As a key family of molecular motors, kinesins can walk along microtubules to drive long-range intracellular transport using the chemical energy derived from ATP hydrolysis. When not transporting cargoes, most kinesin motors adopt an autoinhibited state to avoid futile ATP hydrolysis and potential traffic jams on microtubule tracks. The autoinhibited conformation of kinesin motors would therefore ensure the precise spatial and temporal regulation of the motor motility.

Kinesin-3 is a unique family of kinesin motors for intracellular transport with superprocessivity. A research group led by Prof. FENG Wei from Institute of Biophysics, Chinese Academy of Sciences has been working on kinesin-3 over a number of years. In their previous studies, they have proposed the potential regulatory mechanism for the active conformation of kinesin-3 (Structure 2012, JBC 2016, JMB 2018). However, the mechanism underlying kinesin-3 autoinhibition remains poorly understood.

The autoinhibited conformation of kinesin-3 is predominantly mediated by a coiled-coil segment (coiled-coil 1) that follows the neck and motor domains. In this study, they biochemically characterized the motor domain-containing fragments of kinesin-3 KIF13B and found that the autoinhibitory coiled-coil segment sequesters the neck domain to keep the motor in a monomeric state and also inhibits the ATPase activity of the motor domain.

To explore the underlying mechanism for the coiled-coil 1-mediated autoinhibition, they determined the crystal structure of the autoinhibited fragment of kinesin-3 KIF13B (containing the neck and motor domains and coiled-coil 1). The structure revealed that the autoinhibitory coiled-coil segment is unexpectedly broken into two short helices that interact with both the neck and motor domains and fasten them together. The coiled-coil segment-mediated integration of the neck and motor domains not only inhibits the neck domain-mediated dimerization but also prevents the release of ADP from the motor domain. Based on the structural analysis, they further made the point mutations in the inter-domain interaction interface in the autoinhibited fragment and demonstrated that disruptions of the inter-domain interactions between the three domains relieved the autoinhibited conformation and restored the motor activity.

Based on all the biochemical and structural data, they finally proposed a working model for the coiled-coil 1-mediated autoinhibition of kinesin-3. In this model, the motor domain is also referred to as the head. With the aid of the motor head, the coiled-coil 1 segment tightly locks down the entire neck domain. This "head-aided lockdown of neck" mechanism mediated by the internal coiled-coil segment in kinesin-3 may represent a previously unknown paradigm for kinesin autoinhibition.

This work has been published online ahead of print in Proceedings of the National Academy of Sciences on November 21, 2018 entitled "Coiled-coil 1-mediated fastening of the neck and motor domains for kinesin-3 autoinhibition". The work was supported by grants from the National Key R&D Program of China and the National Natural Science Foundation of China.

Figure 1: A working model for the coiled-coil 1-mediated autoinhibition of kinesin-3

Article link: http://www.pnas.org/content/early/2018/11/21/1811209115

Contact: Wei Feng
Institute of Biophysics, Chinese Academy of Sciences
Beijing 100101,China
Phone: 86-10-64888751
Email: wfeng@ibp.ac.cn

(Reported by Feng Wei's group)