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HEATR5B associates with dynein-dynactin and promotes motility of AP1-bound endosomal membranes

ABSTRACT: The microtubule motor dynein mediates polarised trafficking of a wide variety of organelles, vesicles and macromolecules. These functions are dependent on the dynactin complex, which helps recruit cargoes to dynein's tail and activates motor movement. How the dynein-dynactin complex orchestrates trafficking of diverse cargoes is unclear. Here, we identify HEATR5B, an interactor of the AP1 clathrin adaptor complex, as a novel player in dynein-dynactin function. HEATR5B was recovered in a biochemical screen for proteins whose association with the dynein tail is augmented by dynactin. We show that HEATR5B binds directly to the dynein tail and dynactin and stimulates motility of AP1-associated endosomal membranes in human cells. We also demonstrate that the Drosophila HEATR5B homologue is an essential gene that selectively promotes dynein-based transport of AP1-bound membranes to the Golgi apparatus. As HEATR5B lacks the coiled-coil architecture typical of dynein adaptors, our data point to a non-canonical process orchestrating motor function on a specific cargo. We additionally show that HEATR5B promotes association of AP1 with endosomal membranes independently of dynein. Thus, HEATR5B co-ordinates multiple events in AP1-based trafficking.

SUBMITTER: Dr. Vanesa Madan

PROVIDER: S-SCDT-10_15252-EMBJ_2023114473 | biostudies-other |

REPOSITORIES: biostudies-other

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HEATR5B associates with dynein-dynactin and promotes motility of AP1-bound endosomal membranes.

Project description:The microtubule motor dynein mediates polarised trafficking of a wide variety of organelles, vesicles and macromolecules. These functions are dependent on the dynactin complex, which helps recruit cargoes to dynein's tail and activates motor movement. How the dynein-dynactin complex orchestrates trafficking of diverse cargoes is unclear. Here, we identify HEATR5B, an interactor of the adaptor protein-1 (AP1) clathrin adaptor complex, as a novel player in dynein-dynactin function. HEATR5B was recovered in a biochemical screen for proteins whose association with the dynein tail is augmented by dynactin. We show that HEATR5B binds directly to the dynein tail and dynactin and stimulates motility of AP1-associated endosomal membranes in human cells. We also demonstrate that the Drosophila HEATR5B homologue is an essential gene that selectively promotes dynein-based transport of AP1-bound membranes to the Golgi apparatus. As HEATR5B lacks the coiled-coil architecture typical of dynein adaptors, our data point to a non-canonical process orchestrating motor function on a specific cargo. We additionally show that HEATR5B promotes association of AP1 with endosomal membranes independently of dynein. Thus, HEATR5B co-ordinates multiple events in AP1-based trafficking.

| S-EPMC10690479 | biostudies-literature

HEATR5B associates with dynein-dynactin and selectively promotes motility of AP1- bound endosomal membranes_BioMass@LMB

Project description:The dynein motor complex mediates polarised trafficking of a wide variety of organelles, intracellular vesicles and macromolecules. These functions are dependent on the dynactin 5 complex, which helps recruit cargoes to dynein’s tail region and activates motor movement. How dynein and dynactin orchestrate trafficking of diverse cargoes is unclear. Here, we identify HEATR5B, an interactor of the AP1 clathrin adaptor complex, as a novel player in dynein-dynactin function. HEATR5B is one of several proteins recovered in a biochemical screen for proteins whose association with the human dynein tail complex is augmented by 10 dynactin. We show that HEATR5B binds directly to the dynein tail and dynactin and stimulates motility of AP1-associated endosomal membranes in human cells. We also demonstrate that the HEATR5B homologue in Drosophila is an essential gene that promotes dynein-based transport of AP1-bound membranes to the Golgi apparatus. As HEATR5B lacks the coiledcoil architecture typical of dynein adaptors, our data point to a non-canonical process 15 orchestrating motor function on a specific cargo. We additionally show that HEATR5B promotes association of AP1 with endosomal membranes in a dynein-independent manner. Thus, HEATR5B co-ordinates multiple events in AP1-based trafficking.

2023-10-20 | PXD043387 | Pride

Dynactin p150 promotes processive motility of DDB complexes by minimizing diffusional behavior of dynein.

Project description:Cytoplasmic dynein is activated by forming a complex with dynactin and the adaptor protein BicD2. We used interferometric scattering (iSCAT) microscopy to track dynein-dynactin-BicD2 (DDB) complexes in vitro and developed a regression-based algorithm to classify switching between processive, diffusive, and stuck motility states. We find that DDB spends 65% of its time undergoing processive stepping, 4% undergoing 1D diffusion, and the remaining time transiently stuck to the microtubule. Although the p150 subunit was previously shown to enable dynactin diffusion along microtubules, blocking p150 enhanced the proportion of time DDB diffused and reduced the time DDB processively walked. Thus, DDB diffusive behavior most likely results from dynein switching into an inactive (diffusive) state, rather than p150 tethering the complex to the microtubule. DDB-kinesin-1 complexes, formed using a DNA adapter, moved slowly and persistently, and blocking p150 led to a 70 nm/s plus-end shift in the average velocity of the complexes, in quantitative agreement with the shift of isolated DDB into the diffusive state. The data suggest a DDB activation model in which dynactin p150 enhances dynein processivity not solely by acting as a diffusive tether that maintains microtubule association, but rather by acting as an allosteric activator that promotes a conformation of dynein optimal for processive stepping. In bidirectional cargo transport driven by the opposing activities of kinesin and dynein-dynactin-BicD2, the dynactin p150 subunit promotes retrograde transport and could serve as a target for regulators of transport.

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Project description:Cytoplasmic dynein is a molecular motor that transports a large variety of cargoes (e.g., organelles, messenger RNAs, and viruses) along microtubules over long intracellular distances. The dynactin protein complex is important for dynein activity in vivo, but its precise role has been unclear. Here, we found that purified mammalian dynein did not move processively on microtubules in vitro. However, when dynein formed a complex with dynactin and one of four different cargo-specific adapter proteins, the motor became ultraprocessive, moving for distances similar to those of native cargoes in living cells. Thus, we propose that dynein is largely inactive in the cytoplasm and that a variety of adapter proteins activate processive motility by linking dynactin to dynein only when the motor is bound to its proper cargo.

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Project description:Cytoplasmic dynein associates with dynactin to drive cargo movement on microtubules, but the structure of the dynein-dynactin complex is unknown. Using electron microscopy, we determined the organization of native bovine dynein, dynactin and the dynein-dynactin-microtubule quaternary complex. In the microtubule-bound complex, the dynein motor domains are positioned for processive unidirectional movement, and the cargo-binding domains of both dynein and dynactin are accessible.

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Differential effects of the dynein-regulatory factor Lissencephaly-1 on processive dynein-dynactin motility.

Project description:Cytoplasmic dynein is the primary minus-end-directed microtubule motor protein in animal cells, performing a wide range of motile activities, including transport of vesicular cargos, mRNAs, viruses, and proteins. Lissencephaly-1 (LIS1) is a highly conserved dynein-regulatory factor that binds directly to the dynein motor domain, uncoupling the enzymatic and mechanical cycles of the motor and stalling dynein on the microtubule track. Dynactin, another ubiquitous dynein-regulatory factor, releases dynein from an autoinhibited state, leading to a dramatic increase in fast, processive dynein motility. How these opposing activities are integrated to control dynein motility is unknown. Here, we used fluorescence single-molecule microscopy to study the interaction of LIS1 with the processive dynein-dynactin-BicD2N (DDB) complex. Surprisingly, in contrast to the prevailing model for LIS1 function established in the context of dynein alone, we found that binding of LIS1 to DDB does not strongly disrupt processive motility. Motile DDB complexes bound up to two LIS1 dimers, and mutational analysis suggested that LIS1 binds directly to the dynein motor domains during DDB movement. Interestingly, LIS1 enhanced DDB velocity in a concentration-dependent manner, in contrast to observations of the effect of LIS1 on the motility of isolated dynein. Thus, LIS1 exerts concentration-dependent effects on dynein motility and can synergize with dynactin to enhance processive dynein movement. Our results suggest that the effect of LIS1 on dynein motility depends on both LIS1 concentration and the presence of other regulatory factors such as dynactin and may provide new insights into the mechanism of LIS1 haploinsufficiency in the neurodevelopmental disorder lissencephaly.

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Tyrosination of ?-tubulin controls the initiation of processive dynein-dynactin motility.

Project description:Post-translational modifications (PTMs) of ?/?-tubulin are believed to regulate interactions with microtubule-binding proteins. A well-characterized PTM involves in the removal and re-ligation of the C-terminal tyrosine on ?-tubulin, but the purpose of this tyrosination-detyrosination cycle remains elusive. Here, we examined the processive motility of mammalian dynein complexed with dynactin and BicD2 (DDB) on tyrosinated versus detyrosinated microtubules. Motility was decreased ~fourfold on detyrosinated microtubules, constituting the largest effect of a tubulin PTM on motor function observed to date. This preference is mediated by dynactin's microtubule-binding p150 subunit rather than dynein itself. Interestingly, on a bipartite microtubule consisting of tyrosinated and detyrosinated segments, DDB molecules that initiated movement on tyrosinated tubulin continued moving into the segment composed of detyrosinated tubulin. This result indicates that the ?-tubulin tyrosine facilitates initial motor-tubulin encounters, but is not needed for subsequent motility. Our results reveal a strong effect of the C-terminal ?-tubulin tyrosine on dynein-dynactin motility and suggest that the tubulin tyrosination cycle could modulate the initiation of dynein-driven motility in cells.

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Project description:Bicaudal D2 (BICD2) joins dynein with dynactin into a ternary complex (termed DDB) capable of processive movement. Point mutations in the BICD2 gene have been identified in patients with a dominant form of spinal muscular atrophy, but how these mutations cause disease is unknown. To investigate this question, we have developed in vitro motility assays with purified DDB and BICD2's membrane vesicle partner, the GTPase Rab6a. Rab6a-GTP, either in solution or bound to artificial liposomes, released BICD2 from an autoinhibited state and promoted robust dynein-dynactin transport. In these assays, BICD2 mutants showed an enhanced ability to form motile DDB complexes. Increased retrograde transport by BICD2 mutants also was observed in cells using an inducible organelle transport assay. When overexpressed in rat hippocampal neurons, the hyperactive BICD2 mutants decreased neurite growth. Our results reveal that dominant mutations in BICD2 hyperactivate DDB motility and suggest that an imbalance of minus versus plus end-directed microtubule motility in neurons may underlie spinal muscular atrophy.

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Hook Adaptors Induce Unidirectional Processive Motility by Enhancing the Dynein-Dynactin Interaction.

Project description:Cytoplasmic dynein drives the majority of minus end-directed vesicular and organelle motility in the cell. However, it remains unclear how dynein is spatially and temporally regulated given the variety of cargo that must be properly localized to maintain cellular function. Recent work has suggested that adaptor proteins provide a mechanism for cargo-specific regulation of motors. Of particular interest, studies in fungal systems have implicated Hook proteins in the regulation of microtubule motors. Here we investigate the role of mammalian Hook proteins, Hook1 and Hook3, as potential motor adaptors. We used optogenetic approaches to specifically recruit Hook proteins to organelles and observed rapid transport of peroxisomes to the perinuclear region of the cell. This rapid and efficient translocation of peroxisomes to microtubule minus ends indicates that mammalian Hook proteins activate dynein rather than kinesin motors. Biochemical studies indicate that Hook proteins interact with both dynein and dynactin, stabilizing the formation of a supramolecular complex. Complex formation requires the N-terminal domain of Hook proteins, which resembles the calponin-homology domain of end-binding (EB) proteins but cannot bind directly to microtubules. Single-molecule motility assays using total internal reflection fluorescence microscopy indicate that both Hook1 and Hook3 effectively activate cytoplasmic dynein, inducing longer run lengths and higher velocities than the previously characterized dynein activator bicaudal D2 (BICD2). Together, these results suggest that dynein adaptors can differentially regulate dynein to allow for organelle-specific tuning of the motor for precise intracellular trafficking.

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