Characterisation of Amyloid Nanostructures in the Natural Adhesive of Unicellular Subaerial Algae

Abstract

The composition and nanoscale mechanical characteristics of the adhesive from two species of subaerial green unicellular microalgae (Chlorophyta), Coccomyxa sp. and Glaphyrella trebouxiodes, have been studied using Raman spectroscopy, chemical staining, and atomic force microscopy (AFM). Raman spectroscopy confirmed the adhesive proteins of both species to be predominantly in ß-sheet conformations and composed of a number of hydrophobic amino acid residues. Chemical staining with Congo red and thioflavin-T dyes further confirmed the presence of amyloid-like structures. Probing the adhesives with AFM revealed highly ordered and repetitive mechanical responses indicative of highly ordered structures within the adhesive. The repetitive nature of the sawtooth response is typical of a “sacrificial bond” and “hidden length” mechanism, and what we -propose is the result of mechanical manipulation of individual molecules within an intermolecular ß-sheet that makes up the generic amyloid structure. The mechanical data show how amyloid provides cohesive strength to the adhesives, and this intrinsic mechanical property of an amyloid-based adhesive explains the ecological success of attachment of these subaerial microalgae on various surfaces in urban environments. It is unknown to what extent amyloid fibrils occur in algal adhesives, but we postulate that the amyloid structure could provide a widespread mechanism for mechanical strength.

Keywords:

• Algae
• Amyloid fibrils
• Atomic force microscopy (AFM)
• Nanomechanics
• Natural adhesives

ACKNOWLEDGMENT

We thank Professor Thomas Friedl, University of Göttingen, Germany, for supplying the algal isolates for the cultures used in these experiments. We are very grateful to Manuela Görs, University of Rostock, Germany, for assistance with cultures prepared for the Raman spectroscopy and the light micrographs. This work was funded by Science Foundation Ireland (07/IN1/B931), and in part by the Deutsche Forschungsgemeinschaft (Ka 899-13/1).

Notes

One of a Collection of papers honoring J. Herbert Waite, the recipient in February 2009 of The Adhesion Society Award for Excellence in Adhesion Science, Sponsored by 3M.