Microtubule Motors
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What are the three major cytoskeletal motor families?
Myosins (actin-based), Kinesins (microtubule + end-directed), and Dyneins (microtubule – end-directed).
Which direction do most kinesins move, and what is the exception?
Most move toward the microtubule plus end; exceptions like Ncd move to the minus end.
Which direction do cytoplasmic dyneins move?
Toward the microtubule minus end.
What cellular functions depend on microtubule motors?
Organelle transport, vesicle trafficking, mitosis, ciliary/flagellar motility, and spatial cell organisation.
How do motors achieve functional diversity if their motor domains are conserved?
Through additional accessory and regulatory domains or subunits that confer cargo specificity and control.
What is the composition of the kinesin-1 complex?
A heterotetramer of two heavy chains (KIF5 A/B/C) and two light chains (KLC 1-4).
What are the main functional regions of kinesin-1?
Motor (ATPase) heads, a coiled-coil stalk, and a cargo-binding tail with regulatory domains.
What general type of cargo does KIF5B transport?
Vesicles, mRNAs, large protein complexes, and even viruses.
What is the cellular role of kinesin-1?
Plus-end-directed transport along microtubules, especially critical for axonal trafficking.
What diseases are associated with kinesin-1 mutations?
ALS, hereditary spastic paraplegia (HSP), Alzheimer’s, and MCD depending on gene variant.
How is kinesin-1 activity autoinhibited?
Folding of the heavy-chain tail back onto the motor domains locks them in an ADP-bound inactive state.
Which motif in the tail peptide is crucial for autoinhibition?
The IAK motif.
What experimental techniques first revealed kinesin-1’s folding behaviour?
Rotary-shadowing and negative-stain electron microscopy.
How is kinesin-1 activated from its inhibited conformation?
Cargo-adaptor binding to the light-chain TPR domains relieves inhibition and allows processive movement.
What small GTPase recruits kinesin-1 to lysosomes?
Arl8.
Which adaptor links Arl8-positive lysosomes to kinesin-1?
SKIP (SifA-and-Kinesin-Interacting-Protein).
What motif in SKIP mediates its interaction with kinesin-1?
A W-acidic (“WD”) motif recognised by KLC TPR domains.
What unresolved question remains about adaptor-induced activation?
How binding of a short peptide causes large-scale conformational rearrangement of the motor complex.
What is Nesprin-4 and what does it do?
A nuclear-envelope cargo adaptor that binds kinesin-1 via a W-acidic motif and drives nuclear positioning.
Which microtubule-associated protein enhances kinesin-1 activity with Nesprin-4?
MAP7.
What experimental method visualises single kinesin-1 runs?
Single-molecule TIRF motility assays analysed by kymographs.
What information does a kymograph show?
Displacement (x-axis) vs time (y-axis) revealing motor velocity, run length, and directionality.
Why are kinesin-1 heavy- and light-chain isoforms important biologically?
They confer cell- and cargo-specific regulation; mis-expression causes distinct human diseases.
What high-resolution prediction and validation recently came from Bristol labs?
AlphaFold 3-based model of the folded, inhibited kinesin-1 complex experimentally confirmed by EM.