Broad Velocity Distributions in SFIV Helicases are a Consequence of Heterogeneity

Abstract

Helicases are a class of molecular motors, which utilize chemical energy to translocate along nucleic acids and unwind double stranded nucleic acids. The velocity distribution measured using single molecule experiments is unsually broad suggestive of heterogeneity, a ubiquitous property that now has been found in many helicases. Using a simple stochastic kinetic model to analyze the experimental distribution widths, we quantitatively prove the existence of heterogeneity in two Superfamily-IV helicases, T7 gp4 and T4 gp41. Our theory suggests a plausible origin of heterogeneity in these motors, and also provides a method of distinguishing between various kinds of heterogeneity. Our theory is general, and could be easily applied to other processive helicases to test for the presence of heterogeneity.