Sometimes, a tiny spark is enough to set evolution in motion. An international team led by Juan Carlos De la Concepcion, Nicholas Irwin and Yasin Dagdas at the GMI – Gregor Mendel Institute of Molecular Plant Biology of the Austrian Academy of Sciences (OeAW) discovered that subtle electrostatic changes can cause an ancient plant protein to break free from its original complex and take on new functions.

An Ancient Protein and A Major Puzzle

Cells operate like finely tuned machines: countless proteins interact in tightly coordinated systems. Many of these proteins are organized into fixed complexes – like gears in a clockwork. Such subunits are usually considered highly constrained in their evolution, as changes to one component could disrupt the entire system.

All the more surprising, then, is the case of the protein Exo70. It is part of the so-called eight-subunit exocyst complex, which is found in all eukaryotes – including animals, fungi, and humans – and is responsible for secretory processes within the cell. Despite its tight integration in this complex, Exo70 has multiplied and diversified dramatically over the course of plant evolution. In Arabidopsis thaliana (thale cress), the model organism of plant biology, for instance, more than 20 variants of this protein exist. How this diversity arose has long been a mystery.

Tiny Charge Shifts Unlock New Protein Functions

The team has now shown that the key lies in tiny electrostatic shifts. Subtle changes in the surface charge of Exo70 caused one variant of the protein to lose its tight association with the original exocyst complex. This “release” opened up new possibilities: the protein could become active in other parts of the cell, find new  interaction partners, and take on completely new roles.

Using structural modeling, biochemical analyses, and experiments in Arabidopsis thaliana and the liverwort Marchantia polymorpha, the researchers demonstrated this mechanism in detail. They describe it as “protein complex escape” – the escape of a protein from its original assembly through minimal electrostatic alterations.

A Universal Engine of Evolution?

This “complex escape” could represent a general mechanism by which cells acquire new functions: small physical effects that drive major evolutionary change – without requiring deep genetic mutations. Because multisubunit complexes like the exocyst are widely conserved across the tree of life, the researchers propose that similar “complex escape” events may have occurred throughout evolution. They suggest that electrostatic decoupling may have played a broader role in the evolutionary innovations that gave rise to the immense diversity of modern organisms from a shared ancestral origin.