Electrostatic changes enabled the diversification of an exocyst subunit via protein complex escape

Area of Science:

• Evolutionary biology
• Molecular and cell biology
• Plant science

Background:

• Protein neofunctionalization drives cellular complexity.
• Multimeric protein subunits are typically evolutionarily constrained.
• Plant Exo70 subunits of the exocyst complex show unusual expansion and diversification.

Purpose of the Study:

• Investigate the mechanism behind plant Exo70 diversification.
• Determine how Exo70 subunits achieve functional divergence despite complex integration.
• Explore the evolutionary implications of Exo70's 'complex escape'.

Main Methods:

• Comparative genomics and ancestral reconstruction in land plants.
• Biochemical and functional analyses in Marchantia polymorpha and Arabidopsis thaliana.
• Investigating electrostatic changes in the Exo70 N-terminal helix.

Main Results:

• Electrostatic changes in Exo70's N-terminal helix facilitated dissociation from the exocyst complex.
• This 'complex escape' allowed Exo70 paralogs to gain novel localizations, interactomes, and functions.
• Ancestral reconstructions show the electrostatic shift predates Exo70 family radiation, with later reassociation in some lineages.

Conclusions:

• A reversible 'complex escape' mechanism allows protein subunits to overcome evolutionary constraints.
• This mechanism, driven by electrostatic changes, enables neofunctionalization and cellular innovation.
• The findings offer a generalizable route for protein evolution beyond complex integration limitations.