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Open Access Publications from the University of California

Scholarly Works (16 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2020)

Leucine Rich Repeat Kinase 2 (LRRK2) is the most commonly mutated gene in familial Parkinson’s disease. LRRK2 is proposed to function in membrane trafficking and co-localizes with microtubules. We report the 3.5Å structure of the catalytic half of LRRK2, and an atomic model of microtubule-associated LRRK2 built using a reported 14Å structure obtained by cryo-electron tomography. We propose that the conformation of LRRK2’s kinase domain regulates its microtubule interaction, with a closed conformation favoring binding. We show that the catalytic half of LRRK2 is sufficient for microtubule binding and blocks the motility of the microtubule-based motors kinesin and dynein in vitro. Kinase inhibitors that stabilize an open conformation relieve this interference and reduce LRRK2 filament formation in cells, while those that stabilize a closed conformation do not. Our findings suggest that LRRK2 is a roadblock for microtubule-based motors and have implications for the design of therapeutic LRRK2 kinase inhibitors.

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Cover page: Parkinson’s Disease-Linked LRRK2 Structure and Model for Microtubule Interaction
  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2015)
The advent of a new generation of electron microscopes and direct electron detectors has realized the potential of single particle cryo-electron microscopy (cryo-EM) as a technique to generate high-resolution structures. Calculating these structures requires high performance computing clusters, a resource that may be limiting to many likely cryo-EM users. To address this limitation and facilitate the spread of cryo-EM, we developed a publicly available 'off-the-shelf' computing environment on Amazon's elastic cloud computing infrastructure. This environment provides users with single particle cryo-EM software packages and the ability to create computing clusters with 16-480+ CPUs. We tested our computing environment using a publicly available 80S yeast ribosome dataset and estimate that laboratories could determine high-resolution cryo-EM structures for $50 to $1500 per structure within a timeframe comparable to local clusters. Our analysis shows that Amazon's cloud computing environment may offer a viable computing environment for cryo-EM.
    Cover page: Low cost, high performance processing of single particle cryo-electron microscopy data in the cloud
    • Thesis
    • Peer Reviewed
    UC San Diego Electronic Theses and Dissertations (2021)

    Transcription-coupled nucleotide excision repair (TC-NER) is a highly conserved pathway that removes bulky lesions in the transcribed genome. Cockayne syndrome B protein (CSB), or its yeast ortholog Rad26, plays important roles in the lesion-recognition steps of TC-NER. How Rad26 distinguishes between RNA polymerase II (Pol II) stalled at a DNA lesion or other obstacles, how a lesion-arrested Pol II is committed to the recruitment of downstream repair factors, and what the fate is of a lesion-arrested Pol II remain unknown. Here, we present cryo-EM structures of Pol II-Rad26 complexes stalled at different obstacles to establish a universal mechanism for the Rad26-mediated recognition of stalled Pol II. We also present a 3.1Å cryo-EM structure of lesion-arrested Pol II-Rad26 bound to a newly identified TC-NER factor, ELOF1/Elf1, that provides insights into its role in the commitment of lesion-arrested Pol II to TC-NER. Finally, we provide biochemical data revealing how Rad26 displaces a lesion-stalled Pol II during TC-NER. These results establish the structural basis of lesion-recognition, commitment to repair, and displacement of lesion-arrested Pol II during TC-NER.

      Cover page: Structural Basis for Lesion Recognition and Commitment to Transcription-Coupled Repair
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2019)
      Despite significant advances in all aspects of single particle cryo-electron microscopy (cryo-EM), specimen preparation still remains a challenge. During sample preparation, macromolecules interact with the air-water interface, which often leads to detrimental effects such as denaturation or adoption of preferred orientations, ultimately hindering structure determination. Randomly biotinylating the protein of interest (for example, at its primary amines) and then tethering it to a cryo-EM grid coated with two-dimensional crystals of streptavidin (acting as an affinity surface) can prevent the protein from interacting with the air-water interface. Recently, this approach was successfully used to solve a high-resolution structure of a test sample, a bacterial ribosome. However, whether this method can be used for samples where interaction with the air-water interface has been shown to be problematic remains to be determined. Here we report a 3.1 Å structure of an RNA polymerase II elongation complex stalled at a cyclobutane pyrimidine dimer lesion (Pol II EC(CPD)) solved using streptavidin grids. Our previous attempt to solve this structure using conventional sample preparation methods resulted in a poor quality cryo-EM map due to Pol II EC(CPD)'s adopting a strong preferred orientation. Imaging the same sample on streptavidin grids improved the angular distribution of its view, resulting in a high-resolution structure. This work shows that streptavidin affinity grids can be used to address known challenges posed by the interaction with the air-water interface.
        Cover page: 3.1 Å structure of yeast RNA polymerase II elongation complex stalled at a cyclobutane pyrimidine dimer lesion solved using streptavidin affinity grids
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2020)
        The Cullin 5 (CUL5) Ring E3 ligase uses adaptors Elongins B and C (ELOB/C) to bind different SOCS-box-containing substrate receptors, determining the substrate specificity of the ligase. The 18-member ankyrin and SOCS box (ASB) family is the largest substrate receptor family. Here we report cryo-EM data for the substrate, creatine kinase (CKB) bound to ASB9-ELOB/C, and for full-length CUL5 bound to the RING protein, RBX2, which binds various E2s. To date, no full structures are available either for a substrate-bound ASB nor for CUL5. Hydrogen-deuterium exchange (HDX-MS) mapped onto a full structural model of the ligase revealed long-range allostery extending from the substrate through CUL5. We propose a revised allosteric mechanism for how CUL-E3 ligases function. ASB9 and CUL5 behave as rigid rods, connected through a hinge provided by ELOB/C transmitting long-range allosteric crosstalk from the substrate through CUL5 to the RBX2 flexible linker.
          Cover page: Structure and dynamics of the ASB9 CUL-RING E3 Ligase
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2017)
          Mutations in FAM20A cause tooth enamel defects known as Amelogenesis Imperfecta (AI) and renal calcification. We previously showed that Fam20A is a secretory pathway pseudokinase and allosterically activates the physiological casein kinase Fam20C to phosphorylate secreted proteins important for biomineralization (Cui et al., 2015). Here we report the nucleotide-free and ATP-bound structures of Fam20A. Fam20A exhibits a distinct disulfide bond pattern mediated by a unique insertion region. Loss of this insertion due to abnormal mRNA splicing interferes with the structure and function of Fam20A, resulting in AI. Fam20A binds ATP in the absence of divalent cations, and strikingly, ATP is bound in an inverted orientation compared to other kinases. Fam20A forms a dimer in the crystal, and residues in the dimer interface are critical for Fam20C activation. Together, these results provide structural insights into the function of Fam20A and shed light on the mechanism by which Fam20A mutations cause disease.
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2013)
            The ATP-dependent chromatin-remodeling complex SWR1 exchanges a variant histone H2A.Z/H2B dimer for a canonical H2A/H2B dimer at nucleosomes flanking histone-depleted regions, such as promoters. This localization of H2A.Z is conserved throughout eukaryotes. SWR1 is a 1 megadalton complex containing 14 different polypeptides, including the AAA+ ATPases Rvb1 and Rvb2. Using electron microscopy, we obtained the three-dimensional structure of SWR1 and mapped its major functional components. Our data show that SWR1 contains a single heterohexameric Rvb1/Rvb2 ring that, together with the catalytic subunit Swr1, brackets two independently assembled multisubunit modules. We also show that SWR1 undergoes a large conformational change upon engaging a limited region of the nucleosome core particle. Our work suggests an important structural role for the Rvbs and a distinct substrate-handling mode by SWR1, thereby providing a structural framework for understanding the complex dimer-exchange reaction.
              Cover page: Molecular Architecture of the ATP-Dependent Chromatin-Remodeling Complex SWR1
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2023)
              Cytoplasmic dynein-1 transports intracellular cargo towards microtubule minus ends. Dynein is autoinhibited and undergoes conformational changes to form an active complex that consists of one or two dynein dimers, the dynactin complex, and activating adapter(s). The Lissencephaly 1 gene, LIS1, is genetically linked to the dynein pathway from fungi to mammals and is mutated in people with the neurodevelopmental disease lissencephaly. Lis1 is required for active dynein complexes to form, but how it enables this is unclear. Here, we present a structure of two yeast dynein motor domains with two Lis1 dimers wedged in-between. The contact sites between dynein and Lis1 in this structure, termed Chi, are required for Lis1s regulation of dynein in Saccharomyces cerevisiae in vivo and the formation of active human dynein-dynactin-activating adapter complexes in vitro. We propose that this structure represents an intermediate in dyneins activation pathway, revealing how Lis1 relieves dyneins autoinhibited state.
                Cover page: Lis1 relieves cytoplasmic dynein-1 autoinhibition by acting as a molecular wedge.
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2020)
                Cytoplasmic dynein-1 is a molecular motor that drives nearly all minus-end-directed microtubule-based transport in human cells, performing functions that range from retrograde axonal transport to mitotic spindle assembly1,2. Activated dynein complexes consist of one or two dynein dimers, the dynactin complex and an 'activating adaptor', and they show faster velocity when two dynein dimers are present3-6. Little is known about the assembly process of this massive ~4 MDa complex. Here, using purified recombinant human proteins, we uncover a role for the dynein-binding protein LIS1 in promoting the formation of activated dynein-dynactin complexes that contain two dynein dimers. Complexes activated by proteins representing three families of activating adaptors-BicD2, Hook3 and Ninl-all show enhanced motile properties in the presence of LIS1. Activated dynein complexes do not require sustained LIS1 binding for fast velocity. Using cryo-electron microscopy, we show that human LIS1 binds to dynein at two sites on the motor domain of dynein. Our research suggests that LIS1 binding at these sites functions in multiple stages of assembling the motile dynein-dynactin-activating adaptor complex.
                  Cover page: LIS1 promotes the formation of activated cytoplasmic dynein-1 complexes.
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2017)
                  Regulation is central to the functional versatility of cytoplasmic dynein, a motor involved in intracellular transport, cell division, and neurodevelopment. Previous work established that Lis1, a conserved regulator of dynein, binds to its motor domain and induces a tight microtubule-binding state in dynein. The work we present here-a combination of biochemistry, single-molecule assays, and cryoelectron microscopy-led to the surprising discovery that Lis1 has two opposing modes of regulating dynein, being capable of inducing both low and high affinity for the microtubule. We show that these opposing modes depend on the stoichiometry of Lis1 binding to dynein and that this stoichiometry is regulated by the nucleotide state of dynein's AAA3 domain. The low-affinity state requires Lis1 to also bind to dynein at a novel conserved site, mutation of which disrupts Lis1's function in vivo. We propose a new model for the regulation of dynein by Lis1.
                    Cover page: Lis1 Has Two Opposing Modes of Regulating Cytoplasmic Dynein.
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