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Lissencephaly (‘smooth brain’) is a severe brain disease associated with numerous symptoms, including cognitive impairment, and shortened lifespan. The main causative gene of this disease – lissencephaly-1 (LIS1) – has been a focus of intense scrutiny since its first identification almost 30 years ago. LIS1 is a critical regulator of the microtubule motor cytoplasmic dynein, which transports numerous cargoes throughout the cell, and is a key effector of nuclear and neuronal transport during brain development. Here, we review the role of LIS1 in cellular dynein function and discuss recent key findings that have revealed a new mechanism by which this molecule influences dynein-mediated transport. In addition to reconciling prior observations with this new model for LIS1 function, we also discuss phylogenetic data that suggest that LIS1 may have coevolved with an autoinhibitory mode of cytoplasmic dynein regulation.

Cytoplasmic dynein is an enormous minus end-directed microtubule motor. Rather than existing as bare tracks, microtubules are bound by numerous microtubule-associated proteins (MAPs) that have the capacity to affect various cellular functions, including motor-mediated transport. One such MAP is She1, a dynein effector that polarizes dynein-mediated spindle movements in budding yeast. Here, we characterize the molecular basis by which She1 affects dynein, providing the first such insight into which a MAP can modulate motor motility. We find that She1 affects the ATPase rate, microtubule-binding affinity, and stepping behavior of dynein, and that microtubule binding by She1 is required for its effects on dynein motility. Moreover, we find that She1 directly contacts the microtubule-binding domain of dynein, and that their interaction is sensitive to the nucleotide-bound state of the motor. Our data support a model in which simultaneous interactions between the microtubule and dynein enables She1 to directly affect dynein motility.

Encapsulation of unstable guests is a powerful way to enhance their stability. The lifetimes of organic anions and their radicals produced by reduction are typically short on account of reactivity with oxygen while their larger sizes preclude use of traditional anion receptors. Here we demonstrate the encapsulation and noncovalent stabilization of organic radical anions by C-H hydrogen bonding in π-stacked pairs of cyanostar macrocycles having large cavities. Using electrogenerated tetrazine radical anions, we observe significant extension of their lifetimes, facile molecular switching, and extremely large stabilization energies. The guests form threaded pseudorotaxanes. Complexation extends the radical lifetimes from 2 h to over 20 days without altering its electronic structure. Electrochemical studies show tetrazines thread inside a pair of cyanostar macrocycles following voltage-driven reduction (+e) of the tetrazine at -1.00 V and that the complex disassembles after reoxidation (-e) at -0.05 V. This reoxidation is shifted 830 mV relative to the free tetrazine radical indicating it is stabilized by an unexpectedly large -80 kJ mol. The stabilization is general as shown using a dithiadiazolyl anion. This finding opens up a new approach to capturing and studying unstable anions and a radical anions when encapsulated by size-complementary anion receptors.

Cytoplasmic dynein plays critical roles within the developing and mature nervous systems, including effecting nuclear migration, and retrograde transport of various cargos. Unsurprisingly, mutations in dynein are causative of various developmental neuropathies and motor neuron diseases. These ‘dyneinopathies’ define a broad spectrum of diseases with no known correlation between mutation identity and disease state. To circumvent complications associated with dynein studies in human cells, we employed budding yeast as a screening platform to characterize the motility properties of seventeen disease-correlated dynein mutants. Using this system, we determined the molecular basis for several classes of etiologically related diseases. Moreover, by engineering compensatory mutations, we alleviated the mutant phenotypes in two of these cases, one of which we confirmed with recombinant human dynein. In addition to revealing molecular insight into dynein regulation, our data provide additional evidence that the type of disease may in fact be dictated by the degree of dynein dysfunction.

The existence of two rings in [3]pseudorotaxanes presents opportunities for those rings to undergo double switching and cooperative mechanical coupling. To investigate this capability, we identified a new strategy for bringing two rings into contact with each other and conducted mechanistic studies to reveal their kinetic cooperativity. A redox-active tetrazine ligand bearing two binding sites was selected to allow for two mobile copper(I) macrocycle ring moieties to come together. To realize this switching modality, ligands were screened against their ability to serve as stations on which the rings are initially parked, ultimately identifying 5,5'-dimethyl-2,2'-bipyridine. The kinetics of switching a macrocycle in a single-site [2]pseudorotaxane between bipyridine and single-site tetrazine stations were examined using electrochemistry. The forward movement was rate-limited by the bimolecular reaction between reduced tetrazine and bipyridine [2]pseudorotaxane. Two bipyridines were then used with a double-site tetrazine to verify double switching of two rings. Our results indicated stepwise movements, with the first ring moving 4 times more frequently (faster) than the second. While this behavior is indicative of anticooperative kinetics, positive thermodynamic cooperativity sets the two rings in motion even though just one tetrazine is reduced with one electron. Double switching in this [3]pseudorotaxane uniquely demonstrates how a series of independent thermodynamic states and kinetic paths govern an apparently simple mechanical motion.

45Cytoplasmic dynein is a minus end-directed microtubule motor that transports myriad 46 cargos in various cell types and contexts. How dynein is regulated to perform all these 47 62Cytoplasmic dynein is an enormous minus end-directed microtubule motor 63 complex that transports numerous cargoes. At first glance, this motor seems 64 exceedingly complex in terms of its architecture, size, and reliance on accessories and 65 regulators for proper activity. For instance, processive single molecule motility of human 66 dynein -itself comprised of 4 to 6 subunits -requires the 11 subunit dynactin complex 67 in addition to an adaptor that links them together 1,2 . Although yeast dynein does not 68 require dynactin for in vitro single molecule motility 3 , it does require this complex for in 69 vivo activity 4,5 . Recent studies have yielded invaluable insight into the underlying 70 reasons for the complexity of the dynein motor. For instance, the reliance on adaptors 71 (e.g., BicD2, Spindly, Hook3 1,2 ) to link dynein to dynactin ensures that cytoplasmic 72 dynein-1 -which effects motility of numerous and varied cargoes throughout the cell 73 cycle 6 -and dynactin are linked together at the right place (and presumably time) for 74 appropriate motility. Additionally, recent studies have revealed that dynactin helps to 75 orient the motor domains in a parallel manner that is conducive for motility 7 , thus 76 revealing the mechanistic basis for dynein's reliance on this large complex. Thus, the 77 complexity of this molecular motor ensures that cargoes are transported to their target 78 destinations in accordance with the needs of the cell. 79In addition to its regulation by extrinsic factors, several studies have 80 demonstrated that human dynein-1 and dynein-2 can also be auto-regulated by intra-81 complex interactions. Specifically, intermolecular interactions between the motor 82 domains have been shown to stabilize an autoinhibited conformation of human dynein 83 called the phi particle (named for its resemblance to the Greek letter) 7-10 . In the case of 84 4 dynein-2 (responsible for intraflagellar transport), the phi particle conformation -which 85 has been observed in its native context 10 -reduces its velocity, ATPase activity and 86 microtubule landing rate 9 . Similarly, the autoinhibited dynein-1 conformation has been 87 shown to reduce its microtubule landing rate and motility properties 7,11 . Moreover, unlike 88 dynein-2 which is not regulated by dynactin 12 , uninhibited dynein-1 mutants interact 89 more readily with dynactin and the adaptor BicD2 7 . 90Although it is well established that human dynein adopts the autoinhibited phi 91 particle conformation (both dynein-1 and dynein-2), it is unclear if this conformational 92 state is evolutionarily conserved. Yeast dynein is of particular interest due to two 93 notable in vitro discrepancies with human dynein. In particular, unlike human dynein, 94 yeast dynein is processive in single molecule assays without the need for other factors, 95 such as dynactin...

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