Cryo-EM of dynein microtubule-binding domains shows how an axonemal dynein distorts the microtubule

Alleviatory efficacy of achillea millefolium L. in etoxazole-mediated toxicity in allium cepa L

The application of pesticides may adversely impact a variety of non-target organisms. The use of side-effect-free herbal remedies to protect against the toxicity of harmful pesticides such as etoxazole has gained attention in recent times. The current study aimed to reveal the potential mitigating efficacy of Achillea millefolium L. extract against etoxazole toxicity in Allium cepa L. A. cepa bulbs in the control group were applied with tap water, while bulbs in the treatment groups were applied with etoxazole at dose of 0.5 m/L and two different doses of A. millefolium extract (200 mg/L and 400 mg/L). The impact of the treatments on certain parameters was evaluated. The molecular docking analysis was employed to investigate the potential interactions of etoxazole with DNA species, DNA topoisomerases, tubulin proteins, glutamate-1-semialdehyde aminotransferase, and protochlorophyllide reductase. The phenolic profile of A. millefolium was assessed. Etoxazole exposure reduced rooting percentage, root length, weight gain, mitotic index, and levels of chlorophyll a and chlorophyll b. Conversely, etoxazole treatment led to an increase in chromosomal aberrations and micronuclei occurrence. The most frequently observed chromosomal aberrations induced by etoxazole, which serve as bioindicators of genotoxicity, were fragment, vagrant chromosome, sticky chromosome, unequal chromatin distribution, bridge, reverse polarization, and vacuolated nucleus. The levels of malondialdehyde and antioxidant enzyme (superoxide dismutase and catalase) activities were also elevated. Epidermis cell damage, flattened cell nucleus, thickened cortex cell wall, and thickened conduction tissue were the meristematic cell disorders triggered by etoxazole. Molecular docking studies showed that etoxazole can interact directly with DNA, tubulins, and the enzymes mentioned above. A. millefolium extract was found to contain a substantial quantity of phenolic compounds. A. millefolium extract, when co-administered with etoxazole, attenuated all toxic effects of etoxazole dose-dependently. In conclusion, A. millefolium may potentially serve as a reliable pharmacological shield against the toxicity of pesticides in non-target organisms.

Modeling of Chemomechanical Coupling of Cytoplasmic Dynein Motors

Cytoplasmic dynein homodimer is a motor protein that can step processively on microtubules (MTs) toward the minus end by hydrolyzing ATP molecules. Some dynein motors show a complicated stepping behavior with variable step sizes and having both hand-overhand and inchworm steps, while some mammalian dynein motors show simplistic stepping behavior with a constant step size and having only hand-overhand steps. Here, a model for the chemomechanical coupling of the dynein is presented, based on which an analytical theory is given on the dynamics of the motor. The theoretical results explain consistently and quantitatively the available experimental data on various aspects of the dynamics of dynein with complicated stepping behavior and the dynamics of dynein with simplistic stepping behavior. The very differences in the dynamic behavior between the two motors are due solely to different elastic coefficients of the linkage connecting the two dynein heads, with the dynein motors of the complicated and simplistic stepping behaviors having small and large coefficients, respectively. Moreover, it is analyzed that the ATPase rate of the dynein head with a docked linker being larger than that with an undocked linker is indispensable for the unidirectional motility of the motor, and the small free energy change for the linker docking in the strong MT-binding state facilitates the unidirectional motility.

A force-sensitive mutation reveals a non-canonical role for dynein in anaphase progression

The diverse roles of the dynein motor in shaping microtubule networks and cargo transport complicate in vivo analysis of its functions significantly. To address this issue, we have generated a series of missense mutations in Drosophila Dynein heavy chain. We show that mutations associated with human neurological disease cause a range of defects, including impaired cargo trafficking in neurons. We also describe a novel microtubule-binding domain mutation that specifically blocks the metaphase-anaphase transition during mitosis in the embryo. This effect is independent from dynein's canonical role in silencing the spindle assembly checkpoint. Optical trapping of purified dynein complexes reveals that this mutation only compromises motor performance under load, a finding rationalized by the results of all-atom molecular dynamics simulations. We propose that dynein has a novel function in anaphase progression that depends on it operating in a specific load regime. More broadly, our work illustrates how in vivo functions of motors can be dissected by manipulating their mechanical properties.

Direct and indirect toxicity mechanisms of the natural insecticide azadirachtin based on in-silico interactions with tubulin, topoisomerase and DNA

Natural pesticides, which attract attention with safe properties, pose a threat to many non-target organisms, so their toxic effects should be studied extensively. In this study, the toxic effects of Azadirachtin, a natural insecticide derived from Azadirachta indica, were investigated by in-vivo and in-silico methods. In-vivo toxic effects were determined using the Allium test and bulbs were treated with 5 mg/L (0.5x EC50), 10 mg/L (EC50), and 20 mg/L (2xEC50) Azadirachtin. In the groups treated with Azadirachtin, there was a decline in germination-related parameters and accordingly growth was delayed. This regression may be related to oxidative stress in the plant, and the increase in malondialdehyde and proline levels in Azadirachtin-applied groups confirms oxidative stress. Azadirachtin toxicity increased dose-dependently and the most significant toxic effect was observed in the group administered 20 mg/L Azadirachtin. In this group, the mitotic index decreased by 43.4% and sticky chromosomes, vagrant chromosomes and fragments were detected at rates of 83.1 ± 4.01, 72.7 ± 3.46 and 65.1 ± 3.51, respectively. By comet analysis, it was determined that Azadirachtin caused DNA fragmentation, and tail DNA, which was 0.10 ± 0.32% in the control group, increased to 34.5 ± 1.35% in the Azadirachtin -treated groups. These cytotoxic and genotoxic effects of Azadirachtin may be due to direct interaction with macromolecules as well as induced oxidative stress. Azadirachtin has been found to interact in-silico with alpha-tubulin, beta-tubulin, topoisomerase I and II, and various DNA sequences. Possible deteriorations in macromolecular structure and functions as a result of these interactions may cause cytotoxic and genotoxic effects. These results suggest that natural insecticides may also be unreliable for non-target organisms, and the toxic effects of compounds presented as "natural" should also be investigated.

Tensile Stress on Microtubules Facilitates Dynein-Driven Cargo Transport

Mechanical stress significantly affects the physiological functions of cells, including tissue homeostasis, cytoskeletal alterations, and intracellular transport. As a major cytoskeletal component, microtubules respond to mechanical stimulation by altering their alignment and polymerization dynamics. Previously, we reported that microtubules may modulate cargo transport by one of the microtubule-associated motor proteins, dynein, under compressive mechanical stress. Despite the critical role of tensile stress in many biological functions, how tensile stress on microtubules regulates cargo transport is yet to be unveiled. The present study demonstrates that the low-level tensile stress-induced microtubule deformation facilitates dynein-driven transport. We validate our experimental findings using all-atom molecular dynamics simulation. Our study may provide important implications for developing new therapies for diseases that involve impaired intracellular transport.

Molecular mechanism of dynein-dynactin complex assembly by LIS1

Cytoplasmic dynein is a microtubule motor vital for cellular organization and division. It functions as a ~4-megadalton complex containing its cofactor dynactin and a cargo-specific coiled-coil adaptor. However, how dynein and dynactin recognize diverse adaptors, how they interact with each other during complex formation, and the role of critical regulators such as lissencephaly-1 (LIS1) protein (LIS1) remain unclear. In this study, we determined the cryo-electron microscopy structure of dynein-dynactin on microtubules with LIS1 and the lysosomal adaptor JIP3. This structure reveals the molecular basis of interactions occurring during dynein activation. We show how JIP3 activates dynein despite its atypical architecture. Unexpectedly, LIS1 binds dynactin's p150 subunit, tethering it along the length of dynein. Our data suggest that LIS1 and p150 constrain dynein-dynactin to ensure efficient complex formation.

In-vivo and in-silico studies to identify toxicity mechanisms of permethrin with the toxicity-reducing role of ginger

In this study, the toxic effects of permethrin on Allium cepa L. and the protective role of Zingiber officinale rhizome extract (Zoex) were investigated. In this context, 6 different groups were formed. While the control group was treated with tap water, the groups II and III were treated with 10 µg/mL and 20 µg/mL Zoex, respectively, and the group IV was treated with 100 µg/L permethrin. The protective effect of Zoex against permethrin toxicity was studied as a function of dose, and groups V and VI formed for this purpose were treated with 10 µg/mL Zoex + 100 µg/L permethrin and 20 µg/mL Zoex + 100 µg/L permethrin, respectively. After 72 h of germination, cytogenetic, biochemical, physiological, and anatomical changes in meristematic cells of A. cepa were studied. As a result, permethrin application decreased the mitotic index (MI) and increased the frequency of micronuclei (MN), and chromosomal abnormalities. The increase in malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) and the decrease in glutathione (GSH) indicate that permethrin causes oxidative damage. Compared to the control group, a 68.5% decrease in root elongation (p < 0.05) and an 81.8% decrease (p < 0.05) in weight gain were observed in the permethrin-treated group. It was found that the application of Zoex together with permethrin resulted in regression of all detected abnormalities, reduction in the incidence of anatomical damage, MN and chromosomal aberrations, and improvement in MI rates. The most significant improvement was observed in group VI treated with 20 µg/mL Zoex, and Zoex was also found to provide dose-dependent protection. The toxicity mechanism of permethrin was also elucidated by molecular docking and spectral studies. From the data obtained during the study, it was found that permethrin has toxic effects on A. cepa, a non-target organism, while Zoex plays a protective role by reducing these effects.

Methylation of ciliary dynein motors involves the essential cytosolic assembly factor DNAAF3/PF22

Axonemal dynein motors drive ciliary motility and can consist of up to twenty distinct components with a combined mass of ~2 MDa. In mammals, failure of dyneins to assemble within the axonemal superstructure leads to primary ciliary dyskinesia. Syndromic phenotypes include infertility, rhinitis, severe bronchial conditions, and situs inversus. Nineteen specific cytosolic factors (Dynein Axonemal Assembly Factors; DNAAFs) are necessary for axonemal dynein assembly, although the detailed mechanisms involved remain very unclear. Here, we identify the essential assembly factor DNAAF3 as a structural ortholog of S-adenosylmethionine-dependent methyltransferases. We demonstrate that dynein heavy chains, especially those forming the ciliary outer arms, are methylated on key residues within various nucleotide-binding sites and on microtubule-binding domain helices directly involved in the transition to low binding affinity. These variable modifications, which are generally missing in a Chlamydomonas null mutant for the DNAAF3 ortholog PF22 (DAB1), likely impact on motor mechanochemistry fine-tuning the activities of individual dynein complexes.

Structural mechanism of outer kinetochore Dam1-Ndc80 complex assembly on microtubules

Kinetochores couple chromosomes to the mitotic spindle to segregate the genome during cell division. An error correction mechanism drives the turnover of kinetochore-microtubule attachments until biorientation is achieved. The structural basis for how kinetochore-mediated chromosome segregation is accomplished and regulated remains an outstanding question. In this work, we describe the cryo-electron microscopy structure of the budding yeast outer kinetochore Ndc80 and Dam1 ring complexes assembled onto microtubules. Complex assembly occurs through multiple interfaces, and a staple within Dam1 aids ring assembly. Perturbation of key interfaces suppresses yeast viability. Force-rupture assays indicated that this is a consequence of impaired kinetochore-microtubule attachment. The presence of error correction phosphorylation sites at Ndc80-Dam1 ring complex interfaces and the Dam1 staple explains how kinetochore-microtubule attachments are destabilized and reset.

Microtubule-binding-induced allostery triggers LIS1 dissociation from dynein prior to cargo transport

The lissencephaly-related protein LIS1 is a critical regulator of cytoplasmic dynein that governs motor function and intracellular localization (for example, to microtubule plus-ends). Although LIS1 binding is required for dynein activity, its unbinding prior to initiation of cargo transport is equally important, since preventing dissociation leads to dynein dysfunction. To understand whether and how dynein-LIS1 binding is modulated, we engineered dynein mutants locked in a microtubule-bound (MT-B) or microtubule-unbound (MT-U) state. Whereas the MT-B mutant exhibits low LIS1 affinity, the MT-U mutant binds LIS1 with high affinity, and as a consequence remains almost irreversibly associated with microtubule plus-ends. We find that a monomeric motor domain is sufficient to exhibit these opposing LIS1 affinities, and that this is evolutionarily conserved between yeast and humans. Three cryo-EM structures of human dynein with and without LIS1 reveal microtubule-binding induced conformational changes responsible for this regulation. Our work reveals key biochemical and structural insight into LIS1-mediated dynein activation.

Crystal structure of the stalk region of axonemal inner-arm dynein-d reveals unique features in the coiled-coil and microtubule-binding domain

Axonemal dynein is an ATP-dependent microtubular motor protein responsible for cilia and flagella beating, and its dysfunction can cause diseases such as primary ciliary dyskinesia and sperm dysmotility. Despite its biological importance, structure-based mechanisms underlying axonemal dynein motors remain unclear. Here, we determined the X-ray crystal structure of the human inner-arm dynein-d (DNAH1) stalk region, which contains a long antiparallel coiled-coil and a microtubule-binding domain (MTBD), at 2.7 Å resolution. Notably, differences in the relative orientation of the coiled-coil and MTBD in comparison with other dyneins, as well as the diverse orientations of the MTBD flap region among various isoforms, lead us to propose a 'spike shoe model' with an altered stepping angle for the interaction between IAD-d and microtubules. Based on these findings, we discuss isoform-specific functions of the axonemal dynein stalk MTBDs.

Developing Hybrid All-Atom and Ultra-Coarse-Grained Models to Investigate Taxol-Binding and Dynein Interactions on Microtubules

Simulating the conformations and functions of biological macromolecules by using all-atom (AA) models is a challenging task due to expensive computational costs. One possible strategy to solve this problem is to develop hybrid all-atom and ultra-coarse-grained (AA/UCG) models of the biological macromolecules. In the AA/UCG scheme, the interest regions are described by AA models, while the other regions are described in the UCG representation. In this study, we develop the hybrid AA/UCG models and apply them to investigate the conformational changes of microtubule-bound tubulins. The simulation results of the hybrid models elucidated the mechanism of why the taxol molecules selectively bound microtubules but not tubulin dimers. In addition, we also explore the interactions of the microtubules and dyneins. Our study shows that the hybrid AA/UCG model has great application potential in studying the function of complex biological systems.

Zn2+ decoration of microtubules arrests axonal transport and displaces tau, doublecortin, and MAP2C

Intracellular Zn2+ concentrations increase via depolarization-mediated influx or intracellular release, but the immediate effects of Zn2+ signals on neuron function are not fully understood. By simultaneous recording of cytosolic Zn2+ and organelle motility, we find that elevated Zn2+ (IC50 ≈ 5-10 nM) reduces both lysosomal and mitochondrial motility in primary rat hippocampal neurons and HeLa cells. Using live-cell confocal microscopy and in vitro single-molecule TIRF imaging, we reveal that Zn2+ inhibits activity of motor proteins (kinesin and dynein) without disrupting their microtubule binding. Instead, Zn2+ directly binds to microtubules and selectively promotes detachment of tau, DCX, and MAP2C, but not MAP1B, MAP4, MAP7, MAP9, or p150glued. Bioinformatic predictions and structural modeling show that the Zn2+ binding sites on microtubules partially overlap with the microtubule binding sites of tau, DCX, dynein, and kinesin. Our results reveal that intraneuronal Zn2+ regulates axonal transport and microtubule-based processes by interacting with microtubules.

A force-sensitive mutation reveals a spindle assembly checkpoint-independent role for dynein in anaphase progression

The cytoplasmic dynein-1 (dynein) motor organizes cells by shaping microtubule networks and moving a large variety of cargoes along them. However, dynein's diverse roles complicate in vivo studies of its functions significantly. To address this issue, we have used gene editing to generate a series of missense mutations in Drosophila Dynein heavy chain (Dhc). We find that mutations associated with human neurological disease cause a range of defects in larval and adult flies, including impaired cargo trafficking in neurons. We also describe a novel mutation in the microtubule-binding domain (MTBD) of Dhc that, remarkably, causes metaphase arrest of mitotic spindles in the embryo but does not impair other dynein-dependent processes. We demonstrate that the mitotic arrest is independent of dynein's well-established roles in silencing the spindle assembly checkpoint. In vitro reconstitution and optical trapping assays reveal that the mutation only impairs the performance of dynein under load. In silico all-atom molecular dynamics simulations show that this effect correlates with increased flexibility of the MTBD, as well as an altered orientation of the stalk domain, with respect to the microtubule. Collectively, our data point to a novel role of dynein in anaphase progression that depends on the motor operating in a specific load regime. More broadly, our work illustrates how cytoskeletal transport processes can be dissected in vivo by manipulating mechanical properties of motors.

RNA recoding in cephalopods tailors microtubule motor protein function

RNA editing is a widespread epigenetic process that can alter the amino acid sequence of proteins, termed "recoding." In cephalopods, most transcripts are recoded, and recoding is hypothesized to be an adaptive strategy to generate phenotypic plasticity. However, how animals use RNA recoding dynamically is largely unexplored. We investigated the function of cephalopod RNA recoding in the microtubule motor proteins kinesin and dynein. We found that squid rapidly employ RNA recoding in response to changes in ocean temperature, and kinesin variants generated in cold seawater displayed enhanced motile properties in single-molecule experiments conducted in the cold. We also identified tissue-specific recoded squid kinesin variants that displayed distinct motile properties. Finally, we showed that cephalopod recoding sites can guide the discovery of functional substitutions in non-cephalopod kinesin and dynein. Thus, RNA recoding is a dynamic mechanism that generates phenotypic plasticity in cephalopods and can inform the characterization of conserved non-cephalopod proteins.

Diverse cytomotive actins and tubulins share a polymerization switch mechanism conferring robust dynamics

Protein filaments are used in myriads of ways to organize other molecules within cells. Some filament-forming proteins couple the hydrolysis of nucleotides to their polymerization cycle, thus powering the movement of other molecules. These filaments are termed cytomotive. Only members of the actin and tubulin protein superfamilies are known to form cytomotive filaments. We examined the basis of cytomotivity via structural studies of the polymerization cycles of actin and tubulin homologs from across the tree of life. We analyzed published data and performed structural experiments designed to disentangle functional components of these complex filament systems. Our analysis demonstrates the existence of shared subunit polymerization switches among both cytomotive actins and tubulins, i.e., the conformation of subunits switches upon assembly into filaments. These cytomotive switches can explain filament robustness, by enabling the coupling of kinetic and structural polarities required for cytomotive behaviors and by ensuring that single cytomotive filaments do not fall apart.

Causes, costs and consequences of kinesin motors communicating through the microtubule lattice

Microtubules are critical for a variety of important functions in eukaryotic cells. During intracellular trafficking, molecular motor proteins of the kinesin superfamily drive the transport of cellular cargoes by stepping processively along the microtubule surface. Traditionally, the microtubule has been viewed as simply a track for kinesin motility. New work is challenging this classic view by showing that kinesin-1 and kinesin-4 proteins can induce conformational changes in tubulin subunits while they are stepping. These conformational changes appear to propagate along the microtubule such that the kinesins can work allosterically through the lattice to influence other proteins on the same track. Thus, the microtubule is a plastic medium through which motors and other microtubule-associated proteins (MAPs) can communicate. Furthermore, stepping kinesin-1 can damage the microtubule lattice. Damage can be repaired by the incorporation of new tubulin subunits, but too much damage leads to microtubule breakage and disassembly. Thus, the addition and loss of tubulin subunits are not restricted to the ends of the microtubule filament but rather, the lattice itself undergoes continuous repair and remodeling. This work leads to a new understanding of how kinesin motors and their microtubule tracks engage in allosteric interactions that are critical for normal cell physiology.

DNALI1 deficiency causes male infertility with severe asthenozoospermia in humans and mice by disrupting the assembly of the flagellar inner dynein arms and fibrous sheath

The axonemal dynein arms (outer (ODA) and inner dynein arms (IDAs)) are multiprotein structures organized by light, intermediate, light intermediate (LIC), and heavy chain proteins. They hydrolyze ATP to promote ciliary and flagellar movement. Till now, a variety of dynein protein deficiencies have been linked with asthenospermia (ASZ), highlighting the significance of these structures in human sperm motility. Herein, we detected bi-allelic DNALI1 mutations [c.663_666del (p.Glu221fs)], in an ASZ patient, which resulted in the complete loss of the DNALI1 in the patient's sperm. We identified loss of sperm DNAH1 and DNAH7 rather than DNAH10 in both DNALI1^663_666del patient and Dnali1^-/- mice, demonstrating that mammalian DNALI1 is a LIC protein of a partial IDA subspecies. More importantly, we revealed that DNALI1 loss contributed to asymmetries in the most fibrous sheath (FS) of the sperm flagellum in both species. Immunoprecipitation revealed that DNALI1 might interact with the cytoplasmic dynein complex proteins in the testes. Furthermore, DNALI1 loss severely disrupted the transport and assembly of the FS proteins, especially AKAP3 and AKAP4, during flagellogenesis. Hence, DNALI1 may possess a non-classical molecular function, whereby it regulates the cytoplasmic dynein complex that assembles the flagella. We conclude that a DNALI deficiency-induced IDAs injury and an asymmetric FS-driven tail rigid structure alteration may simultaneously cause flagellum immotility. Finally, intracytoplasmic sperm injection (ICSI) can effectively resolve patient infertility. Collectively, we demonstrate that DNALI1 is a newly causative gene for AZS in both humans and mice, which possesses multiple crucial roles in modulating flagellar assembly and motility.

Composition, organization and mechanisms of the transition zone, a gate for the cilium

The cilium evolved to provide the ancestral eukaryote with the ability to move and sense its environment. Acquiring these functions required the compartmentalization of a dynein-based motility apparatus and signaling proteins within a discrete subcellular organelle contiguous with the cytosol. Here, we explore the potential molecular mechanisms for how the proximal-most region of the cilium, termed transition zone (TZ), acts as a diffusion barrier for both membrane and soluble proteins and helps to ensure ciliary autonomy and homeostasis. These include a unique complement and spatial organization of proteins that span from the microtubule-based axoneme to the ciliary membrane; a protein picket fence; a specialized lipid microdomain; differential membrane curvature and thickness; and lastly, a size-selective molecular sieve. In addition, the TZ must be permissive for, and functionally integrates with, ciliary trafficking systems (including intraflagellar transport) that cross the barrier and make the ciliary compartment dynamic. The quest to understand the TZ continues and promises to not only illuminate essential aspects of human cell signaling, physiology, and development, but also to unravel how TZ dysfunction contributes to ciliopathies that affect multiple organ systems, including eyes, kidney, and brain.

Multi-curve fitting and tubulin-lattice signal removal for structure determination of large microtubule-based motors

Revealing high-resolution structures of microtubule-associated proteins (MAPs) is critical for understanding their fundamental roles in various cellular activities, such as cell motility and intracellular cargo transport. Nevertheless, large flexible molecular motors that dynamically bind and release microtubule networks are challenging for cryo-electron microscopy (cryo-EM). Traditional structure determination of MAPs bound to microtubules needs alignment information from the reconstruction of microtubules, which cannot be readily applied to large MAPs without a fixed binding pattern. Here, we developed a comprehensive approach to estimate the microtubule networks (multi-curve fitting), model the tubulin-lattice signals, and remove them (tubulin-lattice subtraction) from the raw cryo-EM micrographs. The approach does not require an ordered binding pattern of MAPs on microtubules, nor does it need a reconstruction of the microtubules. We demonstrated the capability of our approach using the reconstituted outer-arm dynein (OAD) bound to microtubule doublets. The tubulin-lattice subtraction improves the OAD alignment, thus leading to high-resolution reconstructions. In addition, the multi-curve fitting approach provides an accurate automatic alternative method to pick or segment filaments in 2D images and potentially in 3D tomograms. The accuracy of our approach has been demonstrated by using several other biological filaments. Our work provides a new tool to determine high-resolution structures of large MAPs bound to curved microtubule networks.

Clinical detection, diagnosis and treatment of morphological abnormalities of sperm flagella: A review of literature

Sperm carries male genetic information, and flagella help move the sperm to reach oocytes. When the ultrastructure of the flagella is abnormal, the sperm is unable to reach the oocyte and achieve insemination. Multiple morphological abnormalities of sperm flagella (MMAF) is a relatively rare idiopathic condition that is mainly characterized by multiple defects in sperm flagella. In the last decade, with the development of high-throughput DNA sequencing approaches, many genes have been revealed to be related to MMAF. However, the differences in sperm phenotypes and reproductive outcomes in many cases are attributed to different pathogenic genes or different pathogenic mutations in the same gene. Here, we will review information about the various phenotypes resulting from different pathogenic genes, including sperm ultrastructure and encoding proteins with their location and functions as well as assisted reproductive technology (ART) outcomes. We will share our clinical detection and diagnosis experience to provide additional clinical views and broaden the understanding of this disease.

Structure of dynein-dynactin on microtubules shows tandem adaptor binding

Cytoplasmic dynein is a microtubule motor that is activated by its cofactor dynactin and a coiled-coil cargo adaptor1-3. Up to two dynein dimers can be recruited per dynactin, and interactions between them affect their combined motile behaviour4-6. Different coiled-coil adaptors are linked to different cargos7,8, and some share motifs known to contact sites on dynein and dynactin4,9-13. There is limited structural information on how the resulting complex interacts with microtubules and how adaptors are recruited. Here we develop a cryo-electron microscopy processing pipeline to solve the high-resolution structure of dynein-dynactin and the adaptor BICDR1 bound to microtubules. This reveals the asymmetric interactions between neighbouring dynein motor domains and how they relate to motile behaviour. We found that two adaptors occupy the complex. Both adaptors make similar interactions with the dyneins but diverge in their contacts with each other and dynactin. Our structure has implications for the stability and stoichiometry of motor recruitment by cargos.

Toxicity mechanisms of aflatoxin M1 assisted with molecular docking and the toxicity-limiting role of trans-resveratrol

In this study, AFM₁ toxicity and the protective role of trans-resveratrol (t-rsv) against this toxicity were investigated with the help of multiple parameters in albino mice. As a result, AFM₁ (16 mg/kg b.w) administration caused a decrease in body, kidney and liver weights. This reduction was associated with a decrease in feed consumption. AFM₁ induced an increase in AST and ALT enzyme parameters and BUN, creatinine and MDA levels and a decrease in GSH levels. These increases have been associated with liver and kidney cell damage. AFM₁ decreased MI and encouraged increases in MN and CAs numbers. The decrease in MI was correlated with AFM1-tubulin and the increase in CAs was associated with the AFM₁-DNA interaction, which was demonstrated by molecular docking and spectral shifting. Besides, the decrease in DNA damage and amount was demonstrated by the comet assay technique. Administration of t-rsv (10 and 20 mg/kg b.w) reduced the toxic effects of AFM₁ and caused a dose-dependent improvement in all physiological, biochemical and cytogenetic parameter values studied. For this reason, foods containing t-rsv or food supplements should be consumed in the daily diet to reduce the effect of toxic agents.

Loss of function mutation in DNAH7 induces male infertility associated with abnormalities of the sperm flagella and mitochondria in human

Male infertility is an increasingly serious health problem affecting couples of reproductive age. Mutations in axoneme-associated genes cause male infertility. Dynein arm proteins are essential in sustaining normal axonemes and promote flagellar motility. However, the function of DNAH7 in male fertility in vivo remains unclear. Herein, we showed that DNAH7 disruption in humans results in male infertility, which was characterised by multiple morphological abnormalities of sperm flagella. The axoneme structure of the sperm from a DNAH7-deficient patient revealed the loss of inner dynein arms. Moreover, the mitochondria of the sperm flagella detached and dispersed outside the axoneme, leading to abnormalities in the mitochondrial sheath in the mid-piece region. Live birth was achieved via intracytoplasmic sperm injection. Thus, DNAH7 is critical for axoneme and mitochondrial development in human sperm. These findings further clarify the spectrum of DNAH7 biology and provide new insights for diagnosing infertility and treating patients harbouring DNAH7 mutations. This article is protected by copyright. All rights reserved.

Paraquat toxicity in different cell types of Swiss albino mice

In this study, toxicity caused by 50, 100 and 200 mg/kg b.w doses of Paraquat herbicide in Swiss albino mice was investigated. Body weight, liver and kidney organ weights, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) enzyme activities, blood urea nitrogen (BUN) and creatinine levels, malondialdehyde (MDA) and glutathione (GSH) levels in liver and kidney, micronucleus (MN) formation in buccal mucosal epithelium, erythrocyte and leukocyte cells and chromosomal aberrations (CAs) in bone marrow cells, viability of liver and kidney cells were investigated. Four groups were randomly formed from male Swiss albino mice (one control and three treatment groups). The control group mice were provided tap water and the mice in the treatment groups were treated orally with three different doses of Paraquat (50, 100 and 200 mg/kg b.w) in the drinking water for 28 days. At the end of the application, all mice were sacrificed and routine preparation procedures were carried out to examine physiological, biochemical, oxidative stress and genetic parameters. Paraquat administration decreased physiological parameters (body, liver and kidney organ weights), and increased biochemical parameters (AST, ALT, BUN, creatinine and MDA). GSH levels were decreased depending on the dose. Kidney and liver damage were confirmed by the trypan blue test. Paraquat administration promoted MN formation in buccal mucosal epithelium, erythrocyte and leukocyte cells depending on the dose. The highest MN frequency was observed in leukocyte cells exposed to a dose of 200 mg/kg b.w of Paraquat. Deteriorations in DNA integrity as a result of MN formations were supported by the comet assay. In addition, Paraquat promoted CAs such as break, fragment, acentric, dicentric, gap and ring in bone marrow cells. Break damage was the most common among these damages. These observed genotoxic effects occured as a result of the interaction of DNA and DNA-related proteins with Paraquat. Molecular docking studies showed that Paraquat binds to histone H4 protein with high affinity and has a high intercalation potential. As a result, Paraquat herbicide caused a significant toxicity by changing physiological, biochemical, oxidative stress and genetic parameters of Swiss albino mice depending on the application dose.

Structure Determination of Microtubules and Pili: Past, Present, and Future Directions

Historically proteins that form highly polymeric and filamentous assemblies have been notoriously difficult to study using high resolution structural techniques. This has been due to several factors that include structural heterogeneity, their large molecular mass, and available yields. However, over the past decade we are now seeing a major shift towards atomic resolution insight and the study of more complex heterogenous samples and in situ/ex vivo examination of multi-subunit complexes. Although supported by developments in solid state nuclear magnetic resonance spectroscopy (ssNMR) and computational approaches, this has primarily been due to advances in cryogenic electron microscopy (cryo-EM). The study of eukaryotic microtubules and bacterial pili are good examples, and in this review, we will give an overview of the technical innovations that have enabled this transition and highlight the advancements that have been made for these two systems. Looking to the future we will also describe systems that remain difficult to study and where further technical breakthroughs are required.

Bi-allelic variants in DNAH10 cause asthenoteratozoospermia and male infertility

PURPOSE

Multiple morphological abnormalities in the sperm flagella (MMAF) comprise a severe phenotype of asthenoteratozoospermia with reduced or absent spermatozoa motility. Whereas dozens of candidate pathogenic genes for MMAF have been identified, the genetic cause in a large proportion of patients is unknown. We attempted to identify novel genetic explanations for MMAF.

METHODS

We performed whole-exome sequencing of patients with MMAF to identify pathogenic variants. The phenotypes of spermatozoa in patients carrying DNAH10 variants were investigated using haematoxylin and eosin staining, scanning electron microscopy, and transmission electron microscopy. The expression and location of DNAH10 and other spermatozoa structure-related proteins were analyzed using immunofluorescence assays.

RESULTS

We found one homozygous frameshift DNAH10 variant (NM_207437: c.2514delG:p.L839*) and one compound heterozygous DNAH10 variant (NM_207437: c.10820 T > C:p.M3607T; c.12692C > T:p.T4231I) in two patients with MMAF. These variants were absent or rare in the general population. Haematoxylin and eosin staining and scanning electron microscopy revealed the significant disruption of sperm flagella in the patients. In addition, ultrastructural analysis by transmission electron microscopy showed significant inner dynein arm (IDA) deficiency in sperm flagella. Using immunofluorescence assays, we found a significant reduction in IDA-related proteins including DNAH10 and DNAH1.

CONCLUSIONS

We identified putative novel pathogenic variants in DNAH10 for MMAF, which might advance the genetic diagnosis and clinical genetic counselling for male infertility.

Microtubule Dumbbells to Assess the Effect of Force Geometry on Single Kinesin Motors

The cytoskeletal motors myosin, kinesin, and dynein and their corresponding tracks, actin and microtubules, are force generating ATPases responsible for motility and morphological changes at the intracellular, cellular, and tissue levels. The pioneering application of optical tweezers to measure the force-producing properties of cytoskeletal motors has provided an unparalleled understanding of their mechanochemistry. The mechanosensitivity of processive, microtubule-based motors has largely been studied in the optical trap using the "single-bead" assay, where a bead-attached motor is held adjacent to a cytoskeletal filament as it processively steps along it. However, because of the geometrical constraints in the conventional single-bead assay, the motor-filament bond is not only loaded parallel to the long axis of the filament, but also perpendicular to the long axis of the filament. This perpendicular force, which is inherent in the conventional single-bead assay, accelerates the motor-filament detachment and has not been carefully considered in prior experiments. An alternative approach is the "three-bead" assay, which was developed for the study of non-processive myosin motors. The vertical force component is minimized in this assay, and the total opposing force is mainly parallel to the microtubule. Experiments with kinesin show that microtubule attachment durations can be highly variable and last for up to tenfold longer times in the three-bead assay, compared to the single-bead assay. Thus, the ability of kinesin to bear mechanical load and remain attached to microtubules depends on the forces in more than one dimension. In this chapter, we provide detailed methods for preparing the proteins, buffers, flow chambers, and bead-filament assemblies for performing the three-bead assay with microtubules and their motors.

Cryo-EM structure of a microtubule-bound parasite kinesin motor and implications for its mechanism and inhibition

Plasmodium parasites cause malaria and are responsible annually for hundreds of thousands of deaths. Kinesins are a superfamily of microtubule-dependent ATPases that play important roles in the parasite replicative machinery, which is a potential target for antiparasite drugs. Kinesin-5, a molecular motor that cross-links microtubules, is an established antimitotic target in other disease contexts, but its mechanism in Plasmodium falciparum is unclear. Here, we characterized P. falciparum kinesin-5 (PfK5) using cryo-EM to determine the motor's nucleotide-dependent microtubule-bound structure and introduced 3D classification of individual motors into our microtubule image processing pipeline to maximize our structural insights. Despite sequence divergence in PfK5, the motor exhibits classical kinesin mechanochemistry, including ATP-induced subdomain rearrangement and cover neck bundle formation, consistent with its plus-ended directed motility. We also observed that an insertion in loop5 of the PfK5 motor domain creates a different environment in the well-characterized human kinesin-5 drug-binding site. Our data reveal the possibility for selective inhibition of PfK5 and can be used to inform future exploration of Plasmodium kinesins as antiparasite targets.

Nano-Particles Carried by Multiple Dynein Motors Self-Regulate Their Number of Actively Participating Motors

Intra-cellular active transport by native cargos is ubiquitous. We investigate the motion of spherical nano-particles (NPs) grafted with flexible polymers that end with a nuclear localization signal peptide. This peptide allows the recruitment of several mammalian dynein motors from cytoplasmic extracts. To determine how motor–motor interactions influenced motility on the single microtubule level, we conducted bead-motility assays incorporating surface adsorbed microtubules and combined them with model simulations that were based on the properties of a single dynein. The experimental and simulation results revealed long time trajectories: when the number of NP-ligated motors N_m increased, run-times and run-lengths were enhanced and mean velocities were somewhat decreased. Moreover, the dependence of the velocity on run-time followed a universal curve, regardless of the system composition. Model simulations also demonstrated left- and right-handed helical motion and revealed self-regulation of the number of microtubule-bound, actively transporting dynein motors. This number was stochastic along trajectories and was distributed mainly between one, two, and three motors, regardless of N_m. We propose that this self-regulation allows our synthetic NPs to achieve persistent motion that is associated with major helicity. Such a helical motion might affect obstacle bypassing, which can influence active transport efficiency when facing the crowded environment of the cell.

Comprehensive Analysis of Binding Sites in Tubulin

Tubulin plays essential roles in vital cellular activities and is the target of a wide range of proteins and ligands. Here, using a combined computational and crystallographic fragment screening approach, we addressed the question of how many binding sites exist in tubulin. We identified 27 distinct sites, of which 11 have not been described previously, and analyzed their relationship to known tubulin-protein and tubulin-ligand interactions. We further observed an intricate pocket communication network and identified 56 chemically diverse fragments that bound to 10 distinct tubulin sites. Our results offer a unique structural basis for the development of novel small molecules for use as tubulin modulators in basic research applications or as drugs. Furthermore, our method lays down a framework that may help to discover new pockets in other pharmaceutically important targets and characterize them in terms of chemical tractability and allosteric modulation.

Structure and Mechanics of Dynein Motors

Dyneins make up a family of AAA+ motors that move toward the minus end of microtubules. Cytoplasmic dynein is responsible for transporting intracellular cargos in interphase cells and mediating spindle assembly and chromosome positioning during cell division. Other dynein isoforms transport cargos in cilia and power ciliary beating. Dyneins were the least studied of the cytoskeletal motors due to challenges in the reconstitution of active dynein complexes in vitro and the scarcity of high-resolution methods for in-depth structural and biophysical characterization of these motors. These challenges have been recently addressed, and there have been major advances in our understanding of the activation, mechanism, and regulation of dyneins. This review synthesizes the results of structural and biophysical studies for each class of dynein motors. We highlight several outstanding questions about the regulation of bidirectional transport along microtubules and the mechanisms that sustain self-coordinated oscillations within motile cilia.

Developmental toxicity of the novel PFOS alternative OBS in developing zebrafish: An emphasis on cilia disruption

In recent years, sodium p-perfluorous nonenoxybenzene sulfonate (OBS) has emerged as a substitute for PFOS with large demand and application in the Chinese market. However, little is known about potential developmental effects of OBS. In this study, zebrafish embryos were acutely exposed to different concentrations of OBS and the positive control PFOS for a comparative developmental toxicity assessment. OBS caused hatching delays, body axis curvature, neurobehavioral inhibition and abnormal cardiovascular development. These organismal effects were accompanied by change of development related genes expression profile, in which some cases were similar to PFOS. Overall, the toxic effects induced by OBS were generally milder than that of PFOS. Further investigation suggested that both OBS and PFOS disrupted ciliogenesis, evidenced by the ciliary immunostaining, changes in gene expression of kinesin family, dynein arm family and tubulin family members, as well as downregulation of the abundance of motor proteins including KIF3C, DYNC1H1 and DYNC1LI1. The influence of PFOS was stronger than that of OBS on ciliary genes and proteins. Molecular docking analysis revealed that both OBS and PFOS fitted into the motor proteins tightly, but binding affinity between OBS and motor proteins was lower than PFOS. Collectively, OBS and PFOS may act on ciliary motor proteins to interfere with ciliogenesis, leading to ciliary dysfunction and providing a novel probable action mode linked to developmental toxicity. This raises concerns regarding the health risks of the novel PFOS alternative OBS.

Axonemal Dynein DNAH5 is Required for Sound Sensation in Drosophila Larvae

Chordotonal neurons are responsible for sound sensation in Drosophila. However, little is known about how they respond to sound with high sensitivity. Using genetic labeling, we found one of the Drosophila axonemal dynein heavy chains, CG9492 (DNAH5), was specifically expressed in larval chordotonal neurons and showed a distribution restricted to proximal cilia. While DNAH5 mutation did not affect the cilium morphology or the trafficking of Inactive, a candidate auditory transduction channel, larvae with DNAH5 mutation had reduced startle responses to sound at low and medium intensities. Calcium imaging confirmed that DNAH5 functioned autonomously in chordotonal neurons for larval sound sensation. Furthermore, disrupting DNAH5 resulted in a decrease of spike firing responses to low-level sound in chordotonal neurons. Intriguingly, DNAH5 mutant larvae displayed an altered frequency tuning curve of the auditory organs. All together, our findings support a critical role of DNAH5 in tuning the frequency selectivity and the sound sensitivity of larval auditory neurons.

Structures of outer-arm dynein array on microtubule doublet reveal a motor coordination mechanism

Thousands of outer-arm dyneins (OADs) are arrayed in the axoneme to drive a rhythmic ciliary beat. Coordination among multiple OADs is essential for generating mechanical forces to bend microtubule doublets (MTDs). Using electron microscopy, we determined high-resolution structures of Tetrahymena thermophila OAD arrays bound to MTDs in two different states. OAD preferentially binds to MTD protofilaments with a pattern resembling the native tracks for its distinct microtubule-binding domains. Upon MTD binding, free OADs are induced to adopt a stable parallel conformation, primed for array formation. Extensive tail-to-head (TTH) interactions between OADs are observed, which need to be broken for ATP turnover by the dynein motor. We propose that OADs in an array sequentially hydrolyze ATP to slide the MTDs. ATP hydrolysis in turn relaxes the TTH interfaces to effect free nucleotide cycles of downstream OADs. These findings lead to a model explaining how conformational changes in the axoneme produce coordinated action of dyneins.

Dynamic and asymmetric fluctuations in the microtubule wall captured by high-resolution cryoelectron microscopy

Microtubules are tubular polymers with essential roles in numerous cellular activities. Structures of microtubules have been captured at increasing resolution by cryo-EM. However, dynamic properties of the microtubule are key to its function, and this behavior has proved difficult to characterize at a structural level due to limitations in existing structure determination methods. We developed a high-resolution cryo-EM refinement method that divides an imaged microtubule into its constituent protofilaments, enabling deviations from helicity and other sources of heterogeneity to be quantified and corrected for at the single-subunit level. We demonstrate that this method improves the resolution of microtubule 3D reconstructions and substantially reduces anisotropic blurring artifacts, compared with methods that utilize helical symmetry averaging. Moreover, we identified an unexpected, discrete behavior of the m-loop, which mediates lateral interactions between neighboring protofilaments and acts as a flexible hinge between them. The hinge angle adopts preferred values corresponding to distinct conformations of the m-loop that are incompatible with helical symmetry. These hinge angles fluctuate in a stochastic manner, and perfectly cylindrical microtubule conformations are thus energetically and entropically penalized. The hinge angle can diverge further from helical symmetry at the microtubule seam, generating a subpopulation of highly distorted microtubules. However, the seam-distorted subpopulation disappears in the presence of Taxol, a microtubule stabilizing agent. These observations provide clues into the structural origins of microtubule flexibility and dynamics and highlight the role of structural polymorphism in defining microtubule behavior.

Force-Generating Mechanism of Axonemal Dynein in Solo and Ensemble

In eukaryotic cilia and flagella, various types of axonemal dyneins orchestrate their distinct functions to generate oscillatory bending of axonemes. The force-generating mechanism of dyneins has recently been well elucidated, mainly in cytoplasmic dyneins, thanks to progress in single-molecule measurements, X-ray crystallography, and advanced electron microscopy. These techniques have shed light on several important questions concerning what conformational changes accompany ATP hydrolysis and whether multiple motor domains are coordinated in the movements of dynein. However, due to the lack of a proper expression system for axonemal dyneins, no atomic coordinates of the entire motor domain of axonemal dynein have been reported. Therefore, a substantial amount of knowledge on the molecular architecture of axonemal dynein has been derived from electron microscopic observations on dynein arms in axonemes or on isolated axonemal dynein molecules. This review describes our current knowledge and perspectives of the force-generating mechanism of axonemal dyneins in solo and in ensemble.

The complex of outer-arm dynein light chain-1 and the microtubule-binding domain of the γ heavy chain shows how axonemal dynein tunes ciliary beating

Axonemal dynein is a microtubule-based molecular motor that drives ciliary/flagellar beating in eukaryotes. In axonemal dynein, the outer-arm dynein (OAD) complex, which comprises three heavy chains (α, β, and γ), produces the main driving force for ciliary/flagellar motility. It has recently been shown that axonemal dynein light chain-1 (LC1) binds to the microtubule-binding domain (MTBD) of OADγ, leading to a decrease in its microtubule-binding affinity. However, it remains unclear how LC1 interacts with the MTBD and controls the microtubule-binding affinity of OADγ. Here, we have used X-ray crystallography and pulldown assays to examine the interaction between LC1 and the MTBD, identifying two important sites of interaction in the MTBD. Solving the LC1-MTBD complex from Chlamydomonas reinhardtii at 1.7 Å resolution, we observed that one site is located in the H5 helix and that the other is located in the flap region that is unique to some axonemal dynein MTBDs. Mutational analysis of key residues in these sites indicated that the H5 helix is the main LC1-binding site. We modeled the ternary structure of the LC1-MTBD complex bound to microtubules based on the known dynein-microtubule complex. This enabled us to propose a structural basis for both formations of the ternary LC1-MTBD-microtubule complex and LC1-mediated tuning of MTBD binding to the microtubule, suggesting a molecular model for how axonemal dynein senses the curvature of the axoneme and tunes ciliary/flagellar beating.

Structural basis for two-way communication between dynein and microtubules

The movements of cytoplasmic dynein on microtubule (MT) tracks is achieved by two-way communication between the microtubule-binding domain (MTBD) and the ATPase domain via a coiled-coil stalk, but the structural basis of this communication remains elusive. Here, we regulate MTBD either in high-affinity or low-affinity states by introducing a disulfide bond to the stalk and analyze the resulting structures by NMR and cryo-EM. In the MT-unbound state, the affinity changes of MTBD are achieved by sliding of the stalk α-helix by a half-turn, which suggests that structural changes propagate from the ATPase-domain to MTBD. In addition, MT binding induces further sliding of the stalk α-helix even without the disulfide bond, suggesting how the MT-induced conformational changes propagate toward the ATPase domain. Based on differences in the MT-binding surface between the high- and low-affinity states, we propose a potential mechanism for the directional bias of dynein movement on MT tracks.

Modulation of Kinesin's Load-Bearing Capacity by Force Geometry and the Microtubule Track

Kinesin motors and their associated microtubule tracks are essential for long-distance transport of cellular cargos. Intracellular activity and proper recruitment of kinesins is regulated by biochemical signaling, cargo adaptors, microtubule-associated proteins, and mechanical forces. In this study, we found that the effect of opposing forces on the kinesin-microtubule attachment duration depends strongly on experimental assay geometry. Using optical tweezers and the conventional single-bead assay, we show that detachment of kinesin from the microtubule is likely accelerated by forces vertical to the long axis of the microtubule due to contact of the single bead with the underlying microtubule. We used the three-bead assay to minimize the vertical force component and found that when the opposing forces are mainly parallel to the microtubule, the median value of attachment durations between kinesin and microtubules can be up to 10-fold longer than observed using the single-bead assay. Using the three-bead assay, we also found that not all microtubule protofilaments are equivalent interacting substrates for kinesin and that the median value of attachment durations of kinesin varies by more than 10-fold, depending on the relative angular position of the forces along the circumference of the microtubule. Thus, depending on the geometry of forces across the microtubule, kinesin can switch from a fast detaching motor (median attachment duration <0.2 s) to a persistent motor that sustains attachment (median attachment duration >3 s) at high forces (5 pN). Our data show that the load-bearing capacity of the kinesin motor is highly variable and can be dramatically affected by off-axis forces and forces across the microtubule lattice, which has implications for a range of cellular activities, including cell division and organelle transport.

Structural determinants of microtubule minus end preference in CAMSAP CKK domains

CAMSAP/Patronins regulate microtubule minus-end dynamics. Their end specificity is mediated by their CKK domains, which we proposed recognise specific tubulin conformations found at minus ends. To critically test this idea, we compared the human CAMSAP1 CKK domain (HsCKK) with a CKK domain from Naegleria gruberi (NgCKK), which lacks minus-end specificity. Here we report near-atomic cryo-electron microscopy structures of HsCKK- and NgCKK-microtubule complexes, which show that these CKK domains share the same protein fold, bind at the intradimer interprotofilament tubulin junction, but exhibit different footprints on microtubules. NMR experiments show that both HsCKK and NgCKK are remarkably rigid. However, whereas NgCKK binding does not alter the microtubule architecture, HsCKK remodels its microtubule interaction site and changes the underlying polymer structure because the tubulin lattice conformation is not optimal for its binding. Thus, in contrast to many MAPs, the HsCKK domain can differentiate subtly specific tubulin conformations to enable microtubule minus-end recognition.

A microtubule RELION-based pipeline for cryo-EM image processing

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MiRP is a pipeline for processing cryo-EM images of microtubules in RELION.

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MiRP manages microtubule heterogeneity and pseudo-symmetry.

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MiRP reduces errors in angular and translational alignment.

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MiRP improved reconstructions from three different microtubule datasets.

Microtubules are polar filaments built from αβ-tubulin heterodimers that exhibit a range of architectures in vitro and in vivo. Tubulin heterodimers are arranged helically in the microtubule wall but many physiologically relevant architectures exhibit a break in helical symmetry known as the seam. Noisy 2D cryo-electron microscopy projection images of pseudo-helical microtubules therefore depict distinct but highly similar views owing to the high structural similarity of α- and β-tubulin. The determination of the αβ-tubulin register and seam location during image processing is essential for alignment accuracy that enables determination of biologically relevant structures. Here we present a pipeline designed for image processing and high-resolution reconstruction of cryo-electron microscopy microtubule datasets, based in the popular and user-friendly RELION image-processing package, Microtubule RELION-based Pipeline (MiRP). The pipeline uses a combination of supervised classification and prior knowledge about geometric lattice constraints in microtubules to accurately determine microtubule architecture and seam location. The presented method is fast and semi-automated, producing near-atomic resolution reconstructions with test datasets that contain a range of microtubule architectures and binding proteins.

Tubulin lattice in cilia is in a stressed form regulated by microtubule inner proteins

Cilia, the hair-like protrusions that beat at high frequencies to propel a cell or move fluid around are composed of radially bundled doublet microtubules. In this study, we present a near-atomic resolution map of the Tetrahymena doublet microtubule by cryoelectron microscopy. The map demonstrates that the network of microtubule inner proteins weaves into the tubulin lattice and forms an inner sheath. From mass spectrometry data and de novo modeling, we identified Rib43a proteins as the filamentous microtubule inner proteins in the protofilament ribbon region. The Rib43a-tubulin interaction leads to an elongated tubulin dimer distance every 2 dimers. In addition, the tubulin lattice structure with missing microtubule inner proteins (MIPs) by sarkosyl treatment shows significant longitudinal compaction and lateral angle change between protofilaments. These results are evidence that the MIPs directly affect and stabilize the tubulin lattice. It suggests that the doublet microtubule is an intrinsically stressed filament and that this stress could be manipulated in the regulation of ciliary waveforms.