Approaching microtubule structure with the scanning tunneling microscope (STM)

Area of Science:

• Biophysics
• Cell Biology
• Microscopy

Background:

• Microtubules are essential cytoskeletal polymers composed of alpha and beta tubulin heterodimers.
• Understanding microtubule structure is crucial for cell function and disease research.
• Classical methods like electron microscopy and X-ray scattering provide lower resolution structural data.

Purpose of the Study:

• To investigate the arrangement of tubulin subunits within the microtubule wall using scanning tunneling microscopy (STM).
• To determine the periodicity and lattice type of tubulin monomers.
• To assess the compatibility of observed structures with existing helical models of microtubule assembly.

Main Methods:

• High-resolution imaging of microtubules using scanning tunneling microscopy.
• Analysis of STM images to identify subunit periodicity and arrangement.
• Comparison of experimental data with theoretical models of microtubule structure.

Main Results:

• STM revealed distinct rows of tubulin subunits with a periodicity of 3.8 +/- 0.4 nm.
• The separation between these rows was measured at 4.8 +/- 0.4 nm.
• STM images indicated a 'B-type' lattice arrangement and resolved individual alpha and beta tubulin monomers, supporting a three-start helix model.

Conclusions:

• Scanning tunneling microscopy provides direct, high-resolution structural information on microtubule organization.
• STM can resolve individual tubulin monomers and their lattice arrangement within protofilaments.
• STM serves as a valuable complementary technique to electron microscopy and X-ray scattering for studying macromolecular assemblies.