Biochemical characterization of the meiosis-essential yet evolutionarily divergent topoisomerase VIB-like protein MTOPVIB from Arabidopsis thaliana

Formation of programmed DNA double-strand breaks is essential for initiating meiotic recombination. Genetic studies on Arabidopsis thaliana and Mus musculus have revealed that assembly of a type IIB topoisomerase VI (Topo VI)-like complex, composed of SPO11 and MTOPVIB, is a prerequisite for generating DNA breaks. However, it remains enigmatic if MTOPVIB resembles its Topo VI subunit B (VIB) ortholog in possessing robust ATPase activity, ability to undergo ATP-dependent dimerization, and activation of SPO11-mediated DNA cleavage. Here, we successfully prepared highly pure A. thaliana MTOPVIB and MTOPVIB-SPO11 complex. Contrary to expectations, our findings highlight that MTOPVIB differs from orthologous Topo VIB by lacking ATP-binding activity and independently forming dimers without ATP. Most significantly, our study reveals that while MTOPVIB lacks the capability to stimulate SPO11-mediated DNA cleavage, it functions as a bona fide DNA-binding protein and plays a substantial role in facilitating the dsDNA binding capacity of the MOTOVIB-SPO11 complex. Thus, we illustrate mechanistic divergence between the MTOPVIB-SPO11 complex and classical type IIB topoisomerases.

Effect of Sulfotyrosine and Negatively Charged Amino Acid of Leech-Derived Peptides on Binding and Inhibitory Activity Against Thrombin

Hirudins, natural sulfo(glyco)proteins, are clinical anticoagulants that directly inhibit thrombin, a key coagulation factor. Their potent thrombin inhibition primarily results from antagonistic interactions with both the catalytic and non-catalytic sites of thrombin. Hirudins often feature sulfate moieties on Tyr residues in their anionic C-terminus region, enabling strong interactions with thrombin exosite-I and effectively blocking its engagement with fibrinogen. Although sulfotyrosines have been identified in various hirudin variants, the precise relationship between sulfotyrosine and the number of negatively charged amino acids within the anionic-rich C-terminus peptide domain for the binding of thrombin has remained elusive. By using Fmoc-SPPS, hirudin dodecapeptides homologous to the C-terminus of hirudin variants from various leech species were successfully synthesized, and the effect of sulfotyrosine and the number of negatively charged amino acids on hirudin-thrombin interactions was investigated. Our findings did not reveal any synergistic effect between an increasing number of sulfotyrosines or negatively charged amino acids and their inhibitory activity on thrombin or fibrinolysis in the assays, despite a higher binding level toward thrombin in the sulfated dodecapeptide Hnip_Hirudin was observed in SPR analysis.

Synthesis, evaluation, and mechanism of 1-(4-(arylethylenylcarbonyl)phenyl)-4-carboxy-2-pyrrolidinones as potent reversible SARS-CoV-2 entry inhibitors

A class of 1-(4-(arylethylenylcarbonyl)phenyl)-4-carboxy-2-pyrrolidinones were designed and synthesized via Michael addition, cyclization, aldol condensation, and deprotonation to inhibit the human transmembrane protease serine 2 (TMPRSS2) and Furin, which are involved in priming the SARS-CoV-2 Spike for virus entry. The most potent inhibitor 2f (81) was found to efficiently inhibit the replication of various SARS-CoV-2 delta and omicron variants in VeroE6 and Calu-3 cells, with EC50 range of 0.001-0.026 μM by pre-incubation with the virus to avoid the virus entry. The more potent antiviral activities than the proteases inhibitory activities led to discovery that the synthesized compounds also inhibited Spike's receptor binding domain (RBD):angiotensin converting enzyme 2 (ACE2) interaction as a main target, and their antiviral activities were enhanced by inhibiting TMPRSS2 and/or Furin. To further confirm the blocking effect of 2f (81) on virus entry, SARS-CoV-2 Spike pseudovirus was used in the entry assay and the results showed that the compound inhibited the pseudovirus entry in a ACE2-dependent pathway, via mainly inhibiting RBD:ACE2 interaction and TMPRSS2 activity in Calu-3 cells. Finally, in the in vivo animal model of SARS-CoV-2 infection, the oral administration of 25 mg/kg 2f (81) in hamsters resulted in reduced bodyweight loss and 5-fold lower viral RNA levels in nasal turbinate three days post-infection. Our findings demonstrated the potential of the lead compound for further preclinical investigation as a potential treatment for SARS-CoV-2.

Characterization and Crystal Structures of a Cubebol-Producing Sesquiterpene Synthase from Antrodia cinnamomea

Antrodia cinnamomea is an endemic species found in Taiwan, known for its medicinal properties in treating various discomforts, including inflammation, diarrhea, abdominal pain, and other diseases. A. cinnamomea contains terpenoids that exhibit numerous bioactivities, making them potential food additives. This discovery piqued our interest in uncovering their biosynthetic pathway. Herein, we conducted functional and structural characterization of a sesquiterpene synthase Cop4 from A. cinnamomea (AcCop4). Through gas chromatography-mass spectrometry analysis, we observed that AcCop4 catalyzes the cyclization of farnesyl pyrophosphate (FPP), primarily producing cubebol. Cubebol is widely used as a long-lasting cooling and refreshing agent in the food industry. The structure of AcCop4, complexed with pyrophosphate and magnesium ions, revealed the closure of the active site facilitated by R311. Interestingly, binding of pyrophosphate and magnesium ions did not cause any significant conformational change in the G1/2 helix of AcCop4, indicating that the apo form is not fully open. This high-resolution structure serves as a solid basis for understanding the biosynthetic mechanism of AcCop4 and supports further production and modification of cubebol for its applications in the food industry.

Acetylation-Mimic Mutation of TRIM28-Lys304 to Gln Attenuates the Interaction with KRAB-Zinc-Finger Proteins and Affects Gene Expression in Leukemic K562 Cells

TRIM28/KAP1/TIF1β is a crucial epigenetic modifier. Genetic ablation of trim28 is embryonic lethal, although RNAi-mediated knockdown in somatic cells yields viable cells. Reduction in TRIM28 abundance at the cellular or organismal level results in polyphenism. Posttranslational modifications such as phosphorylation and sumoylation have been shown to regulate TRIM28 activity. Moreover, several lysine residues of TRIM28 are subject to acetylation, but how acetylation of TRIM28 affects its functions remains poorly understood. Here, we report that, compared with wild-type TRIM28, the acetylation-mimic mutant TRIM28-K304Q has an altered interaction with Krüppel-associated box zinc-finger proteins (KRAB-ZNFs). The TRIM28-K304Q knock-in cells were created in K562 erythroleukemia cells by CRISPR-Cas9 (Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein nuclease 9) gene editing method. Transcriptome analysis revealed that TRIM28-K304Q and TRIM28 knockout K562 cells had similar global gene expression profiles, yet the profiles differed considerably from wild-type K562 cells. The expression levels of embryonic-related globin gene and a platelet cell marker integrin-beta 3 were increased in TRIM28-K304Q mutant cells, indicating the induction of differentiation. In addition to the differentiation-related genes, many zinc-finger-proteins genes and imprinting genes were activated in TRIM28-K304Q cells; they were inhibited by wild-type TRIM28 via binding with KRAB-ZNFs. These results suggest that acetylation/deacetylation of K304 in TRIM28 constitutes a switch for regulating its interaction with KRAB-ZNFs and alters the gene regulation as demonstrated by the acetylation mimic TRIM28-K304Q.

An FMEA model for risk assessment of university sustainability: using a combined ITARA with TOPSIS-AL approach based neutrosophic sets

It is necessary to emphasize both the process and results of performance management to find the balance between quality and quantity needed to ensure the sustainable development of universities to make the best use of limited educational resources and meet the diverse needs of students. This study applies failure mode and effects analysis (FMEA) to analyze obstacles to university sustainability by constructing complete risk assessment modes and reference indicators. The neutrosophic set theory was incorporated into the FMEA to account for information uncertainty and asymmetry. A specialist team then evaluated the importance of the risk factors using neutrosophic indifference threshold-based attribute ratio analysis to determine objective weights for the risk factors. Furthermore, the neutrosophic technique for order preference by similarity to the ideal solution based on aspiration level (N-TOPSIS-AL) is employed to aggregate the total risk scores of the failure modes. Using neutrosophic sets to measure truth, falsity, and indeterminacy in the assessment significantly improve the adaptability of the fuzzy theory to real-world problems. The study results indicate that when assessing university affairs management and analyzing possible risks, priority must be given to the occurrence of risks and that the lack of educational facilities is the riskiest item in the specialist assessment. The proposed assessment model can be applied as a basis for university sustainability assessments to accelerate the development of other forward-looking approaches.

A binding tie: why do customers stick to omnichannel retailers?

Purpose

This study employed the commitment–trust theory in social psychology and relationship marketing to explore female customers' perception of channel integration quality in omnichannel retailing and its influence on their relationship commitment to and trust in the relationship with retailers, and thus on their stickiness. Channel integration quality consists of two dimensions: channel service configuration (channel choice breadth and channel service transparency) and integrated interactions (content consistency, process consistency and perceived fluency).

Design/methodology/approach

The study was carried out via a questionnaire survey, to which 868 valid responses were collected. The partial least squares technique was used to test the hypotheses.

Findings

Channel service transparency and perceived fluency influence relationship commitment; content consistency, process consistency and perceived fluency all have significant effects on trust. Interestingly, although less influential than integrated interactions, channel service configuration is the foundation of channel integration quality, testifying to its significant role.

Originality/value

This study provides strong evidence on how channel integration quality affects customer stickiness. Moreover, this study replicates the finding of significant relationships among relationship commitment, trust and stickiness in omnichannel retailing.

Preparation of Cas9 Ribonucleoproteins for Genome Editing

Genome editing by the delivery of pre-assembled Cas9 ribonucleoproteins (Cas9 RNP) is an increasingly popular approach for cell types that are difficult to manipulate genetically by the conventional plasmid and viral methods. Cas9 RNP editing is robust, precise, capable of multiplexing, and free of genetic materials. Its transient presence in cells limits residual editing activity. This protocol describes the preparation of recombinant Streptococcus pyogenes Cas9 (SpCas9) protein by heterologous expression and purification from Escherichia coli, and the synthesis of CRISPR guide RNA by in vitro transcription and PAGE purification. SpCas9 is the first CRISPR Cas9 discovered ( Jinek et al., 2012 ) and is also one of the most characterized Cas enzymes for genome editing applications. Using this formulation of Cas9 RNP, we have demonstrated highly efficient genome editing in primary human T and natural killer (NK) cells by electroporation, and in fungi and plants by polyethylene glycol-mediated transformation. Our protocol of Cas9 RNP preparation is consistent and straightforward to adopt for genome editing in other cell types and organisms. Graphical abstract.

A chemical probe inhibitor targeting STAT1 restricts cancer stem cell traits and angiogenesis in colorectal cancer

Background

Colorectal cancer (CRC) is a worldwide cancer with rising annual incidence. New medications for patients with CRC are still needed. Recently, fluorescent chemical probes have been developed for cancer imaging and therapy. Signal transducer and activator of transcription 1 (STAT1) has complex functions in tumorigenesis and its role in CRC still needs further investigation.

Methods

RNA sequencing datasets in the NCBI GEO repository were analyzed to investigate the expression of STAT1 in patients with CRC. Xenograft mouse models, tail vein injection mouse models, and azoxymethane/dextran sodium sulfate (AOM/DSS) mouse models were generated to study the roles of STAT1 in CRC. A ligand-based high-throughput virtual screening approach combined with SWEETLEAD chemical database analysis was used to discover new STAT1 inhibitors. A newly designed and synthesized fluorescently labeled 4’,5,7-trihydroxyisoflavone (THIF) probe (BODIPY-THIF) elucidated the mechanistic actions of STAT1 and THIF in vitro and in vivo. Colonosphere formation assay and chick chorioallantoic membrane assay were used to evaluate stemness and angiogenesis, respectively.

Results

Upregulation of STAT1 was observed in patients with CRC and in mouse models of AOM/DSS-induced CRC and metastatic CRC. Knockout of STAT1 in CRC cells reduced tumor growth in vivo. We then combined a high-throughput virtual screening approach and analysis of the SWEETLEAD chemical database and found that THIF, a flavonoid abundant in soybeans, was a novel STAT1 inhibitor. THIF inhibited STAT1 phosphorylation and might bind to the STAT1 SH2 domain, leading to blockade of STAT1-STAT1 dimerization. The results of in vitro and in vivo binding studies of THIF and STAT1 were validated. The pharmacological treatment with BODIPY-THIF or ablation of STAT1 via a CRISPR/Cas9-based strategy abolished stemness and angiogenesis in CRC. Oral administration of BODIPY-THIF attenuated colitis symptoms and tumor growth in the mouse model of AOM/DSS-induced CRC.

Conclusions

This study demonstrates that STAT1 plays an oncogenic role in CRC. BODIPY-THIF is a new chemical probe inhibitor of STAT1 that reduces stemness and angiogenesis in CRC. BODIPY-THIF can be a potential tool for CRC therapy as well as cancer cell imaging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00803-4.

The functional characterization of phosphorylation of tristetraprolin at C-terminal NOT1-binding domain

Background

Tristetraprolin (TTP) family proteins contain conserved tandem CCCH zinc-finger binding to AU-rich elements and C-terminal NOT1-binding domain. TTP is phosphorylated extensively in cells, and its mRNA destabilization activity is regulated by protein phosphorylation.

Methods

We generated an antibody against phospho-Serine316 located at the C-terminal NOT1-binding site and examined TTP phosphorylation in LPS-stimulated RAW264.7 cells. Knockout of TTP was created in RAW264.7 cells using CRISPR/Cas9 gene editing to explore TTP functions.

Results

We demonstrated that Ser316 was phosphorylated by p90 ribosomal S6 kinase 1 (RSK1) and p38-activated protein kinase (MK2) and dephosphorylated by Protein Phosphatase 2A (PP2A). A phosphorylation-mimic mutant of S316D resulted in dissociation with the CCR4-NOT deadenylase complex through weakening interaction with CNOT1. Furthermore, Ser316 and serines 52 and 178 were independently contributed to the CCR4-NOT complex recruitment in the immunoprecipitation assay using phosphor-mimic mutants. In RAW264.7 macrophages, TTP was induced, and Ser316 was phosphorylated through RSK1 and MK2 by LPS stimulation. Knockout of TTP resulted in TNFα mRNA increased due to mRNA stabilization. Overexpression of non-phosphorylated S316A TTP mutant can restore TTP activity and lead to TNFα mRNA decreased. GST pull-down and RNA pull-down analyses demonstrated that endogenous TTP with Ser316 phosphorylation decreased the interaction with CNOT1.

Conclusions

Our results suggest that the TTP-mediated mRNA stability is modulated by Ser316 phosphorylation via regulating the TTP interaction with the CCR4-NOT deadenylase complex.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12950-021-00288-2.

Structural and bioinformatic analyses of Azemiops venom serine proteases reveal close phylogeographic relationships to pitvipers from eastern China and the New World

The semi-fossil and pit-less Azemiops feae is possibly the most primitive crotalid species. Here, we have cloned and sequenced cDNAs encoding four serine proteases (vSPs) from the venom glands of Chinese A. feae. Full amino-acid sequences of the major vSP (designated as AzKNa) and three minor vSPs (designated as AzKNb, AzKNc and Az-PA) were deduced. Using Protein-BLAST search, the ten most-similar vSPs for each Azemiops vSP have been selected for multiple sequence alignment, and all the homologs are crotalid vSPs. The results suggest that the A. feae vSPs are structurally most like those of eastern-Chinese Gloydius, Viridovipera, Protobothrops and North American pitvipers, and quite different from more-specialized vSPs such as Agkistrodon venom Protein-C activators. The vSPs from Chinese A. feae and those from Vietnamese A. feae show significant sequence variations. AzKNa is acidic and contains six potential N-glycosylation sites and its surface-charge distribution differs greatly from that of AzKNb, as revealed by 3D-modeling. AzKNb and AzKNc do not contain N-glycosylation sites although most of their close homologs contain one or two. Az-PA belongs to the plasminogen-activator subtype with a conserved N²⁰-glycosylation site. The evolution of this subtype of vSPs in Azemiops and related pitvipers has been traced by phylogenetic analysis.

TRIM28 Regulates Dlk1 Expression in Adipogenesis

The tripartite motif-containing protein 28 (TRIM28) is a transcription corepressor, interacting with histone deacetylase and methyltransferase complexes. TRIM28 is a crucial regulator in development and differentiation. We would like to investigate its function and regulation in adipogenesis. Knockdown of Trim28 by transducing lentivirus-carrying shRNAs impairs the differentiation of 3T3-L1 preadipocytes, demonstrated by morphological observation and gene expression analysis. To understand the molecular mechanism of Trim28-mediated adipogenesis, the RNA-seq was performed to find out the possible Trim28-regulated genes. Dlk1 (delta-like homolog 1) was increased in Trim28 knockdown 3T3-L1 cells both untreated and induced to differentiation. Dlk1 is an imprinted gene and known as an inhibitor of adipogenesis. Further knockdown of Dlk1 in Trim28 knockdown 3T3-L1 would rescue cell differentiation. The epigenetic analysis showed that DNA methylation of Dlk1 promoter and differentially methylated regions (DMRs) was not altered significantly in Trim28 knockdown cells. However, compared to control cells, the histone methylation on the Dlk1 promoter was increased at H3K4 and decreased at H3K27 in Trim28 knockdown cells. Finally, we found Trim28 might be recruited by transcription factor E2f1 to regulate Dlk1 expression. The results imply Trim28-Dlk1 axis is critical for adipogenesis.

Exploring the relationship between employee engagement and its antecedents: the moderating role of smartphone use

Purpose

This study empirically verified employee engagement (EE) as an outcome of organizational communication and confirmed that the formation of EE is strengthened when smartphone use (SU) is at a higher level.

Design/methodology/approach

A quantitative approach was used in this research, whereby 408 valid samples were collected with an online survey. The hypotheses of direct effects were tested using the structural equation modeling (SEM) procedure, and the moderating effects were tested using the unconstrained product indicator method and the PROCESS macro.

Findings

The results showed that EE was significantly influenced by person–organizationvalue fit (POVF), transformational leadership (TFL) and job autonomy (JA), and the effects of POVF and TFL were moderated significantly by SU. Although the influence of social support (SS) on EE was insignificant in the full model, SU moderated the effect of SS. The evidence also showed that work–family conflict (WFC) had no negative impact on EE.

Research limitations/implications

The participants of this study were restricted to a local area.

Practical implications

Organizations should develop job designs via two-way communication to bring up EE and SU can facilitate the process.

Originality/value

Previous research has identified EE as an outcome of organizational communication, but this concept has not yet been empirically verified. This research provides evidence to verify the above-mentioned concept and additionally confirms the moderating role of SU.

Dynamic eco-efficiency evaluation of the semiconductor industry: a sustainable development perspective

Serious environmental problems have accompanied remarkable global economic growth for decades. To assist managers in the semiconductor industry with economic and environmental management, this study executes DuPont analysis to examine economic impacts from the effective implementation of sustainability initiatives. We propose a two-stage process including economic development efficiency and environmental protection efficiency through the dynamic data envelopment analysis (DDEA) to reflect the characteristics of eco-efficiency. Through DuPont analysis, the main finding shows the potential improvement in firms' return on equity (ROE) by efficiently utilizing assets to generate sales quickly.Relative to economic development efficiency, the firms show lower scores and higher standard deviations in the environmental protection ability, thus denoting a large gap in the level of environmental protection production technology. The findings in this study reveal that the financial foundations and sustainable development of industries should be improved simultaneously even though specific levels of semiconductor industrial eco-efficiency improvement vary among companies in Taiwan.

CoII(Chromomycin)₂ Complex Induces a Conformational Change of CCG Repeats from i-Motif to Base-Extruded DNA Duplex

We have reported the propensity of a DNA sequence containing CCG repeats to form a stable i-motif tetraplex structure in the absence of ligands. Here we show that an i-motif DNA sequence may transition to a base-extruded duplex structure with a GGCC tetranucleotide tract when bound to the (Co^II)-mediated dimer of chromomycin A3, Co^II(Chro)₂. Biophysical experiments reveal that CCG trinucleotide repeats provide favorable binding sites for Co^II(Chro)₂. In addition, water hydration and divalent metal ion (Co^II) interactions also play a crucial role in the stabilization of CCG trinucleotide repeats (TNRs). Our data furnish useful structural information for the design of novel therapeutic strategies to treat neurological diseases caused by repeat expansions.

[Association between hypertension and serum microRNA21 and microRNA133a in ocean seamen]

OBJECTIVE

To investigate the prevalence of hypertension in ocean seamen and major influencing factors, as well as the association between hypertension and serum microRNA21 and microRNA133a.

METHODS

Health examination and a questionnaire survey were performed for 780 ocean seamen who underwent physical examination in an international travel healthcare center in Fujian, China from January to June, 2014. TaqMan RT-qPCR was used to measure the serum levels of microRNA21 and microRNA133a in seamen with hypertension.

RESULTS

The prevalence of hypertension differed significantly between the ocean seamen with different ages, education levels, marital status, body mass index (BMI) values, drinking frequencies, and numbers of sailing years (P<0.05). The prevalence rate of hypertension in the ocean seamen increased with the increasing drinking frequency (χ(2)=9.02, P<0.05) , decreased with the increase in degree of education (χ(2)=11.578, P<0.05) , and increased with the increase in the number of sailing years (χ(2)=28.06, P<0.05). The hypertensive ocean seamen had significantly higher expression levels of microRNA21 and MicroRNA133a than the healthy ocean seamen (microRNA21: 7.87±5.46 vs 1.03±0.80, P<0.05; MicroRNA133a: 7.45±1.94 vs 4.52±1.15, P<0.05). The multivariate analysis showed that a high level of microRNA21 (OR=1.61, 95% CI: 1.22~2.11) , a high level of microRNA133a (OR=1.52, 95% CI: 1.24~1.87) , drinking (OR=1.64, 95% CI: 1.08~2.50) , overweight based on BMI (OR=1.18, 95%CI: 1.07~1.30) , and many sailing years (OR=2.89, 95% CI: 1.14~7.30) were risk factors for hypertension.

CONCLUSION

The prevention and treatment of hypertension in ocean seamen should be enhanced. Excessive drinking should be controlled, and sailing time should be arranged reasonably. The microRNA21 and microRNA133a may be associated with the development and progression of hypertension in ocean seamen.

Identification, synthesis and evaluation of SARS-CoV and MERS-CoV 3C-like protease inhibitors

Severe acute respiratory syndrome (SARS) led to a life-threatening form of atypical pneumonia in late 2002. Following that, Middle East Respiratory Syndrome (MERS-CoV) has recently emerged, killing about 36% of patients infected globally, mainly in Saudi Arabia and South Korea. Based on a scaffold we reported for inhibiting neuraminidase (NA), we synthesized the analogues and identified compounds with low micromolar inhibitory activity against 3CL(pro) of SARS-CoV and MERS-CoV. Docking studies show that a carboxylate present at either R(1) or R(4) destabilizes the oxyanion hole in the 3CL(pro). Interestingly, 3f, 3g and 3m could inhibit both NA and 3CL(pro) and serve as a starting point to develop broad-spectrum antiviral agents.

Upregulation of Haploinsufficient Gene Expression in the Brain by Targeting a Long Non-coding RNA Improves Seizure Phenotype in a Model of Dravet Syndrome

Dravet syndrome is a devastating genetic brain disorder caused by heterozygous loss-of-function mutation in the voltage-gated sodium channel gene SCN1A. There are currently no treatments, but the upregulation of SCN1A healthy allele represents an appealing therapeutic strategy. In this study we identified a novel, evolutionary conserved mechanism controlling the expression of SCN1A that is mediated by an antisense non-coding RNA (SCN1ANAT). Using oligonucleotide-based compounds (AntagoNATs) targeting SCN1ANAT we were able to induce specific upregulation of SCN1A both in vitro and in vivo, in the brain of Dravet knock-in mouse model and a non-human primate. AntagoNAT-mediated upregulation of Scn1a in postnatal Dravet mice led to significant improvements in seizure phenotype and excitability of hippocampal interneurons. These results further elucidate the pathophysiology of Dravet syndrome and outline a possible new approach for the treatment of this and other genetic disorders with similar etiology.

Role of the RAD51-SWI5-SFR1 Ensemble in homologous recombination

During DNA double-strand break and replication fork repair by homologous recombination, the RAD51 recombinase catalyzes the DNA strand exchange reaction via a helical polymer assembled on single-stranded DNA, termed the presynaptic filament. Our published work has demonstrated a dual function of the SWI5-SFR1 complex in RAD51-mediated DNA strand exchange, namely, by stabilizing the presynaptic filament and maintaining the catalytically active ATP-bound state of the filament via enhancement of ADP release. In this study, we have strived to determine the basis for physical and functional interactions between Mus musculus SWI5-SFR1 and RAD51. We found that SWI5-SFR1 preferentially associates with the oligomeric form of RAD51. Specifically, a C-terminal domain within SWI5 contributes to RAD51 interaction. With specific RAD51 interaction defective mutants of SWI5-SFR1 that we have isolated, we show that the physical interaction is indispensable for the stimulation of the recombinase activity of RAD51. Our results thus help establish the functional relevance of the trimeric RAD51-SWI5-SFR1 complex and provide insights into the mechanistic underpinnings of homology-directed DNA repair in mammalian cells.

Predominant structural configuration of natural antibody repertoires enables potent antibody responses against protein antigens

Humoral immunity against diverse pathogens is rapidly elicited from natural antibody repertoires of limited complexity. But the organizing principles underlying the antibody repertoires that facilitate this immunity are not well-understood. We used HER2 as a model immunogen and reverse-engineered murine antibody response through constructing an artificial antibody library encoded with rudimentary sequence and structural characteristics learned from high throughput sequencing of antibody variable domains. Antibodies selected in vitro from the phage-displayed synthetic antibody library bound to the model immunogen with high affinity and specificities, which reproduced the specificities of natural antibody responses. We conclude that natural antibody structural repertoires are shaped to allow functional antibodies to be encoded efficiently, within the complexity limit of an individual antibody repertoire, to bind to diverse protein antigens with high specificity and affinity. Phage-displayed synthetic antibody libraries, in conjunction with high-throughput sequencing, can thus be designed to replicate natural antibody responses and to generate novel antibodies against diverse antigens.

Galectin-3 Binding Protein and Galectin-1 Interaction in Breast Cancer Cell Aggregation and Metastasis

Galectin-3 binding protein (Gal-3BP) is a large hyperglycosylated protein that acts as a ligand for several galectins through glycan-dependent interactions. Gal-3BP can induce galectin-mediated tumor cell aggregation to increase the survival of cancer cells in the bloodstream during the metastatic process. However, the galectin interacting with Gal-3BP and its binding specificity has not been identified and structurally elucidated, mainly due to the limitation of mass spectrometry in glycan sequencing. To understand the role of Gal-3BP, we here used liquid chromatography-mass spectrometry combined with specific exoglycosidase reactions to determine the sequences of N-glycans on Gal-3BP from MCF-7 and MDA-MB-231 cells, especially the sequences with terminal sialylation and fucosylation, and addition of LacNAc repeat structures. The N-glycans from both strains are complex type with terminal α2,3-sialidic acid and core fucose linkages, with additional α1,2- and α1,3 fucose linkages found in MCF-7 cells. Compared with that from MCF-7, the Gal-3BP from MDA-MB-231 cells had fewer tetra-antennary structures, only α1,6-linked core fucoses, and more LacNAc repeat structures; the MDA-MB-231 cells had no surface galectin-3 but used surface galectin-1 for interaction with Gal-3BP to form large oligomers and cell aggregates. This study elucidates the specificity of Gal-3BP interacting with galectin-1 and the role of Gal-3BP in cancer cell aggregation and metastasis.

Functional Relationship of ATP Hydrolysis, Presynaptic Filament Stability, and Homologous DNA Pairing Activity of the Human Meiotic Recombinase DMC1

DMC1 and RAD51 are conserved recombinases that catalyze homologous recombination. DMC1 and RAD51 share similar properties in DNA binding, DNA-stimulated ATP hydrolysis, and catalysis of homologous DNA strand exchange. A large body of evidence indicates that attenuation of ATP hydrolysis leads to stabilization of the RAD51-ssDNA presynaptic filament and enhancement of DNA strand exchange. However, the functional relationship of ATPase activity, presynaptic filament stability, and DMC1-mediated homologous DNA strand exchange has remained largely unexplored. To address this important question, we have constructed several mutant variants of human DMC1 and characterized them biochemically to gain mechanistic insights. Two mutations, K132R and D223N, that change key residues in the Walker A and B nucleotide-binding motifs ablate ATP binding and render DMC1 inactive. On the other hand, the nucleotide-binding cap D317K mutant binds ATP normally but shows significantly attenuated ATPase activity and, accordingly, forms a highly stable presynaptic filament. Surprisingly, unlike RAD51, presynaptic filament stabilization achieved via ATP hydrolysis attenuation does not lead to any enhancement of DMC1-catalyzed homologous DNA pairing and strand exchange. This conclusion is further supported by examining wild-type DMC1 with non-hydrolyzable ATP analogues. Thus, our results reveal an important mechanistic difference between RAD51 and DMC1.

Mechanisms to motivate knowledge sharing: integrating the reward systems and social network perspectives

Purpose

– The purpose of this study is to develop a theoretical model that integrates two different mechanisms to explain knowledge sharing. First, adapted from traditional reward systems, the calculative-based mechanism (CBM) serves as the benchmark. Second, the relational-based mechanism (RBM) plays a complementary role. RBM is founded on social interaction and consists of two social network constructs: relational deposits (i.e. network and valued network centralities) and withdrawals (i.e. network and valued network densities).

Design/methodology/approach

– This study collected survey data in collaboration with a health-care organization. The data collected from 180 respondents were tested against the research model using a partial least squares analysis.

Findings

– This study found the CBM to be beneficial for knowledge sharing. The findings support the RBM prediction of a positive relationship between the deposit construct and knowledge sharing, but fail to support the RBM prediction on the withdrawal construct. The RBM explained about 15 per cent more of the variance than the CBM. In addition, the withdrawal construct of the RBM predicts respondents’ beliefs in reciprocal obligation.

Research limitations/implications

– RBM does not as strongly associate with economic benefits as the CBM, but it still plays a noteworthy role in increasing the possibility of an individual knowledge sharing.

Originality/value

– The study is the first to propose the concepts of relational deposits and withdrawals. The authors use a roster-based sociometric approach to collect the social network data and to benchmark the effect of RBM with that of CBM on individual knowledge sharing and his/her beliefs in reciprocal obligation.

Role of N-linked glycans in the interactions of recombinant HCV envelope glycoproteins with cellular receptors

Hepatitis C virus (HCV) infection is a major cause of chronic hepatitis and hepatocellular carcinoma. It infects human liver cells through several cellular protein receptors including CD81, SR-BI, claudin-1, and occludin. Previous reports also show that lectin receptors can mediate HCV recognition and entry. The envelope proteins of HCV (E1 and E2) are heavily glycosylated, further indicating the possible roles of lectin receptor-virus interaction in HCV infection. However, there is limited study investigating the relationship of HCV envelope glycoproteins and lectin as well as non-lectin receptors. Here we used surface plasmon resonance to examine the binding affinity of different glycoforms of recombinant HCV envelope protein to receptors and inspected the infectivity and assembly of HCV pseudoparticles composed of different glycoforms of envelope proteins. Our results indicated that DC-SIGN, L-SIGN, and Langerin had higher affinity to recombinant HCV envelope proteins in the presence of calcium ions than non-lectin receptors, and envelope proteins with Man8/9 N-glycans showed approximate 10-fold better binding to lectin receptors than envelope proteins with Man5 and complex type N-glycans. Interestingly, comparing among glycoforms, recombinant envelope proteins with Man5 N-glycans showed the highest binding affinity when interacting with non-lectin receptors. In summary, the glycans on HCV envelope protein play a modulatory role in HCV assembly and infection and direct HCV-receptor interaction, which mediates viral entry in different cells. Receptors with high affinity to HCV envelope proteins may be considered as targets for development of a therapeutic strategy against HCV.

Highly efficient beamline and spectrometer for inelastic soft X-ray scattering at high resolution

The design, construction and commissioning of a beamline and spectrometer for inelastic soft X-ray scattering at high resolution in a highly efficient system are presented. Based on the energy-compensation principle of grating dispersion, the design of the monochromator-spectrometer system greatly enhances the efficiency of measurement of inelastic soft X-rays scattering. Comprising two bendable gratings, the set-up effectively diminishes the defocus and coma aberrations. At commissioning, this system showed results of spin-flip, d-d and charge-transfer excitations of NiO. These results are consistent with published results but exhibit improved spectral resolution and increased efficiency of measurement. The best energy resolution of the set-up in terms of full width at half-maximum is 108 meV at an incident photon energy tuned about the Ni L3-edge.

Enhancement of ADP release from the RAD51 presynaptic filament by the SWI5-SFR1 complex

Homologous recombination catalyzed by the RAD51 recombinase eliminates deleterious DNA lesions from the genome. In the presence of ATP, RAD51 forms a nucleoprotein filament on single-stranded DNA, termed the presynaptic filament, to initiate homologous recombination-mediated DNA double-strand break repair. The SWI5-SFR1 complex stabilizes the presynaptic filament and enhances its ability to mediate the homologous DNA pairing reaction. Here we characterize the RAD51 presynaptic filament stabilization function of the SWI5-SFR1 complex using optical tweezers. Biochemical experiments reveal that SWI5-SFR1 enhances ATP hydrolysis by single-stranded DNA-bound RAD51. Importantly, we show that SWI5-SFR1 acts by facilitating the release of ADP from the presynaptic filament. Our results thus provide mechanistic understanding of the function of SWI5-SFR1 in RAD51-mediated DNA recombination.

Moiety-linkage map reveals selective nonbisphosphonate inhibitors of human geranylgeranyl diphosphate synthase

Bisphosphonates are potent inhibitors of farnesyl pyrophosphate synthase (FPPS) and geranylgeranyl diphosphate synthase (GGPPS). Current bisphosphonate drugs (e.g., Fosamax and Zometa) are highly efficacious in the treatment of bone diseases such as osteoporosis, Paget's disease, and tumor-induced osteolysis, but they are often less potent in blood and soft-tissue due to their phosphate moieties. The discovery of nonbisphosphonate inhibitors of FPPS and/or GGPPS for the treatment of bone diseases and cancers is, therefore, a current goal. Here, we propose a moiety-linkage-based method, combining a site-moiety map with chemical structure rules (CSRs), to discover nonbisphosphonate inhibitors from thousands of commercially available compounds and known crystal structures. Our moiety-linkage map reveals the binding mechanisms and inhibitory efficacies of 51 human GGPPS (hGGPPS) inhibitors. To the best of our knowledge, we are the first team to discover two novel selective nonbisphosphonate inhibitors, which bind to the inhibitory site of hGGPPS, using CSRs and site-moiety maps. These two compounds can be considered as a novel lead for the potent inhibitors of hGGPPS for the treatment of cancers and mevalonate-pathway diseases. Moreover, based on our moiety-linkage map, we identified two key residues of hGGPPS, K202, and K212, which play an important role for the inhibitory effect of zoledronate (IC50 = 3.4 μM and 2.4 μM, respectively). This result suggests that our method can discover specific hGGPPS inhibitors across multiple prenyltransferases. These results show that the compounds that highly fit our moiety-linkage map often inhibit hGGPPS activity and induce tumor cell apoptosis. We believe that our method is useful for discovering potential inhibitors and binding mechanisms for pharmaceutical targets.

Functional attributes of the Saccharomyces cerevisiae meiotic recombinase Dmc1

The role of Dmc1 as a meiosis-specific general recombinase was first demonstrated in Saccharomyces cerevisiae. Progress in understanding the biochemical mechanism of ScDmc1 has been hampered by its tendency to form inactive aggregates. We have found that the inclusion of ATP during protein purification prevents Dmc1 aggregation. ScDmc1 so prepared is capable of forming D-loops and responsive to its accessory factors Rad54 and Rdh54. Negative staining electron microscopy and iterative helical real-space reconstruction revealed that the ScDmc1-ssDNA nucleoprotein filament harbors 6.5 protomers per turn with a pitch of ∼106Å. The ScDmc1 purification procedure and companion molecular analyses should facilitate future studies on this recombinase.

Control activity of yeast geranylgeranyl diphosphate synthase from dimer interface through H-bonds and hydrophobic interaction

Previously we showed that yeast geranylgeranyl diphosphate synthase (GGPPS) becomes an inactive monomer when the first N-terminal helix involved in dimerization is deleted. This raises questions regarding why dimerization is required for GGPPS activity and which amino acids in the dimer interface are essential for dimerization-mediated activity. According to the GGPPS crystal structure, three amino acids (N101, N104, and Y105) located in the helix F of one subunit are near the active site of the other subunit. As presented here, when these residues were replaced individually with Ala caused insignificant activity changes, N101A/Y105A and N101A/N104A but not N104A/Y105A showed remarkably decreased k(cat) values (200-250-fold). The triple mutant N101A/N104A/Y105A displayed no detectable activity, although dimer was retained in these mutants. Because N101 and Y105 form H-bonds with H139 and R140 in the other subunit, respectively, we generated H139A/R140A double mutant and found it was inactive and became monomeric. Therefore, the multiple mutations apparently influence the integrity of the catalytic site due to the missing H-bonding network. Moreover, Met111, also on the highly conserved helix F, was necessary for dimer formation and enzyme activity. When Met111 was replaced with Glu, the negative-charged repulsion converted half of the dimer into a monomer. In conclusion, the H-bonds mainly through N101 for maintaining substrate binding stability and the hydrophobic interaction of M111 in dimer interface are essential for activity of yeast GGPPS.

Enhancing a cancer prevention and control curriculum through interactive group discussions

The Principles and Practice of Cancer Prevention and Control course (Principles course) is offered annually by the National Cancer Institute Cancer Prevention Fellowship Program. This 4-week postgraduate course covers the spectrum of cancer prevention and control research (e.g., epidemiology, laboratory, clinical, social, and behavioral sciences) and is open to attendees from medical, academic, government, and related institutions across the world. In this report, we describe a new addition to the Principles course syllabus, which was exclusively a lecture-based format for over 20 years. In 2011, cancer prevention fellows and staff designed and implemented small group discussion sessions as part of the curriculum. The goals of these sessions were to foster an interactive environment, discuss concepts presented during the Principles course, exchange ideas, and enhance networking among the course participants and provide a teaching and leadership opportunity to current cancer prevention fellows. Overall, both the participants and facilitators who returned the evaluation forms (n=61/87 and 8/10, respectively) reported a high satisfaction with the experience for providing both an opportunity to explore course concepts in a greater detail and to network with colleagues. Participants (93%) and facilitators (100%) stated that they would like to see this component remain a part of the Principles course curriculum, and both groups provided recommendations for the 2012 program. The design, implementation, and evaluation of this initial discussion group component of the Principles course are described herein. The findings in this report will not only inform future discussion group sessions in the Principles course but may also be useful to others planning to incorporate group learning into large primarily lecture-based courses.

Rad51 presynaptic filament stabilization function of the mouse Swi5-Sfr1 heterodimeric complex

Homologous recombination (HR) represents a major error-free pathway to eliminate pre-carcinogenic chromosomal lesions. The DNA strand invasion reaction in HR is mediated by a helical filament of the Rad51 recombinase assembled on single-stranded DNA that is derived from the nucleolytic processing of the primary lesion. Recent studies have found that the human and mouse Swi5 and Sfr1 proteins form a complex that influences Rad51-mediated HR in cells. Here, we provide biophysical evidence that the mouse Swi5–Sfr1 complex has a 1:1 stoichiometry. Importantly, the Swi5–Sfr1 complex, but neither Swi5 nor Sfr1 alone, physically interacts with Rad51 and stimulates Rad51-mediated homologous DNA pairing. This stimulatory effect stems from the stabilization of the Rad51–ssDNA presynaptic filament. Moreover, we provide evidence that the RSfp (rodent Sfr1 proline rich) motif in Sfr1 serves as a negative regulatory element. These results thus reveal an evolutionarily conserved function in the Swi5–Sfr1 complex and furnish valuable information as to the regulatory role of the RSfp motif that isspecific to themammalianSfr1 orthologs.

Generation of a novel factor IX with augmented clotting activities in vitro and in vivo

BACKGROUND

Hemophilia B is an X-linked inherited disorder caused by the lack of functional factor IX (FIX). Currently, treatment of hemophilia B is performed by intravenous infusion of plasma-derived or recombinant FIX.

OBJECTIVE

In an effort to reduce factor usage and cost, we investigated the potential use of FIX variants with enhanced specific clotting activity.

METHODS

Seven recombinant FIX variants using alanine replacement were generated and assayed for their activity in vitro and in vivo.

RESULTS

One variant containing three substitutions (V86A/E277A/R338A, FIX-Triple) exhibited 13-fold higher specific clotting activity and a 10-fold increased affinity for human FVIIIa compared with FIX-wild-type (FIX-WT) and was thus investigated systematically in vivo. Liver-specific FIX-Triple gene expression following hydrodynamic plasmid delivery revealed a 3.5-fold higher specific clotting activity compared with FIX-WT. Human FIX-Triple and FIX-WT knock-in mice were generated and it was confirmed that FIX-Triple has 7-fold higher specific clotting activity than FIX-WT under normal physiological conditions. Protein infusion of FIX-Triple into hemophilia B mice resulted in greater improvement of hemostasis than that achieved with FIX-WT. Moreover, tail-vein administration of a serotype 8 recombinant Adeno-associated vector (AAV8) expressing either FIX-WT or FIX-Triple in hemophilia B mice demonstrated a 7-fold higher specific clotting activity of FIX-Triple than FIX-WT.

CONCLUSIONS

Our results indicate that the FIX-Triple variant exhibits significantly enhanced clotting activity relative to FIX-WT due to tighter binding to FVIIIa, as demonstrated both in vitro and in vivo. Therefore, FIX-Triple is a good candidate for further evaluation in protein replacement therapy as well as gene-based therapeutic strategies.

First measurement of Bose-Einstein correlations in proton-proton collisions at √s=0.9 and 2.36 TeV at the LHC

Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 and 2.36 TeV center-of-mass energies, recorded by the CMS experiment at the CERN Large Hadron Collider. The signal is observed in the form of an enhancement of pairs of same-sign charged particles with small relative four-momentum. The size of the correlated particle emission region is seen to increase significantly with the particle multiplicity of the event.

Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at square root of s = 7 TeV

Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at square root of s = 7  TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity dN(ch)/dη|(|η|<0.5) = 5.78 ± 0.01(stat) ± 0.23(syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from square root of s = 0.9 to 7 TeV is [66.1 ± 1.0(stat) ± 4.2(syst)]%. The mean transverse momentum is measured to be 0.545 ± 0.005(stat) ± 0.015(syst)  GeV/c. The results are compared with similar measurements at lower energies.

On the mechanism of oscillations in the "beating mercury heart"

The discovery of a class of electrochemical-mechanical oscillators-similar to the beating mercury heart -are reported and characterized. Chemical and physical effects on the voltage-time oscillations in these systems have been measured and a mechanism consistent with these effects is given. Interesting cross-catalytic effects involving the electrocapillarity of mercury are proposed to be the origin of the oscillations in these systems.

Fabrication and temperature-dependent photoluminescence of silicon-silicon oxide core-shell nanoparticle thin film

A novel Si nanocrystals embedded SiO2 thin film has been fabricated by the synthesis of Si-SiO2 core-shell (Si@SiO2) nanoparticles via the surface SiO2 coating of Si nanocrystals and the followed drop-coating on a silicon wafer. The resultant Si@SiO2 nanoparticles had a mean diameter of 30.43 +/- 2.63 nm and a mean shell thickness of 13.16 nm. They exhibited a stronger peak around 360 nm and a weaker green-yellow emission around 530 nm. The 360 nm peak could be attributed to the electron-hole recombination in the Si cores and that via the oxide-related defects originally present on the surface of oxide-passivated Si cores, while the green-yellow emission might be attributed to the transfer of the electron-hole pairs generated in the Si cores across the core-shell interface and the followed recombination in the SiO2 shells. The resultant Si@SiO2 nanoparticle thin film had a mean grain size of about 100 nm. It showed not only blue emission and green-yellow emission but also red emission which might be due to the transfer of the electron-hole pairs generated in the Si cores across the core-shell interface and the followed recombination via the Si==O double bonds at the particle surface. Because blue emission was significant relatively, both the Si@SiO2 nanoparticles and Si@SiO2 nanoparticle thin film still exhibited bright blue fluorescence under UV excitation. In addition, by investigating the temperature dependence of photoluminescence in the temperature range of 77 to 297 K, the nature of photoluminescence from the Si@SiO2 nanoparticle thin film was also clarified.

Electro-optic narrowband multi-wavelength filter in aperiodically poled lithium niobate

We report on an iterative design scheme for and the first experimental demonstration of active narrowband multi-wavelength filters based on aperiodically poled lithium niobate crystals. A simultaneous transmission of 8 wavelengths, each with a ~0.45-nm linewidth and nearly 100% peak transmittance, was achieved in such a device. The transmission spectrum of this device can be tuned by temperature at a rate of ~0.65 nm/ degrees C.

A text input system developed by using lips image recognition based LabVIEW for the seriously disabled

In this paper, we present a text input system for the seriously disabled by using lips image recognition based on LabVIEW. This system can be divided into the software subsystem and the hardware subsystem. In the software subsystem, we adopted the technique of image processing to recognize the status of mouth-opened or mouth-closed depending the relative distance between the upper lip and the lower lip. In the hardware subsystem, parallel port built in PC is used to transmit the recognized result of mouth status to the Morse-code text input system. Integrating the software subsystem with the hardware subsystem, we implement a text input system by using lips image recognition programmed in LabVIEW language. We hope the system can help the seriously disabled to communicate with normal people more easily.

Structure and mechanism of Helicobacter pylori fucosyltransferase. A basis for lipopolysaccharide variation and inhibitor design

Helicobacter pylori alpha1,3-fucosyltransferase (FucT) is involved in catalysis to produce the Lewis x trisaccharide, the major component of the bacteria's lipopolysaccharides, which has been suggested to mimic the surface sugars in gastric epithelium to escape host immune surveillance. We report here three x-ray crystal structures of FucT, including the FucT.GDP-fucose and FucT.GDP complexes. The protein structure is typical of the glycosyltransferase-B family despite little sequence homology. We identified a number of catalytically important residues, including Glu-95, which serves as the general base, and Glu-249, which stabilizes the developing oxonium ion during catalysis. The residues Arg-195, Tyr-246, Glu-249, and Lys-250 serve to interact with the donor substrate, GDP-fucose. Variations in the protein and ligand conformations, as well as a possible FucT dimer, were also observed. We propose a catalytic mechanism and a model of polysaccharide binding not only to explain the observed variations in H. pylori lipopolysaccharides, but also to facilitate the development of potent inhibitors.

Intramuscular rather than oral administration of replication-defective adenoviral vaccine vector induces specific CD8+ T cell responses in the gut

Gut-associated lymphoid tissue (GALT) is the primary replication site for HIV-1, resulting in a pronounced CD4(+) T cell loss in this tissue during primary infection. A mucosal vaccine that generates HIV-specific CD8(+) T cells in the gut could prevent the establishment of founder populations and broadcasting of virus. Here, we immunized mice orally and systemically with a chimpanzee derived adenoviral vector expressing HIV gag (AdC68gag) and measured frequencies of gag-specific interferon-gamma (IFN-gamma) producing CD8(+) T cells in the GALT. A single oral administration was inefficient at eliciting responses in the mesenteric lymph nodes and Peyer's Patches, while a single intramuscular administration elicited strong systemic and detectable mucosal responses. The gag-specific CD8(+) T cell responses were present in both acute and memory phases following intramuscular administration.

Carboxyl terminus of Helicobacter pylori alpha1,3-fucosyltransferase determines the structure and stability

Helicobacter pylori is well known as the primary cause of gastritis, duodenal ulcers, and gastric cancer. The pathogenic bacteria produces Lewis x and Lewis y epitopes in the O-antigens of lipopolysaccharides to mimic the carbohydrate antigens of gastric epithelial cells to avoid detection by the host's immune system. The enzyme alpha1,3-fucosyltransferase from H. pylori catalyzes the glycosyl addition of fucose from the donor GDP-fucose to the acceptor N-acetyllactosamine. The poor solubility of the enzyme was resolved by systematic deletion of the C-terminus. We report here the first structural analysis using CD spectroscopy and analytical ultracentrifugation. The results indicate that up to 80 residues, including the tail rich in hydrophobic and positively charged residues (sequence 434-478) and 5 of the 10 tandem repeats of 7 amino acids each (399-433), can be removed without significant change in structure and catalysis. Half of the heptad repeats are required to maintain both the secondary and native quaternary structures. Removal of more residues in the C-terminus led to major structural alteration, which was correlated with the loss of enzymatic activity. In accordance with the thermal denaturation studies, the results support the idea that a higher number of tandem repeats functioning to facilitate a dimeric structure helps to prevent the protein from unfolding during incubation at higher temperatures.