Structure of LRRK2 in Parkinson's disease and model for microtubule interaction

Leucine-rich repeat kinase 2 (LRRK2) is the most commonly mutated gene in familial Parkinson's disease1 and is also linked to its idiopathic form2. LRRK2 has been proposed to function in membrane trafficking3 and colocalizes with microtubules4. Despite the fundamental importance of LRRK2 for understanding and treating Parkinson's disease, structural information on the enzyme is limited. Here we report the structure of the catalytic half of LRRK2, and an atomic model of microtubule-associated LRRK2 built using a reported cryo-electron tomography in situ structure5. We propose that the conformation of the LRRK2 kinase domain regulates its interactions with microtubules, with a closed conformation favouring oligomerization on microtubules. We show that the catalytic half of LRRK2 is sufficient for filament formation and blocks the motility of the microtubule-based motors kinesin 1 and cytoplasmic dynein 1 in vitro. Kinase inhibitors that stabilize an open conformation relieve this interference and reduce the formation of LRRK2 filaments in cells, whereas inhibitors that stabilize a closed conformation do not. Our findings suggest that LRRK2 can act as a roadblock for microtubule-based motors and have implications for the design of therapeutic LRRK2 kinase inhibitors.

Tug-of-war in motor protein ensembles revealed with a programmable DNA origami scaffold

Cytoplasmic dynein and kinesin-1 are microtubule-based motors with opposite polarity that transport a wide variety of cargo in eukaryotic cells. Many cellular cargos demonstrate bidirectional movement due to the presence of ensembles of dynein and kinesin, but are ultimately sorted with spatial and temporal precision. To investigate the mechanisms that coordinate motor ensemble behavior, we built a programmable synthetic cargo using three-dimensional DNA origami to which varying numbers of DNA oligonucleotide-linked motors could be attached, allowing for control of motor type, number, spacing, and orientation in vitro. In ensembles of one to seven identical-polarity motors, motor number had minimal affect on directional velocity, whereas ensembles of opposite-polarity motors engaged in a tug-of-war resolvable by disengaging one motor species.

Structural basis for microtubule binding and release by dynein

Cytoplasmic dynein is a microtubule-based motor required for intracellular transport and cell division. Its movement involves coupling cycles of track binding and release with cycles of force-generating nucleotide hydrolysis. How this is accomplished given the ~25 nanometers separating dynein's track- and nucleotide-binding sites is not understood. Here, we present a subnanometer-resolution structure of dynein's microtubule-binding domain bound to microtubules by cryo-electron microscopy that was used to generate a pseudo-atomic model of the complex with molecular dynamics. We identified large rearrangements triggered by track binding and specific interactions, confirmed by mutagenesis and single-molecule motility assays, which tune dynein's affinity for microtubules. Our results provide a molecular model for how dynein's binding to microtubules is communicated to the rest of the motor.

Role of actin and Myo2p in polarized secretion and growth of Saccharomyces cerevisiae

We examined the role of the actin cytoskeleton in secretion in Saccharomyces cerevisiae with the use of several quantitative assays, including time-lapse video microscopy of cell surface growth in individual living cells. In latrunculin, which depolymerizes filamentous actin, cell surface growth was completely depolarized but still occurred, albeit at a reduced level. Thus, filamentous actin is necessary for polarized secretion but not for secretion per se. Consistent with this conclusion, latrunculin caused vesicles to accumulate at random positions throughout the cell. Cortical actin patches cluster at locations that correlate with sites of polarized secretion. However, we found that actin patch polarization is not necessary for polarized secretion because a mutant, bee1Delta(las17Delta), which completely lacks actin patch polarization, displayed polarized growth. In contrast, a mutant lacking actin cables, tpm1-2 tpm2Delta, had a severe defect in polarized growth. The yeast class V myosin Myo2p is hypothesized to mediate polarized secretion. A mutation in the motor domain of Myo2p, myo2-66, caused growth to be depolarized but with only a partial decrease in the level of overall growth. This effect is similar to that of latrunculin, suggesting that Myo2p interacts with filamentous actin. However, inhibition of Myo2p function by expression of its tail domain completely abolished growth.

The tail of a yeast class V myosin, myo2p, functions as a localization domain

Myo2p is a yeast class V myosin that functions in membrane trafficking. To investigate the function of the carboxyl-terminal-tail domain of Myo2p, we have overexpressed this domain behind the regulatable GAL1 promoter (MYO2DN). Overexpression of the tail domain of Myo2p results in a dominant-negative phenotype that is phenotypically similar to a temperature-sensitive allele of myo2, myo2-66. The tail domain of Myo2p is sufficient for localization at low- expression levels and causes mislocalization of the endogenous Myo2p from sites of polarized cell growth. Subcellular fractionation of polarized, mechanically lysed yeast cells reveals that Myo2p is present predominantly in a 100,000 x g pellet. The Myo2p in this pellet is not solubilized by Mg++-ATP or Triton X-100, but is solubilized by high salt. Tail overexpression does not disrupt this fractionation pattern, nor do mutations in sec4, sec3, sec9, cdc42, or myo2. These results show that overexpression of the tail domain of Myo2p does not compete with the endogenous Myo2p for assembly into a pelletable structure, but does compete with the endogenous Myo2p for a factor that is necessary for localization to the bud tip.