Recent progress in frequency modulation atomic force microscopy (FM-AFM) has enabled true atomic resolution imaging in liquid with piconewton order loading forces [1]. Significant advantages of using FM-AFM compared to contact-mode AFM is small loading forces especially in the lateral direction. The capability of high-resolution imaging with small loading force has made it possible to image individual hydration layers weakly interacting with the biological membranes with Angstrom resolution [2]. Moreover, lipid-ion networks formed by the mobile ions interacting with the lipid headgroups are directly imaged by FM-AFM with sub-Angstrom resolution [3]. These striking results have demonstrated that FM-AFM can provide biologically important information that cannot be obtained by conventional AFM techniques. In contrast to contact-mode AFM, the small lateral force in FM-AFM should also allow imaging of isolated macromolecules. However, FM-AFM imaging of isolated biomolecules with Angstrom resolution in liquid have not been reported. In this paper, we present first results showing the FM-AFM imaging capability of isolated biomolecules with Angstrom resolution in liquids.
Amyloid fibrils are quaternary protein structures formed from the non-specific folding (or misfolding), and subsequent aggregation of proteins into intermolecular β-sheets of infinite propagation. Since the deposition of amyloid fibrils are considered to cause major neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, they have been intensively investigated. In spite of the great interests, the molecular structure of the amyloid fibril has remained elusive because of the difficulty of growing well diffracting crystals. Here we directly image the internal structures of amyloid fibrils such as alpha-synuclein and IAPP as well as their constituent proto-filaments with Angstrom-resolution in water and phosphate buffer solution. The results clearly demonstrate the unique capability of FM-AFM to image Angstrom-scale structures of isolated biomolecules.
[1] T. Fukuma et al., Appl. Phys. Lett. 87 (2005) 034101.
[2] T. Fukuma et al., Biophys. J. in press.
[3] T. Fukuma et al., Phys. Rev. Lett. 98 (2007) 106101.
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