An siRNA-based microbicide protects mice from lethal herpes simplex virus 2 infection

Herpes simplex virus 2 (HSV-2) infection causes significant morbidity and is an important cofactor for the transmission of HIV infection. A microbicide to prevent sexual transmission of HSV-2 would contribute substantially to controlling the spread of HIV and other infections. Because RNA interference (RNAi) provides effective antiviral defence in plants and other organisms, several studies have focused on harnessing RNAi to inhibit viral infection. Here we show that vaginal instillation of small interfering RNAs (siRNAs) targeting HSV-2 protects mice from lethal infection. siRNAs mixed with lipid are efficiently taken up by epithelial and lamina propria cells and silence gene expression in the mouse vagina and ectocervix for at least nine days. Intravaginal application of siRNAs targeting the HSV-2 UL27 and UL29 genes (which encode an envelope glycoprotein and a DNA binding protein, respectively) was well tolerated, did not induce interferon-responsive genes or cause inflammation, and protected mice when administered before and/or after lethal HSV-2 challenge. These results suggest that siRNAs are attractive candidates for the active component of a microbicide designed to prevent viral infection or transmission.

Ten years of dengue drug discovery: progress and prospects

To combat neglected diseases, the Novartis Institute of Tropical Diseases (NITD) was founded in 2002 through private-public funding from Novartis and the Singapore Economic Development Board. One of NITD's missions is to develop antivirals for dengue virus (DENV), the most prevalent mosquito-borne viral pathogen. Neither vaccine nor antiviral is currently available for DENV. Here we review the progress in dengue drug discovery made at NITD as well as the major discoveries made by academia and other companies. Four strategies have been pursued to identify inhibitors of DENV through targeting both viral and host proteins: (i) HTS (high-throughput screening) using virus replication assays; (ii) HTS using viral enzyme assays; (iii) structure-based in silico docking and rational design; (iv) repurposing hepatitis C virus inhibitors for DENV. Along the developmental process from hit finding to clinical candidate, many inhibitors did not advance beyond the stage of hit-to-lead optimization, due to their poor selectivity, physiochemical or pharmacokinetic properties. Only a few compounds showed efficacy in the AG129 DENV mouse model. Two nucleoside analogs, NITD-008 and Balapiravir, entered preclinical animal safety study and clinic trial, but both were terminated due to toxicity and lack of potency, respectively. Celgosivir, a host alpha-glucosidase inhibitor, is currently under clinical trial; its clinical efficacy remains to be determined. The knowledge accumulated during the past decade has provided a better rationale for ongoing dengue drug discovery. Though challenging, we are optimistic that this continuous, concerted effort will lead to an effective dengue therapy.

Herpesviral latency-associated transcript gene promotes assembly of heterochromatin on viral lytic-gene promoters in latent infection

Herpes simplex virus (HSV) persists in its human host and evades the immune response by undergoing a latent infection in sensory neurons, from which it can reactivate periodically. HSV expresses >80 gene products during productive ("lytic") infection, but only the latency-associated transcript (LAT) gene is expressed at abundant levels during latent infection. The LAT gene has been shown to repress lytic-gene expression in sensory neurons. In this study, we use chromatin immunoprecipitation to show that HSV lytic-gene promoters become complexed with modified histones associated with heterochromatin during the course of establishment of latent infection. Experiments comparing LAT-negative and LAT-positive viruses show that a function encoded by the LAT gene increases the amount of dimethyl lysine 9 form of histone H3 or heterochromatin and reduces the amount of dimethyl lysine 4 form of histone H3, a part of active chromatin, on viral lytic-gene promoters. Thus, HSV, and in particular the HSV LAT gene, may manipulate the cellular histone modification machinery to repress its lytic-gene expression and contribute to the persistence of its genome in a quiescent form in sensory neurons.

A small-molecule dengue virus entry inhibitor

The incidence of dengue fever epidemics has increased dramatically over the last few decades. However, no vaccine or antiviral therapies are available. Therefore, the need for safe and effective antiviral drugs has become imperative. The entry of dengue virus into a host cell is mediated by its major envelope (E) protein. The crystal structure of the E protein reveals a hydrophobic pocket that is presumably important for low-pH-mediated membrane fusion. High-throughput docking with this hydrophobic pocket was performed, and hits were evaluated in cell-based assays. Compound 6 was identified as one of the inhibitors and had an average 50% effective concentration of 119 nM against dengue virus serotype 2 in a human cell line. Mechanism-of-action studies demonstrated that compound 6 acts at an early stage during dengue virus infection. It arrests dengue virus in vesicles that colocalize with endocytosed dextran and inhibits NS3 expression. The inhibitors described in this report can serve as molecular probes for the study of the entry of flavivirus into host cells.

NMR analysis of a novel enzymatically active unlinked dengue NS2B-NS3 protease complex

The dengue virus (DENV) is a mosquito-borne pathogen responsible for an estimated 100 million human infections annually. The viral genome encodes a two-component trypsin-like protease that contains the cofactor region from the nonstructural protein NS2B and the protease domain from NS3 (NS3pro). The NS2B-NS3pro complex plays a crucial role in viral maturation and has been identified as a potential drug target. Using a DENV protease construct containing NS2B covalently linked to NS3pro via a Gly4-Ser-Gly4 linker ("linked protease"), previous x-ray crystal structures show that the C-terminal fragment of NS2B is remote from NS3pro and exists in an open state in the absence of an inhibitor; however, in the presence of an inhibitor, NS2B complexes with NS3pro to form a closed state. This linked enzyme produced NMR spectra with severe signal overlap and line broadening. To obtain a protease construct with a resolved NMR spectrum, we expressed and purified an unlinked protease complex containing a 50-residue segment of the NS2B cofactor region and NS3pro without the glycine linker using a coexpression system. This unlinked protease complex was catalytically active at neutral pH in the absence of glycerol and produced dispersed cross-peaks in a (1)H-(15)N heteronuclear single quantum correlation spectrum that enabled us to conduct backbone assignments using conventional techniques. In addition, titration with an active-site peptide aldehyde inhibitor and paramagnetic relaxation enhancement studies demonstrated that the unlinked DENV protease exists predominantly in a closed conformation in solution. This protease complex can serve as a useful tool for drug discovery against DENV.

Isolation of female-specific AFLP markers and molecular identification of genetic sex in half-smooth tongue sole (Cynoglossus semilaevis)

The sex-specific molecular marker is a useful gene resource for studying sex- determining mechanisms and controlling fish sex. Artificially produced male and female half-smooth tongue sole (Cynoglossus semilaevis) were used to screen sex-specific amplified fragment length polymorphism (AFLPs) molecular markers. The phenotypic sex of 28 tongue soles was determined by histological sectioning of gonads. The AFLP analysis of 15 females and 13 males via 64 primer combinations produced a total of 4681 scorable bands, of which 42.11% and 43.39% of bands were polymorphic in females and males, respectively. Seven female-specific AFLP markers were identified and designated as CseF382, CseF575, CseF783, CseF464, CseF136, CseF618, and CseF305, respectively. One female-specific AFLP marker (CseF382) was amplified, recovered from the gels, cloned, and sequenced (accession no. DQ487760). This female-specific AFLP marker was converted into a single-locus polymerase-chain reaction (PCR) marker of a sequence-characterized amplified region (SCAR). A simple PCR method of using the specific primers was developed for identifying genetic sex of half-smooth tongue sole. PCR products demonstrated that the initial 15 females produced the female-specific band of about 350 bp, but the initial 13 male individuals failed to produce the band. We also investigated the applicability of the PCR primers in other tongue sole individuals. The same female-specific fragment of about 350 bp was found in the additional 59 female individuals, but not in the additional 58 male individuals. This AFLP-based molecular sexing technique may have great application potential in elucidation of sex determination mechanisms and sex control in half-smooth tongue sole.

Genetic diversity of human parvovirus B19: sequence analysis of the VP1/VP2 gene from multiple isolates

To evaluate the genetic variability of human parvovirus B19, the complete coding region of the VP1/VP2 structural proteins of 29 B19 isolates obtained from 25 infected patients were sequenced and compared with each other and with two previously published B19 isolates. The VP1/VP2 gene was amplified by PCR using B19-specific oligonucleotide primers and the amplification products were sequenced directly. Overall, the average nucleotide and predicted amino acid identity among B19 isolates was high. Sequential virus isolates from the same cases and isolates obtained from two cases linked by transmission in the same household were essentially identical. Sequence variation was minimal among isolates obtained from a single community-wide B19 outbreak, ranging between 0 and 10 (0.4%) base substitutions, although there appeared to be more than one genetic lineage circulating in the outbreak. A comparison with 18 additional isolates from distinct epidemiological settings found greater variability. These isolates differed from each other by between 11 (0.5%) and 112 (4.8%) base substitutions. B19 isolates from Xi'an, China, were significantly different from other isolates at both the nucleotide and amino acid levels, and were more closely related to a single isolate from Japan, obtained 10 years earlier, than to isolates from other countries. Isolates examined in this study included distinct genotypes from patients with similar clinical presentations and similar genotypes from patients with diverse clinical presentations. These data suggest that geographically defined genetic lineages of B19 may exist and that no particular B19 genotype was associated with a particular clinical outcome.

Prenatal diagnosis of intrauterine infection with parvovirus B19 by the polymerase chain reaction technique

Human parvovirus B19 is a recently recognized cause of fetal hydrops and death. Efforts to characterize the natural history of fetal infection with this virus have been hampered by the lack of sensitive and specific tests for diagnosis in utero. Using the highly sensitive polymerase chain reaction (PCR) assay, we determined the fetal infection status in 56 pregnancies by testing amniotic fluid, fetal serum, and maternal serum for B19 DNA and antibodies. Factors associated with a high risk of B19 infection were fetal disease, exposure to persons with erythema infectiosum, or signs or symptoms of acute B19 infection. Fifteen women (27%) were B19 IgM-positive, a status suggesting recent infection; the positivity of all of the corresponding fetal specimens for B19 DNA in the PCR was indicative of fetal infection. In four of these cases, serial ultrasonographic examinations documented spontaneous resolution of fetal hydrops. Twenty-four women (43%) were IgG-positive and IgM-negative; this pattern suggested prior infection. The PCR gave positive results, consistent with recent maternal infection, in four of these cases. Seventeen women (30%) were IgG-negative and IgM-negative, a pattern suggesting no prior infection; the PCR results in four cases were indicative of a possible early maternal infection or a possible atypical immune response. The PCR is a sensitive and rapid method for the diagnosis of intrauterine infection with human parvovirus B19 and promises to facilitate studies of the natural history and treatment of this infection.

New concepts in severe presacral hemorrhage during proctectomy

In the past, surgeons thought that severe presacral hemorrhage during proctectomy was caused by damage of the presacral venous plexus. By studying the anatomy and clinical data, we found that injury of the sacral basivertebral vein also caused this serious complication. Presacral hemorrhage is seen as massive bleeding from the distal pelvic surface of sacrum or from one to several large-caliber foramina of sacral basivertebral veins in that area. This type of presacral hemorrhage is more dangerous than that from simple injury of presacral venous plexus and sometimes it is fatal. We describe the anatomic features of the vertebral venous system and its close relationship with severe presacral hemorrhage. We also propose some new concepts about cause, hemostatic measures, and principles of prevention.

Cold acclimation can induce microtubular cold stability in a manner distinct from abscisic acid

The response of cortical microtubules to low temperature was investigated for the Chinese winter wheat (Triticum aestivum L.) cultivar Jing Nong 934. Microtubules in the cortex of the root elongation zone disassembled rapidly in response to a cold shock of -7 degrees C and reassembled upon rewarming to 25 degrees C. The microtubules acquired resistance against this cold shock in response to cold acclimation in chilling, but non-freezing, temperature or after a treatment with abscisic acid (ABA). Cold acclimation and ABA differed with respect to the appearance of microtubules: fine, transverse strands were observed after cold acclimation, whereas ABA produced steeply oblique microtubule bundles. The findings are discussed in terms of an ABA-independent pathway for acquired cold stability of microtubules.

Anti-dengue-virus activity and structure-activity relationship studies of lycorine derivatives

Dengue is a systemic viral infection that is transmitted to humans by Aedes mosquitoes. No vaccines or specific therapeutics are currently available for dengue. Lycorine, which is a natural plant alkaloid, has been shown to possess antiviral activities against flaviviruses. In this study, a series of novel lycorine derivatives were synthesized and assayed for their inhibition of dengue virus (DENV) in cell cultures. Among the lycorine analogues, 1‐acetyllycorine exhibited the most potent anti‐DENV activity (EC₅₀=0.4 μm) with a reduced cytotoxicity (CC₅₀>300 μm), which resulted in a selectivity index (CC₅₀/EC₅₀) of more than 750. The ketones 1‐acetyl‐2‐oxolycorine (EC₅₀=1.8 μm) and 2‐oxolycorine (EC₅₀=0.5 μm) also exhibited excellent antiviral activities with low cytotoxicity. Structure–activity relationships for the lycorine derivatives against DENV are discussed. A three‐dimensional quantitative structure–activity relationship model was established by using a comparative molecular‐field analysis protocol in order to rationalize the experimental results. Further modifications of the hydroxy group at the C1 position with retention of a ketone at the C2 position could potentially lead to inhibitors with improved overall properties.

PROC c.574_576del polymorphism: a common genetic risk factor for venous thrombosis in the Chinese population

BACKGROUND

There are ethnic differences in the genetic risk factors for venous thrombosis (VT). The genetic causes of VT in the Chinese population are not fully understood.

OBJECTIVES

To identify possible common abnormal factors that could contribute to thrombosis susceptibility.

METHODS/RESULTS

We measured the levels of nine types of plasma coagulation factor, three types of anticoagulation factor and two types of fibrinolytic factor in 310 VT patients. Factor V activity was higher in 32 cases. Eleven of the 32 cases also had low protein C (PC) or protein S (PS) activities, indicating PC or PS deficiency. No other abnormalities were observed in the other 21 cases. All of the samples were sensitive to activated PC inactivation. Therefore, the abnormal factor involved may be FV inactivator or its cofactor rather than FV itself. Resequencing identified a common PROC c.574_576del variant in 10 of the 32 subjects. In a case-control study, this variant was detected in 68 of the 1003 patients and in 25 of the 1031 controls. It had an adjusted odds ratio of 2.71 (95% confidence interval [CI] 1.68-4.36). PC amidolytic activities of most variant carriers were similar to those of non-carriers, but the mean anticoagulant activity was only 72.7 U dL(-1). Expression studies in vitro showed that the anticoagulant activity of the mutant PC was 43.6% of that of the wild-type PC.

CONCLUSIONS

We identified what is, so far, the most common genetic risk factor for VT in the Chinese population, with its prevalence being approximately 2.36%.

Characterizing polymorphisms and allelic diversity of von Willebrand factor gene in the 1000 Genomes

BACKGROUND

The von Willebrand factor (VWF) gene is highly polymorphic, with variants correlated with VWF antigen levels, adhesion activity, clearance and factor VIII binding. VWF mutations are detected in patients with von Willebrand disease (VWD), whereas polymorphic variants could be associated with thrombosis. However, information on the ethnic diversity of VWF variants and their association with diseases is limited.

OBJECTIVES

To characterize novel VWF variants from different ethnicities in the general population.

PATIENTS/METHODS

We analyzed samples from 1092 subjects of 14 ethnicities available in the 1000 Genomes database for VWF variants and their potential functional impacts.

RESULTS

We identified 2728 SNPs and 91 insertions and deletions that had a high level of ethnic diversity, with Africans having the highest number of variants. The highest level of diversity was found in the D' and D2 domains. Among 94 non-synonymous variants, 31 were predicted to be deleterious, including 19 that were previously associated with VWD. Most of these 'VWD variants' had allele frequencies consistent with disease incidence in European subjects, but some had a significantly higher frequency in other ethnicities. The mutations R2185Q, H817Q and M740I associated with type 1 and type 2N VWD were present in more than 13% of African subjects.

CONCLUSIONS

These results highlight the complexity of VWF variations in different ethnic groups and emphasize the importance of interrogating variations on multiple ethnic backgrounds for associations with bleeding and thrombosis.

Regulation of Vibrio alginolyticus virulence by the LuxS quorum-sensing system

Quorum sensing (QS) is a bacterial intercommunication system that controls the expression of multiple genes in response to population density. The LuxS QS system regulates the expression of several virulence factors in a wide variety of pathogenic bacteria. LuxS has been characterized to be responsible for producing a type of autoinducer, AI-2, which stimulates the expression of the luciferase operon in Vibrio harveyi. Vibrio alginolyticus is established as an opportunistic pathogen of several marine animals, and its LuxS QS system remains undefined. To investigate the pathogenic role of luxS in V. alginolyticus, the luxS mutants of both the standard strain ATCC 33787 and a fish-clinical isolate MVP01, named MYJS and MYJM, respectively, were constructed. The mutation resulted in reduced lethality to Pagrus major. Intraperitoneal LD(50) of MYJS and MYJM increased by 15- and 93-fold, respectively. The two luxS mutants exhibited a lower growth rate and defective flagellar biosynthesis. They also showed a significant decrease in protease production and an increase in both extracellular polysaccharide production and biofilm development. The results suggest that the LuxS QS system plays an important role in regulating the expression of virulence factors in V. alginolyticus.

NITD-688, a pan-serotype inhibitor of the dengue virus NS4B protein, shows favorable pharmacokinetics and efficacy in preclinical animal models

Dengue virus (DENV) is a mosquito-borne flavivirus that poses a threat to public health, yet no antiviral drug is available. We performed a high-throughput phenotypic screen using the Novartis compound library and identified candidate chemical inhibitors of DENV. This chemical series was optimized to improve properties such as anti-DENV potency and solubility. The lead compound, NITD-688, showed strong potency against all four serotypes of DENV and demonstrated excellent oral efficacy in infected AG129 mice. There was a 1.44-log reduction in viremia when mice were treated orally at 30 milligrams per kilogram twice daily for 3 days starting at the time of infection. NITD-688 treatment also resulted in a 1.16-log reduction in viremia when mice were treated 48 hours after infection. Selection of resistance mutations and binding studies with recombinant proteins indicated that the nonstructural protein 4B is the target of NITD-688. Pharmacokinetic studies in rats and dogs showed a long elimination half-life and good oral bioavailability. Extensive in vitro safety profiling along with exploratory rat and dog toxicology studies showed that NITD-688 was well tolerated after 7-day repeat dosing, demonstrating that NITD-688 may be a promising preclinical candidate for the treatment of dengue.

Pioglitazone up-regulates long non-coding RNA MEG3 to protect endothelial progenitor cells via increasing HDAC7 expression in metabolic syndrome

Long non-coding RNA (lncRNA) maternally expressed 3 (MEG3) is expressed in endothelial cells and involved in angiogenesis and vascular function. It was proposed that MEG3 participates in the process of endothelial progenitor cells (EPCs) functions in metabolic syndrome (MetS). In this study, the circulating EPCs number and function were decreased in MetS subjects. The MEG3 expression was expressed at a lower level and microRNA-140-5p (miR-140-5p) was expressed at a higher level in circulating EPCs of subjects with MetS. Pioglitazone reversed the alterations of EPCs function and the expression levels of MEG3 and miR-140-5p in EPCs. In bone marrow-derived EPCs exposed to palmitate, down-regulation of miR-140-5p canceled the increase of MEG3 expression level induced by Pioglitazone. Overexpression of MEG3 resulted in the down-regulation of miR-140-5p. The luciferase reporter assay and RIP assay showed that MEG3 targeted miR-140-5p. In addition, the HDAC7 expression levels were regulated by miR-140-5p and MEG3. These findings demonstrated that Pioglitazone up-regulated MEG3 expression to protect EPCs via decreasing miR-140-5p expression and increasing HDAC7 expression in MetS, which may be a novel therapeutic target for preventing and treating MetS.

Flavivirus Entry Inhibitors

Many flaviviruses are significant human pathogens that are transmitted by mosquitoes and ticks. Although effective vaccines are available for yellow fever virus, Japanese encephalitic virus, and tick-borne encephalitis virus, these and other flaviviruses still cause thousands of human deaths and millions of illnesses each year. No clinically approved antiviral therapy is available for flavivirus treatment. To meet this unmet medical need, industry and academia have taken multiple approaches to develop antiflavivirus therapy, among which targeting viral entry has been actively pursued in the past decade. Here we review the current knowledge of flavivirus entry and its use for small molecule drug discovery. Inhibitors of two major steps of flaviviral entry have been reported: (i) molecules that block virus-receptor interaction; (ii) compounds that prevent conformational change of viral envelope protein during virus-host membrane fusion. We also discuss the advantages and disadvantages of targeting viral entry for treatment of flavivirus infection as compared to targeting viral replication proteins.

Mechanical properties and microstructure analysis of fly ash geopolymeric recycled concrete

Six mixtures with different recycled aggregate (RA) replacement ratios of 0%, 50% and 100% were designed to manufacture recycled aggregate concrete (RAC) and alkali-activated fly ash geopolymeric recycled concrete (GRC). The physical and mechanical properties were investigated indicating different performances from each other. Optical microscopy under transmitted light and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) were carried out in this study in order to identify the mechanism underlying the effects of the geopolymer and RA on concrete properties. The features of aggregates, paste and interfacial transition zone (ITZ) were compared and discussed. Experimental results indicate that using alkali-activated fly ash geopolymer as replacement of ordinary Portland cement (OPC) effectively improved the compressive strength. With increasing of RA contents in both RAC and GRC, the compressive strength decreased gradually. The microstructure analysis shows that, on one hand, the presence of RA weakens the strength of the aggregates and the structure of ITZs; on the other hand, due to the alkali-activated fly ash in geopolymer concrete, the contents of Portlandite (Ca(OH)(2)) and voids were reduced, as well as improved the matrix homogeneity. The microstructure of GRC was changed by different reaction products, such as aluminosilicate gel.

The Role of a Conserved Acidic Residue in Calcium-dependent Protein Folding for a Low Density Lipoprotein (LDL)-A Module

One common feature of the more than 1,000 complement-type repeats (or low density lipoprotein (LDL)-A modules) found in LDL receptor and the other members of the LDL receptor superfamily is a cluster of five highly conserved acidic residues in the C-terminal region, DXXXDXXDXXDE. However, the role of the third conserved aspartate of these LDL-A modules in protein folding and ligand recognition has not been elucidated. In this report, using a model LDL-A module and several experimental approaches, we demonstrate that this acidic residue, like the other four conserved acidic residues, is involved in calcium-dependent protein folding. These results suggest an alternative calcium coordination conformation for the LDL-A modules. The proposed model provides a plausible explanation for the conservation of this acidic residue among the LDL-A modules. Furthermore, the model can explain why mutations of this residue in human LDL receptor cause familial hypercholesterolemia.

Solution structure of the viral receptor domain of Tva and its implications in viral entry

Tva is the cellular receptor for subgroup A avian sarcoma and leukosis virus (ASLV-A). The viral receptor function of Tva is determined by a 40-residue, cysteine-rich motif called the LDL-A module. Here we report the solution structure of the LDL-A module of Tva, determined by nuclear magnetic resonance (NMR) spectroscopy. Although the carboxyl terminus of the Tva LDL-A module has a structure similar to those of other reported LDL-A modules, the amino terminus adopts a different conformation. The LDL-A module of Tva does not contain the signature antiparallel beta-sheet observed in other LDL-A modules, and it is more flexible than other reported LDL-A modules. The LDL-A structure of Tva provides mechanistic insights into how a simple viral receptor functions in retrovirus entry. The side chains of H38 and W48 of Tva, which have been identified as viral contact residues by mutational analysis, are solvent exposed, suggesting that they are directly involved in EnvA binding. However, the side chain of L34, another potential viral contact residue identified previously, is buried inside of the module and forms the hydrophobic core with other residues. Thus L34 likely stabilizes the Tva structure but is not a viral interaction determinant. In addition, we propose that the flexible amino-terminal region of Tva plays an important role in determining specificity in the Tva-EnvA interaction.

Development and properties of Ti-In binary alloys as dental biomaterials

The objective of this study is to investigate the effect of alloying element indium on the microstructure, mechanical properties, corrosion behavior and in vitro cytotoxicity of Ti-In binary alloys, with the addition of 1, 5, 10 and 15 at.% indium. The phase constitution was studied by optical microscopic observation and X-ray diffraction measurements. The mechanical properties were characterized by tension and microhardness tests. Potentiodynamic polarization measurements were employed to investigate the corrosion behavior in artificial saliva solutions with and without fluoride. In vitro cytotoxicity was conducted by using L929 and NIH 3T3 mouse fibroblast cell lines, with commercially pure Ti (CP-Ti, ASTM grade 2) as negative control. All of the binary Ti-In alloys investigated in this work were found to have higher strength and microhardness than CP-Ti. Electrochemical results showed that Ti-In alloys exhibited the same order of magnitude of passivation current densities with CP-Ti in artificial saliva solutions. With the presence of NaF, Ti-10In and Ti-15In showed transpassive behavior and lower current densities at high potentials. All experimental Ti-In alloys showed good cytocompatibility, at the same level as CP-Ti. The addition of indium to titanium was effective on increasing the strength and microhardness, without impairing its good corrosion resistance and cytocompatibility.

Role of calcium in protein folding and function of Tva, the receptor of subgroup A avian sarcoma and leukosis virus

Tva is the cellular receptor for subgroup A avian sarcoma and leukosis virus (ASLV-A). The viral receptor function of Tva is determined by a 40-residue cysteine-rich motif called the LDL-A module. In this study, we expressed and purified the wild-type (wt) Tva LDL-A module as well as several mutants and examined their in vitro folding properties. We found that, as for other LDL-A modules, correct folding and structure of the Tva LDL-A module is Ca2+ dependent. When calcium was present during in vitro protein folding, the wt module was eluted as a single peak by reverse-phase high-pressure liquid chromatography. Furthermore, two-dimensional nuclear magnetic resonance (NMR) spectroscopy gave well-dispersed spectra in the presence of calcium. In contrast, the same protein folded in vitro in the absence of calcium was eluted as multiple broad peaks and gave a poorly dispersed NMR spectrum in the presence of calcium. The calcium affinity (Kd) of the Tva LDL-A module, determined by isothermal titration calorimetry, is approximately 40 microM. Characterization of several Tva mutants provided further evidence that calcium is important in protein folding and function of Tva. Mutations of the Ca2+-binding residues (D46A and E47A) completely abrogated the Ca2+-binding ability of Tva, and the proteins were not correctly folded. Interestingly, mutations of two non-calcium-binding residues (W48A and L34A) also exerted adverse effect on Ca2+-dependent folding, albeit to a much less extent. Our results provide new insights regarding the structure and function of Tva in ASLV-A entry.