The Relative Diffusivities of Bound and Unbound Protein Can Control Chemotactic Directionality

TL;DR

This paper presents a kinetic model showing how the relative diffusivities of bound and unbound proteins influence their chemotactic movement, predicting directional responses based on diffusivity differences.

Contribution

It introduces a theoretical framework linking protein diffusivity differences to chemotactic directionality, highlighting the importance of measuring bound and unbound protein diffusivities.

Findings

Net movement up the gradient when bound diffusivity is lower

Movement down the gradient when bound diffusivity is higher

Emphasizes measuring bound protein diffusivity for understanding chemotaxis

Abstract

Enzyme-based systems have been shown to undergo directional motion in response to their substrate gradient. Here, we formulate a kinetic model to analyze the directional movement of an ensemble of protein molecules in response to a gradient of the ligand. A similar analysis has been performed to probe the motion of enzyme molecules in response to a gradient of the substrate under catalytic conditions. In both cases, a net movement up the ligand/substrate gradient is predicted when the diffusivity of the ligand/substrate-bound protein is lower than that of the unbound protein (positive chemotaxis). Conversely, movement down the ligand/substrate gradient is expected when the diffusivity of the ligand/substrate-bound protein is higher than that of the unbound protein (negative chemotaxis). The work underscores the critical importance of measuring the diffusivity of the bound protein and compare it with that of the free protein.