Aqueous Two-Phase Systems for Cleanup and Recovery of Enzymes from Plants and Plant-Derived Extracts.

The increasing interest of the biopharmaceutical industry to exploit plants as a commercially viable production system is demanding the development of new strategies to maximize product recovery. Aqueous two-phase systems (ATPSs) are a primary recovery technique that has shown great potential for the efficient extraction and purification of biological products, from organelles to proteins and low-molecular-weight compounds. The evaluation of different system parameters upon the partitioning behavior can provide the conditions that favor the concentration of contaminants and the desired target protein in opposite phases. The protocols described here provide the basic strategy to explore the use of ATPSs for the isolation and partial purification of native and recombinant proteins from plants and plant-derived extracts.

COMET Functions as a PCH2 Cofactor in Regulating the HORMA Domain Protein ASY1.

The formation of the chromosome axis is key to meiotic recombination and hence the correct distribution of chromosomes to meiotic products. A key component of the axis in Arabidopsis is the HORMA domain protein (HORMAD) ASY1, the homolog of Hop1 in yeast and HORMAD1/2 in mammals. The chromosomal association of ASY1 is dynamic, i.e., ASY1 is recruited to the axis at early prophase and later largely removed when homologous chromosomes synapse. PCH2/TRIP13 proteins are well-known regulators of meiotic HORMADs and required for their depletion from synapsed chromosomes. However, no direct interaction has been found between PCH2/TRIP13 and the presumptive HORMAD substrates in any organism other than in budding yeast. Thus, it remains largely elusive how the dynamics of ASY1 and other meiotic HORMADs are controlled. Here, we have identified COMET, the Arabidopsis homolog of human p31comet, which is known for its function in the spindle assembly checkpoint (SAC), as a central regulator of ASY1 dynamics in meiosis. We provide evidence that COMET controls ASY1 localization by serving as an adaptor for PCH2. Because ASY1 accumulates in the cytoplasm in early prophase and is persistently present on chromosomes in comet, we conclude that COMET is required for both the recruitment of ASY1 to the nucleus and the subsequent removal from the axis. The here-revealed function of COMET as an adaptor for PCH2 remarkably resembles the regulation of another HORMAD, Mad2, in the SAC in yeast and animals, revealing a conserved regulatory module of HORMA-domain-containing protein complexes.

Bulk and single-molecule analysis of a bacterial DNA2-like helicase-nuclease reveals a single-stranded DNA looping motor.

DNA2 is an essential enzyme involved in DNA replication and repair in eukaryotes. In a search for homologues of this protein, we identified and characterised Geobacillus stearothermophilus Bad, a bacterial DNA helicase-nuclease with similarity to human DNA2. We show that Bad contains an Fe-S cluster and identify four cysteine residues that are likely to co-ordinate the cluster by analogy to DNA2. The purified enzyme specifically recognises ss-dsDNA junctions and possesses ssDNA-dependent ATPase, ssDNA binding, ssDNA endonuclease, 5' to 3' ssDNA translocase and 5' to 3' helicase activity. Single molecule analysis reveals that Bad is a processive DNA motor capable of moving along DNA for distances of >4 kb at a rate of ∼200 bp per second at room temperature. Interestingly, as reported for the homologous human and yeast DNA2 proteins, the DNA unwinding activity of Bad is cryptic and can be unmasked by inactivating the intrinsic nuclease activity. Strikingly, our experiments show that the enzyme loops DNA while translocating, which is an emerging feature of processive DNA unwinding enzymes. The bacterial Bad enzymes will provide an excellent model system for understanding the biochemical properties of DNA2-like helicase-nucleases and DNA looping motor proteins in general.

Membrane Protein Solubilization and Quality Control: An Example of a Primary Active Transporter.

When purifying a membrane protein, finding a detergent for solubilization is one of the first steps to master. Ideally, only little time is invested to identify the best-suited detergent, which on the one hand would solubilize large amounts of the target protein but on the other hand would sustain the protein's activity. Here we describe the solubilization screen and subsequent activity assay we have optimized for the bacterial P-type ATPase KdpFABC. In just 2 days, more than 70 detergents were tested for their solubilization potential. Afterwards, a smaller selection of the successful detergents was assayed for their ability to retain the activity of the membrane protein complex.

Cancer-associated V-ATPase induces delayed apoptosis of protumorigenic neutrophils.

Tumors and neutrophils undergo an unexpected interaction, in which products released by tumor cells interact to support neutrophils that in turn support cancer growth, angiogenesis, and metastasis. A key protein that is highly expressed by cancer cells in tumors is the a2 isoform V-ATPase (a2V). A peptide from a2V (a2NTD) is secreted specifically by cancer cells, but not normal cells, into the tumor microenvironment. This peptide reprograms neutrophils to promote angiogenesis, cancer cell invasiveness, and neutrophil recruitment. Here, we provide evidence that cancer-associated a2V regulates the life span of protumorigenic neutrophils by influencing the intrinsic pathway of apoptosis. Immunohistochemical analysis of human cancer tissue sections collected from four different organs shows that levels of a2NTD and neutrophil counts are increased in cancer compared with normal tissues. Significant increases in neutrophil counts were present in both poorly and moderately differentiated tumors. In addition, there is a positive correlation between the number of neutrophils and a2NTD expression. Human neutrophils treated with recombinant a2NTD show significantly delayed apoptosis, and such prolonged survival was dependent on NF-κB activation and ROS generation. Induction of antiapoptotic protein expression (Bcl-xL and Bcl-2A1) and decreased expression of proapoptotic proteins (Bax, Apaf-1, caspase-3, caspase-6, and caspase-7) were a hallmark of these treated neutrophils. Autocrine secretion of prosurvival cytokines of TNF-α and IL-8 by treated neutrophils prolongs their survival. Our findings highlight the important role of cancer-associated a2V in regulating protumorigenic innate immunity, identifying a2V as a potential important target for cancer therapy.

Structural insights into substrate recognition by the type VII secretion system.

Type VII secretion systems (T7SSs) are found in many disease related bacteria including Mycobacterium tuberculosis (Mtb). ESX-1 [early secreted antigen 6 kilodaltons (ESAT-6) system 1] is one of the five subtypes (ESX-1~5) of T7SSs in Mtb, where it delivers virulence factors into host macrophages during infection. However, little is known about the molecular details as to how this occurs. Here, we provide high-resolution crystal structures of the C-terminal ATPase3 domains of EccC subunits from four different Mtb T7SS subtypes. These structures adopt a classic RecA-like ɑ/ß fold with a conserved Mg-ATP binding site. The structure of EccCb1 in complex with the C-terminal peptide of EsxB identifies the location of substrate recognition site and shows how the specific signaling module "LxxxMxF" for Mtb ESX-1 binds to this site resulting in a translation of the bulge loop. A comparison of all the ATPase3 structures shows there are significant differences in the shape and composition of the signal recognition pockets across the family, suggesting that distinct signaling sequences of substrates are required to be specifically recognized by different T7SSs. A hexameric model of the EccC-ATPase3 is proposed and shows the recognition pocket is located near the central substrate translocation channel. The diameter of the channel is ~25-Å, with a size that would allow helix-bundle shaped substrate proteins to bind and pass through. Thus, our work provides new molecular insights into substrate recognition for Mtb T7SS subtypes and also a possible transportation mechanism for substrate and/or virulence factor secretion.

Architecture of the mycobacterial type VII secretion system.

Host infection by pathogenic mycobacteria, such as Mycobacterium tuberculosis, is facilitated by virulence factors that are secreted by type VII secretion systems1. A molecular understanding of the type VII secretion mechanism has been hampered owing to a lack of three-dimensional structures of the fully assembled secretion apparatus. Here we report the cryo-electron microscopy structure of a membrane-embedded core complex of the ESX-3/type VII secretion system from Mycobacterium smegmatis. The core of the ESX-3 secretion machine consists of four protein components-EccB3, EccC3, EccD3 and EccE3, in a 1:1:2:1 stoichiometry-which form two identical protomers. The EccC3 coupling protein comprises a flexible array of four ATPase domains, which are linked to the membrane through a stalk domain. The domain of unknown function (DUF) adjacent to the stalk is identified as an ATPase domain that is essential for secretion. EccB3 is predominantly periplasmatic, but a small segment crosses the membrane and contacts the stalk domain. This suggests that conformational changes in the stalk domain-triggered by substrate binding at the distal end of EccC3 and subsequent ATP hydrolysis in the DUF-could be coupled to substrate secretion to the periplasm. Our results reveal that the architecture of type VII secretion systems differs markedly from that of other known secretion machines2, and provide a structural understanding of these systems that will be useful for the design of antimicrobial strategies that target bacterial virulence.

Spermathecae: Morphofunctional features and correlation with fat bodies and trachea in six species of vectors of Chagas disease.

Since spermatheca is able to transport spermatozoa and maintain a specific microenvironment for the storage of viable sperm cells for long periods of time, specific morphofunctional features must be involved in this capacity, and an efficient nutritional and oxygen supply must be required. In this study, we investigated the histological features of spermathecae and fat bodies in six species of three genera of epidemiological importance for Chagas' disease. The association of the reproductive system with the fat bodies and tracheal system was also focused in these species. The reproductive system, tracheae and fat bodies were fixed in 4% formaldehyde, and embedded in glycol methacrylate. The sections were stained with H.E., picrosirius red and Periodic-Acid Schiff methods for morphological analyses. Paraffin-embedded spermatheca sections were submitted to immunofluorescence for detection of V-ATPase. In P. lignarius, R. montenegrensis and R. prolixus, the spermatheca contains a slightly dilated tubular distal portion. In P. megistus and T. tibiamaculata, the spermatheca shows a large bulbous distal portion, and in T. infestans, a large oval-shaped distal portion. In all species, this portion was surrounded by a thin muscular layer, and the epithelial height varied according to the shape of this terminal portion. All spermathecal proximal portions showed simple columnar epithelium surrounded by a thick muscular layer. The epithelial cells of spermathecae showed PAS-positive cytoplasm and V-ATPase immunofluorescence in the apical surface. Tracheoles and polysaccharide-rich fat body cells were found next or in close contact to the oviduct or spermathecal tissues. The results indicate that the spermatheca proximal portion is related to contraction and sperm transport, whose oxygen and energy supply is guaranteed by the associated tracheal branches and fat bodies. In the storage portion, fat bodies and tracheae seem to be crucial for the maintenance of an optimal spermathecal microenvironment and storage of viable sperm cells. The participation of V-ATPase in the spermathecae epithelial cells may contribute for the maintenance of an optimal luminal milieu to spermatozoa, by alkalinization and/or acidification of lumen, similarly to the other epithelial cell types in insects. Further studies are necessary to clarify the role of this proton pump in the spermathecal epithelial cells.

Strategies for purification of the bacteriophage HK97 small and large terminase subunits that yield pure and homogeneous samples that are functional.

Packaging the viral genome in the head of double-stranded DNA viruses, such as bacteriophages, requires the activity of a terminase. The bacteriophage terminase consists of a small terminase subunit (TerS), which binds the viral DNA, and a large terminase subunit (TerL) that possesses the ATPase and nuclease activities for packaging the DNA in the phage head. Some phages require additional components for DNA packaging, such as the HNH endonuclease gp74 in the bacteriophage HK97. Gp74 enhances the activity of terminase-mediated digestion of the cohesive (cos) site that connects individual genomes in phage concatemeric DNA, a pre-requisite to DNA packaging, and this enhancement requires an intact HNH motif in gp74. Testing of whether gp74 alters the terminase DNA binding or enzymatic activities requires obtaining isolated samples of pure TerS and TerL, which has been challenging owing to the poor solubility of these proteins. To this end, we developed methods to obtain purified TerS and TerL proteins that are active. TerS is expressed solubly in E. coli as a fusion with SUMO, which can be removed during purification to yield a TerS nonamer (TerS9). Homogenous samples of a TerL monomer are also obtained, but the homogeneity of the sample depends on the solution conditions, as seen for other terminases. DNA binding, ATPase, and nuclease assays demonstrate that our preparations of TerS9 and TerL are functional, and that they also function with gp74. Purified TerS9 and TerL enable studies into the molecular basis by which gp74 regulates terminase activity in phage maturation.

Mechanism for autoinhibition and activation of the MORC3 ATPase.

Microrchidia 3 (MORC3) is a human protein linked to autoimmune disorders, Down syndrome, and cancer. It is a member of a newly identified family of human ATPases with an uncharacterized mechanism of action. Here, we elucidate the molecular basis for inhibition and activation of MORC3. The crystal structure of the MORC3 region encompassing the ATPase and CW domains in complex with a nonhydrolyzable ATP analog demonstrates that the two domains are directly coupled. The extensive ATPase:CW interface stabilizes the protein fold but inhibits the catalytic activity of MORC3. Enzymatic, NMR, mutational, and biochemical analyses show that in the autoinhibited, off state, the CW domain sterically impedes binding of the ATPase domain to DNA, which in turn is required for the catalytic activity. MORC3 autoinhibition is released by disrupting the intramolecular ATPase:CW coupling through the competitive interaction of CW with histone H3 tail or by mutating the interfacial residues. Binding of CW to H3 leads to a marked rearrangement in the ATPase-CW cassette, which frees the DNA-binding site in active MORC3 (on state). We show that ATP-induced dimerization of the ATPase domain is strictly required for the catalytic activity and that the dimeric form of ATPase-CW might cooperatively bind to dsDNA. Together, our findings uncovered a mechanism underlying the fine-tuned regulation of the catalytic domain of MORC3 by the epigenetic reader, CW.

Schiff bases of tryptamine as potent inhibitors of nucleoside triphosphate diphosphohydrolases (NTPDases): Structure-activity relationship.

Overexpression of NTPDases leads to a number of pathological situations such as thrombosis, and cancer. Thus, effective inhibitors are required to combat these pathological situations. Different classes of NTPDase inhibitors are reported so far including nucleotides and their derivatives, sulfonated dyes such as reactive blue 2, suramin and its derivatives, and polyoxomatalates (POMs). Suramin is a well-known and potent NTPDase inhibitor, nonetheless, a range of side effects are also associated with it. Reactive blue 2 also had non-specific side effects that become apparent at high concentrations. In addition, most of the NTPDase inhibitors are high molecular weight compounds, always required tedious chemical steps to synthesize. Hence, there is still need to explore novel, low molecular weight, easy to synthesize, and potent NTPDase inhibitors. Keeping in mind the known NTPDase inhibitors with imine functionality and nitrogen heterocycles, Schiff bases of tryptamine, 1-26, were synthesized and characterized by spectroscopic techniques such as EI-MS, HREI-MS, 1H-, and 13C NMR. All the synthetic compounds were evaluated for the inhibitory avidity against activities of three major isoforms of NTPDases: NTPDase-1, NTPDase-3, and NTPDase-8. Cumulatively, eighteen compounds were found to show potent inhibition (Ki = 0.0200-0.350 µM) of NTPDase-1, twelve (Ki = 0.071-1.060 µM) of NTPDase-3, and fifteen compounds inhibited (Ki = 0.0700-4.03 µM) NTPDase-8 activity. As a comparison, the Kis of the standard inhibitor suramin were 1.260 ±â€¯0.007, 6.39 ±â€¯0.89 and 1.180 ±â€¯0.002 µM, respectively. Kinetic studies were performed on lead compounds (6, 5, and 21) with human (h-) NTPDase-1, -3, and -8, and Lineweaver-Burk plot analysis showed that they were all competitive inhibitors. In silico study was conducted on compound 6 that showed the highest level of inhibition of NTPDase-1 to understand the binding mode in the active site of the enzyme.

Determination of Sec18-Lipid Interactions by Liposome-Binding Assay.

Protein-lipid binding interactions play a key role in the regulation of peripheral membrane protein function. Liposome-binding assays are a simple and affordable means of screening for specific protein-lipid interactions. Liposomes are prepared by mixing phospholipid combinations of interest before drying and rehydration. Sonication of the lipid mixture produces small unilamellar vesicles (SUVs) which are incubated with a protein of interest to allow for any binding to occur. Liposomes and liposome-protein complexes are floated on a sucrose gradient by centrifugation to separate them from unbound protein. Bound protein levels are easily determined by SDS-PAGE and Western blotting. This approach provides a reliable means of assaying novel protein-lipid interactions in vitro. Here we use liposome floatation to show the binding of the SNARE-activating protein Sec18 (mammalian NSF) to phosphatidic acid.

[In silico Analyses of Transcriptomes of the Marine Green Microalga Dunaliella tertiolecta: Identification of Sequences Encoding P-type ATPases].

De novo assembled transcriptomes of the marine microalga Dunaliella tertiolecta (Chlorophyta) were analyzed. Transcriptome assemblies were performed using short-read RNA-seq data deposited in the SRA database (DNA and RNA Sequence Read Archive, NCBI). A merged transcriptome was assembled using a pooled RNA-seq data set. The goal of the study was in silico identification of nucleotide sequences encoding P-type ATPases in D. tertiolecta transcriptomes. P-type ATPases play a considerable role in the adaptation of an organism to a variable environment, and this problem is particularly significant for microalgae inhabiting an environment with an unstable ionic composition. Particular emphasis was given to searching for a sequence coding Na^(+)-ATPase. This enzyme is expected to function in the plasma membrane of D. tertiolecta like in some marine algae, in particular, in the closely related alga Dunaliella maritima. An ensemble of 12 P-type ATPases consisting of members belonging to the five main subfamilies of the P-type ATPase family was revealed in the assembled transcriptomes. The genes of the following P-type ATPases were found: (1) heavy metal ATPases (subfamily PIB); (2) Ca^(2+)-ATPases of SERCA type (subfamily P2A); (3) H^(+)-ATPases (subfamily P3); (4) phospholipid-transporting ATPases (flippases) (subfamily P4); (5) cation-transporting ATPases of uncertain specificities (subfamily P5). The presence of functional Na^(+)-ATPases in marine algae is presently undoubted. However, contrary to expectations, we failed to find a nucleotide sequence encoding a protein that could unequivocally be considered a Na^(+)-ATPase. Further study is necessary to elucidate the roles of in silico revealed D. tertiolecta ATPases in Na^(+) transport.

A highly efficient, one-step purification of the Hsp70 chaperone Ssa1.

Chaperone proteins are required to maintain the overall fold and function of proteins in the cell. As part of the Hsp70 family, Ssa1 acts to maintain cellular proteostasis through a variety of diverse pathways aimed to preserve the native conformation of target proteins, thereby preventing aggregation and future states of cellular toxicity. Studying the structural dynamics of Ssa1 in vitro is essential to determining their precise mechanisms and requires the development of purification methods that result in highly pure chaperones. Current methods of expressing and purifying Ssa1 utilize affinity tagged constructs expressed in Escherichia coli, however, expression in an exogenous source produces proteins that lack post-translational modifications leading to undesired structural and functional effects. Current protocols to purify Ssa1 from Saccharomyces cerevisiae require large amounts of starting material, multiple steps of chromatography, and result in low yield. Our objective was to establish a small-scale purification of Ssa1 expressed from its endogenous source, Saccharomyces cerevisiae, with significant yield and purity. We utilized a protein A affinity tag that was previously used to purify large protein complexes from yeast, combined with magnetic Dynabeads that are conjugated with rabbit immunoglobulin G (IgG). Our results show that we can produce native, highly pure, active Ssa1 via this one-step purification with minimal amounts of starting material, and this Ssa1-protein A fusion does not alter cellular phenotypes. This methodology is a significant improvement in Ssa1 purification and will facilitate future experiments that will elucidate the biochemical and biophysical properties of Hsp70 chaperones.

Glycosyl-Substituted Dicarboxylates as Detergents for the Extraction, Overstabilization, and Crystallization of Membrane Proteins.

To tackle the problems associated with membrane protein (MP) instability in detergent solutions, we designed a series of glycosyl-substituted dicarboxylate detergents (DCODs) in which we optimized the polar head to clamp the membrane domain by including, on one side, two carboxyl groups that form salt bridges with basic residues abundant at the membrane-cytoplasm interface of MPs and, on the other side, a sugar to form hydrogen bonds. Upon extraction, the DCODs 8 b, 8 c, and 9 b preserved the ATPase function of BmrA, an ATP-binding cassette pump, much more efficiently than reference or recently designed detergents. The DCODs 8 a, 8 b, 8 f, 9 a, and 9 b induced thermal shifts of 20 to 29 °C for BmrA and of 13 to 21 °C for the native version of the G-protein-coupled adenosine receptor A2A R. Compounds 8 f and 8 g improved the diffraction resolution of BmrA crystals from 6 to 4 Å. DCODs are therefore considered to be promising and powerful tools for the structural biology of MPs.

Purification and Characterization of an ATPase GsiA from Salmonella enterica.

The coding sequence of Salmonella enterica gsiA was cloned and expressed in E. coli. The protein was purified and ATPase activity was characterized by NADH oxidation method. GsiA exhibited optimum activity at 30°C and at pH 8 in Tris/HCl buffer. GsiA protein was stable at 20°C. 66% and 44% activity remained after incubation at 30°C and 40°C for 30 min. pH 7 and pH 9 incubation would obviously reduce the ATPase activity. In vivo functionality of gsiA was determined by constructing gene deletion strains. gsiA was shown to be essential for GSI mediated glutathione uptake and gsiA deletion could decrease the virulence of Salmonella enterica. Interactions of glutathione import proteins GsiA, GsiB, GsiC, and GsiD were investigated by using bacterial two-hybrid system. GsiA could interact with itself and inner membrane proteins GsiC and GsiD. This report provides the first description of gsiA functions in Salmonella enterica. The results could help elucidating the glutathione uptake mechanism and glutathione functions in bacteria.

Molecular Mechanism of Substrate Processing by the Cdc48 ATPase Complex.

The Cdc48 ATPase and its cofactors Ufd1/Npl4 (UN) extract polyubiquitinated proteins from membranes or macromolecular complexes, but how they perform these functions is unclear. Cdc48 consists of an N-terminal domain that binds UN and two stacked hexameric ATPase rings (D1 and D2) surrounding a central pore. Here, we use purified components to elucidate how the Cdc48 complex processes substrates. After interaction of the polyubiquitin chain with UN, ATP hydrolysis by the D2 ring moves the polypeptide completely through the double ring, generating a pulling force on the substrate and causing its unfolding. ATP hydrolysis by the D1 ring is important for subsequent substrate release from the Cdc48 complex. This release requires cooperation of Cdc48 with a deubiquitinase, which trims polyubiquitin to an oligoubiquitin chain that is then also translocated through the pore. Together, these results lead to a new paradigm for the function of Cdc48 and its mammalian ortholog p97/VCP.

Purification and biochemical characterization of NpABCG5/NpPDR5, a plant pleiotropic drug resistance transporter expressed in Nicotiana tabacum BY-2 suspension cells.

Pleiotropic drug resistance (PDR) transporters belong to the ABCG subfamily of ATP-binding cassette (ABC) transporters and are involved in the transport of various molecules across plasma membranes. During evolution, PDR genes appeared independently in fungi and in plants from a duplication of a half-size ABC gene. The enzymatic properties of purified PDR transporters from yeast have been characterized. This is not the case for any plant PDR transporter, or, incidentally, for any purified plant ABC transporter. Yet, plant PDR transporters play important roles in plant physiology such as hormone signaling or resistance to pathogens or herbivores. Here, we describe the expression, purification, enzymatic characterization and 2D analysis by electron microscopy of NpABCG5/NpPDR5 from Nicotiana plumbaginifolia, which has been shown to be involved in the plant defense against herbivores. We constitutively expressed NpABCG5/NpPDR5, provided with a His-tag in a homologous system: suspension cells from Nicotiana tabacum (Bright Yellow 2 line). NpABCG5/NpPDR5 was targeted to the plasma membrane and was solubilized by dodecyl maltoside and purified by Ni-affinity chromatography. The ATP-hydrolyzing specific activity (27 nmol min-1 mg-1) was stimulated seven-fold in the presence of 0.1% asolectin. Electron microscopy analysis indicated that NpABCG5/NpPDR5 is monomeric and with dimensions shorter than those of known ABC transporters. Enzymatic data (optimal pH and sensitivity to inhibitors) confirmed that plant and fungal PDR transporters have different properties. These data also show that N. tabacum suspension cells are a convenient host for the purification and biochemical characterization of ABC transporters.

Dissecting biochemical peculiarities of the ATPase activity of TcSub2, a component of the mRNA export pathway in Trypanosoma cruzi.

The RNA helicase DEAD-box protein Sub2 (yeast)/UAP56 (mammals) is conserved across eukaryotes and is essential for mRNA export in trypanosomes. Despite the high conservation of Sub2 in lower eukaryotes such as Trypanosoma cruzi, the low conservation of other mRNA export factors raises questions regarding whether the mode of action of TcSub2 is similar to that of orthologs from other eukaryotes. Mutation of the conserved K87 residue of TcSub2 abolishes ATPase activity, showing that its ATPase domain is functional. However, the Vmax of TcSub2 was much higher than the Vmax described for the human protein UAP56, which suggests that the TcSub2 enzyme hydrolyzes ATP faster than its human homolog. Furthermore, we demonstrate that RNA association is less important to the activity of TcSub2 compared to UAP56. Our results show differences in activity of this protein, even though the structure of TcSub2 is very similar to UAP56. Functional complementation assays indicate that these differences may be common to other trypanosomatids. Distinct features of RNA influence and ATPase efficiency between UAP56 and TcSub2 may reflect distinct structures for functional sites of TcSub2. For this reason, ligand-based or structure-based methodologies can be applied to investigate the potential of TcSub2 as a target for new drugs.

Structure and Function of a Novel ATPase that Interacts with Holliday Junction Resolvase Hjc and Promotes Branch Migration.

Holliday junction (HJ) is a hallmark intermediate in DNA recombination and must be processed by dissolution (for double HJ) or resolution to ensure genome stability. Although HJ resolvases have been identified in all domains of life, there is a long-standing effort to search in prokaryotes and eukarya for proteins promoting HJ migration. Here, we report the structural and functional characterization of a novel ATPase, Sulfolobus islandicusPilT N-terminal-domain-containing ATPase (SisPINA), encoded by the gene adjacent to the resolvase Hjc coding gene. PINA is conserved in archaea and vital for S. islandicus viability. Purified SisPINA forms hexameric rings in the crystalline state and in solution, similar to the HJ migration helicase RuvB in Gram-negative bacteria. Structural analysis suggests that ATP binding and hydrolysis cause conformational changes in SisPINA to drive branch migration. Further studies reveal that SisPINA interacts with SisHjc and coordinates HJ migration and cleavage.