Biology subjects

Cianfrocco, M. A.

Publications and source records attributed to Cianfrocco, M. A..

27 records · Page 2Linked to original sources

bioRxiv2021

Kinesin-binding protein remodels the kinesin motor to prevent microtubule-binding

Kinesins are tightly regulated in space and time to control their activation in the absence of cargo-binding. Kinesin-binding protein (KIFBP) was recently discovered to bind the catalytic motor heads of 8 of the 45 known kinesin superfamily members and inhibit binding to microtubules. In humans, mutation of KIFBP gives rise to Goldberg-Shprintzen syndrome (GOSHS), but the kinesin(s) that is misregulated to produce clinical features of the disease is not known. Understanding the structural mechanism by which KIFBP selects its kinesin binding partners will be key to unlocking this knowledge. Using a combination of cryo-electron microscopy and crosslinking mass spectrometry, we determined structures of KIFBP alone and in complex with two mitotic kinesins, revealing regions of KIFBP that participate in complex formation. KIFBP adopts an alpha-helical solenoid structure composed of TPR repeats. We find that KIFBP uses a 2-pronged mechanism to remodel kinesin motors and block microtubule-binding. First, KIFBP engages the microtubule-binding interface and sterically blocks interaction with microtubules. Second, KIFBP induces allosteric conformational changes to the kinesin motor head that displace a key structural element in the kinesin motor head (-helix 4) required for microtubule binding. We identified two regions of KIFBP necessary for in vitro kinesin-binding as well as cellular regulation during mitosis. Taken together, this work establishes the mechanism of kinesin inhibition by KIFBP and provides the first example of motor domain remodeling as a means to abrogate kinesin activity.

cell biology↗

bioRxiv2020

Molecular determinants for α-tubulin methylation by SETD2

Post-translational modifications to tubulin are important for many microtubule-based functions inside cells. A recently identified tubulin modification, methylation, occurs on mitotic spindle microtubules during cell division, and is enzymatically added to tubulin by the histone methyltransferase SETD2. We used a truncated version of human SETD2 (tSETD2) containing the catalytic SET and C-terminal Set2 Rpb1 interacting (SRI) domains to investigate the biochemical mechanism of tubulin methylation. We found that recombinant tSETD2 has a higher activity towards tubulin dimers than polymerized microtubules. Using recombinant single-isotype tubulin, we demonstrate that methylation is restricted to lysine 40 (K40) of -tubulin. We then introduced pathogenic mutations into tSETD2 to probe the recognition of histone and tubulin substrates. A mutation in the catalytic domain, R1625C, bound to tubulin but could not methylate it whereas a mutation in the SRI domain, R2510H, caused loss of both tubulin binding and methylation. We thus further probed a role for the SRI domain in substrate binding and found that mutations within this region had differential effects on the ability of tSETD2 to bind to tubulin versus RNA Polymerase II substrates, suggesting distinct mechanisms for tubulin and histone methylation by SETD2. Lastly, we found that substrate recognition also requires the negatively-charged C-terminal tail of -tubulin. Together, this work provides a framework for understanding how SETD2 serves as a dual methyltransferase for histone and tubulin methylation.

biochemistry↗

bioRxiv2020

SETD2 is an actin lysine methyltransferase

SET-domain-containing-2 (SETD2) was identified as the methyltransferase responsible for the histone 3 lysine 36 trimethyl (H3K36me3) mark of the histone code. Most recently, SETD2 has been shown to be a dual-function remodeler that regulates genome stability via methylation of dynamic microtubules during mitosis and cytokinesis. Here we show that actin is a bona fide target for methylation by SETD2 in vitro and in cells. Antibodies against the SETD2 trimethyl lysine epitope recognize methylated actin, with this methyl mark localizing to areas of active actin cytoskeleton reorganization in migrating cells. Disruption of this methylation activity causes defects in actin polymerization and impairs collective cell migration. Together, these data identify SETD2 as a multifunctional cytoskeletal remodeler regulating methylation and polymerization of actin filaments, and provide new avenues for understanding how defects in SETD2 drive disease via aberrant cytoskeletal methylation.

cell biology↗

bioRxiv2020

High-resolution cryo-EM using beam-image shift at 200 keV

Recent advances in single-particle cryo-electron microscopy (cryo-EM) data collection utilizes beam-image shift to improve throughput. Despite implementation on 300 keV cryo-EM instruments, it remains unknown how well beam-image shift data collection affects data quality on 200 keV instruments and how much aberrations can be computationally corrected. To test this, we collected and analyzed a cryo-EM dataset of aldolase at 200 keV using beam-image shift. This analysis shows that beam tilt on the instrument initially limited the resolution of aldolase to 4.9[A]. After iterative rounds of aberration correction and particle polishing in RELION, we were able to obtain a 2.8[A] structure. This analysis demonstrates that software correction of microscope aberrations can provide a significant improvement in resolution at 200 keV.

biophysics↗

bioRxiv2019

High-throughput cryo-EM enabled by user-free preprocessing routines

The growth of single-particle cryo-EM into a mainstream structural biology tool has allowed for many important biological discoveries. Continued developments in data collection strategies alongside new sample preparation devices heralds a future where users will collect multiple datasets per microscope session. To make cryo-EM data processing more automatic and user-friendly, we have developed an automatic pipeline for cryo-EM data preprocessing and assessment using a combination of deep learning and image analysis tools. We have verified the performance of this pipeline on a number of datasets and extended its scope to include sample screening by the user-free assessment of the qualities of a series of datasets under different conditions. We propose that our workflow provides a decision-free solution for cryo-EM, making data preprocessing more generalized and robust in the high-throughput era as well as more convenient for users from a range of backgrounds.

biophysics↗

bioRxiv2019

Cryo-EM structure of the human Mixed Lineage Leukemia-1 complex bound to the nucleosome

Mixed Lineage Leukemia (MLL) family histone methyltransferases are the key enzymes that deposit histone H3 Lys4 (K4) mono-/di-/tri-methylation and regulate gene expression in mammals. Despite extensive structural and biochemical studies, the molecular mechanism by which the MLL complexes recognize histone H3K4 within the nucleosome core particle (NCP) remains unclear. Here, we report the single-particle cryo-electron microscopy (cryo-EM) structure of the human MLL1 core complex bound to the NCP. The MLL1 core complex anchors on the NCP through RbBP5 and ASH2L, which interacts extensively with nucleosomal DNA as well as the surface close to histone H4 N-terminal tail. Concurrent interactions of RbBP5 and ASH2L with the NCP uniquely align the catalytic MLL1SET domain at the nucleosome dyad, allowing symmetrical access to both H3K4 substrates within the NCP. Our study sheds light on how the MLL1 complex engages chromatin and how chromatin binding promotes MLL1 tri-methylation activity.

biochemistry↗

bioRxiv2018

Generative adversarial networks as a tool to recover structural information from cryo-electron microscopy data

Cryo-electron microscopy (cryo-EM) is a powerful structural biology technique capable of determining atomic-resolution structures of biological macromolecules. Despite this ability, the low signal-to-noise ratio of cryo-EM data continues to remain a hurdle for assessing raw cryo-EM micrographs and subsequent image analysis. To help address this problem, we have performed proof-of-principle studies with generative adversarial networks, a form of artificial intelligence, to denoise individual particles. This approach effectively recovers global structural information for both synthetic and real cryo-EM data, facilitating per-particle assessment from noisy raw images. Our results suggest that generative adversarial networks may be able to provide an approach to denoise raw cryo-EM images to facilitate particle selection and raw particle interpretation for single particle and tomography cryo-EM data.

biochemistry↗

bioRxiv2018

An integrated, pipeline-based approach for cryo-EM structure determination and atomic model refinement in the cloud

Access to streamlined computational resources remains a significant bottleneck for new users of cryo-electron microscopy (cryo-EM). To address this, we have built upon our previous work (Cianfrocco & Leschziner 2015) to develop software tools that will submit cryo-EM analysis routines and atomic model building jobs directly to Amazon Web Services (AWS) from a local computer or laptop. These new software tools (\"cryoem-cloud-tools\") have incorporated optimal data movement, security, and cost-saving strategies, giving novice users access to complex cryo-EM data processing pipelines. Integrating these tools into the RELION processing pipeline and graphical user interface we determined a 2.2 [A] structure of {beta}-galactosidase in ~55 hours on AWS. We implemented a similar strategy to submit Rosetta atomic model building and refinement to AWS. These software tools dramatically reduce the barrier for entry of new users to cloud computing for cryo-EM and are freely available at cryoem-tools.cloud.

biochemistry↗

bioRxiv2017

Lis1 has two opposing modes of regulating cytoplasmic dynein

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 and ubiquitous 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, cryo-electron microscopy and in vivo experiments--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 dyneins AAA3 domain. We present data on the in vitro and in vivo consequences of abolishing the novel Lis1-induced weak microtubule-binding state in dynein and propose a new model for the regulation of dynein by Lis1.

cell biology↗