Single Adhesive Nanofibers from a Live Diatom Have the Signature Fingerprint of Modular Proteins

Abstract

The adhesive and mechanical properties of a cell-substratum adhesive secreted by live diatom cells were examined in situ using atomic force microscopy. The resulting force curves have a regular saw-tooth pattern, the characteristic fingerprint of modular proteins, and when bridged between tip and surface can repeatedly be stretched and relaxed resulting in precisely overlaying saw-tooth curves (up to approximately 600 successive cycles). The average rupture force of the peaks is 0.794 +/- 0.007 (mean +/- SE) nN at a loading rate of 0.8 microm/s and the average persistence length is 0.026 +/- <0.001 (mean +/- SE) nm (fit using the worm-like chain model). We propose that we are pulling on single adhesive nanofibers, each a cohesive unit composed of a set number of modular proteins aligned in register. Furthermore, we can observe and differentiate when up to three adhesive nanofibers are pulled based upon multimodal distributions of force and persistence length. The high force required for bond rupture, high extensibility (approximately 1.2 microm), and the accurate and rapid refolding upon relaxation, together provide strong and flexible properties ideally suited for the cell-substratum adhesion of this fouling diatom and allow us to understand the mechanism responsible for the strength of adhesion.

Nanomechanics of new materials — AFM and computer modelling studies of trichoptera silk

“…These resemble a pattern seen when unfolding globular proteins [30] or amyloidal beta structures [27] and cloned nanofiber proteins from spiderwebs [31]. Such a pattern was also observed in secretions of microorganisms that stick to underwater surfaces [32,33]. A hysteresis in stretching/relaxation, providing good energy dissipation during stretching is also present.…”

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

“…However, in the present case, the initial force -extension curves did not represent single-protein pulling. Rather, it is likely that we observed the stretching of bundles of protein aggregates and nanofibres, connected via sacrificial bonds (Smith et al 1999;Dugdale et al 2005Dugdale et al , 2006aFantner et al 2005Fantner et al , 2006Groshong 2007). Once a sacrificial bond was broken, the shielded polypeptide chain of the protein unfolded, resulting in a sharp reduction in tension.…”

“…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.…”

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).…”