 2c (3) is a high-resolution AFM image of unmodified, hydrated footprint material on R-NH 2 . Diagnostic 'fingerprint' signatures of selfassembled adhesive nanofibres have been observed by AFM force spectroscopy in the mucilage of diatoms and the terrestrial alga Prasiola linearis (Higgins et al 2003;Dugdale et al 2005Dugdale et al , 2006Mostaert et al 2006). These adhesive proteins are able to form web-like networks to provide mechanical toughness which enhances the adhesive's ability to resist deformation under shear forces (Smith et al 1999).…”