Medicine and Health Sciences Commons^™

Assembly Of Synaptic Protein-Dna Complexes: Critical Role Of Non-Specific Interactions, Sridhar Vemulapalli, Mohtadin Hashemi, Anatoly B. Kolomeisky, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The synaptic protein-DNA complexes, formed by specialized proteins that bridge two or more distant sites on DNA, are critically involved in various genetic processes. However, the molecular mechanism by which the protein searches for these sites and how it brings them together is not well understood. Our previous studies directly visualized search pathways used by SfiI, and we identified two pathways, DNA threading and site-bound transfer pathways, specific to the site-search process for synaptic DNA-protein systems. To investigate the molecular mechanism behind these site-search pathways, we assembled complexes of SfiI with various DNA substrates corresponding to different transient states and …

Amyloid Cascade Hypothesis For Alzheimer’S Disease. Does It Work Under Physiological Conditions?, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

Plaques in the brain consisting of proteins are a hallmark of diseases like Alzheimer’s disease (AD) and Parkinson’s disease (PD). Such aggregates can be assembled spontaneously by specialized proteins such as amyloid beta (Ab) proteins in the case of AD. Numerous in vitro studies made a foundation for the Amyloid Cascade Hypothesis (ACH), according to which the misfolding of proteins leads to their self-assembly into toxic oligomers along with the formation of amyloid fibrils assembled as plaques in the brain. Notably physiological concentration of Ab proteins in the brain is in the low nanomolar concentration, so no spontaneous aggregation of …

The Sequence Dependent Nanoscale Structure Of Cenp-A Nucleosomes, Tommy Stormberg, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

CENP-A is a histone variant found in high abundance at the centromere in humans. At the centromere, this histone variant replaces the histone H3 found throughout the bulk chromatin. Additionally, the centromere comprises tandem repeats of α-satellite DNA, which CENP-A nucleosomes assemble upon. However, the effect of the DNA sequence on the nucleosome assembly and centromere formation remains poorly understood. Here, we investigated the structure of nucleosomes assembled with the CENP-A variant using Atomic Force Microscopy. We assembled both CENP-A nucleosomes and H3 nucleosomes on a DNA substrate containing an α-satellite motif and characterized their positioning and wrapping efficiency. We …

Peroxide Antimalarial Drugs Target Redox Homeostasis In Plasmodium Falciparum Infected Red Blood Cells, Ghizal Siddiqui, Carlo Giannangelo, Amanda De Paoli, Anna Katharina Schuh, Kim C. Heimsch, Dovile Anderson, Timothy G. Brown, Christopher A. Macraild, Jianbo Wu, Xiaofang Wang, Yuxiang Dong, Jonathan L. Vennerstrom, Katja Becker, Darren J. Creek

Journal Articles: Pharmaceutical Sciences

Plasmodium falciparum causes the most lethal form of malaria. Peroxide antimalarials based on artemisinin underpin the frontline treatments for malaria, but artemisinin resistance is rapidly spreading. Synthetic peroxide antimalarials, known as ozonides, are in clinical development and offer a potential alternative. Here, we used chemoproteomics to investigate the protein alkylation targets of artemisinin and ozonide probes, including an analogue of the ozonide clinical candidate, artefenomel. We greatly expanded the list of proteins alkylated by peroxide antimalarials and identified significant enrichment of redox-related proteins for both artemisinins and ozonides. Disrupted redox homeostasis was confirmed by dynamic live imaging of the glutathione …

Nanorings To Probe Mechanical Stress Of Single-Stranded Dna Mediated By The Dna Duplex, Karen Zagorski, Tommy Stormberg, Mohtadin Hashemi, Anatoly B. Kolomeisky, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The interplay between the mechanical properties of double-stranded and single-stranded DNA is a phenomenon that contributes to various genetic processes in which both types of DNA structures coexist. Highly stiff DNA duplexes can stretch single-stranded DNA (ssDNA) segments between the duplexes in a topologically constrained domain. To evaluate such an effect, we designed short DNA nanorings in which a DNA duplex with 160 bp is connected by a 30 nt single-stranded DNA segment. The stretching effect of the duplex in such a DNA construct can lead to the elongation of ssDNA, and this effect can be measured directly using atomic …

Free Cholesterol Accelerates Aβ Self-Assembly On Membranes At Physiological Concentration, Mohtadin Hashemi, Siddhartha Banerjee, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The effects of membranes on the early-stage aggregation of amyloid β (Aβ) have come to light as potential mechanisms by which neurotoxic species are formed in Alzheimer's disease. We have shown that direct Aβ-membrane interactions dramatically enhance the Aβ aggregation, allowing for oligomer assembly at physiologically low concentrations of the monomer. Membrane composition is also a crucial factor in this process. Our results showed that apart from phospholipids composition, cholesterol in membranes significantly enhances the aggregation kinetics. It has been reported that free cholesterol is present in plaques. Here we report that free cholesterol, along with its presence inside the …

Patient-Derived Induced Pluripotent Stem Cell Models For Phenotypic Screening In The Neuronal Ceroid Lipofuscinoses, Ahmed Morsy, Angelica V. Carmona, Paul C. Trippier

Journal Articles: Pharmaceutical Sciences

Batten disease or neuronal ceroid lipofuscinosis (NCL) is a group of rare, fatal, inherited neurodegenerative lysosomal storage disorders. Numerous genes (CLN1-CLN8, CLN10-CLN14) were identified in which mutations can lead to NCL; however, the underlying pathophysiology remains elusive. Despite this, the NCLs share some of the same features and symptoms but vary in respect to severity and onset of symptoms by age. Some common symptoms include the progressive loss of vision, mental and motor deterioration, epileptic seizures, premature death, and in the rare adult-onset, dementia. Currently, all forms of NCL are fatal, and no curative treatments are available. Induced pluripotent stem …

Aldo-Keto Reductases And Cancer Drug Resistance, Trevor M. Penning, Sravan Jonnalagadda, Paul C. Trippier, Tea Lanišnik Rižner

Journal Articles: Pharmaceutical Sciences

Human aldo-keto reductases (AKRs) catalyze the NADPH-dependent reduction of carbonyl groups to alcohols for conjugation reactions to proceed. They are implicated in resistance to cancer chemotherapeutic agents either because they are directly involved in their metabolism or help eradicate the cellular stress created by these agents (e.g., reactive oxygen species and lipid peroxides). Furthermore, this cellular stress activates the Nuclear factor-erythroid 2 p45-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 pathway. As many human AKR genes are upregulated by the NRF2 transcription factor, this leads to a feed-forward mechanism to enhance drug resistance. Resistance to major classes of chemotherapeutic agents (anthracyclines, …

Effect Of Histone H4 Tail On Nucleosome Stability And Internucleosomal Interactions, Tommy Stormberg, Sridhar Vemulapalli, Shaun Filliaux, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

Chromatin structure is dictated by nucleosome assembly and internucleosomal interactions. The tight wrapping of nucleosomes inhibits gene expression, but modifications to histone tails modulate chromatin structure, allowing for proper genetic function. The histone H4 tail is thought to play a large role in regulating chromatin structure. Here we investigated the structure of nucleosomes assembled with a tail-truncated H4 histone using Atomic Force Microscopy. We assembled tail-truncated H4 nucleosomes on DNA templates allowing for the assembly of mononucleosomes or dinucleosomes. Mononucleosomes assembled on nonspecific DNA led to decreased DNA wrapping efficiency. This effect is less pronounced for nucleosomes assembled on positioning …

Site-Search Process For Synaptic Protein-Dna Complexes, Sridhar Vemulapalli, Mohtadin Hashemi, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The assembly of synaptic protein-DNA complexes by specialized proteins is critical for bringing together two distant sites within a DNA molecule or bridging two DNA molecules. The assembly of such synaptosomes is needed in numerous genetic processes requiring the interactions of two or more sites. The molecular mechanisms by which the protein brings the sites together, enabling the assembly of synaptosomes, remain unknown. Such proteins can utilize sliding, jumping, and segmental transfer pathways proposed for the single-site search process, but none of these pathways explains how the synaptosome assembles. Here we used restriction enzyme SfiI, that requires the assembly of …

Sex-Specific Gene Expression In Flupirtine-Treated Cln3Δex7/8 Mouse Brain, Joelle Makoukji, Sara Saab, Katia Maalouf, Nadine J. Makhoul, Angelica V. Carmona, Nihar Kinarivala, Paul C. Trippier, Rose-Mary Boustany

Journal Articles: Pharmaceutical Sciences

Gene expression is a powerful tool to understand structure-function relationships in the nervous system. This study reports global gene expression changes induced by flupirtine in brain of male and female Cln3Δex7/8 mice, exposing potential flupirtine targets at the molecular level. Gene expression analysis of male and female Cln3Δex7/8 mouse brain was determined following oral administration of flupirtine for 14 weeks, using Mouse Genome 430 2.0 array Chips and an Affymetrix platform. Fifty-six genes in males and 79 in females were differentially expressed in flupirtine- versus vehicle-treated Cln3Δex7/8 mouse brain. Flupirtine altered several pathways in Cln3Δex7/8 mouse brain: apoptosis, the complement …

Two C-Terminal Sequence Variations Determine Differential Neurotoxicity Between Human And Mouse Α-Synuclein, Natalie Landeck, Katherine E. Strathearn, Daniel Ysselstein, Kerstin Buck, Sayan Dutta, Siddhartha Banerjee, Zhengjian Lv, John D. Hulleman, Jagadish Hindupur, Li-Kai Lin, Sonal Padalkar, Lia A. Stanciu, Yuri L. Lyubchenko, Deniz Kirik, Jean-Christophe Rochet

Journal Articles: Pharmaceutical Sciences

BACKGROUND: α-Synuclein (aSyn) aggregation is thought to play a central role in neurodegenerative disorders termed synucleinopathies, including Parkinson's disease (PD). Mouse aSyn contains a threonine residue at position 53 that mimics the human familial PD substitution A53T, yet in contrast to A53T patients, mice show no evidence of aSyn neuropathology even after aging. Here, we studied the neurotoxicity of human A53T, mouse aSyn, and various human-mouse chimeras in cellular and in vivo models, as well as their biochemical properties relevant to aSyn pathobiology.

METHODS: Primary midbrain cultures transduced with aSyn-encoding adenoviruses were analyzed immunocytochemically to determine relative dopaminergic neuron viability. …

Neuronal-Derived Extracellular Vesicles Are Enriched In The Brain And Serum Of Hiv-1 Transgenic Rats, Raghubendra S. Dagur, Ke Liao, Susmita Sil, Fang Niu, Zhiqiang Sun, Yuri L. Lyubchenko, Eric S. Peebles, Guoku Hu, Shilpa Buch

Journal Articles: Pharmaceutical Sciences

Despite the efficacy of combination antiretroviral therapy (ART) in controlling human immunodeficiency virus (HIV-1) replication, cytotoxic viral proteins such as HIV-1 transactivator of transcription (Tat) persist in tissues such as the brain. Although HIV-1 does not infect neuronal cells, it is susceptible to viral Tat protein-mediated toxicity, leading to neuroinflammation that underlies HIV-associated neurocognitive disorders (HAND). Given the role of extracellular vesicles (EVs) in both cellular homoeostasis and under pathological conditions, we sought to investigate the alterations in the quantity of neuronal-derived EVs in the brain–as defined by the presence of cell adhesion molecule L1 (L1CAM) and to evaluate the …

The Current State Of Drug Repurposing And Rare Diseases: An Interview With Paul Trippier, Paul C. Trippier

Journal Articles: Pharmaceutical Sciences

Paul Tripper is an Associate Professor of Medicinal Chemistry at the University of Nebraska Medical Center (UNMC, NE, USA) and an Editorial Board member of Future Drug Discovery. Here, he speaks to Managing Editor Francesca Lake about drug repurposing, focusing on the key challenges, its application to rare diseases and what we can look forward to in the future.

Nanoscale Interaction Of Recg With Mobile Fork Dna, Zhiqiang Sun, Yaqing Wang, Piero R. Bianco, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

RecG DNA helicase is a guardian of the bacterial genome where it dominates stalled DNA replication fork rescue. The single-stranded DNA binding protein (SSB) is involved in this process and promotes the binding of RecG to stalled replication forks. Atomic force microscopy (AFM) was used to investigate the interaction of RecG and SSB on a mobile fork substrate capable of being regressed. In the absence of proteins, the fork undergoes spontaneous dynamics between two states, defined by the length of the DNA complementarity at the fork. The binding of SSB does not affect these dynamics as it binds to single-stranded …

Afm Probing Of Amyloid-Beta 42 Dimers And Trimers, Sibaprasad Maity, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

Elucidating the molecular mechanisms in the development of such a devastating neurodegenerative disorder as Alzheimer's disease (AD) is currently one of the major challenges of molecular medicine. Evidence strongly suggests that the development of AD is due to the accumulation of amyloid β (Aβ) oligomers; therefore, understanding the molecular mechanisms defining the conversion of physiologically important monomers of Aβ proteins into neurotoxic oligomeric species is the key for the development of treatments and preventions of AD. However, these oligomers are unstable and unavailable for structural, physical, and chemical studies. We have recently developed a novel flexible nano array (FNA)-oligomer scaffold …

Interaction Of Aβ42 With Membranes Triggers The Self-Assembly Into Oligomers, Siddhartha Banerjee, Mohtadin Hashemi, Karen Zagorski, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The self-assembly of amyloid β (Aβ) proteins into oligomers is the major pathogenic event leading to Alzheimer's disease (AD). Typical in vitro experiments require high protein concentrations, whereas the physiological concentration of Aβ is in the picomolar to low nanomolar range. This complicates the translation of results obtained in vitro to understanding the aggregation process in vivo. Here, we demonstrate that Aβ42 self-assembles into aggregates on membrane bilayers at low nanomolar concentrations - a pathway in which the membrane plays the role of a catalyst. Additionally, physiological ionic conditions (150 mM NaCl) significantly enhance on-membrane aggregation, leading to the rapid …

Exogenous Flupirtine As Potential Treatment For Cln3 Disease, Katia Maalouf, Joelle Makoukji, Sara Saab, Nadine J. Makhoul, Angelica V. Carmona, Nihar Kinarivala, Noël Ghanem, Paul C. Trippier, Rose-Mary Boustany

Journal Articles: Pharmaceutical Sciences

CLN3 disease is a fatal neurodegenerative disorder affecting children. Hallmarks include brain atrophy, accelerated neuronal apoptosis, and ceramide elevation. Treatment regimens are supportive, highlighting the importance of novel, disease-modifying drugs. Flupirtine and its new allyl carbamate derivative (compound 6) confer neuroprotective effects in CLN3-deficient cells. This study lays the groundwork for investigating beneficial effects in Cln3^Δex7/8 mice. WT/Cln3^Δex7/8 mice received flupirtine/compound 6/vehicle for 14 weeks. Short-term effect of flupirtine or compound 6 was tested using a battery of behavioral testing. For flupirtine, gene expression profiles, astrogliosis, and neuronal cell counts were determined. Flupirtine improved neurobehavioral parameters in …

Insight Into The Dynamics Of Apobec3g Protein In Complexes With Dna Assessed By High Speed Afm, Yangang Pan, Luda S. Shlyakhtenko, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

APOBEC3G (A3G) is a single-stranded DNA (ssDNA) binding protein that restricts the HIV virus by deamination of dC to dU during reverse transcription of the viral genome. A3G has two zinc-binding domains: the N-terminal domain (NTD), which efficiently binds ssDNA, and the C-terminal catalytic domain (CTD), which supports deaminase activity of A3G. Until now, structural information on A3G has been lacking, preventing elucidation of the molecular mechanisms underlying its interaction with ssDNA and deaminase activity. We have recently built a computational model for the full-length A3G monomer and validated its structure using data obtained by time-lapse High-Speed Atomic Force Microscopy …

Conformational Studies Of Glucose Transporter 1 (Glut1) As An Anticancer Drug Target, Suliman Almahmoud, Xiaofang Wang, Jonathan L. Vennerstrom, Haizhen A. Zhong

Journal Articles: Pharmaceutical Sciences

Glucose transporter 1 (GLUT1) is a facilitative glucose transporter overexpressed in various types of tumors; thus, it has been considered as an important target for cancer therapy. GLUT1 works through conformational switching from an outward-open (OOP) to an inward-open (IOP) conformation passing through an occluded conformation. It is critical to determine which conformation is preferred by bound ligands because the success of structure-based drug design depends on the appropriate starting conformation of the target protein. To find out the most favorable GLUT 1 conformation for ligand binding, we ran systemic molecular docking studies for different conformations of GLUT1 using known …

Spontaneous Self-Assembly Of Amyloid Β (1–40) Into Dimers, Mohtadin Hashemi, Yuliang Zhang, Zhengjian Lv, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The self-assembly and fibrillation of amyloid β (Aβ) proteins is the neuropathological hallmark of Alzheimer's disease. However, the molecular mechanism of how disordered monomers assemble into aggregates remains largely unknown. In this work, we characterize the assembly of Aβ (1–40) monomers into dimers using long-time molecular dynamics simulations. Upon interaction, the monomers undergo conformational transitions, accompanied by change of the structure, leading to the formation of a stable dimer. The dimers are stabilized by interactions in the N-terminal region (residues 5–12), in the central hydrophobic region (residues 16–23), and in the C-terminal region (residues 30–40); with inter-peptide interactions focused around …

Absolute Oral Bioavailability Of Creatine Monohydrate In Rats: Debunking A Myth, Eman A. Alraddadi, Ryan Lillico, Jonathan L. Vennerstrom, Ted M. Lakowski, Donald W. Miller

Journal Articles: Pharmaceutical Sciences

Creatine is an ergogenic compound used by athletes to enhance performance. Supplementation with creatine monohydrate (CM) has been suggested for musculoskeletal and neurological disorders. Until now, little is known about its pharmacokinetic profile. Our objective was to determine the oral bioavailability of CM and the influence of dose on oral absorption. Rats were dosed orally with low dose (10 mg/kg) or high dose (70 mg/kg)

The Enzymatic Activity Of Apobe3g Multimers, Yangang Pan, Karen Zagorski, Luda S. Shlyakhtenko, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

APOBEC3G (A3G) belongs to the family of cytosine deaminases that play an important role in the innate immune response. Similar to other, two-domain members of the APOBEC family, A3G is prone to concentration-dependent oligomerization, which is an integral for its function in the cell. It is shown that oligomerization of A3G is related to the packing mechanism into virus particle and, is critical for the so-called roadblock model during reverse transcription of proviral ssDNA. The role of oligomerization for deaminase activity of A3G is widely discussed in the literature; however, its relevance to deaminase activity for different oligomeric forms of …

Flupirtine Derivatives As Potential Treatment For The Neuronal Ceroid Lipofuscinoses, Joelle Makoukji, Fadi Saadeh, Karl Albert Mansour, Sally El-Sitt, Jamal Al Ali, Nihar Kinarivala, Paul C. Trippier, Rose-Mary Boustany

Journal Articles: Pharmaceutical Sciences

OBJECTIVE: Neuronal Ceroid Lipofuscinoses (NCL) are fatal inherited neurodegenerative diseases with established neuronal cell death and increased ceramide levels in brain, hence, a need for disease-modifying drug candidates, with potential to enhance growth, reduce apoptosis and lower ceramide in neuronal precursor PC12 cells and human NCL cell lines using enhanced flupirtine aromatic carbamate derivatives in vitro.

METHODS: Aromatic carbamate derivatives were tested by establishing growth curves under pro-apoptotic conditions and activity evaluated by trypan blue and JC-1 staining, as well as a drop in pro-apoptotic ceramide in neuronal precursor PC12 cells following siRNA knockdown of the

RESULTS: Retigabine, the benzyl-derivatized …

Nano-Assembly Of Amyloid Β Peptide: Role Of The Hairpin Fold., Sibaprasad Maity, Mohtadin Hashemi, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

Structural investigations have revealed that β hairpin structures are common features in amyloid fibrils, suggesting that these motifs play an important role in amyloid assembly. To test this hypothesis, we characterized the effect of the hairpin fold on the aggregation process using a model β hairpin structure, consisting of two Aβ(14-23) monomers connected by a turn forming YNGK peptide. AFM studies of the assembled aggregates revealed that the hairpin forms spherical structures whereas linear Aβ(14-23) monomers form fibrils. Additionally, an equimolar mixture of the monomer and the hairpin assembles into non-fibrillar aggregates, demonstrating that the hairpin fold dramatically changes the …

A Novel Pathway For Amyloids Self-Assembly In Aggregates At Nanomolar Concentration Mediated By The Interaction With Surfaces., Siddhartha Banerjee, Mohtadin Hashemi, Zhengjian Lv, Sibaprasad Maity, Jean-Christophe Rochet, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

A limitation of the amyloid hypothesis in explaining the development of neurodegenerative diseases is that the level of amyloidogenic polypeptide in vivo is below the critical concentration required to form the aggregates observed in post-mortem brains. We discovered a novel, on-surface aggregation pathway of amyloidogenic polypeptide that eliminates this long-standing controversy. We applied atomic force microscope (AFM) to demonstrate directly that on-surface aggregation takes place at a concentration at which no aggregation in solution is observed. The experiments were performed with the full-size Aβ protein (Aβ42), a decapeptide Aβ(14-23) and α-synuclein; all three systems demonstrate a dramatic preference of the …

Near Infrared Fluorescent Nanoparticles Derived From Hyaluronic Acid Improve Tumor Contrast For Image-Guided Surgery., Tanner K. Hill, Sneha S. Kelkar, Nicholas E. Wojtynek, Joshua J. Souchek, William M. Payne, Kristina Stumpf, Frank C. Marini, Aaron M. Mohs

Journal Articles: Pharmaceutical Sciences

Tumor tissue that remains undetected at the primary surgical site can cause tumor recurrence, repeat surgery, and treatment strategy alterations that impose a significant patient and healthcare burden. Intraoperative near infrared fluorescence (NIRF) imaging is one potential method to identify remaining tumor by visualization of NIR fluorophores that are preferentially localized to the tumor. This requires development of fluorophores that consistently identify tumor tissue in different patients and tumor types. In this study we examined a panel of NIRF contrast agents consisting of polymeric nanoparticle (NP) formulations derived from hyaluronic acid (HA), with either physically entrapped indocyanine green (ICG) or …

Apobec3g Interacts With Ssdna By Two Modes: Afm Studies., Luda S. Shlyakhtenko, Samrat Dutta, Jaspreet Banga, Ming Li, Reuben S. Harris, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

APOBEC3G (A3G) protein has antiviral activity against HIV and other pathogenic retroviruses. A3G has two domains: a catalytic C-terminal domain (CTD) that deaminates cytidine, and a N-terminal domain (NTD) that binds to ssDNA. Although abundant information exists about the biological activities of A3G protein, the interplay between sequence specific deaminase activity and A3G binding to ssDNA remains controversial. We used the topographic imaging and force spectroscopy modalities of Atomic Force Spectroscopy (AFM) to characterize the interaction of A3G protein with deaminase specific and nonspecific ssDNA substrates. AFM imaging demonstrated that A3G has elevated affinity for deaminase specific ssDNA than for …

Samhd1 Is A Single-Stranded Nucleic Acid Binding Protein With No Active Site-Associated Nuclease Activity., Kyle J. Seamon, Zhiqiang Sun, Luda S. Shlyakhtenko, Yuri L. Lyubchenko, James T. Stivers

Journal Articles: Pharmaceutical Sciences

The HIV-1 restriction factor SAMHD1 is a tetrameric enzyme activated by guanine nucleotides with dNTP triphosphate hydrolase activity (dNTPase). In addition to this established activity, there have been a series of conflicting reports as to whether the enzyme also possesses single-stranded DNA and/or RNA 3'-5' exonuclease activity. SAMHD1 was purified using three chromatography steps, over which the DNase activity was largely separated from the dNTPase activity, but the RNase activity persisted. Surprisingly, we found that catalytic and nucleotide activator site mutants of SAMHD1 with no dNTPase activity retained the exonuclease activities. Thus, the exonuclease activity cannot be associated with any …

Remodeling Of Recg Helicase At The Dna Replication Fork By Ssb Protein., Zhiqiang Sun, Hui Yin Tan, Piero R. Bianco, Yuri L. Lyubchenko

Journal Articles: Pharmaceutical Sciences

The RecG DNA helicase a key player in stalled replication fork rescue. The single-stranded DNA binding protein (SSB) participates in this process, but its role in the interaction of RecG with the fork remains unclear. We used atomic force microscopy (AFM) to visualize the interaction of RecG with a fork DNA in the presence of SSB. We discovered that SSB enhances RecG loading efficiency onto the DNA fork by threefold. Additionally, SSB interacts with RecG leading to the RecG remodeling. As a result, RecG separates from the fork, but remains bound to the DNA duplex. Moreover, in this new binding …