Kinesin binding

Abstract: The membrane anchor for the molecular motor kinesin is a critical site involved in intracellular membrane trafficking. Monoclonal antibodies specific for the cytoplasmic surface of chick brain microsomes were used to define proteins involved in microtubule-dependent transport. One of four antibodies tested inhibited plus-end-directed vesicle motility by approximately 90 percent even as a monovalent Fab fragment and reduced kinesin binding to vesicles. This antibody bound to the cytoplasmic domain of kinectin, an integral membrane protein of the endoplasmic reticulum that binds to kinesin. Thus, kinectin acted as a membrane anchor protein for kinesin-driven vesicle motility.

Abstract: Microtubules (MTs) are polymers assembled from αβ-tubulin heterodimers that display the hallmark behavior of dynamic instability. MT dynamics are driven by GTP hydrolysis within the MT lattice, and are highly regulated by a number of MT-associated proteins (MAPs). How MAPs affect MTs is still not fully understood, partly due to a lack of high-resolution structural data on undecorated MTs, which need to serve as a baseline for further comparisons. Here we report three structures of MTs in different nucleotide states (GMPCPP, GDP, and GTPγS) at near-atomic resolution and in the absence of any binding proteins. These structures allowed us to differentiate the effects of nucleotide state versus MAP binding on MT structure. Kinesin binding has a small effect on the extended, GMPCPP-bound lattice, but hardly affects the compacted GDP-MT lattice, while binding of end-binding (EB) proteins can induce lattice compaction (together with lattice twist) in MTs that were initially in an extended and more stable state. We propose a MT lattice-centric model in which the MT lattice serves as a platform that integrates internal tubulin signals, such as nucleotide state, with outside signals, such as binding of MAPs or mechanical forces, resulting in global lattice rearrangements that in turn affect the affinity of other MT partners and result in the exquisite regulation of MT dynamics.