Refined structure of alpha beta-tubulin at 3.5 A resolution

Delta and epsilon tubulin in mammalian development

Delta (δ-) and epsilon (ε-) tubulin are lesser-known cousins of alpha (α-) and beta (β-) tubulin. They are likely to regulate centriole function in a broad range of species; however, their in vivo role and mechanism of action in mammals remain mysterious. In unicellular species and mammalian cell lines, mutations in δ- and ε-tubulin cause centriole destabilization and atypical mitosis and, in the most severe cases, cell death. Beyond the centriole, δ- and ε-tubulin localize to the manchette during murine spermatogenesis and interact with katanin-like 2 (KATNAL2), a protein with microtubule (MT)-severing properties, indicative of novel non-centriolar functions. Herein we summarize the current knowledge surrounding δ- and ε-tubulin, identify pathways for future research, and highlight how and why spermatogenesis and embryogenesis are ideal systems to define δ- and ε-tubulin function in vivo.

Synthesis and Preclinical Evaluation of Indole Triazole Conjugates as Microtubule Targeting Agents that are Effective against MCF-7 Breast Cancer Cell Lines

CDATA[Background: Microtubules are considered to be an important therapeutic target for most of the anticancer drugs. These are highly dynamic structures comprising of α-tubulin and β-tubulin which are usually heterodimers and found to be involved in cell movement, intracellular trafficking, and mitosis inhibition of which might kill the tumour cells or inhibit the abnormal proliferation of cells. Most of the tubulin polymerization inhibitors, such as Vinca alkaloids, consist of Indole as the main scaffold. The literature also suggests using triazole moiety in the chemical entities, potentiating the inhibitory activity against cell proliferation. So, in our study, we used indole triazole scaffolds to synthesize the derivatives against tubulin polymerization.

OBJECTIVE

The main objective of this study to synthesize indole triazole conjugates by using environmentally friendly solvents (green chemistry) and click chemistry. To carry out the MTT assay and tubulin polymerization assay for the synthesized indole triazole conjugates.

METHODS

All the synthesized molecules were subjected to molecular docking studies using Schrodinger suite and the structural confirmation was performed by Mass, proton-NMR and carbon-NMR, documented in DMSO and CDCL3. Biological studies were performed using DU145 (prostate cancer), A-549 (lung cancer) and, MCF-7 (breast cancer), cell lines obtained from ATCC were maintained as a continuous culture. MTT assay was performed for the analogues using standard protocol. Cell cycle analysis was carried out using flow cytometry.

RESULTS

The Indole triazole scaffolds were synthesized using the principles of Green chemistry. The triazole formation is mainly achieved by using the Click chemistry approach. Structural elucidation of synthesized compounds was performed using Mass spectroscopy (HR-MS), Proton-Nuclear Magnetic Spectroscopy (¹H-NMR) and Carbon-Nuclear Magnetic Spectroscopy (¹³C-NMR). The XP-docked poses and free energy binding calculations revealed that 2c and 2g molecules exhibited the highest docking affinity against the tubulin-colchicine domain (PDB:1SA0). In vitro cytotoxic assessment revealed that 2c and 2g displayed promising cytotoxicity in MTT assay (with CTC50 values 3.52μM and 2.37μM) which are in good agreement with the computational results. 2c and 2g also arrested 63 and 66% of cells in the G₂/M phase, respectively, in comparison to control cells (10%) and tubulin polymerization inhibition assay revealed that 2c and 2g exhibited significant inhibition of tubulin polymerization with IC₅₀ values of 2.31μM, and 2.62μM, respectively in comparison to Nocodazole, a positive control, resulted in an IC₅₀ value of 2.51μM.

CONCLUSION

Indole triazole hybrids were synthesized using click chemistry, and docking studies were carried out using Schrodinger for the designed molecules. Process Optimization has been done for both the schemes. Twelve compounds (2a-2l) have been successfully synthesized and analytical evaluation was performed using NMR and HR-MS. In vitro evaluation was for the synthesized molecules to check tubulin polymerization inhibition for antiproliferative action. Among the synthesized compounds, 2c and 2g have potent anticancer activities by inhibiting tubulin polymerization.

Genome-Wide Analysis of Tubulin Gene Family in Cassava and Expression of Family Member FtsZ2-1 during Various Stress

Filamentous temperature-sensitive protein Z (Tubulin/FtsZ) family is a group of conserved GTP-binding (guanine nucleotide-binding) proteins, which are closely related to plant tissue development and organ formation as the major component of the cytoskeleton. According to the published genome sequence information of cassava (Manihot esculenta Crantz), 23 tubulin genes (MeTubulins) were identified, which were divided into four main groups based on their type and phylogenetic characteristics. The same grouping generally has the same or similar motif composition and exon–intron structure. Collinear analysis showed that fragment repetition event is the main factor in amplification of cassava tubulin superfamily gene. The expression profiles of MeTubulin genes in various tissue were analyzed, and it was found that MeTubulins were mainly expressed in leaf, petiole, and stem, while FtsZ2-1 was highly expressed in storage root. The qRT-PCR results of the FtsZ2-1 gene under hormone and abiotic stresses showed that indole-3-acetic acid (IAA) and gibberellin A3 (GA3) stresses could significantly increase the expression of the FtsZ2-1 gene, thereby revealing the potential role of FtsZ2-1 in IAA and GA3 stress-induced responses.

The proline-rich domain promotes Tau liquid-liquid phase separation in cells

Tau protein in vitro can undergo liquid–liquid phase separation (LLPS); however, observations of this phase transition in living cells are limited. To investigate protein state transitions in living cells, we attached Cry2 to Tau and studied the contribution of each domain that drives the Tau cluster in living cells. Surprisingly, the proline-rich domain (PRD), not the microtubule binding domain (MTBD), drives LLPS and does so under the control of its phosphorylation state. Readily observable, PRD-derived cytoplasmic condensates underwent fusion and fluorescence recovery after photobleaching consistent with the PRD LLPS in vitro. Simulations demonstrated that the charge properties of the PRD predicted phase separation. Tau PRD formed heterotypic condensates with EB1, a regulator of plus-end microtubule dynamic instability. The specific domain properties of the MTBD and PRD serve distinct but mutually complementary roles that use LLPS in a cellular context to implement emergent functionalities that scale their relationship from binding α-beta tubulin heterodimers to the larger proportions of microtubules.

The Game of Tubulins

Members of the tubulin superfamily are GTPases; the activities of GTPases are necessary for life. The members of the tubulin superfamily are the constituents of the microtubules and the γ-tubulin meshwork. Mutations in members of the tubulin superfamily are involved in developmental brain disorders, and tubulin activities are the target for various chemotherapies. The intricate functions (game) of tubulins depend on the activities of the GTP-binding domain of α-, β-, and γ-tubulin. This review compares the GTP-binding domains of γ-tubulin, α-tubulin, and β-tubulin and, based on their similarities, recapitulates the known functions and the impact of the γ-tubulin GTP-binding domain in the regulation of the γ-tubulin meshwork and cellular homeostasis.

Role of Phosphorylation and Hyperphosphorylation of Tau in Its Interaction with βα Dimeric Tubulin Studied from a Bioinformatics Perspective

Background:

Tau is a disordered Microtubule Associated Protein (MAP) which prefers to bind and stabilize microtubules. Phosphorylation of tau in particular enhances tautubulin interaction which otherwise detaches from tubulin during hyperphosphorylation. The reason behind their destabilization, detachment and the role of β subunit (from microtubule) and the projection domain (Tau) in microtubule stability remains elusive till date. Thus, a complete 3D structural investigation of tau protein is much needed to address these queries as the existing crystal structures are in fragments and quite limited.

Methods:

In this study, the modelled human tau protein was subjected to phosphorylation and hyperphosphorylation which were later considered for docking with micro-tubules (βα subunits-inter dimer) and vinblastine.

Results:

Phosphorylated tau protein interacts with both α- and β subunits. But stronger bonding was with α- compared to β subunits. Regarding β subunit, proline rich loop and projection domain actively participated in tau binding. Interestingly, hyperphosphorylation of tau increases MAP domain flexibility which ultimately results in tau detachment, the main reason behind tangle formation in Alzheimer’s disease.

Conclusion:

This study being the first of its kind emphasizes the role of projection domain and proline rich region of β-subunit in stabilizing the tau-tubulin interaction and also the effect of hyperphosphorylation in protein-protein and protein-drug binding.

An insight into the anticancer potential of carbamates and thiocarbamates of 10-demethoxy-10-methylaminocolchicine

Colchicine shows very high antimitotic activity, therefore, it is used as a lead compound for generation of new anticancer agents. In the hope of developing novel, useful drugs with more favourable pharmacological profiles, a series of doubly modified colchicine derivatives has been designed, synthesized and characterized. These novel carbamate or thiocarbamate derivatives of 10-demethoxy-10-methylaminocolchicine have been tested for their antiproliferative activity against four human cancer cell lines. Additionally, their mode of action has been evaluated as colchicine binding site inhibitors, using molecular docking studies. Most of the tested compounds showed greater cytotoxicity (IC₅₀ in a low nanomolar range) and were characterized by a higher selectivity index than standard chemotherapeutics such as cisplatin and doxorubicin as well as unmodified colchicine. Their pharmacological use in cancer therapy could possibly be accomplished with lower dosages and result in less acute toxicity problems than in the case of colchicine. In addition, we present a QSAR model for predicting the antiproliferative activity of doubly modified derivatives for two tumour cell lines.

Atomistic Basis of Microtubule Dynamic Instability Assessed Via Multiscale Modeling

Microtubule “dynamic instability,” the abrupt switching from assembly to disassembly caused by the hydrolysis of GTP to GDP within the β subunit of the αβ-tubulin heterodimer, is necessary for vital cellular processes such as mitosis and migration. Despite existing high-resolution structural data, the key mechanochemical differences between the GTP and GDP states that mediate dynamic instability behavior remain unclear. Starting with a published atomic-level structure as an input, we used multiscale modeling to find that GTP hydrolysis results in both longitudinal bond weakening (~ 4 k_BT) and an outward bending preference (~ 1.5 k_BT) to both drive dynamic instability and give rise to the microtubule tip structures previously observed by light and electron microscopy. More generally, our study provides an example where atomic level structural information is used as the sole input to predict cellular level dynamics without parameter adjustment.

Covalent Modification of Proteins by Plant-Derived Natural Products: Proteomic Approaches and Biological Impacts

Plant-derived natural products (NPs) with electrophilic functional groups engage various subsets of the proteome via covalent modification of nucleophilic cysteine residues. This electrophile-nucleophile interaction can change protein conformation, alter protein function, and modulate their biological action. The biological significance of these covalent protein modifications in health and disease is increasingly recognized. One way to understand covalent NP-protein interactions is to utilize traditional proteomics and modern mass spectrometry (MS)-based proteomic strategies. These strategies have proven effective in uncovering specific NP protein targets and are critical first steps that allow for a much deeper understanding of the ability of NPs to modulate cellular processes. Here, plant-derived NPs that covalently modify proteins are reviewed, the biological significance of these covalent modifications, and the different proteomic strategies that have been employed to study these NP-protein interactions.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Furan-2-carboxamide derivative, a novel microtubule stabilizing agent induces mitotic arrest and potentiates apoptosis in cancer cells

The vital role played by microtubules in the cell division process, marks them as a potential druggable target to decimate cancer. A novel furan-2-carboxamide based small molecule, is a selective microtubule stabilizing agent (MSA) with IC₅₀ ranging from 4 µM to 8 µM in different cancer cell lines. Inhibition of tubulin polymerization or stabilization of tubulin polymers abrogates chromosomal segregation during cell division, results in cell cycle arrest and leads to cell death due to the delayed repair mechanism. A novel furan-2-carboxamide based small molecule exhibited potent anti-proliferative and anti-metastatic property In-Vitro against the panel of cancer cells. Annexin V-FITC/PI, double staining reveals potent cytotoxic effect of SH09 against HeLa cells. FACS analysis displays induction of G2/M arrest and accumulation of subG1 population of cells upon treatment with SH09. Molecular docking study unveils SH09 binding affinity to the Taxol binding pocket of tubulin proteins and MM-GBSA also confirms strong binding energies of SH09 with tubulin proteins.

Phenyl 4-(2-oxopyrrolidin-1-yl)benzenesulfonates and phenyl 4-(2-oxopyrrolidin-1-yl)benzenesulfonamides as new antimicrotubule agents targeting the colchicine-binding site

We recently designed and prepared new families of potent antimicrotubule agents designated as N-phenyl 4-(2-oxoimidazolidin-1-yl)benzenesulfonates (PIB-SOs) and phenyl 4-(2-oxoimidazolidin-1-yl)benzenesulfonamides (PIB-SAs). Our previous structure-activity relationship studies (SAR) focused on the aromatic ring B of PIB-SOs and PIB-SAs leaving the impact of the phenylimidazolidin-2-one moiety (ring A) on the binding to the colchicine-binding site (C-BS) poorly studied. Therefore, the aim of the present study was to evaluate the effect of replacing the imidazolidin-2-one (IMZ) group by a pyrrolidin-2-one moiety. To that end, 15 new phenyl 4-(2-oxopyrrolidin-1-yl)benzenesulfonate (PYB-SO) and 15 phenyl 4-(2-oxopyrrolidin-1-yl)benzenesulfonamide (PYB-SA) derivatives were designed, prepared, chemically characterised and biologically evaluated. PYB-SOs and PYB-SAs exhibit antiproliferative activity in the low nanomolar to low micromolar range (0.0087-8.6 μM and 0.056-21 μM, respectively) on human HT-1080, HT-29, M21 and MCF7 cancer cell lines. Moreover, they block cell cycle progression in G2/M phase. Immunofluorescence, tubulin affinity and tubulin polymerisation assays show that they cause microtubule depolymerisation by docking the C-BS. In addition, docking assays with the most potent derivatives show binding affinity toward the C-BS and they also exhibit weak or no toxicity toward chick embryos. Finally, physicochemical properties calculated using the SwissADME algorithm show that PYB-SOs and PYB-SAs are promising new families of antimicrotubule agents.

2D Electron Crystallography of Membrane Protein Single-, Double-, and Multi-Layered Ordered Arrays

The electron cryo-microscopy (cryo-EM) approach of 2D electron crystallography allows for structure determination of two-dimensional (2D) crystals of soluble and membrane proteins, employing identical principles and methods once 2D crystals are obtained. Two-dimensional crystallization trials of membrane proteins can result in multiple outcomes of ordered arrays, which may be suited for either 2D electron crystallography, helical analysis, or MicroED.The membrane protein 2D crystals used for 2D electron crystallography are either single- or double-layered ordered proteoliposome vesicles or sheet-like membranes. We have developed a cryo-EM grid preparation approach, which allows for the analysis of stacked 2D crystals that are neither suitable for MicroED nor for directly applying 2D electron crystallography. This new grid preparation approach, the peel-blot, uses the capillary force generated by submicron filter paper and mechanical means for the separation of stacked 2D crystals into single-layered 2D crystals, for which standard 2D electron crystallography can then be employed. The preparation of 2D crystals, the peel-blot grid preparation, and the structure determination by 2D electron crystallography are described here.

Recombinant antibody against Trypanosoma cruzi from patients with chronic Chagas heart disease recognizes mammalian nervous system

BACKGROUND

To deeply understand the role of antibodies in the context of Trypanosoma cruzi infection, we decided to characterize A2R1, a parasite antibody selected from single-chain variable fragment (scFv) phage display libraries constructed from B cells of chronic Chagas heart disease patients.

METHODS

Immunoblot, ELISA, cytometry, immunofluorescence and immunohistochemical assays were used to characterize A2R1 reactivity. To identify the antibody target, we performed an immunoprecipitation and two-dimensional electrophoresis coupled to mass spectrometry and confirmed A2R1 specific interaction by producing the antigen in different expression systems. Based on these data, we carried out a comparative in silico analysis of the protein target´s orthologues, focusing mainly on post-translational modifications.

FINDINGS

A2R1 recognizes a parasite protein of ~50 kDa present in all life cycle stages of T. cruzi, as well as in other members of the kinetoplastid family, showing a defined immunofluorescence labeling pattern consistent with the cytoskeleton. A2R1 binds to tubulin, but this interaction relies on its post-translational modifications. Interestingly, this antibody also targets mammalian tubulin only present in brain, staining in and around cell bodies of the human peripheral and central nervous system.

INTERPRETATION

Our findings demonstrate for the first time the existence of a human antibody against T. cruzi tubulin capable of cross-reacting with a human neural protein. This work re-emphasizes the role of molecular mimicry between host and parasitic antigens in the development of pathological manifestations of T. cruzi infection.

Heck macrocyclization in natural product total synthesis

Covering: 1981-2020 Heck macrocyclization is a logical extension of the award-winning Mizoroki-Heck reaction. Through covalent linking of two otherwise discrete coupling partners, the resultant chimeric substrate is transformed into a large ring with enhanced rigidity and unique functional group disposition. Pioneered in the early 1980s, this methodology has evolved into a competent option for creating diverse macrocycles. Despite its growing influence, hitherto no systematic survey has ever appeared in the literature. The present review delineates the state-of-the-art of Heck macrocyclization in the context of natural product synthesis. Sixteen selected cases, each examined from a different perspective, coalesce into the view that the title reaction is a viable tool for synthesis-enabled macrocycle research.

Intracellular Organization by Jumbo Bacteriophages

Since their discovery more than 100 years ago, the viruses that infect bacteria (bacteriophages) have been widely studied as model systems. Largely overlooked, however, have been "jumbo phages," with genome sizes ranging from 200 to 500 kbp. Jumbo phages generally have large virions with complex structures and a broad host spectrum. While the majority of jumbo phage genes are poorly functionally characterized, recent work has discovered many unique biological features, including a conserved tubulin homolog that coordinates a proteinaceous nucleus-like compartment that houses and segregates phage DNA. The tubulin spindle displays dynamic instability and centers the phage nucleus within the bacterial host during phage infection for optimal reproduction. The shell provides robust physical protection for the enclosed phage genomes against attack from DNA-targeting bacterial immune systems, thereby endowing jumbo phages with broad resistance. In this review, we focus on the current knowledge of the cytoskeletal elements and the specialized nuclear compartment derived from jumbo phages, and we highlight their importance in facilitating spatial and temporal organization over the viral life cycle. Additionally, we discuss the evolutionary relationships between jumbo phages and eukaryotic viruses, as well as the therapeutic potential and drawbacks of jumbo phages as antimicrobial agents in phage therapy.

Correlating STED and synchrotron XRF nano-imaging unveils cosegregation of metals and cytoskeleton proteins in dendrites

Zinc and copper are involved in neuronal differentiation and synaptic plasticity but the molecular mechanisms behind these processes are still elusive due in part to the difficulty of imaging trace metals together with proteins at the synaptic level. We correlate stimulated-emission-depletion microscopy of proteins and synchrotron X-ray fluorescence imaging of trace metals, both performed with 40 nm spatial resolution, on primary rat hippocampal neurons. We reveal the co-localization at the nanoscale of zinc and tubulin in dendrites with a molecular ratio of about one zinc atom per tubulin-αβ dimer. We observe the co-segregation of copper and F-actin within the nano-architecture of dendritic protrusions. In addition, zinc chelation causes a decrease in the expression of cytoskeleton proteins in dendrites and spines. Overall, these results indicate new functions for zinc and copper in the modulation of the cytoskeleton morphology in dendrites, a mechanism associated to neuronal plasticity and memory formation.

Antimicrobial Action and Reversal of Resistance in MRSA by Difluorobenzamide Derivatives Targeted at FtsZ

The bacterial cell division protein, FtsZ, has been identified as a target for antimicrobial development. Derivatives of 3-methoxybenzamide have shown promising activities as FtsZ inhibitors in Gram-positive bacteria. We sought to characterise the activity of five difluorobenzamide derivatives with non-heterocyclic substituents attached through the 3-oxygen. These compounds exhibited antimicrobial activity against methicillin resistant Staphylococcus aureus (MRSA), with an isopentyloxy-substituted compound showing modest activity against vancomycin resistant Enterococcus faecium (VRE). The compounds were able to reverse resistance to oxacillin in highly resistant clinical MRSA strains at concentrations far below their MICs. Three of the compounds inhibited an Escherichia coli strain lacking the AcrAB components of a drug efflux pump, which suggests the lack of Gram-negative activity can partly be attributed to efflux. The compounds inhibited cell division by targeting S. aureus FtsZ, producing a dose-dependent increase in GTPase rate which increased the rate of FtsZ polymerization and stabilized the FtsZ polymers. These compounds did not affect the polymerization of mammalian tubulin and did not display haemolytic activity or cytotoxicity. These derivatives are therefore promising compounds for further development as antimicrobial agents or as resistance breakers to re-sensitive MRSA to beta-lactam antibiotics.

Tubulin mutations in neurodevelopmental disorders as a tool to decipher microtubule function

Malformations of cortical development (MCDs) are a group of severe brain malformations associated with intellectual disability and refractory childhood epilepsy. Human missense heterozygous mutations in the 9 α-tubulin and 10 β-tubulin isoforms forming the heterodimers that assemble into microtubules (MTs) were found to cause MCDs. However, how a single mutated residue in a given tubulin isoform can perturb the entire microtubule population in a neuronal cell remains a crucial question. Here, we examined 85 MCD-associated tubulin mutations occurring in TUBA1A, TUBB2, and TUBB3 and their location in a three-dimensional (3D) microtubule cylinder. Mutations hitting residues exposed on the outer microtubule surface are likely to alter microtubule association with partners, while alteration of intradimer contacts may impair dimer stability and straightness. Other types of mutations are predicted to alter interdimer and lateral contacts, which are responsible for microtubule cohesion, rigidity, and dynamics. MCD-associated tubulin mutations surprisingly fall into all categories, thus providing unexpected insights into how a single mutation may impair microtubule function and elicit dominant effects in neurons.

A proteomic survey of microtubule-associated proteins in a R402H TUBA1A mutant mouse

Microtubules play a critical role in multiple aspects of neurodevelopment, including the generation, migration and differentiation of neurons. A recurrent mutation (R402H) in the α-tubulin gene TUBA1A is known to cause lissencephaly with cerebellar and striatal phenotypes. Previous work has shown that this mutation does not perturb the chaperone-mediated folding of tubulin heterodimers, which are able to assemble and incorporate into the microtubule lattice. To explore the molecular mechanisms that cause the disease state we generated a new conditional mouse line that recapitulates the R402H variant. We show that heterozygous mutants present with laminar phenotypes in the cortex and hippocampus, as well as a reduction in striatal size and cerebellar abnormalities. We demonstrate that homozygous expression of the R402H allele causes neuronal death and exacerbates a cell intrinsic defect in cortical neuronal migration. Microtubule sedimentation assays coupled with quantitative mass spectrometry demonstrated that the binding and/or levels of multiple microtubule associated proteins (MAPs) are perturbed by the R402H mutation including VAPB, REEP1, EZRIN, PRNP and DYNC1l1/2. Consistent with these data we show that the R402H mutation impairs dynein-mediated transport which is associated with a decoupling of the nucleus to the microtubule organising center. Our data support a model whereby the R402H variant is able to fold and incorporate into microtubules, but acts as a gain of function by perturbing the binding of MAPs.

Microtubules are polymers composed of tubulin proteins, which play an important role in the development of the human brain. Genetic mutations in tubulin genes are known to cause neurodevelopmental diseases, including lissencephaly which is characterised by an impairment in the migration of neurons. In this study we investigate how a common mutation (R402H) in TUBA1A causes lissencephaly by generating and characterising a mouse with the same variant. We show that affected animals recapitulate multiple aspects of the human disease; including laminar perturbations in the cortex and hippocampus, attributable to defects in neuronal migration at key developmental time points. To characterize the molecular implications of the R402H mutation we purified microtubules from the developing brain, and analysed the proteins present by mass spectrometry. This revealed that the binding of DYNC1I1/2 to microtubules is altered in mice with the R402H mutation. Our results provide insight into the molecular pathology underlying tubulin related disease states, and provide a foundation for the rational design of therapeutic interventions.

Non-Canonical Functions of the Gamma-Tubulin Meshwork in the Regulation of the Nuclear Architecture

Simple Summary

The appearance of a cell is connected to its function. For example, the fusiform of smooth muscle cells is adapted to facilitate muscle contraction, the lobed nucleus in white blood cells assists with the migratory behavior of these immune cells, and the condensed nucleus in sperm aids in their swimming efficiency. Thus, changes in appearance have been used for decades by doctors as a diagnostic method for human cancers. Here, we summarize our knowledge of how a cell maintains the shape of the nuclear compartment. Specifically, we discuss the role of a novel protein meshwork, the gamma-tubulin meshwork, in the regulation of nuclear morphology and as a therapeutic target against cancer.

Abstract

The nuclear architecture describes the organization of the various compartments in the nucleus of eukaryotic cells, where a plethora of processes such as nucleocytoplasmic transport, gene expression, and assembly of ribosomal subunits occur in a dynamic manner. During the different phases of the cell cycle, in post-mitotic cells and after oncogenic transformation, rearrangements of the nuclear architecture take place, and, among other things, these alterations result in reorganization of the chromatin and changes in gene expression. A member of the tubulin family, γtubulin, was first identified as part of a multiprotein complex that allows nucleation of microtubules. However, more than a decade ago, γtubulin was also characterized as a nuclear protein that modulates several crucial processes that affect the architecture of the nucleus. This review presents the latest knowledge regarding changes that arise in the nuclear architecture of healthy cells and under pathological conditions and, more specifically, considers the particular involvement of γtubulin in the modulation of the biology of the nuclear compartment.

DYT-TUBB4A (DYT4 Dystonia): New Clinical and Genetic Observations

OBJECTIVE

To report 4 novel TUBB4A mutations leading to laryngeal and cervical dystonia with frequent generalization.

METHODS

We screened 4 families including a total of 11 definitely affected members with a clinical picture resembling the original description.

RESULTS

Four novel variants in the TUBB4A gene have been identified: D295N, R46M, Q424H, and R121W. In silico modeling showed that all variants have characteristics similar to R2G. The variants segregate with the disease in 3 of the families with evidence of incomplete penetrance in 2 of them. All 4 variants would be classified as likely pathogenic. The clinical picture particularly included laryngeal dystonia (often the site of onset), associated with cervical and upper limb dystonia and frequent generalization. Laryngeal dystonia was extremely prevalent (>90%) both in the original cases and in this case series. The hobby horse gait was evident in only 1 patient in this case series.

CONCLUSIONS

Our interpretation is that laryngeal involvement is a hallmark feature of DYT-TUBB4A. Nevertheless, TUBB4A mutations remain an exceedingly rare cause of laryngeal or other isolated dystonia.

Photoswitchable paclitaxel-based microtubule stabilisers allow optical control over the microtubule cytoskeleton

Small molecule inhibitors are prime reagents for studies in microtubule cytoskeleton research, being applicable across a range of biological models and not requiring genetic engineering. However, traditional chemical inhibitors cannot be experimentally applied with spatiotemporal precision suiting the length and time scales inherent to microtubule-dependent cellular processes. We have synthesised photoswitchable paclitaxel-based microtubule stabilisers, whose binding is induced by photoisomerisation to their metastable state. Photoisomerising these reagents in living cells allows optical control over microtubule network integrity and dynamics, cell division and survival, with biological response on the timescale of seconds and spatial precision to the level of individual cells within a population. In primary neurons, they enable regulation of microtubule dynamics resolved to subcellular regions within individual neurites. These azobenzene-based microtubule stabilisers thus enable non-invasive, spatiotemporally precise modulation of the microtubule cytoskeleton in living cells, and promise new possibilities for studying intracellular transport, cell motility, and neuronal physiology.

Light-based modulation of the microtubule (MT) cytoskeleton is an attractive goal for spatiotemporally-resolved MT studies. Here the authors develop a first generation photoswitchable small molecule MT stabiliser based on paclitaxel, allowing optical control over cellular MT dynamics.

A novel orally active microtubule destabilizing agent S-40 targets the colchicine-binding site and shows potent antitumor activity

The tubulin colchicine binding site has been recognized as an attractive drug target to combat cancer, but none of the candidate drugs have been approved for medical treatment. We recently identified a structurally distinct small molecule S-40 as an oral potent tubulin destabilizing agent. Crystal structure analysis of S-40 in a complex with tubulin at a resolution of 2.4 Å indicated that S-40 occupies all 3 zones in the colchicine pocket with interactions different from known microtubule inhibitors, presenting unique effects on assembly and curvature of tubulin dimers. S-40 overcomes paclitaxel resistance and lacks neurotoxicity, which are the main obstacles limiting clinical applications of paclitaxel. Moreover, S-40 harbors the ability to inhibit growth of cancer cell lines as well as patient-derived organoids, induce mitotic arrest and cell apoptosis. Xenograft mouse models of human prostate cancer DU145, non-small cell lung cancer NCI-H1299 and paclitaxel-resistant A549 were strongly restrained without apparent side effects by S-40 oral administration once daily. These findings provide evidence for the development of S-40 as the next generation of orally effective microtubule inhibitors for cancer therapy.

C-terminal Tail of β-Tubulin and its Role in the Alterations of Dynein Binding Mode

Dynein is a cytoskeletal molecular motor protein that moves along the microtubule (MT) and transports various cellular cargos during its movement. Using standard Molecular Dynamics (MD) simulation, Principle Component Analysis (PCA), and Normal Mode Analysis (NMA) methods, this investigation studied large-scale movements and local interactions of dynein's Microtubule Binding Domain (MTBD) when bound to tubulin heterodimer subunits. Examination of the interactions between the MTBD segments, and their adjustments in terms of intra- and intermolecular distances at the interfacial area with tubulin heterodimer, particularly at α-H16, β-H18, and β-tubulin C-terminal tail (CTT), was the main focus of this study. The specific intramolecular interactions, electrostatic forces, and the salt bridge residue pairs were shown to be the dominating factors in orchestrating movements of the MTBD and MT interfacial segments in the dynein's low-high-affinity binding modes. Important interactions included β-Glu447 and β-Glu449 (CTT) with Arg3469 (MTBD-H6), Lys3472 (MTBD-H6-H7 loop) and Lys3479 (MTBD-H7); β-Glu449 with Lys3384 (MTBD-H8), Lys3386 and His3387 (MTBD-H1). The structural and precise position, orientation, and functional effects of the CTTs on the MT-MTBD, within reasonable cut-off distance for non-bonding interactions and under physiological conditions, are unavailable from previous studies. The absence of the residues in the highly flexible MT-CTTs in the experimentally solved structures is perhaps in some cases due to insufficient data from density maps, but these segments are crucial in protein binding. The presented work contributes to the information useful for the MT-MTBD structure refinement.

Tubulin Double Helix: Lateral and Longitudinal Curvature Changes of Tubulin Protofilament

By virtue of their native structures, tubulin dimers are protein building blocks that are naturally preprogrammed to assemble into microtubules (MTs), which are cytoskeletal polymers. Here, polycation-directed (i.e., electrostatically tunable) assembly of tubulins is demonstrated by conformational changes to the tubulin protofilament in longitudinal and lateral directions, creating tubulin double helices and various tubular architectures. Synchrotron small-angle X-ray scattering and transmission electron microscopy reveal a remarkable range of nanoscale assembly structures: single- and double-layered double-helix tubulin tubules. The phase transitions from MTs to the new assemblies are dependent on the size and concentration of polycations. Two characteristic scales that determine the number of observed phases are the size of polycation compared to the size of tubulin (≈4 nm) and to MT diameter (≈25 nm). This work suggests the feasibility of using polycations that have scissor- and glue-like properties to achieve "programmable breakdown" of protein nanotubes, tearing MTs into double-stranded tubulins and building up previously undiscovered nanostructures. Importantly, a new role of tubulins is defined as 2D shape-controllable building blocks for supramolecular architectures. These findings provide insight into the design of protein-based functional materials, for example, as metallization templates for nanoscale electronic devices, molecular screws, and drug delivery vehicles.

Viriditoxin Stabilizes Microtubule Polymers in SK-OV-3 Cells and Exhibits Antimitotic and Antimetastatic Potential

Microtubules play a crucial role in mitosis and are attractive targets for cancer therapy. Recently, we isolated viriditoxin, a cytotoxic and antibacterial compound, from a marine fungus Paecilomyces variotii. Viriditoxin has been reported to inhibit the polymerization of bacterial FtsZ, a tubulin-like GTPase that plays an essential role in bacterial cell division. Given the close structural homology between FtsZ and tubulin, we investigated the potential antimitotic effects of viriditoxin on human cancer cells. Viriditoxin, like paclitaxel, enhanced tubulin polymerization and stabilized microtubule polymers, thereby perturbing mitosis in the SK-OV-3 cell line. However, the morphology of the stabilized microtubules was different from that induced by paclitaxel, indicating subtle differences in the mode of action of these compounds. Microtubule dynamics are also essential in cell movement, and viriditoxin repressed migration and colony formation ability of SK-OV-3 cells. Based on these results, we propose that viriditoxin interrupts microtubule dynamics, thus leading to antimitotic and antimetastatic activities.

Intrinsic and Extrinsic Factors Affecting Microtubule Dynamics in Normal and Cancer Cells

Microtubules (MTs), highly dynamic structures composed of α- and β-tubulin heterodimers, are involved in cell movement and intracellular traffic and are essential for cell division. Within the cell, MTs are not uniform as they can be composed of different tubulin isotypes that are post-translationally modified and interact with different microtubule-associated proteins (MAPs). These diverse intrinsic factors influence the dynamics of MTs. Extrinsic factors such as microtubule-targeting agents (MTAs) can also affect MT dynamics. MTAs can be divided into two main categories: microtubule-stabilizing agents (MSAs) and microtubule-destabilizing agents (MDAs). Thus, the MT skeleton is an important target for anticancer therapy. This review discusses factors that determine the microtubule dynamics in normal and cancer cells and describes microtubule-MTA interactions, highlighting the importance of tubulin isoform diversity and post-translational modifications in MTA responses and the consequences of such a phenomenon, including drug resistance development.

A new method for protein characterization and classification using geometrical features for 3D face analysis: An example of tubulin structures

This article reports on the results of research aimed to translate biometric 3D face recognition concepts and algorithms into the field of protein biophysics in order to precisely and rapidly classify morphological features of protein surfaces. Both human faces and protein surfaces are free-forms and some descriptors used in differential geometry can be used to describe them applying the principles of feature extraction developed for computer vision and pattern recognition. The first part of this study focused on building the protein dataset using a simulation tool and performing feature extraction using novel geometrical descriptors. The second part tested the method on two examples, first involved a classification of tubulin isotypes and the second compared tubulin with the FtsZ protein, which is its bacterial analog. An additional test involved several unrelated proteins. Different classification methodologies have been used: a classic approach with a support vector machine (SVM) classifier and an unsupervised learning with a k-means approach. The best result was obtained with SVM and the radial basis function kernel. The results are significant and competitive with the state-of-the-art protein classification methods. This leads to a new methodological direction in protein structure analysis.

A novel taxane, difluorovinyl-ortataxel, effectively overcomes paclitaxel-resistance in breast cancer cells

Paclitaxel (PTX) is widely used to treat breast and ovarian cancers, but innate and acquired resistance often compromises its applications. The objective of this study was to screen new-generation taxanes for their efficiency against both PTX-sensitive and PTX-resistant breast cancer cells. From twelve compounds, difluorovinyl-ortataxel (DFV-OTX) displayed potent cytotoxic activities against both PTX-sensitive and PTX-resistant breast cancer cells. Moreover, DFV-OTX effectively induced tubulin/microtubule polymerization and G2/M phase arrest, leading to apoptosis in both PTX-sensitive and PTX-resistant cancer cells. Molecular docking analysis showed that DFV-OTX possesses unique hydrogen-bonding and van der Waals interactions with β-tubulin. LC-MS/MS analysis also demonstrated that the intracellular drug amount of DFV-OTX was lower than that of PTX, which would be critical to overcome PTX-resistance. Furthermore, DFV-OTX exhibited clear efficacy in the MCF-7R and MDA-MB-231R tumor xenografts in mouse models. Taken together, our results demonstrate that the novel taxane, DFV-OTX, can effectively overcome PTX-resistance in MDA-MB-231R cells, wherein the drug resistance was attributed to ABCB1/ABCG2 upregulation and a distinct mode of action in MCF-7R cells. Our results strongly indicate that DFV-OTX is a promising chemotherapeutic agent for the treatment of PTX-resistant cancers.

The recurrent TUBB3 Gly98Ser substitution is the first described to inconsistently result in CFEOM3

Missense variants in TUBB3 have historically been associated with either congenital fibrosis of the extraocular muscles type 3 (CFEOM3) or malformations of cortical development (MCD). Until a recent report identified two amino acid substitutions in four patients that had clinical features of both disorders, pathogenic variants of TUBB3 were thought distinct to either respective disorder. Three recurrent de novo Gly71Arg TUBB3 substitutions and a single patient with a de novo Gly98Ser substitution blurred the MCD and CFEOM3 phenotypic distinctions. Here we report a second patient with a missense c.292G>A (p.Gly98Ser) substitution, but without CFEOM3, the first reported evidence that even the same TUBB3 substitution can produce a spectrum of TUBB3 syndrome phenotypes. Our patient presented with amblyopia, exotropia, optic disc pallor, and developmental delay. Neuroimaging identified hypoplasia of the corpus callosum, interdigitation of the frontal lobe gyri, and dysplasia or hypoplasia of the optic nerves, basal ganglia, brainstem, and cerebellum. This report identifies the TUBB3 Gly98Ser substitution to be recurrent but inconsistently including CFEOM3, and identifies the absence of joint contractures and the presence of optic disc abnormalities that may be genotype-specific to the TUBB3 Gly98Ser substitution.

Profilin choreographs actin and microtubules in cells and cancer

Actin and microtubules play essential roles in aberrant cell processes that define and converge in cancer including: signaling, morphology, motility, and division. Actin and microtubules do not directly interact, however shared regulators coordinate these polymers. While many of the individual proteins important for regulating and choreographing actin and microtubule behaviors have been identified, the way these molecules collaborate or fail in normal or disease contexts is not fully understood. Decades of research focus on Profilin as a signaling molecule, lipid-binding protein, and canonical regulator of actin assembly. Recent reports demonstrate that Profilin also regulates microtubule dynamics and polymerization. Thus, Profilin can coordinate both actin and microtubule polymer systems. Here we reconsider the biochemical and cellular roles for Profilin with a focus on the essential cytoskeletal-based cell processes that go awry in cancer. We also explore how the use of model organisms has helped to elucidate mechanisms that underlie the regulatory essence of Profilin in vivo and in the context of disease.

MRI Features in a Rat Model of H-ABC Tubulinopathy

Tubulinopathies are a group of recently described diseases characterized by mutations in the tubulin genes. Mutations in TUBB4A produce diseases such as dystonia type 4 (DYT4) and hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), which are clinically diagnosed by magnetic resonance imaging (MRI). We propose the taiep rat as the first animal model for tubulinopathies. The spontaneous mutant suffers from a syndrome related to a central leukodystrophy and characterized by tremor, ataxia, immobility, epilepsy, and paralysis. The pathological signs presented by these rats and the morphological changes we found by our longitudinal MRI study are similar to those of patients with mutations in TUBB4A. The diffuse atrophy we found in brain, cerebellum and spinal cord is related to the changes detectable in many human tubulinopathies and in particular in H-ABC patients, where myelin degeneration at the level of putamen and cerebellum is a clinical trademark of the disease. We performed Tubb4a exon analysis to corroborate the genetic defect and formulated hypotheses about the effect of amino acid 302 change on protein physiology. Optical microscopy of taiep rat cerebella and spinal cord confirmed the optical density loss in white matter associated with myelin loss, despite the persistence of neural fibers.

Cell division protein FtsZ: from structure and mechanism to antibiotic target

Antimicrobial resistance to virtually all clinically applied antibiotic classes severely limits the available options to treat bacterial infections. Hence, there is an urgent need to develop and evaluate new antibiotics and targets with resistance-breaking properties. Bacterial cell division has emerged as a new antibiotic target pathway to counteract multidrug-resistant pathogens. New approaches in antibiotic discovery and bacterial cell biology helped to identify compounds that either directly interact with the major cell division protein FtsZ, thereby perturbing the function and dynamics of the cell division machinery, or affect the structural integrity of FtsZ by inducing its degradation. The impressive antimicrobial activities and resistance-breaking properties of certain compounds validate the inhibition of bacterial cell division as a promising strategy for antibiotic intervention.

Plant tissue culture as a perpetual source for production of industrially important bioactive compounds

Plants have been used throughout the world for its medicinal powers since ancient time. The pharmacological properties of plants are based on their phytochemical components especially the secondary metabolites which are outstanding sources of value added bioactive compounds. Secondary metabolites have complex chemical composition and are produced in response to various forms of stress to perform different physiological tasks in plants. They are used in pharmaceutical industries, cosmetics, dietary supplements, fragrances, flavors, dyes, etc. Extended use of these metabolites in various industrial sectors has initiated a need to focus research on increasing the production by employing plant tissue culture (PTC) techniques and optimizing their large scale production using bioreactors. PTC techniques being independent of climatic and geographical conditions will provide an incessant, sustainable, economical and viable production of secondary metabolites. This review article intends to assess the advantages of using plant tissue culture, distribution of important secondary metabolites in plant families, strategies involved for optimal metabolite production and the industrial importance of selected secondary metabolites.

Microtubule-targeting agents and their impact on cancer treatment

Microtubule-targeting agents (MTAs) constitute a diverse group of chemical compounds that bind to microtubules and affect their properties and function. Disruption of microtubules induces various cellular responses often leading to cell cycle arrest or cell death, the most common effect of MTAs. MTAs have found a plethora of practical applications in weed control, as fungicides and antiparasitics, and particularly in cancer treatment. Here we summarize the current knowledge of MTAs, the mechanisms of action and their role in cancer treatment. We further outline the potential use of MTAs in anti-metastatic therapy based on inhibition of cancer cell migration and invasiveness. The two main problems associated with cancer therapy by MTAs are high systemic toxicity and development of resistance. Toxic side effects of MTAs can be, at least partly, eliminated by conjugation of the drugs with various carriers. Moreover, some of the novel MTAs overcome the resistance mediated by both multidrug resistance transporters as well as overexpression of specific β-tubulin types. In anti-metastatic therapy, MTAs should be combined with other drugs to target all modes of cancer cell invasion.

Microtubule Simulations Provide Insight into the Molecular Mechanism Underlying Dynamic Instability

The dynamic instability of microtubules (MTs), which refers to their ability to switch between polymerization and depolymerization states, is crucial for their function. It has been proposed that the growing MT ends are protected by a "GTP cap" that consists of GTP-bound tubulin dimers. When the speed of GTP hydrolysis is faster than dimer recruitment, the loss of this GTP cap will lead the MT to undergo rapid disassembly. However, the underlying atomistic mechanistic details of the dynamic instability remains unclear. In this study, we have performed long-time atomistic molecular dynamics simulations (1 μs for each system) for MT patches as well as a short segment of a closed MT in both GTP- and GDP-bound states. Our results confirmed that MTs in the GDP state generally have weaker lateral interactions between neighboring protofilaments (PFs) and less cooperative outward bending conformational change, where the difference between bending angles of neighboring PFs tends to be larger compared with GTP ones. As a result, when the GDP state tubulin dimer is exposed at the growing MT end, these factors will be more likely to cause the MT to undergo rapid disassembly. We also compared simulation results between the special MT seam region and the remaining material and found that the lateral interactions between MT PFs at the seam region were comparatively much weaker. This finding is consistent with the experimental suggestion that the seam region tends to separate during the disassembly process of an MT.

Synthesis, Antiproliferative Activity and Molecular Docking Studies of Novel Doubly Modified Colchicine Amides and Sulfonamides as Anticancer Agents

Colchicine is a well-known compound with strong antiproliferative activity that has had limited use in chemotherapy because of its toxicity. In order to create more potent anticancer agents, a series of novel colchicine derivatives have been obtained by simultaneous modification at C7 (amides and sulfonamides) and at C10 (methylamino group) positions and characterized by spectroscopic methods. All the synthesized compounds have been tested in vitro to evaluate their cytotoxicity toward A549, MCF-7, LoVo, LoVo/DX and BALB/3T3 cell lines. Additionally, the activity of the studied compounds was investigated using computational methods involving molecular docking of the colchicine derivatives to β-tubulin. The majority of the obtained derivatives exhibited higher cytotoxicity than colchicine, doxorubicin or cisplatin against tested cancer cell lines. Furthermore, molecular modeling studies of the obtained compounds revealed their possible binding modes into the colchicine binding site of tubulin.

In silico design of peptide inhibitors of tubulin: amyloid-β as a lead compound

Microtubule is one of the most studied targets in cancer research. Stabilizing and destabilizing of the microtubule by targeting its building block tubulin are common mechanisms of microtubule targeting agents. Cancer associates inversely with Alzheimer's disease (AD). So the rate of developing AD is significantly slower in patients with cancer and vice versa. Amyloid-β (Aβ) peptide inhibits tubulin polymerization and induces apoptotic death of cancer cells. We studied the interactions of Aβ with tubulin using protein-protein docking and MD simulation. Aβ bond to the vicinity of the vinblastine binding site and interacted with the H6-H7 loop. Interaction of Aβ with H6-H7 loop blocked nucleotide exchange and may be attributed as a possible reason for blocking of tubulin polymerization. We designed new Aβ-based peptidic inhibitors of tubulin using visual inspection and alanine scanning method. P1 (FRHYHHFFELV) and P9 (HYHHF) bound efficiently to tubulin and also interacted with the H6-H7 loop. Obtained results indicated that proposed peptides could potentially inhibit nucleotide exchange as Aβ.Communicated by Ramaswamy H. Sarma.

Structural model for differential cap maturation at growing microtubule ends

Microtubules (MTs) are hollow cylinders made of tubulin, a GTPase responsible for essential functions during cell growth and division, and thus, key target for anti-tumor drugs. In MTs, GTP hydrolysis triggers structural changes in the lattice, which are responsible for interaction with regulatory factors. The stabilizing GTP-cap is a hallmark of MTs and the mechanism of the chemical-structural link between the GTP hydrolysis site and the MT lattice is a matter of debate. We have analyzed the structure of tubulin and MTs assembled in the presence of fluoride salts that mimic the GTP-bound and GDP•P_i transition states. Our results challenge current models because tubulin does not change axial length upon GTP hydrolysis. Moreover, analysis of the structure of MTs assembled in the presence of several nucleotide analogues and of taxol allows us to propose that previously described lattice expansion could be a post-hydrolysis stage involved in P_i release.

Identification of a lathyrane-type diterpenoid EM-E-11-4 as a novel paclitaxel resistance reversing agent with multiple mechanisms of action

P-glycoprotein (P-gp) and βIII-tubulin overexpression-mediated drug resistance leads to clinical therapy failure for paclitaxel. However, the development of paclitaxel-resistance reversal agents has not had much success. In this study, EM-E-11-4, a lathyrane-type diterpenoid extracted from Euphorbia micractina, demonstrated good anti-MDR (multidrug resistance) activity in paclitaxel-resistant tumor cells overexpressing either P-gp or βIII-tubulin. EM-E-11-4 was able to recover the effects of paclitaxel in inducing arrest at G₂/M phase and apoptosis in both A549/Tax (P-gp overexpression) and Hela/βIII (βIII-tubulin overexpression) cells, respectively, at a non-cytotoxic dose. EM-E-11-4 could enable Flutax-1 and Rhodamine 123 be accumulated intracellularly at an accelerating rate in A549/Tax cells by inhibiting the activity of P-gp ATPase, rather than affecting the expression of P-gp. In addition, it also strengthened the effects of paclitaxel in promoting tubulin polymerization and the binding of paclitaxel to microtubules in vitro. It inhibited the expression of βIII-tubulin in Hela/βIII cells in a dose-dependent manner while not exerting influence on the other β-tubulin subtypes. As far as we know, this is the first study to report that a small molecule natural product could specifically inhibit the expression of βIII-tubulin. These results suggest EM-E-11-4 may serve as a promising MDR reversal agent, particularly for patients bearing tumors with high expression of P-gp and βIII-tubulin.

Hec1/Ndc80 Tail Domain Function at the Kinetochore-Microtubule Interface

Successful mitotic cell division is critically dependent on the formation of correct attachments between chromosomes and spindle microtubules. Microtubule attachments are mediated by kinetochores, which are large proteinaceous structures assembled on centromeric chromatin of mitotic chromosomes. These attachments must be sufficiently stable to transduce force; however, the strength of these attachments are also tightly regulated to ensure timely, error-free progression through mitosis. The highly conserved, kinetochore-associated NDC80 complex is a core component of the kinetochore-microtubule attachment machinery in eukaryotic cells. A small, disordered region within the Hec1 subunit of the NDC80 complex – the N-terminal “tail” domain – has been actively investigated during the last decade due to its roles in generating and regulating kinetochore-microtubule attachments. In this review, we discuss the role of the NDC80 complex, and specifically the Hec1 tail domain, at the kinetochore-microtubule interface, and how recent studies provide a more unified view of Hec1 tail domain function.

Preliminary Results, Perspectives, and Proposal for a Screening Method of In Vitro Susceptibility of Prototheca Species to Antimicrotubular Agents

Microorganisms belonging to the genus Prototheca are achlorophyllous microalgae, occasionally behaving as environmental pathogens that cause severe mastitis in milk cows, as well as localized or systemic infections in humans and animals. Among the different species belonging to the genus, Prototheca zopfii genotype 2 (recently reclassified as P. bovis) and P. blaschkeae are most commonly associated with bovine mastitis. To date, no pharmacological treatment is available to cure protothecal mastitis, and infected animals must be quarantined to avoid spreading the infection. The few antibiotic and antifungal drugs effective in vitro against Prototheca give poor results in vivo This failure is likely due to the lack of specificity of such drugs. As microalgae are more closely related to plants than to bacteria or fungi, an alternative possibility is to test molecules with herbicidal properties, in particular, antimicrotubular herbicides, for which plant rather than animal tubulin is the selective target. Once a suitable test protocol was set up, a panel of 11 antimicrotubular agents belonging to different chemical classes and selective for plant tubulin were tested for the ability to inhibit growth of Prototheca cells in vitro Two dinitroanilines, dinitramine and chloralin, showed strong inhibitory effects on P. blaschkeae at low micromolar concentrations, with half-maximal inhibitory concentrations (IC₅₀) of 4.5 and 3 μM, respectively, while both P. zopfii genotype 1 (now reclassified as P. ciferrii) and P. bovis showed susceptibility to dinitramine only, to different degrees. Suitable screening protocols for antimitotic agents are suggested.