Targeting Holliday junctions by origin DNA-binding protein of herpes simplex virus type 1.

In the present paper, the interactions of the origin binding protein (OBP) of herpes simplex virus type 1 (HSV1) with synthetic four-way Holliday junctions (HJs) were studied using electrophoresis mobility shift assay and the FRET method and compared with the interactions of the protein with duplex and single-stranded DNAs. It has been found that OBP exhibits a strong preference for binding to four-way and three-way DNA junctions and possesses much lower affinities to duplex and single-stranded DNAs. The protein forms three types of complexes with HJs. It forms complexes I and II which are reminiscent of the tetramer and octamer complexes with four-way junction of HJ-specific protein RuvA of Escherichia coli. The binding approaches saturation level when two OBP dimers are bound per junction. In the presence of Mg2+ ions (≥2 mM) OBP also interacts with HJ in the stacked arm form (complex III). In the presence of 5 mM ATP and 10 mM Mg2+ ions OBP catalyzes processing of the HJ in which one of the annealed oligonucleotides has a 3'-terminal tail containing 20 unpaired thymine residues. The observed preference of OBP for binding to the four-way DNA junctions provides a basis for suggestion that OBP induces large DNA structural changes upon binding to Box I and Box II sites in OriS. These changes involve the bending and partial melting of the DNA at A+T-rich spacer and also include the formation of HJ containing Box I and Box II inverted repeats and flanking DNA sequences.

Single-domain antibody-based ligands for immunoaffinity separation of recombinant human lactoferrin from the goat lactoferrin of transgenic goat milk.

Single-domain antibody generation technology was applied to make new Sepharose-bound ligands for affinity separation of closely related proteins, such as human and goat lactoferrin. We generated recombinant antibodies that can selectively bind/recognize only lactoferrins having amino acid sequences identical to that of human natural lactoferrin (anti-hLF Ab). Selected and purified histidine-tagged single-domain antibodies were used as ligands, and different lactoferrins were used as analytes in the kinetics analysis of lactoferrin binding to captured anti-hLF Abs using the Bio-Rad ProteOn XPR36 protein interaction array system. The data obtained were consistent with a 1:1 binding model with very high affinity, practically equal in the case of hLF and rec-hLF (calculated KD varied from 0.43nM to 3.7nM). Interaction of captured fsdAbs with goat LF was significantly weaker and not detectable under the same analysis conditions. We demonstrated the high efficiency of the recombinant human lactoferrin purification from goat lactoferrin and other proteins using the obtained single domain antibody-based affinity ligands. We believe this approach can be used for the generation of single-domain antibody-based affinity media for the efficient separation/purification of a wide spectrum of other highly homologous proteins.

Complex of the herpes simplex virus type 1 origin binding protein UL9 with DNA as a platform for the design of a new type of antiviral drugs.

The herpes simplex virus type 1 origin-binding protein, OBP, is a DNA helicase encoded by the UL9 gene. The protein binds in a sequence-specific manner to the viral origins of replication, two OriS sites and one OriL site. In order to search for efficient inhibitors of the OBP activity, we have obtained a recombinant origin-binding protein expressed in Escherichia coli cells. The UL9 gene has been amplified by PCR and inserted into a modified plasmid pET14 between NdeI and KpnI sites. The recombinant protein binds to Box I and Box II sequences and possesses helicase and ATPase activities. In the presence of ATP and viral protein ICP8 (single-strand DNA-binding protein), the initiator protein induces unwinding of the minimal OriS duplex (≈80 bp). The protein also binds to a single-stranded DNA (OriS*) containing a stable Box I-Box III hairpin and an unstable AT-rich hairpin at the 3'-end. In the present work, new minor groove binding ligands have been synthesized which are capable to inhibit the development of virus-induced cytopathic effect in cultured Vero cells. Studies on binding of these compounds to DNA and synthetic oligonucleotides have been performed by fluorescence methods, gel mobility shift analysis and footprinting assays. Footprinting studies have revealed that Pt-bis-netropsin and related molecules exhibit preferences for binding to the AT-spacer in OriS. The drugs stabilize structure of the AT-rich region and inhibit the fluctuation opening of AT-base pairs which is a prerequisite to unwinding of DNA by OBP. Kinetics of ATP-dependent unwinding of OriS in the presence and absence of netropsin derivatives have been studied by measuring the efficiency of Forster resonance energy transfer (FRET) between fluorophores attached to 5'- and 3'- ends of an oligonucleotide in the minimal OriS duplex. The results are consistent with the suggestion that OBP is the DNA Holiday junction (HJ) binding helicase. The protein induces conformation changes (bending and partial melting) of OriS duplexes and stimulates HJ formation in the absence of ATP. The antiviral activity of bis-netropsins is coupled with their ability to inhibit the fluctuation opening of АТ base pairs in the А + Т cluster and their capacity to stabilize the structure of the АТ-rich hairpin in the single-stranded oligonucleotide corresponding to the upper chain in the minimal duplex OriS. The antiviral activities of bis-netropsins in cell culture and their therapeutic effects on HSV1-infected laboratory animals have been studied.

Interaction between kringle and growth-factor-like domains in the urokinase molecule: possible role in stimulation of chemotaxis.

The results presented in this paper suggest the presence of an interaction between the kringle- and the growth-factor-like urokinase domains. This interaction regulates chemotactic properties of urokinase. We also show that interaction of urokinase with its "classical" receptor (uPAR) has a "permissive" effect on the interactions between the kringle domain and other targets on the cell surface. On the basis of our data we can suggest that uPAR serves as an "adaptor" for urokinase, and the binding of urokinase kringle domain to its receptor causes immediate activation of intracellular signaling and induction of cell migration.

Chemotactic effect of urokinase plasminogen activator: a major role for mechanisms independent of its proteolytic or growth factor domains.

Urokinase type plasminogen activator (uPA) converts plasminogen to plasmin and is highly chemotactic for many cell types. We examined, using recombinant wild type and mutated forms of uPA, the extent to which its proteolytic properties, its growth-like domain (GFD) and/or interactions with the specific receptor (uPAR) contribute to the chemotactic activity towards vascular smooth muscle cells (SMC). Recombinant wild type uPA (r-uPA) stimulated cell migration nearly 5.8-fold, inactive r-uPA, with a mutation in the catalitic domain (r-uPA(H/Q)), 3-fold, uPA without growth factor like domain (r-uPA(GFD )), 2.6-fold, and a form containing both mutations (r-uPA(H/Q, GFD ), 3.3-fold. All recombinant forms of uPA, wild type and those with mutations were equally and highly effective (IC50 approximately 20 nM) in displacing 125I-r-uPA bound to SMC. These results indicate that additional mechanisms, not dependent on uPA's proteolytic activity or the binding ability of its GFD to uPAR, are the major contributors to its chemotactic action on SMC.

The increase in gene expression induced by introduction of rare codons into the C terminus of the template.

Short oligodeoxynucleotides (oligos) possessing two tandem Arg codons followed by TGA stop codon were inserted near the 3' end of a modified cat gene. It was found that while being decoded in vivo, the AGGAGGTGA oligo increased the yield of gene product and, in addition, caused -1 frameshifting. The 3-10-fold increase of the yield of the polypeptide was accompanied by increased accumulation of corresponding mRNA, indicating a protection from messenger decay. Transformation of the cells by a plasmid overproducing tRNA(4Arg) gene compensates for all the anomalies.