Vectorial Loading of Processive Motor Proteins: Implementing a Landscape Picture

TL;DR

This paper explores the effects of vectorial forces on processive motor proteins, providing a framework to understand how different directional loads influence their movement and force generation.

Contribution

It introduces a landscape picture for analyzing how multi-directional forces affect molecular motor function, extending previous scalar load models to a vectorial force context.

Findings

Develops a theoretical framework for vectorial force effects on motors.

Analyzes experimental data involving perpendicular and assisting loads.

Provides insights into the molecular mechanisms under complex force conditions.

Abstract

Individual processive molecular motors, of which conventional kinesin is the most studied quantitatively, move along polar molecular tracks and, by exerting a force ${\bm F} = (F_x,F_y,F_z)$ on a tether, drag cellular cargoes, {\em in vivo}, or spherical beads, {\em in vitro}, taking up to hundreds of nanometer-scale steps. From observations of velocities and the dispersion of displacements with time, under measured forces and controlled fuel supply (typically ATP), one may hope to obtain insight into the molecular motions undergone in the individual steps. In the simplest situation, the load force ${\bm F}$ may be regarded as a scalar resisting force, $F_x < 0$, acting parallel to the track: however, experiments, originally by Gittes {\em et al.} (1996), have imposed perpendicular (or vertical) loads, $F_z > 0$, while more recently Block and coworkers (2002, 2003) and Carter and Cross (2005) have studied {\em assisting} (or reverse) loads, $F_x > 0$, and also sideways (or transverse) loads $F_y \neq 0$.