High-resolution structure of the diphtheria toxin repressor complexed with cobalt and manganese reveals an SH3-like third domain and suggests a possible role of phosphate as co-corepressor

The crystal structure of diphtheria toxin repressor (DtxR) in complex with the corepressor Co2+ has been determined at 2.0 A resolution and in complex with Mn2+ at 2.2 A resolution. The structure of the flexible third domain could be determined at this high resolution. It appears to contain five antiparallel strands exhibiting a fold very similar to the SH3 domain. A superposition of 46 equivalent C alpha atoms of DtxR and alpha-spectrin SH3 resulted in an rms deviation of 3.0 A. The sequence identity is only 7%. This third domain of DtxR appears to have no interactions with the DNA binding domain nor with the metal binding domain of the repressor. Yet, flexibility in the region between the second and the third domain allows in principle significant conformational changes such as might occur upon DNA binding. The two metal binding sites in the second domain have been unraveled in considerable detail. Metal binding site 1 was well occupied in both the cobalt and manganese structures and showed a surprising sulfate ion as ligand. The sulfate was proven beyond doubt by the high peak at its position in a selenate versus sulfate difference Fourier. The presence of the intriguing sulfate ion at such a crucial position near the metal corepressor suggests the possibility that under physiological conditions phosphate may act as a "co-corepressor" for this class of metal-regulated DNA binding proteins in Corynebacteria, Mycobacteria, and related organisms. The second metal binding site is significantly different in these two DtxR structures. In the 2.0 A cobalt structure, the site is not occupied by a metal ion. In the 2.2 A manganese structure the site is well occupied, at approximately the same position as observed previously in cadmium DtxR. The ligands are Glu105, His106, the carbonyl oxygen of Cys102, and a water molecule. The reasons for differential occupancy of this site in different structures are intriguing and require further investigations.

Unique fold and active site in cytomegalovirus protease

Human herpesviruses are responsible for a variety of diseases. They are divided into three subfamilies: alpha includes herpes simplex viruses (HSV-1 and HSV-2) and varicella-zoster virus (VZV); beta includes cytomegalovirus (CMV) and human herpesvirus-6 (HHV-6); and gamma includes Epstein-Barr virus (EBV). Each virus encodes a serine protease that is essential for its replication and is a potential target for therapeutic intervention. Human CMV is a ubiquitous opportunistic pathogen that can result in life-threatening infections in congenitally infected infants, immunocompromised individuals and immunosuppressed cancer or transplant patients. Here we report the crystal structure of human CMV protease at 2.5 angstroms resolution. The structure reveals a fold that has not been reported for any other serine protease, and an active site consisting of a novel catalytic triad in which the third member is a histidine instead of an aspartic acid, or possibly a catalytic tetrad consisting of a serine, two histidines and an aspartic acid. An unusual dimer interface that is important to the protease activity has also been identified.

Surgical treatment of bone tumors in conjunction with microwave-induced hyperthermia and adjuvant immunotherapy. A preliminary report

OBJECTIVE

To develop an alternative approach in conjunction with microwave-induced hyperthermia.

PATIENTS AND METHODS

Thermotherapy with microwave intracorporeal irradiation was used to treat 73 patients with bone tumors. The series was composed of 58 patients with malignant tumors and 15 with benign tumors: most of tumors occurred about knee joints (53/73 = 72.6%). The surgical procedure included separating the tumor bearing segment from surrounding normal tissues with a safe margin, cooling the normal tissues including the neurovascular bundle and the intraarticular structures with a water circulation system, while heating the tumor with the antenna array of a microwave system and providing an adequate soft-tissue cover for the dead bone. Postoperatively, an immune therapy regimen was carried out regularly. The patients' immunologic functions were monitored by assay of the subpopulation of T cells, IL-2 and sIL-2 R (soluble IL-2 receptor).

RESULTS

Follow-up varied from 3 to 38 months (mean 19 months). Excluding 3 patients with malignancy in the vertebrae treated for palliation, 70 were evaluated according to oncological and orthopedic criteria. Five patients had local recurrence and required amputation. The remaining 65 had excellent local control. In 6 of the 55 patients with malignancy of the extremities, lung metastasis occurred one to two years after surgery. The oncological results were similar to those obtained by other limb-saving procedures. Pathological fracture occurred at devitalized bone in 5 patients. In 72.5% of the patients (29 of 40 tumor-free cases followed more than one year), knee joints functioned well, being stable and painless with almost full range of motion. Single photon emission computered tomography (SPECT) for 16 patients revealed revascularization of the devitalized tumor bearing bone segment could accomplish in one year or more. The immune states were improved in various extends after thermotherapy plus immunotherapy in the majority of patients.

CONCLUSION

These results show that the use of microwave hyperthermia and adjuvant immunotherapy in conjunction with the surgical treatment of bone tumors can be considered a definitive procedure, which is safe and well-tolerated. The oncological and orthopedic results are encouraging.

Identification and characterization of a C(K/R)TC motif as a common epitope present in all subtypes of hepatitis B surface antigen

The a determinant of hepatitis B surface antigen (HBsAg) is the most critical determinant for both diagnosis and immunoprophylaxis of the hepatitis B virus. We have used synthetic peptides and an anti-a mAb to identify a peptide sequence corresponding to amino acid residues 117 to 128 of HBsAg as an antigenic epitope contributing to the a determinant. Compared to the native protein HBsAg, the cyclic form of the peptide (aa 117-128) is only 20-fold less effective, whereas the linear form of the peptide is 160-fold less effective in the inhibition of mAb binding to HBsAg. Based on these results, we have postulated a previously unidentified disulfide bond between residue Cysl21 and Cysl24. Individual substitution of amino acids in the peptide (aa 117-128) with alanine identified three residues Cys121, Thr123, and Cys124 as the most critical residues for mAb recognition. Substitution of alanine for any one of the three residues caused a substantial loss in binding free energy (greater than 4.5 kcal/mol). Sequence analysis indicated that the C(K/R)TC motif is highly conserved among 100 subtypes and mutants of HBsAg isolates. Collectively, these results show that the cyclic C(K/R)TC motif is an essential part of the a determinant of HBsAg. Synthetic peptides containing the C(K/R)TC motif are potentially useful as alternative hepatitis B vaccines and as diagnostic reagents for the detection of the hepatitis B virus.

Identification and characterization of a C(K/R)TC motif as a common epitope present in all subtypes of hepatitis B surface antigen

The a determinant of hepatitis B surface antigen (HBsAg) is the most critical determinant for both diagnosis and immunoprophylaxis of the hepatitis B virus. We have used synthetic peptides and an anti-a mAb to identify a peptide sequence corresponding to amino acid residues 117 to 128 of HBsAg as an antigenic epitope contributing to the a determinant. Compared to the native protein HBsAg, the cyclic form of the peptide (aa 117-128) is only 20-fold less effective, whereas the linear form of the peptide is 160-fold less effective in the inhibition of mAb binding to HBsAg. Based on these results, we have postulated a previously unidentified disulfide bond between residue Cysl21 and Cysl24. Individual substitution of amino acids in the peptide (aa 117-128) with alanine identified three residues Cys121, Thr123, and Cys124 as the most critical residues for mAb recognition. Substitution of alanine for any one of the three residues caused a substantial loss in binding free energy (greater than 4.5 kcal/mol). Sequence analysis indicated that the C(K/R)TC motif is highly conserved among 100 subtypes and mutants of HBsAg isolates. Collectively, these results show that the cyclic C(K/R)TC motif is an essential part of the a determinant of HBsAg. Synthetic peptides containing the C(K/R)TC motif are potentially useful as alternative hepatitis B vaccines and as diagnostic reagents for the detection of the hepatitis B virus.

Regulation of human clotting factor IX cDNA expression in transgenic mice

To study the expression of human clotting factor IX cDNA in transgenic mice, which is an essential work on gene therapy for hemophilia B, 3 recombinant constructions containing different lengths of human clotting factor IX cDNA have been introduced into the cultured cells. All of the recombinant constructions were found to be expressed well in vitro. They were then microinjected into the male pronuclei of the fertilized mouse eggs respectively for generating transgenic mice. Unfortunately, none of them was expressed in any transgenic mice. These results show that the expression of the human clotting factor IX cDNA in the transgenic mice can be determined by cis regulatory element(s). As compared with the results from other related works, it is suggested that the cis regulatory element(s) is resided in the 5'-end non-coding region.

Construction and high expression of retroviral vector with human clotting factor IX cDNA in vitro

The construction of the high titer and highly expressed safety retroviral vector carrying human clotting factor IX cDNA is reported. Retroviral vectors LNCIX, LIXSN and LCIXSN, driven by hCMV, LTR and hCMV combined with LTR promoter respectively, were constructed, based on the retroviral vector LNL6, and transferred into packaging cell line PA317 with electroporation. Human clotting factor IX was detected in the cultured cells transduced with LNCIX and LIXSN but not in the cells transduced with LCIXSN. The viral titer of PA317/LNCIX was 800,000 CFU per mL. With ELISA detection, it was found that the cells transduced with this vector can express human clotting factor IX at the level of 3.3 micrograms per 10(6) cells in 24 h in human fibrosarcoma cells HT-1080 and 2.5 micrograms per 10(6) cells in 24 h in hemophilia B patients' skin fibroblast HSF cells, and more than 80% of them were biologically active. The viral titer and expression of human FIX were increased, and the construction of retroviral vector backbone was improved and the safety was guaranteed as compared to those vectors used previously. These vectors may produce a sufficient quantity of factor IX proteins to cause the phenotypic modification for hemophilia B patients.

[Causes of intraocular lens removal]

The causes of 25 cases of intraocular lens (IOL) explanation were reviewed retrospectively. Of the IOLs removed, 4 were anterior chamber (AC) IOLs and 21 posterior chamber (PC) IOLs. The average interval between cataract extraction with lens implantation and the IOL explantation in AC IOLs was 23.5 months and in PC IOLs 7.1 months. The causes of AC IOL removal were pseudophakic bullous keratopathy in 1 and uveitis-glaucoma-hyphema syndrome in 3 cases. The causes of PC IOL explantation included dislocation or subluxation in 12, pseudophakic bullous keratopathy in 4, pseudophakic retinal detachment in 3 and endophthalmitis in 2 cases. Surgical procedures included simple IOL removal or combined with 3 port-vitrectomy, penetrating keratoplasty, vitreoretinal microsurgery, anterior vitrectomy and pupillary membranectomy. Post-operatively, the visual outcome in most of the eyes showed improvement or stabilization.

IAM chromatography: an in vitro screen for predicting drug membrane permeability

Fluid cell membranes are the main barrier to drug absorption when diffusion limits uptake. Immobilized artificial membranes (IAMs) are solid phase models of fluid membranes that predicted oral drug absorption in mice for a homologous set of cephalosporins. IAMs also predicted drug permeability through Caco-2 cells. Since drug permeability in Caco-2 cells is known to correlate with the oral absorption of drugs in humans, IAMs may also model drug absorption in humans. IAM analysis is experimentally simple, and large-volume screening of experimental compounds for drug absorption is possible.

Membrane partition coefficients chromatographically measured using immobilized artificial membrane surfaces

Immobilized artificial membranes (IAMs) are chromatographic surfaces prepared by covalently immobilizing cell membrane phospholipids. IAM surfaces mimic fluid cell membranes. Solute capacity factors (k'IAM) measured on IAM columns correlate very well with solute equilibrium partition coefficients (Km') measured in fluid liposome systems. For 23 structurally unrelated compounds, log-(k'IAM) correlates with log(Km') with a linear correlation coefficient r = 0.907. This indicates that solute partitioning between the IAM bonded phase and the aqueous mobile phase is similar to the solute partitioning between liposomes and the aqueous phase. Although both IAM chromatography and liposome partitioning can be used as in vitro methods to predict solute partitioning into cell membranes, IAM chromatography is experimentally convenient compared to liposome systems. To study the effect of lipid structure on drug binding to IAMs, IAMs were prepared from three different phosphatidylcholine ligands: (i) a diacylated phosphatidylcholine ligand, (ii) a single chain ether phosphatidylcholine ligand, and (iii) a single chain phosphatidylcholine ligand that lacks a glycerol backbone. Solute retention data were identical for all of these IAMs, and consequently, predictions of solute binding to fluid membranes were also identical. This indicates that the structure of the phosphatidylcholine ligand that is immobilized is not critical for the binding of solutes. Since the structure is not important, the binding of solutes to membranes is a bulk phase property, i.e., it is the interface created by the ligands that determines the solute binding properties, not the ligands themselves. Solute partitioning using octanol/water systems does not correlate with k'IAM unless a homologous series of hydrophobic solutes is being evaluated.

Three-dimensional structure of the diphtheria toxin repressor in complex with divalent cation co-repressors

BACKGROUND

When Corynebacterium diphtheriae encounters an environment with a low concentration of iron ions, it initiates the synthesis of several virulence factors, including diphtheria toxin. The diphtheria toxin repressor (DtxR) plays a key role in this iron-dependent, global regulatory system and is the prototype for a new family of iron-dependent repressor proteins in Gram-positive bacteria. This study aimed to increase understanding of the general regulatory principles of cation binding to DtxR.

RESULTS

The crystal structure of dimeric DtxR holo-repressor in complex with different transition metals shows that each subunit comprises an amino-terminal DNA-binding domain, an interface domain (which contains two metal-binding sites) and a third, very flexible carboxy-terminal domain. Each DNA-binding domain contains a helix-turn-helix motif and has a topology which is very similar to catabolite gene activator protein (CAP). Molecular modeling suggests that bound DNA adopts a bent conformation with helices alpha 3 of DtxR interacting with the major grooves. The two metal-binding sites lie approximately 10 A apart. Binding site 2 is positioned at a potential hinge region between the DNA-binding and interface domains. Residues 98-108 appear to be crucial for the functioning of the repressor; these provide four of the ligands of the two metal-binding sites and three residues at the other side of the helix which are at the heart of the dimer interface.

CONCLUSIONS

The crystal structure of the DtxR holorepressor suggests that the divalent cation co-repressor controls motions of the DNA-binding domain. In this way the metal co-repressor governs the distance between operator recognition elements in the two subunits and, consequently, DNA recognition.

Polymorphism in both X and Y box motifs controls level of expression of HLA-DRB1 genes

The HLA class II antigens of the human major histocompatibility complex play an important role in immune response. The quality of the immune response is determined not only by polymorphisms in their coding region, but also by the level of their cell-surface expression which affects, for example, the extent of T-cell activation. We have previously described allelic polymorphisms in the upstream regulatory regions of HLA-DRB genes, which affected DNA-protein interactions and resulted in significantly different promoter strengths. In the present study, we investigated the effect of polymorphisms in the X and Y box motifs on the transcriptional activity of DRB1 gene promoters in the DR1, DR51, and DR53 haplotype groups. We used normal, chimeric, and mutated DRB promoters and compared their relative abilities to initiate transcription of the CAT reporter gene in human B-cell lines. The results show that polymorphisms in both the X1 and Y box motifs play a dominant role in the promoter strength. In the gel mobility shift assay, we observed differential ability of nuclear proteins that bind to the polymorphic X1 and Y box elements. The results in the present study confirm earlier data in that the nucleotide variation in the X1 box affects the level of expression of DRB1 genes. In addition, the present data demonstrate that polymorphism in the Y box, which affects the inverted CCAAT sequence, also plays a dominant role in the transcriptional activity of DRB1 promoters.

[An uni-dimensional ordinal coma scale]

With the introduction and wide acceptance of the Glasgow coma scale, some progress was made in 1980s. Various types of coma scale were offered from different centers of the world for assessing coma and impaired consciousness. The existing coma scales may be divided into two main categories: (1) multi-dimensional scale, e.g., Glasgow coma scale (GCS), Glasgow-Liege coma scale (G-LCS), Maryland coma scale (MCS); and (2) uni-dimensional scale, e.g., Edinburgh-2 coma scale (E2CS). There is evidence that the uni-dimensional coma scale is better than the multi-dimensional coma scale. The major drawbacks in the multi-dimensional coma scale is the total figure of coma level must be envisaged stereographially. The sum of scores of three dimensions of GCS, as in a multi-dimensional scale, consists of 13 levels from 3 through 15, but the numbers of simple combination constituting each score are considerable. No. 9 in GCS scale may be made up of 18 combinations. E2CS, as an uni-dimensional scale, seems to be an improvement over GCS. On the basis of comparison between two main categories of coma scale and considering the shortcomings of E2CS, a modified uni-dimensional ordinal coma scale called "Chengdu-1 Coma scale" (C1CS) was proposed and applied for evaluating the depth of coma and for prognosticating the patients' outcome. This study was based on 98 acutely head-injured patients treated in the Neurosurgical department of 1st Affiliated Hospital of WCUMS, from October 1983 through May 1984. The follow-up results showed that a good correlation was observed between the score of C1CS and the outcome scale score (Glasgow outcome scale, GOS) of the patients.

Phospholipid immobilization on solid surfaces

Single chain ether phospholipids (PLs) containing omega-carboxyl groups in the alkyl chain were immobilized on silica propylamine (SPA) to form IAM chromatography packing material. The PL ligands are analogs of phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidic acid (PA). All of these PLs contain polar functional groups in the lipid head group that require protection prior to PL immobilization and then deprotection after immobilization. The IAM surface was prepared in four steps: (i) the omega-carboxyl group was activated with carbonyldiimidazole, (ii) the activated PL-imidazolide ligand was bonded to SPA, (iii) the surface was end capped with a long chain anhydride and then end-capped with a short chain anhydride, and (iv) protecting groups were removed to form the IAM surface. The extent of deblocking the protecting groups was typically > or = 90%. This immobilization strategy generated a phospholipid surface that was stable when solvated with all organic solvents and aqueous buffers between pH 2 and 8. Both FT-IR spectroscopy and elemental analysis indicated that the bonding densities were 64-83 mg of PL/g of SPA, which corresponds to an area per molecule of 66-104 A2. These bonding densities for the immobilized PLs are very close to the area per molecule of mobile phospholipids comprising liposome membrane. The similar areas per molecule of immobilized PLs and mobile phospholipid in liposomes indicate that the lipid environments are similar.

Membrane properties of antiviral phospholipids containing heteroatoms in the acyl chains

Phospholipids containing heteroatoms in the lipid acyl chains, e.g., 1,2-bis(12-methoxydodecanoyl)-sn-3-phosphocholine (L-AC2), exhibit potent anti-HIV activity [Pidgeon, C., Markovich, R. J., Liu, M. D., Holzer, T., Novak, R., & Keyer, K. (1993) J. Biol. Chem. 268, 7773-7778]. AC2 is a synthetic chemical analog of the long-chain phospholipid, dimyristoylphosphatidylcholine (DMPC). Sonicated AC2 lipid dispersions would not entrap either Dextran-4000 or Mn2+ used as aqueous space markers. The lack of entrapment of aqueous space markers indicates that the AC2 structures do not contain an aqueous core that is the characteristic morphology of conventional lipid vesicles formed by sonication. Transmission electron microscopy (TEM) showed that sonicated AC2 lipid dispersions are small homogeneous particles approximately 70-100 A in diameter. 1H NMR experiments using Mn2+ as a broadening reagent indicated that Mn2+ was accessible to all of the AC2 phospholipid headgroups in the AC2 lipid particles formed by sonication. The temperature dependence of 1H spin-lattice (T1) relaxation time measurements revealed that the motional activation energies increased from the choline headgroup to the end of the acyl chains of AC2 molecules in the AC2 lipid particles formed by sonication. Collectively these results demonstrate that AC2 forms micelles. NOESY experiments showed that the AC2 molecules forming the micelle structures have hindered motion compared to conventional short-chain phosphatidylcholine micelles. 31P NMR spectroscopy and TEM showed that the AC2 micelles extensively fuse into giant bilayer liposomes (single-layered) when the temperature is reduced from above to below the main phase transition temperature of AC2. This micelle-to-liposome transition is an irreversible process; increasing the temperature above the Tm does not cause the formation of micelles. Thus, a main finding is that AC2 micelles formed by sonication are not thermodynamically stable because they fuse into large unilamellar vesicles that are stable to further changes in temperature. These unusual membrane properties of sonicated AC2 dispersions may be important for the antiviral activity and metabolism of the phospholipids.

Serologic survey of giant pandas (Ailuropoda melanoleuca), and domestic dogs and cats in the Wolong Reserve, China

Sera from captive and recently rescued giant pandas (Ailuropoda melanoleuca) in the Wolong Reserve, China, were examined by serum neutralization or hemagglutination inhibition for antibodies to canine distemper virus (CDV), canine coronavirus (CCV), canine herpesvirus (CHV), pseudorabies virus (PRV), canine adenovirus type 2 (CAV), and canine parvovirus (CPV). Serum samples from village domestic dogs and cats, which run free throughout the reserve also were examined. Antibodies against CPV were detected in six of eight giant pandas and all dogs and cats tested. The origin of the virus was not determined. Two of eight giant pandas and two of seven dogs had CDV antibody titers. Three of eight pandas and three of seven dogs had CCV antibody titers. Four of eight pandas and two of seven dogs had CAV titers; the titers in dogs were very high. No pandas or dogs had evidence of exposure to CHV or PRV.

Polymorphisms in the TAP2 gene and their association with rheumatoid arthritis

The human major histocompatibility complex (MHC) contains two closely related genes (TAP) that encode a family of transporter proteins. It is known that the TAP genes, like other MHC (class I and class II) genes, are polymorphic. In this study we investigated the polymorphisms in the ATP-binding domain of the TAP2 gene and examined the relationship of these polymorphisms to susceptibility to rheumatoid arthritis (RA). On the basis of the distribution of polymorphisms in these genes, three TAP2 alleles could be identified in homozygous typing cell lines, RA patients and normal subjects: TAP2*0101-1693.G, TAP2*0101-1693.A and TAP2*0201-1693.G. The prevalence of the variant (nucleotide A at position 1693), and thus also of the TAP2*0101-1693.A allele, was significantly (p < 0.006, RR = 4.25) higher in RA patients (35.3%) than in normal controls (11.4%). In addition, the TAP2*0101-1693.A allele showed significant (r = 0.45, p < 0.0003) association with HLA-DR4 only in RA patients and the prevalence of both TAP2*0101-1693.A and DR4 genes gave the highest relative risk (RR = 19.21, p < 0.0002) for RA. These data suggest that the MHC region containing both class II and TAP genes confers the strongest susceptibility to RA, with the highest RR value reported so far. It is likely that the genetic variability in the putative peptide transporter could also be implicated in immunological disorders associated with MHC.

Structures of thrombin complexes with a designed and a natural exosite peptide inhibitor

The structures of two hirudin-based fibrinogen recognition exosite peptide inhibitors with significantly different sequences complexed with alpha-thrombin at a site distinct from the active site (exosite) have been determined crystallographically at 2.2 and 2.3 A resolution. One is a designed synthetic peptide with some nonconventional amino acid residues (MDL-28050), and the other is a natural COOH-terminal peptide isolated from the leech Hirudinaria manillensis (hirullin P18). The structures have been refined by restrained least squares methods to R values of 0.161 and 0.155, respectively. The first stretch of each peptide, corresponding to hirudin 55-59, associates with thrombin similar to hirudin and hirugen (hirudin 53-64). Although the remaining residues of the inhibitors interact with and bind to thrombin, the binding is accomplished. through a rigid body conformational adjustment of the peptide with respect to the conformation displayed by hirudin and hirugen (40 degrees rotation about the Ile59, CA-C bond). This causes the side groups of cyclohexylalanine 64' of MDL-28050 and Ile60, of hirullin to point in the opposite direction of the all important Tyr63, ring of hirudin and hirugen but permits the residues to penetrate and interact with the 3(10) turn hydrophobic binding pocket of thrombin. Thus, the hydrophobic interaction is accomplished in a different way by virtue of the substrate conformational readjustment. The results show that the first stretch of peptide makes concerted and efficient binding interactions with thrombin, and the peptide positions of the inhibitors are fairly specific and homologous so that the stretch appears to be related to specific recognition associated with the exosite. The relative flexibility of structure and sequence of the second stretch is a display of tolerance of imprecision by thrombin in its COOH-terminal hydrophobic association with hirudin-based inhibitors.