[Show abstract][Hide abstract] ABSTRACT: The enzymatic hydrolysis of DNA phosphodiester bonds has been widely studied, but the chemical reaction has not yet been observed. Here we follow the generation of a DNA double-strand break (DSB) by the Desulfurococcus mobilis homing endonuclease I-DmoI, trapping sequential stages of a two-metal-ion cleavage mechanism. We captured intermediates of the different catalytic steps, and this allowed us to watch the reaction by 'freezing' multiple states. We observed the successive entry of two metals involved in the reaction and the arrival of a third cation in a central position of the active site. This third metal ion has a crucial role, triggering the consecutive hydrolysis of the targeted phosphodiester bonds in the DNA strands and leaving its position once the DSB is generated. The multiple structures show the orchestrated conformational changes in the protein residues, nucleotides and metals during catalysis.
[Show abstract][Hide abstract] ABSTRACT: chTOG is a conserved microtubule polymerase that catalyses the addition of tubulin dimers to promote microtubule growth. chTOG interacts with TACC3, a member of the transforming acidic coiled-coil (TACC) family. Here we analyse their association using the Xenopus homologues, XTACC3 (TACC3) and XMAP215 (chTOG), dissecting the mechanism by which their interaction promotes microtubule elongation during spindle assembly. Using SAXS, we show that the TACC domain (TD) is an elongated structure that mediates the interaction with the C terminus of XMAP215. Our data suggest that one TD and two XMAP215 molecules associate to form a four-helix coiled-coil complex. A hybrid methods approach was used to define the precise regions of the TACC heptad repeat and the XMAP215 C terminus required for assembly and functioning of the complex. We show that XTACC3 can induce the recruitment of larger amounts of XMAP215 by increasing its local concentration, thereby promoting efficient microtubule elongation during mitosis.
[Show abstract][Hide abstract] ABSTRACT: DNA editing offers new possibilities in synthetic biology and biomedicine for modulation or modification of cellular functions to organisms. However, inaccuracy in this process may lead to genome damage. To address this important problem, a strategy allowing specific gene modification has been achieved through the addition, removal or exchange of DNA sequences using customized proteins and the endo-genous DNA-repair machinery. Therefore, the engineering of specific protein–DNA interactions in protein scaffolds is key to providing 'toolkits' for precise genome modification or regulation of gene expression. In a search for putative DNA-binding domains, BurrH, a protein that recognizes a 19 bp DNA target, was identified. Here, its apo and DNA-bound crystal structures are reported, revealing a central region containing 19 repeats of a helix–loop–helix modular domain (BurrH domain; BuD), which identifies the DNA target by a single residue-to-nucleotide code, thus facilitating its redesign for gene targeting. New DNA-binding specificities have been engineered in this template, showing that BuD-derived nucleases (BuDNs) induce high levels of gene targeting in a locus of the human haemoglobin (HBB) gene close to mutations responsible for sickle-cell anaemia. Hence, the unique combination of high efficiency and specificity of the BuD arrays can push forward diverse genome-modification approaches for cell or organism redesign, opening new avenues for gene editing.
[Show abstract][Hide abstract] ABSTRACT: Tousled-like kinases (TLKs) are an evolutionarily conserved family of serine/threonine protein kinases involved in chromatin dynamics, including DNA replication and repair, transcription and chromosome segregation. The two members of the family reported in humans, namely TLK1 and TLK2, localize to the cell nucleus and are capable of forming homo- or hetero-oligomers by themselves. To characterize the role of TLK2, its C-terminal kinase domain was cloned and overexpressed in Escherichia coli followed by purification to homogeneity. Crystallization experiments in the presence of ATP-γ-S yielded crystals suitable for X-ray diffraction analysis belonging to two different space groups: tetragonal I4122 and cubic P213. The latter produced the best diffracting crystal (3.4 Å resolution using synchrotron radiation), with unit-cell parameters a = b = c = 126.05 Å, α = β = γ = 90°. The asymmetric unit contained one protein molecule, with a Matthews coefficient of 4.59 Å(3) Da(-1) and a solvent content of 73.23%.
[Show abstract][Hide abstract] ABSTRACT: A key issue when designing and using DNA-targeting nucleases is specificity. Ideally, an optimal DNA-targeting tool has only one recognition site within a genomic sequence. In practice, however, almost all designer nucleases available today can accommodate one to several mutations within their target site. The ability to predict the specificity of targeting is thus highly desirable. Here, we describe the first comprehensive experimental study focused on the specificity of the four commonly used repeat variable diresidues (RVDs; NI:A, HD:C, NN:G and NG:T) incorporated in transcription activator-like effector nucleases (TALEN). The analysis of >15 500 unique TALEN/DNA cleavage profiles allowed us to monitor the specificity gradient of the RVDs along a TALEN/DNA binding array and to present a specificity scoring matrix for RVD/nucleotide association. Furthermore, we report that TALEN can only accommodate a relatively small number of position-dependent mismatches while maintaining a detectable activity at endogenous loci in vivo, demonstrating the high specificity of these molecular tools. We thus envision that the results we provide will allow for more deliberate choices of DNA binding arrays and/or DNA targets, extending our engineering capabilities.
Nucleic Acids Research 02/2014; · 8.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Homing endonucleases are highly specific DNA-cleaving enzymes that recognize long stretches of DNA. The engineering of these enzymes provides novel instruments for genome modification in a wide range of fields, including gene targeting, by inducing specific double-strand breaks. I-CvuI is a homing endonuclease from the green alga Chlorella vulgaris. This enzyme was purified after overexpression in Escherichia coli. Crystallization experiments of I-CvuI in complex with its DNA target in the presence of Mg(2+) yielded crystals suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group P212121, with unit-cell parameters a = 62.83, b = 83.56, c = 94.40 Å. The self-rotation function and the Matthews coefficient suggested the presence of one protein-DNA complex per asymmetric unit. The crystals diffracted to a resolution limit of 1.9 Å using synchrotron radiation.
[Show abstract][Hide abstract] ABSTRACT: Synopsis: The homing endonuclease I-CvuI from C. vulgaris has been expressed, purified and crystallized in complex with its target DNA. Preliminary X-ray diffraction analysis is reported. ARTICLE IN PRESS – Acta Cryst. F Crystallization and preliminary X-ray diffraction analysis on the homing endonuclease of Chlorella vulgaris I-CvuI in complex with its target DNA How to cite your article in press Your article has not yet been assigned page numbers, but may be cited using the doi: You will be sent the full citation when your article is published and also given instructions on how to download an electronic reprint of your article. Proof instructions Proof corrections should be returned by 19 January 2014. After this period, the Editors reserve the right to publish your article with only the Managing Editor's corrections. Please (1) Read these proofs and assess whether any corrections are necessary. (2) Check that any technical editing queries highlighted in bold underlined text have been answered. (3) Send corrections by e-mail to email@example.com. Please describe corrections using plain text, where possible, giving the line numbers indicated in the proof. Please do not make corrections to the pdf file electronically and please do not return the pdf file. If no corrections are required please let us know. If you wish to make your article open access or purchase printed offprints, please complete the attached order form and return it by e-mail as soon as possible. Thumbnail image for contents page Files: f/fw5442/fw5442.3d f/fw5442/fw5442.sgml FW5442 XC IU-1414/43(16)1 1412/29(16)1 () Homing endonucleases are highly specific DNA-cleaving enzymes that recognize long stretches of DNA. The engineering of these enzymes provides novel instruments for genome modification in a wide range of fields, including gene targeting by inducing specific double-strand breaks. I-CvuI is a homing endonuclease from the green alga Chlorella vulgaris. This enzyme was purified after overexpression in Escherichia coli. Crystallization experiments of I-CvuI in complex with its DNA target in the presence of Mg 2+ yielded crystals suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group P2 1 2 1 2 1 , with unit-cell parameters a = 62.83, b = 83.56, c = 94.40 Å , = = = 90 . The self-rotation function and the Matthews coefficient suggested the presence of one protein–DNA complex per asymmetric unit. The crystals diffracted to a resolution limit of 1.9 Å using synchrotron radiation.
[Show abstract][Hide abstract] ABSTRACT: Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr. For further information see Acta Crystallographica Section F: Structural Biology Communications is a rapid all-electronic journal, which provides a home for short communications on the crystalliza-tion and structure of biological macromolecules. Structures determined through structural genomics initiatives or from iterative studies such as those used in the pharmaceutical industry are particularly welcomed. Articles are available online when ready, making publication as fast as possible, and include unlimited free colour illustrations, movies and other enhancements. The editorial process is completely electronic with respect to deposition, submission, refereeing and publication. Expression, purification, crystallization and preliminary X-ray diffraction analysis of the novel modular DNA-binding protein BurrH in its apo form and in complex with its target DNA Different genome-editing strategies have fuelled the development of new DNA-targeting molecular tools allowing precise gene modifications. Here, the expression, purification, crystallization and preliminary X-ray diffraction of BurrH, a novel DNA-binding protein from Burkholderia rhizoxinica, are reported. Crystallization experiments of BurrH in its apo form and in complex with its target DNA yielded crystals suitable for X-ray diffraction analysis. The crystals of the apo form belonged to the primitive hexagonal space group P3 1 or its enantiomorph P3 2 , with unit-cell parameters a = b = 73.28, c = 268.02 Å , = = 90, = 120 . The BurrH–DNA complex crystallized in the monoclinic space group P2 1 , with unit-cell parameters a = 70.15, b = 95.83, c = 76.41 Å , = = 90, = 109.51 . The self-rotation function and the Matthews coefficient suggested the presence of two protein molecules per asymmetric unit in the apo crystals and one protein–DNA complex in the monoclinic crystals. The crystals diffracted to resolution limits of 2.21 and 2.65 Å , respectively, using synchrotron radiation.
Acta Crystallographica Section F Structural Biology and Crystallization Communications 01/2014; · 0.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Transcription activator-like effectors contain a DNA-binding domain organized in tandem repeats. The repeats include two adjacent residues known as the repeat variable di-residue, which recognize a single base pair, establishing a direct code between the dipeptides and the target DNA. This feature suggests this scaffold as an excellent candidate to generate new protein-DNA specificities for biotechnological applications. Here, the crystal structure of AvrBs3 (residues 152-895, molecular mass 82 kDa) in complex with its target DNA sequence is presented, revealing a new mode of interaction with the initial thymine of the target sequence, together with an analysis of both the binding specificity and the thermodynamic properties of AvrBs3. This study quantifies the affinity and the specificity between AvrBs3 and its target DNA. Moreover, in vitro and in vivo analyses reveal that AvrBs3 does not show a strict nucleotide-binding preference for the nucleotide at the zero position of the DNA, widening the number of possible sequences that could be targeted by this scaffold.
[Show abstract][Hide abstract] ABSTRACT: Purification from a source enriched in large macromolecular machines with basic cellular function is still the method of choice in many cases. Such complexes occur in sufficiently high copy numbers in the cell and can be isolated using classical protein purification protocols. Although advanced DNA recombinant technologies and sophisticated overexpression strategies are available, many complexes like the ribosome, RNA polymerase II and membrane protein complexes involved in photosynthesis or in oxidative phosphorylation can only be purified from a rich source. Here, we review recent accomplishments and limitations in applying this strategy.
Current Opinion in Structural Biology 02/2013; · 8.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we perform a large-scale study of the structural properties and the expression of proteins that constitute the human Centrosome. Centrosomal proteins tend to be larger than generic human proteins (control set), since their genes contain in average more exons (20.3 versus 14.6). They are rich in predicted disordered regions, which cover 57% of their length, compared to 39% in the general human proteome. They also contain several regions that are dually predicted to be disordered and coiled-coil at the same time: 55 proteins (15%) contain disordered and coiled-coil fragments that cover more than 20% of their length. Helices prevail over strands in regions homologous to known structures (47% predicted helical residues against 17% predicted as strands), and even more in the whole centrosomal proteome (52% against 7%), while for control human proteins 34.5% of the residues are predicted as helical and 12.8% are predicted as strands. This difference is mainly due to residues predicted as disordered and helical (30% in centrosomal and 9.4% in control proteins), which may correspond to alpha-helix forming molecular recognition features (α-MoRFs). We performed expression assays for 120 full-length centrosomal proteins and 72 domain constructs that we have predicted to be globular. These full-length proteins are often insoluble: Only 39 out of 120 expressed proteins (32%) and 19 out of 72 domains (26%) were soluble. We built or retrieved structural models for 277 out of 361 human proteins whose centrosomal localization has been experimentally verified. We could not find any suitable structural template with more than 20% sequence identity for 84 centrosomal proteins (23%), for which around 74% of the residues are predicted to be disordered or coiled-coils. The three-dimensional models that we built are available at http://ub.cbm.uam.es/centrosome/models/index.php.
PLoS ONE 01/2013; 8(5):e62633. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tubulin cofactors (TBCs) participate in the folding, dimerization, and dissociation pathways of the tubulin dimer. Among them, TBCB and TBCE are two CAP-Gly domain-containing proteins that together efficiently interact with and dissociate the tubulin dimer. In the study reported here we showed that TBCB localizes at spindle and midzone microtubules during mitosis. Furthermore, the motif DEI/M-COO(-) present in TBCB, which is similar to the EEY/F-COO(-) element characteristic of EB proteins, CLIP-170, and α-tubulin, is required for TBCE-TBCB heterodimer formation and thus for tubulin dimer dissociation. This motif is responsible for TBCB autoinhibition, and our analysis suggests that TBCB is a monomer in solution. Mutants of TBCB lacking this motif are derepressed and induce microtubule depolymerization through an interaction with EB1 associated with microtubule tips. TBCB is also able to bind to the chaperonin complex CCT containing α-tubulin, suggesting that it could escort tubulin to facilitate its folding and dimerization, recycling or degradation.
Cellular and Molecular Life Sciences CMLS 09/2012; · 5.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we asked whether CpG methylation could influence the DNA binding affinity and activity of meganucleases used for genome engineering applications. A combination of biochemical and structural approaches enabled us to demonstrate that CpG methylation decreases I-CreI DNA binding affinity and inhibits its endonuclease activity in vitro. This inhibition depends on the position of the methylated cytosine within the DNA target and was almost total when it is located inside the central tetrabase. Crystal structures of I-CreI bound to methylated cognate target DNA suggested a molecular basis for such inhibition, although the precise mechanism still has to be specified. Finally, we demonstrated that the efficacy of engineered meganucleases can be diminished by CpG methylation of the targeted endogenous site, and we proposed a rational design of the meganuclease DNA binding domain to alleviate such an effect. We conclude that although activity and sequence specificity of engineered meganucleases are crucial parameters, target DNA epigenetic modifications need to be considered for successful gene editions.
Journal of Biological Chemistry 06/2012; 287(36):30139-50. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Homing endonucleases represent protein scaffolds that provide powerful tools for genome manipulation, as these enzymes possess a very low frequency of DNA cleavage in eukaryotic genomes due to their high specificity. The basis of protein-DNA recognition must be understood to generate tailored enzymes that target the DNA at sites of interest. Protein-DNA interaction engineering of homing endonucleases has demonstrated the potential of these approaches to create new specific instruments to target genes for inactivation or repair. Protein-DNA interface studies have been focused mostly on specific contacts between amino acid side chains and bases to redesign the binding interface. However, it has been shown that 4 bp in the central DNA sequence of the 22-bp substrate of a homing endonuclease (I-CreI), which do not show specific protein-DNA interactions, is not devoid of content information. Here, we analyze the mechanism of target discrimination in this substrate region by the I-CreI protein, determining how it can occur independently of the specific protein-DNA interactions. Our data suggest the important role of indirect readout in this substrate region, opening the possibility for a fully rational search of new target sequences, thus improving the development of redesigned enzymes for therapeutic and biotechnological applications.
Nucleic Acids Research 04/2012; 40(14):6936-45. · 8.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PIM kinases have become targets of interest due to their association with biochemical mechanisms affecting survival, proliferation and cytokine production. 1,2,3-Triazolo[4,5-b]pyridines were identified as PIM inhibitors applying a scaffold hopping approach. Initial exploration around this scaffold and X-ray crystallographic data are hereby described.
[Show abstract][Hide abstract] ABSTRACT: The protein ING4 binds to histone H3 trimethylated at Lys-4 (H3K4me3) through its C-terminal plant homeodomain, thus recruiting the HBO1 histone acetyltransferase complex to target promoters. The structure of the plant homeodomain finger bound to an H3K4me3 peptide has been described, as well as the disorder and flexibility in the ING4 central region. We report the crystal structure of the ING4 N-terminal domain, which shows an antiparallel coiled-coil homodimer with each protomer folded into a helix-loop-helix structure. This arrangement suggests that ING4 can bind simultaneously two histone tails on the same or different nucleosomes. Dimerization has a direct impact on ING4 tumor suppressor activity because monomeric mutants lose the ability to induce apoptosis after genotoxic stress. Homology modeling based on the ING4 structure suggests that other ING dimers may also exist.
Journal of Biological Chemistry 02/2012; 287(14):10876-84. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: DNA replication is strictly regulated through a sequence of steps that involve many macromolecular protein complexes. One of them is the replicative helicase, which is required for initiation and elongation phases. A MCM helicase found as a prophage in the genome of Bacillus cereus is fused with a primase domain constituting an integrative arrangement of two essential activities for replication. We have isolated this helicase-primase complex (BcMCM) showing that it can bind DNA and displays not only helicase and primase but also DNA polymerase activity. Using single-particle electron microscopy and 3D reconstruction, we obtained structures of BcMCM using ATPγS or ADP in the absence and presence of DNA. The complex depicts the typical hexameric ring shape. The dissection of the unwinding mechanism using site-directed mutagenesis in the Walker A, Walker B, arginine finger and the helicase channels, suggests that the BcMCM complex unwinds DNA following the extrusion model similarly to the E1 helicase from papillomavirus.
Nucleic Acids Research 02/2012; 40(3):1366-80. · 8.81 Impact Factor