Commensurability between protein nanotubes in contractile ejection nanomachines

Area of Science:

• Biophysics
• Structural Biology
• Nanotechnology

Background:

• Contractile ejection nanomachines, such as bacteriophage T4 tails and pyocin R2, are essential for translocating molecules across cell membranes.
• These machines function as sheath-tube assemblies, utilizing structural rearrangements for their operation.

Purpose of the Study:

• To investigate the geometrical relationship between the sheath and inner tube structures in contractile ejection nanomachines.
• To elucidate how sheath contraction and twisting impact nanomachine efficiency and function.

Main Methods:

• Analysis of the structural rearrangements in bacteriophage T4 tail and pyocin R2 sheath contraction.
• Application of the Frank and van der Merwe theory of commensurability to model protein nanotube interactions.
• Derivation of an expression for the interaction energy between the sheath and inner tube.

Main Results:

• The contracted sheath becomes commensurate with the inner tube, revealing a novel geometrical relationship between their symmetries.
• Commensurability between the sheath and inner tube reduces both interaction and total system energy.
• The observed energy gain enhances the torque of the inner tube, facilitating cell membrane penetration.

Conclusions:

• The commensurability of the contracted sheath with the inner tube is a key factor in the efficient operation of these nanomachines.
• This geometrical relationship optimizes energy transfer, leading to increased torque for membrane disruption.
• The findings provide fundamental insights into the mechanics of viral and bacterial protein nanomachines.