Lis1 activates dynein motility by modulating its pairing with dynactin

Abstract

Lissencephaly-1 (Lis1) is a key cofactor for dynein-mediated intracellular transport towards the minus-ends of microtubules (MTs). It remains unclear whether Lis1 serves as an inhibitor or an activator of mammalian dynein motility. Here we use single-molecule imaging and optical trapping to show that Lis1 does not directly alter the stepping and force production of individual dynein motors assembled with dynactin and a cargo adaptor. Instead, Lis1 promotes the formation of an active complex with dynactin. Lis1 also favors the recruitment of two dyneins to dynactin, resulting in increased velocity, higher force production and more effective competition against kinesin in a tug-of-war. Lis1 dissociates from motile complexes, indicating that its primary role is to orchestrate the assembly of the transport machinery. We propose that Lis1 binding releases dynein from its auto-inhibited state, which provides a mechanistic explanation for why Lis1 is required for efficient transport of many dynein-associated cargoes in cells.

Cargo-Mediated Activation of Cytoplasmic Dynein in vivo

“…Importantly, a phi mutation that promotes open dynein (Zhang K. et al, 2017) bypasses the requirement for LIS1 to a significant extent (Qiu et al, 2019), suggesting that LIS1 is involved in promoting open dynein, thereby facilitating cargo adapter-mediated dynein activation (Qiu et al, 2019). This main conclusion agrees with three other recent studies (Elshenawy et al, 2020;Htet et al, 2020;Marzo et al, 2020), although LIS1 in A. nidulans does not seem to significantly affect the formation of the dynein-dynactin-C-Hook complex (Qiu et al, 2019), while LIS1 enhances the recruitment of the second dynein to the dynein-dynactin-BicD2N complexes in vitro (Elshenawy et al, 2020;Htet et al, 2020). Possibly, A. nidulans LIS1 still enhances the dynein-dynactin interaction as described in other systems (Dix et al, 2013;Wang et al, 2013), but this effect was not easily detected when the concentration of cytosolic cargo adapters is high enough.…”

“…In contrast to dynactin that binds to the dynein tail (Karki and Holzbaur, 1995;Vaughan and Vallee, 1995;Chowdhury et al, 2015;Urnavicius et al, 2015), LIS1 binds directly to the dynein motor ring at AAA3/AAA4 as shown by cryo-EM studies (Huang et al, 2012;Toropova et al, 2014;Desantis et al, 2017;Htet et al, 2020). LIS1's binding to this site is not compatible with the autoinhibited phi conformation of dynein (Htet et al, 2020;Marzo et al, 2020), which supports a "check valve" (Markus et al, 2020) model of LIS1 mechanism of action: it stabilizes the open dynein conformation and prevents it from switching to the autoinhibited phi state, thereby facilitating cargo-adapter-mediated dynein activation (Qiu et al, 2019;Canty and Yildiz, 2020;Elshenawy et al, 2020;Htet et al, 2020;Markus et al, 2020;Marzo et al, 2020).…”

“…This may be part of the reason why some of the dynein-dynactin-Hook3 complexes move with a higher velocity compared to the dynein-dynactin-BicD2 complexes (Olenick et al, 2016). Recently, the dynein regulator LIS1 has also been shown to enhance the recruitment of the second dynein dimer to the dynein-dynactin-cargo adapter complex in vitro (Elshenawy et al, 2020;Htet et al, 2020), further suggesting the importance of the second dynein dimer. However, it still remains to be determined what proportion of cargo-bound dynactin in live cells contain two dynein dimers associated with the Arp1 mini-filament and how different regulators change this proportion.…”

“…Beside dynactin and cargo adapters, another important protein involved in dynein activation is LIS1 (Lissencephaly-1) (Markus et al, 2020). The mechanism of LIS1 action in the dynein pathway has been controversial, but multiple recent studies suggest that LIS1 promotes the open dynein conformation, thereby facilitating dynein activation (Qiu et al, 2019;Elshenawy et al, 2020;Htet et al, 2020;Marzo et al, 2020;McKenney, 2020). LIS1, a WD40-repeats-containing protein, was initially identified as a causal gene for type 1 lissencephaly, a human brain developmental disorder (Reiner et al, 1993).…”

Tubulin mutations in neurodevelopmental disorders as a tool to decipher microtubule function

“…However, Lis1 is best known as a key dynein motor regulator and is required for the efficient transport of many dynein‐associated cargoes within cells [105,110–112]. In vitro studies using purified recombinant protein, and more recently single‐molecule imaging and motility assays, have established that Lis1 promotes dynein activity and orchestrates dynein–dynactin transport machinery assembly [72,73,113–115]. Lis1 also interacts with the MT plus‐end‐binding protein CLIP‐170 (see below) [116,117] and with the dynein regulator Nde1 [109,118–121].…”