Modulating the Schottky barrier of MXenes/2D SiC contacts via functional groups and biaxial strain: a first-principles study.

Two-dimensional (2D) graphene-like SiC has attracted intense interest recently due to its unique electrical and physical properties. In implementing 2D semiconductors in device applications, one of the main challenges so far has been the formation of a high-quality Schottky barrier owing to the strong Fermi level pinning (FLP) at the interface of traditional metal-2D semiconductor contacts. In this paper, the 2D MXenes Ti3C2T2 (T = F, O, OH) are proposed to serve as electrodes for 2D SiC. The structural and barrier properties of the Ti3C2T2/SiC contacts were systematically investigated based on first-principles calculations combined with the GGA-PBE and HSE06 functionals. It is found that Ti3C2T2 can be bonded with 2D SiC by van der Waals (vdW) interactions. Weak FLP is exhibited at Ti3C2T2/SiC vdW contacts. The type of contact can be tuned by changing the functional T group of Ti3C2T2. Ti3C2F2/SiC and Ti3C2O2/SiC contacts exhibit a p-type Schottky contact and p-type Ohmic contact, respectively, whereas an n-type Ohmic contact occurs in the Ti3C2(OH)2/SiC contact. In addition, the calculated tunneling possibility (TB) is ∼20% between Ti3C2T2 and SiC, indicating weak bonding at the Ti3C2T2/SiC vdW junctions. Furthermore, the Schottky barrier height and TB of the Ti3C2(OH)2/SiC contacts can be modulated via the biaxial strain. The controllable contact type and barrier in Ti3C2T2/SiC contacts provide guidelines for developing high-performance 2D SiC optoelectronic and electronic devices.

[Non-structural protein NS1 of canine parvovirus induces the apoptosis of cells].

OBJECTIVE: To investigate the effects of canine parvovirus (CPV) non-structural protein-1 (NS1) on the cell apoptosis induced by CPV and preliminarily explore the mechanism of CPV-induced apoptosis. METHODS: First, the NS1 gene was amplified by PCR from CPV genomic DNA and subcloned into pcDNA3. 1A vector to generate NS1 eukaryotic expression vector pcDNA-NS1. To verify whether pcDNA-NS1 vector can mediate NS1 expression in eukaryotic cells, the human embryo kideny (HEK) 293FT cells were used to transiently express the recombinant NS1. The effects of NS1 on CPV-induced apoptosis were investigated by infecting the F81 host cells with CPV and transfecting the cells with NS1 vector. The apoptosis of the cells was detected by AnnexinV/PI double staining for phosphatidylserine externalization on membrane and by luminescence method for caspase-3/7 activities. RESULTS: The results show that the sequence of NS1 gene amplified was consistent with the GenBank. The NS1 expression vector was shown to be correct and could mediate NS1 expression in eukaryotic cells. The phosphatidylserine on outside of membrane was detected and the caspase-3/7 activities were increased in both CPV-infected cells and NS1-transfected cells. These results indicate that both CPV and NS1 protein can induce the apoptosis of the cells. CONCLUSION: CPV-induced apoptosis was closely related to its non-structural protein NS1.

[Escherichia coli heat-labile enterotoxin B subunit enhances the immune response against canine parvovirus VP2 in mice immunized by VP2 DNA vaccine].

OBJECTIVE: To investigate the effect of Escherichia coli heat-labile enterotoxin (LT) B subunit (LTB) gene on canine parvovirus (CPV) VP2 gene vaccine. METHODS: The LTB gene was amplified by PCR from genomic DNA of E. coli 44815 strain. The VP2-70 fragment (210 bp) encoding major epitope of VP2 (70 amino acids) was amplified by PCR from a plasmid encoding VP2 gene. VP2-70 and LTB genes were inserted into the eukaryotic vector to construct VP2-70 gene,LTB gene and VP2-70-LTB fused gene vectors. The mice were immunized with VP2-70 vector, VP2-70-LTB fused vector, or VP2-70 vector plus LTB vector, respectively. The antibody titers at the different time were measured by using ELISA method. The spleen lymphocyte proliferation activity was analyzed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. RESULTS: The sequence of VP2-70 and LTB genes was identified. The recombinant VP2-70 and LTB proteins could be expressed in HEK293T cells in a secretory manner. The mice immunized with VP2-70 vector, VP2-70-LTB vector or VP2-70 vector plus LTB vector could generate the specific antibody against VP2 protein. The antibody titer immunized with VP2-70-LTB vector reached 1:5120 at 35 d post immunization, significantly higher than that of other two groups (P < 0.01). For antibody isotype analysis, the IgG1 isotype antibody titers in all test groups were significantly higher than of IgG2a (P < 0.01). The high-level spleen lymphocyte stimulation index was observed in the three test groups under the stimulation with Con A, higher than that in control groups (P < 0.01). CONCLUSION: LTB gene could enhance the humoral immune response of CPV VP2 gene vaccine in mice.

[Secreting expression and characterization of canine parvovirus VP2 protein in eukaryotic cells].

OBJECTIVE: To study and characterize secretive expression of canine parvovirus capsid protein 2 (VP2) gene in eukaryotic cells. METHODS: To construct secreting expression vector of VP2 gene, we obtained CD5 signal peptide (SP) DNA fragment from plasmid containing human CD5 SP DNA sequence and inserted the fragment into multiple clone site of eukaryotic expression vector pcDNA3.1A. The canine parvovirus VP2 gene was amplified by PCR and inserted into expression vector pcDNA3.1-CD5sp down stream of CD5 SP. The recombinant pcDNA-CD5sp-VP2 plasmids were transfected into HEK293T cells mediated by calcium phosphate. VP2 binding activity for canine transferrin receptor was analyzed by ELISA method. RESULTS: Recombinant pcDNA-CD5sp-VP2 plasmid proved to be correct by sequencing. VP2 proteins were detected by Western-blot in the culture medium of transfected 293T cells, which indicated that the expressed VP2 protein could be secreted into the medium mediated by human CD5 SP. VP2 protein had the activity to bind canine transferrin receptor (TfR). CONCLUSION: The secreting expression of VP2 in eukaryotic cells was achieved by using human CD5 SP. Recombinant VP2 showed the ability to bind canine TfR.

Soluble form of canine transferrin receptor inhibits canine parvovirus infection in vitro and in vivo.

Canine parvovirus (CPV) disease is an acute, highly infectious disease threatening the dog-raising industry. So far there are no effective therapeutic strategies to control this disease. Although the canine transferrin receptor (TfR) was identified as a receptor for CPV infection, whether extracellular domain of TfR (called soluble TfR (sTfR)) possesses anti-CPV activities remains elusive. Here, we used the recombinant sTfR prepared from HEK293T cells with codon-optimized gene structure to investigate its anti-CPV activity both in vitro and in vivo. Our results indicated that codon optimization could significantly improve sTfR expression in HEK293T cells. The prepared recombinant sTfR possessed a binding activity to both CPV and CPV VP2 capsid proteins and significantly inhibited CPV infection of cultured feline F81 cells and decreased the mortality of CPV-infected dogs, which indicates that the sTfR has the anti-CPV activity both in vitro and in vivo.

Inhibition of canine parvovirus replication in cultured cells by small interfering RNAs expressed from plasmid vectors.

Small interfering RNAs (siRNAs) target complementary mRNA for specific degradation, a mechanism many viruses are susceptible too. Thus, siRNA degradation of target RNAs can be exploited as novel therapeutics. In this report, we show that the vector-based siRNAs (psiSTRIKEs) expressed by a human U6 promoter could efficiently inhibit CPV replication in cell culture. A series of PsiSTRIKE vectors expressing siRNA were constructed that target structural protein genes or nonstructural protein genes of CPV genome. These plasmids were transfected into FK81 cells via lipofectin and the stable transfection clones were selected. The immunostaining, plaque assay, and cell proliferation assay of the cells infected by CPV were performed. The results show that siRNAs against nonstructural protein genes effectively inhibited CPV replication. The inhibition efficiencies detected by immunostaining assay of psiSTRIKE/vp1510, psiSTRIKE/NS160, and psiSTRIKE/NS1939 were 66%, 76% and 78%, respectively at 48h, and 69%, 46% and 67%, respectively at 96h. Plaque assay showed that, comprising to the control, the psiSTRIKE/NS160 reduced the virion production by 100-fold, and psiSTRIKE/NS1939 or psiSTRIKE/VP1510 reduced the virion production 13-fold. When compared to control, the viability of cells transfected psiSTRIKE/NS160 increased 78% and 124%, respectively at 72 and 120h. Our study may provide a potential therapy against CPV infection.