Selection for size in molecular self-assembly drives the de novo evolution of a molecular machine

TL;DR

This paper theoretically investigates how molecular machines, specifically filament treadmilling, can evolve de novo through selection for a single physical trait, revealing insights into the emergence of complex molecular functions.

Contribution

It demonstrates that complex molecular functions like filament treadmilling can evolve de novo under simple selection pressures for a physical feature.

Findings

Filament treadmilling can emerge as a result of selecting for target polymer length.

Other assembly dynamics do not evolve under the same selection conditions.

Complex molecular functions can arise de novo from simple physical feature selection.

Abstract

The functioning of machines typically requires a concerted action of their parts. This requirement also holds for molecular motors that drive vital cellular processes and imposes constraints on their conformational changes as well as the rates at which they occur. It remains unclear whether features required for functional molecular machines can emerge simultaneously or require sequential adaptation to different selection pressures during evolution. We address this question by theoretically analyzing the evolution of filament treadmilling. This process refers to the self-assembly of linear polymers that grow and shrink at equal rates at their opposite ends. It constitutes a simple biological molecular machine that is notably involved in bacterial cell division and requires that several conditions are met. In our simulation framework, treadmilling emerges as a consequence of selecting for a target average polymer length. We discuss, why other forms of assembly dynamics, which also reach the imposed target length, do not evolve in our simulations. Our work shows that complex molecular functions can evolve de novo under selection for a single physical feature.