Herding of proteins by the ends of shrinking polymers

TL;DR

This paper introduces a novel mechanism called 'herding' where proteins bind to shrinking biopolymers, become enriched at the ends, and regulate their dynamics, supported by theoretical models and experimental evidence.

Contribution

It proposes and formalizes a new 'herding' mechanism for protein localization at shrinking polymer ends, with experimental validation involving spastin.

Findings

Proteins can spontaneously enrich at shrinking polymer ends via herding.

The herding mechanism is supported by both lattice-gas and continuum models.

Experimental evidence shows spastin employs this herding process.

Abstract

The control of biopolymer length is mediated by proteins that localize to polymer ends and regulate polymerization dynamics. Several mechanisms have been proposed to achieve end localization. Here, we propose a novel mechanism by which a protein that binds to a shrinking polymer and slows its shrinkage will be spontaneously enriched at the shrinking end through a "herding" effect. We formalize this process using both a lattice-gas model and a continuum description, and we present experimental evidence that the microtubule regulator spastin employs this mechanism. Our findings extend to more general problems involving diffusion within shrinking domains.