Imaging of proteins by scanning tunnelling microscopy

Area of Science:

• Biophysics
• Biochemistry
• Materials Science

Background:

• Understanding protein structure is crucial for molecular biology and medicine.
• Traditional methods like X-ray crystallography and electron microscopy have limitations.
• Scanning tunnelling microscopy (STM) offers a high-resolution surface imaging technique.

Purpose of the Study:

• To investigate the potential of Scanning Tunnelling Microscopy (STM) for visualizing protein structures.
• To examine the surface topography of specific proteins: immunoglobulin G (IgG), Complement component 1q (C1q), and ATP-citrate lyase (ACL).
• To compare STM findings with existing structural data from other techniques.

Main Methods:

• Proteins (IgG, C1q, ACL) were deposited onto a highly ordered pyrolytic graphite surface.
• Scanning Tunnelling Microscopy (STM) was employed to image the deposited protein molecules at high resolution.
• Structural interpretations were made based on the obtained topographical images.

Main Results:

• Images of immunoglobulin G (IgG) were consistent with its known tri-lobed structure.
• Complement component 1q (C1q) images presented a different morphology than the "tulip bunch" model, suggesting potential aggregation of its globular heads.
• ATP-citrate lyase (ACL) molecules appeared as distinct units, with some evidence of internal substructure.

Conclusions:

• STM demonstrates significant potential for studying protein structures at the nanoscale.
• Interpreting STM images of proteins, especially those with unknown structures, requires careful consideration and can be challenging.
• Further development and validation are needed to fully leverage STM in structural biology.