Time traces of individual kinesin motors suggest functional heterogeneity

TL;DR

This study reveals significant functional heterogeneity among individual kinesin motors, challenging the assumption of uniformity in motor protein assays and proposing a new analysis method for heterogeneous data.

Contribution

It demonstrates the existence of motor-to-motor variability in kinesin velocities and introduces a decomposition approach to analyze heterogeneous single-molecule data.

Findings

Individual kinesin motors show wide velocity variation.

Heterogeneity affects ensemble-averaged measurements.

Proposed method decomposes data into homogeneous subensembles.

Abstract

Conventional analysis of in vitro assays of motor proteins rests on the assumption that all proteins with the same chemical composition function identically; however molecule-to-molecule variation is often seen even in well-controlled experiments. In an effort to obtain a statistically meaningful set of time traces that simultaneously avoid any experimental artifacts, we performed quantum-dot labeled kinesin experiments on both surface and levitated microtubules. Similar to glassy systems, we found that mean velocities of individual kinesin motors vary widely from one motor to another, the variation of which is greater than that expected from the stochastic variation of stepping times. In the presence of heterogeneity, an ensemble-averaged quantity such as diffusion constant or randomness parameter is ill-defined. We propose to analyze heterogeneous data from single molecule measurements by decomposing them into homogeneous subensembles.