Processivity of the monomeric KLP-6 kinesin and a Brownian ratchet model with symmetric potentials

Abstract

Most kinesin molecular motors dimerize to move processively and efficiently along microtubules; however, some can maintain processivity even in a monomeric state. Previous studies have suggested that asymmetric potentials between the motor domain and microtubules underlie this motility. In this study, we demonstrate that the kinesin-3 family motor protein KLP-6 can move along microtubules as a monomer upon release of autoinhibition. This motility can be explained by a change in length between the head and tail, rather than by asymmetric potentials. Using mass photometry and single-molecule assays, we confirmed that activated full-length KLP-6 is monomeric both in solution and on microtubules. KLP-6 possesses a microtubule-binding tail domain, and its motor domain does not exhibit biased movement, indicating that the tail domain is crucial for the processive movement of monomeric KLP-6. We developed a mathematical model to explain the unidirectional movement of monomeric KLP-6. Our model concludes that a slight conformational change driven by neck-linker docking in the motor domain enables the monomeric kinesin to move unidirectionally if a second microtubule-binding domain exists. SIGNIFICANCEKinesin molecular motors are designed to move efficiently using two heads. Studying these biological molecular motors provides valuable insights into the mechanisms that generate unidirectional movements amidst intense thermal fluctuations. This study reveals that the monomeric kinesin-3 KLP-6 can move along microtubules through interactions with its tail domain. The proposed Brownian ratchet model explains this movement by considering a change in stalk length caused by neck-linker docking rather than asymmetric potentials. This model suggests that a slight conformational change can achieve robust processive movement of kinesin. These findings have significant implications for understanding Brownian ratchet motors and designing rational artificial molecular motors.