Microtubule seams are not mechanically weak defects.

Area of Science:

• Cell biology
• Biophysics
• Structural biology

Background:

• Microtubule rigidity is essential for cellular structure and intracellular transport.
• Altering tubulin dimer arrangement affects microtubule protofilament number and lattice type.
• High salt concentrations can induce altered lattice types and increased seam defects in microtubules.

Purpose of the Study:

• To experimentally determine the mechanical properties of microtubules polymerized under high salt conditions.
• To investigate the impact of altered lattice types and seam defects on microtubule flexibility.
• To test the hypothesis that microtubule seams are mechanically weaker points.

Main Methods:

• Direct measurement of the persistence length of freely fluctuating microtubules.
• Comparison of microtubules polymerized with and without high salt concentrations.
• Analysis of the relationship between cross-sectional radius and bending rigidity.

Main Results:

• Microtubules polymerized in high salt exhibited a two-fold decrease in persistence length, indicating increased flexibility.
• The reduced flexibility was attributed to a smaller cross-sectional radius, not altered lattice interactions.
• The study found no evidence that microtubule seams are mechanically weaker than the typical lattice.

Conclusions:

• High salt conditions increase microtubule flexibility primarily by reducing their radius.
• The mechanical integrity of the microtubule seam is comparable to the regular lattice structure.
• This finding challenges previous speculations about seam defects representing a significant mechanical weakness.