Applications brief: Nanoscale resolution in infrared imaging of protein-containing lipid membranes

Key points


  • Achieved very clear resolution of a single trimeric protein structure (~10nm)
  • Resolution is almost three orders of magnitude lower than conventional IR-adsorption microscopy
  • AFM-IR was used to examine lipoprotein multi-bilayers formed by lipid-protein membranes that contain a mixture of two chloroplast lipids
  • Results showed that protein distribution in the multilayer is highly inhomogeneous and revealed the formation of supramolecular structures and that that they can be stabilized by intermolecular hydrogen bonds

Key words

AFM-IR | nanoIR | multi-bilayers | proteins

Authors

W. I. Gruszecki, A. J. Kulik, E. Janik, J. Bednarska, R. Luchowski, W. Grudzinskia and G. Dietler

Abstract

The precise imaging of biomolecular entities contributes to an understanding of the relationship between their structure and function. However, the resolution of conventional infrared microscopic imaging is diffraction limited and does not exceed a few micrometers. Atomic force microscopy, on the other hand, can detect infrared absorption down to the sub-micrometer level.

In the present report, we demonstrate that for multi-bilayer lipid samples containing the plant photosynthetic pigment–protein complex LHCII, the resolution of this latter technique can be better than 20 nm. Such a high resolution is attributable to two factors: (i) the relatively high infrared absorption by the complex that is integrated perpendicular to the plane of the multilayer film, and (ii) the distinctly different mechanical properties and thermal conductivity of the lipid and protein components of the sample.

Topography, stiffness map, and IR-adsorption pattern of a 1.2µm thick lipoprotein multi-bilayer. The white crosses in the IR-adsorption image are locations on the sample where spectra were recorded.
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