The catalytic properties of human hepatitis B virus polymerase

The DNA-dependent DNA polymerase (DDDP) and RNA-dependent DNA polymerase (RDDP) activities of hepadnavirus polymerases are both essential for viral replication. Human hepatitis B virus (HBV) polymerase has been successfully expressed in Escherichia coli as a fusion protein in frame with maltose-binding protein. The present study was undertaken to characterize these two activities and introduce an in vitro assay system. In situ activity gel assays show that the polymerase has both types of activities. One hundred thirty-four kilodaltons of active full-length product was proteolytically cleaved into approximately 73 kDa of active fragment by proteinase K preincubation. Mutation of conserved YMDD motif also confirms that the activities were due to the recombinant polymerase and that this motif is essential to polymerase activity. Two activities of the polymerase show their optima under conditions of 1 mM (DDDP) or 0.25 mM (RDDP) of MnCl2, 400 mM KCl, 37 degrees C (DDDP) or 24 degrees C (RDDP), and pH 7.0-7.7. Substitution of Mg2+ for Mn2+ results in reduction of processivity, which may explain why Mn2+ supports nucleotide incorporation to a higher level than Mg2+. The polymerase is resistant to aphidicolin. Actinomycin D acts selectively on DDDP activity, whereas phosphonoformic acid inhibits both activities. The in vitro HBV polymerase assay system demonstrated herein will be useful for screening potential HBV polymerase inhibitor for the development of anti-HBV drugs.

Determination of T cell epitopes with random peptide libraries

A new approach to T cell epitope determination is presented. Critical amino acids for the induction of cytotoxic T cell responses were identified using synthetic peptide libraries with single defined sequence positions combined with randomized sequence positions. Sequences for potential T cell epitopes were deduced from scan profiles using combinations of the active amino acids. Highly potent epitopes for cytotoxic T lymphocytes were obtained. Epitopes defined by this approach are, as shown in this communication, not necessarily the natural epitopes and, therefore, were named synthetic epitopes. They can serve effectively for the development of vaccines or for the determination of T cell receptor antagonists.

Natural ligand motifs of closely related HLA-DR4 molecules predict features of rheumatoid arthritis associated peptides

Rheumatoid arthritis (RA), one of the most common autoimmune disorders, is believed to be mediated via. T lymphocytes and genetic studies have shown that it is strongly associated with HLA-DR4. The DR4 subtypes DR4Dw4, DR4Dw14 and DR4Dw15 represent increased risk factors for RA, whereas DR4Dw10 is not associated with the disorder. Our study determines and compares the natural ligand motifs of these MHC class II molecules and identifies 60 natural ligands. At relative position 4 (P4), only the RA-associated DR4 molecules allow, or even prefer, negatively charged amino acids, but do not allow those which are positively charged (Arg, Lys). In the case of DR4Dw10 the preference for these amino acids is reversed. The results predict features of the putative RA-inducing peptide(s). A remarkable specificity, almost exclusively for negative charges (Asp, Glu), is found at P9 of the DR4Dw15 motif. This specificity can be ascribed to amino acid beta57 of the DR beta chain, and gives an important insight into the beta57-association of another autoimmune disease, insulin-dependent diabetes mellitus type I.

Specificity and degeneracy of minor histocompatibility antigen-specific MHC-restricted CTL

Random peptide libraries were employed to investigate the specificity of Ag recognition by H-3-specific, H-2K(b)-restricted CTL clones. The peptide libraries consist of octapeptides with one defined sequence position and mixtures of 19 amino acids (all proteinogenic amino acids except for cysteine) in the remaining seven sequence positions. The complete set of 152 peptide libraries includes all octapeptides possible with these amino acids. Responses of the CTL clones to these peptide libraries reveal patterns of preferred epitope amino acids. Depending on the CTL clone tested, varying numbers of different amino acids were identified for the different sequence positions indicating degeneracy of Ag recognition. Sequences for synthetic epitopes active at low pM concentrations could be deduced from these patterns. They confirm that TCRs of CTL clones do not exhibit specificity for unique ligand structures but rather can interact with sets of ligands. The sequences of peptides recognized by a single clone exhibit great sequence heterogeneity.

Cathepsin L is an intracellular and extracellular protease in Paramecium tetraurelia. Purification, cloning, sequencing and specific inhibition by its expressed propeptide

The ciliate Paramecium tetraurelia secretes large amounts of a cysteine protease into the growth medium, presumably for extracellular food digestion. Two endoprotease isozymes (30 and 33 kDa on SDS/PAGE, respectively), both present in cell homogenates and in spent growth medium, were purified to homogeneity. Peptide sequence analysis revealed that these isozymes share identities at the amino acid level but are probably differently processed. Enzymatic characterization of the isolated proteases and sequencing of the cloned cDNA demonstrated that the enzymes belong to the cathepsin-L protease subfamily. Although the identity with mammalian and other protozoan L cathepsins was only around 30%, all important signature sequences for cathepsin L in the preproregion as well as in the catalyst of the enzyme were fully retained. The cDNA of this cysteine protease codes for a preproregion of 108 amino acids. The putative proregion of 86 amino acids which contained the characteristic conserved ERFNIN motif, was fused with a His6 tag, expressed in Escherichia coli, and purified. Both cathepsin L isozymes of Paramecium tetraurelia were inhibited by their cognate propeptide in the nanomolar concentration range. All other cysteine proteases tested (papain and mammalian cathepsin B, G and H) were unaffected by the propeptide up to 10 microM.

Specificity and degeneracy of minor histocompatibility antigen-specific MHC-restricted CTL

Random peptide libraries were employed to investigate the specificity of Ag recognition by H-3-specific, H-2K(b)-restricted CTL clones. The peptide libraries consist of octapeptides with one defined sequence position and mixtures of 19 amino acids (all proteinogenic amino acids except for cysteine) in the remaining seven sequence positions. The complete set of 152 peptide libraries includes all octapeptides possible with these amino acids. Responses of the CTL clones to these peptide libraries reveal patterns of preferred epitope amino acids. Depending on the CTL clone tested, varying numbers of different amino acids were identified for the different sequence positions indicating degeneracy of Ag recognition. Sequences for synthetic epitopes active at low pM concentrations could be deduced from these patterns. They confirm that TCRs of CTL clones do not exhibit specificity for unique ligand structures but rather can interact with sets of ligands. The sequences of peptides recognized by a single clone exhibit great sequence heterogeneity.

[Postoperative follow-up in hepatic echinococcosis]

OBJECTIVE

To determine whether the monitoring of patients who have undergone surgical excision of hydatid cysts of the liver is useful. Furthermore, sonographic and computertomographic criteria of recurrent hydatid disease should be described.

PATIENTS AND METHODS

Of 84 patients operated on for hepatic hydatid disease 42 (22 men, 20 women; mean age 44 [25-82] years) were examined between 6 months and 15 years post-operatively (median of 6 years) clinically, serologically (complement-fixation reaction, immunohaemagglutination) and by ultrasound. If the latter was positive, computed tomography was also performed.

RESULTS

Recurrence of hydatid disease in the liver was diagnosed in three patients and in the peritoneal cavity in one patient. The demonstration of internal septa by solitary or multiple daughter cysts proved to be a reliable imaging criterion.

CONCLUSION

Ultrasonography should be performed as a baseline test after surgical removal of hydatid cysts in the liver and specific antibody titres measured. This will make it easier to distinguish a recurrence from postoperative changes.

Dictyostelium mutants lacking multiple classic myosin I isoforms reveal combinations of shared and distinct functions

Dictyostelium cells that lack the myoB isoform were previously shown to exhibit reduced efficiencies of phagocytosis and chemotactic aggregation ("streaming") and to crawl at about half the speed of wild-type cells. Of the four other Dictyostelium myosin I isoforms identified to date, myoC and myoD are the most similar to myoB in terms of tail domain sequence. Furthermore, we show here that myoC, like myoB and myoD, is concentrated in actin-rich cortical regions like the leading edge of migrating cells. To look for evidence of functional overlap between these isoforms, we analyzed myoB, myoC, and myoD single mutants, myoB/myoD double mutants, and myoB/myoC/myoD triple mutants, which were created using a combination of gene targeting techniques and constitutive expression of antisense RNA. With regard to the speed of locomoting, aggregation-stage cells, of the three single mutants, only the myoB mutant was significantly slower. Moreover, double and triple mutants were only slightly slower than the myoB single mutant. Consistent with this, the protein level of myoB alone rises dramatically during early development, suggesting that a special demand is placed on this one isoform when cells become highly motile. We also found, however, that the absolute amount of myoB protein in aggregation-stage cells is much higher than that for myoC and myoD, suggesting that what appears to be a case of nonoverlapping function could be the result of large differences in the amounts of functionally overlapping isoforms. Streaming assays also suggest that myoC plays a significant role in some aspect of motility other than cell speed. With regard to phagocytosis, both myoB and myoC single mutants exhibited significant reductions in initial rate, suggesting that these two isoforms perform nonredundant roles in supporting the phagocytic process. In triple mutants these defects were not additive, however. Finally, because double and triple mutants exhibited significant and progressive decreases in doubling times, we also measured the kinetics of fluid phase endocytic flux (uptake, transit time, efflux). Not only do all three isoforms contribute to this process, but their contributions are synergistic. While these results, when taken together, refute the simple notion that these three "classic" myosin I isoforms perform exclusively identical functions, they do reveal that all three share in supporting at least one cellular process (endocytosis), and they identify several other processes (motility, streaming, and phagocytosis) that are supported to a significant extent by either individual isoforms or various combinations of them.

Bone marrow-derived macrophage lines and immortalized cloned macrophage and dendritic cells support priming of Borrelia burgdorferi--specific T cell responses in vitro and/or in vivo

In vitro propagated bone marrow-derived macrophage populations (BMMO) as well as cloned immortalized macrophage (MT2/1) and dendritic (D2SC/1) cell lines were analyzed for their capacity to promote activation and/or proliferation of naïve T cells to Borrelia burgdorferi antigens in vitro and in vivo. All three cell types constitutively express high levels of MHC class I structures as well as the co-stimulatory molecules B7/BB1 and heat-stable antigen (HSA); MHC class II molecules (I-A) are upregulated following incubation with either intact spirochetes or the purified lipoprotein OspA (Lip-OspA) but not with its delipidated from (MDP-OspA). Only BMMO were able to induce proliferation of naïve T cells or T cells derived from infected mice to intact spirochetes in vitro. However, all three accessory populations could support primary and secondary T cell responses to Lip-OspA but not, or only marginally, to MDP-OspA under similar conditions. The number of accessory cells required for optimal stimulation of naïve or pre-sensitized T cells was approximately 3 x lower for D2SC 1 than for BMMO or MT2/1. In addition, BMMO pre-pulsed with Lip-OspA were able to prime T cells in vivo, indicating a crucial role for the lipid moiety in antigen presentation. From two truncated lipopeptides of Lip-OspA containing either 20 or 6 aminoterminal residues, only Lip-OspApep20 but not Lip-OspApep6 induced significant proliferation in naïve for pre-sensitized T cells in vitro, suggesting that T cells mainly respond to the protein rather than the lipid moiety of OspA. Thus, the data demonstrate that BMMO, MT2/1 and D2SC/1 have differential capacities to prime spirochete-reactive T cells and to support their growth in vitro, suggesting that optimal activation and propagation of T cells also depends on the quality of the antigen.

Activation of T cells by the ragged tail of MHC class II-presented peptides of the measles virus fusion protein

The efficient and sustained immune response of an antigen requires T cell epitopes, capable of inducing a long lasting T cell memory. To detect T cell epitopes of the measles virus fusion protein (MV-F), the proliferation of lymphocytes from late convalescent donors in response to overlapping pentadecapeptides covering the whole protein sequence was studied. Three major immunodominant regions (F51-70, F121-135 and F211-225) containing promiscuous peptides induce proliferation in peripheral blood lymphocytes in approximately 50% of the donors. Potential DR1-restricted epitopes were mapped using an MHC competition binding assay. Both the proliferation and the binding data identified a DR1-restricted T cell epitope (F51-65). Contact sites of the peptide HQSLVIKLMPNITLL with MHC were characterized using substitution analogs. Alanine substitutions at most positions did not interfere with F51-65 binding. These analogs were therefore useful for studying the residues which were recognized by the TCR of MV- and F51-induced T cells lines. In addition to amino acid residues of the core of peptide F51-65 both the C-terminal and the N-terminal amino acids were essential for T cell interaction. Since peptides presented by class II molecules vary in length, these findings suggest that residues of the ragged tail are important for T cell activation. It is speculated that in late convalescent donors the length of the flanking sequence of MHC II-restricted peptides may play a role in controlling the heterogeneity of MV-specific T cell clones recruited as T helper/memory cells.

The sequence of the dictyostelium myo J heavy chain gene predicts a novel, dimeric, unconventional myosin with a heavy chain molecular mass of 258 kDa

The complete sequence of the Dictyostelium myo J heavy chain gene has been determined from overlapping genomic clones. The gene spans approximately 7400 base pairs, is split by two small introns, and encodes a 2241-residue, 258-kDa heavy chain polypeptide that that is composed of an N-terminal 944-residue myosin head domain, a central 863-residue domain that is predicted to form an alpha helical coiled-coil containing six hinges, and a C-terminal 434-residue globular domain. The head domain is notable in that it contains a approximately 30 residue insert near the nucleotide binding pocket, and five potential calmodulin/myosin light chain binding sites at the head/tail junction. The existence within the Myo J tail domain of both an extensive coiled-coil structure and a large globular domain suggests that this myosin is dimeric and incapable of self-assembly into filaments. While these properties, as well as the overall predicted structure of the Myo J protein, are reminiscent of class V myosins, the sequence of the 434-residue globular tail piece of Myo J shows no similarity to that of either yeast or vertebrate myosins V. Consistent with this, phylogenetic analyses based on myosin head sequence comparisons do not classify Myo J as a type V myosin. These and other sequence comparisons indicate that Myo J and two as-yet-unclassified unconventional myosins from Arabidopsis represent members of the newest class within the myosin superfamily (class XI). Northern blots analyses suggest that Myo J may function predominantly in vegetative Dictyostelium cells. Finally, Southern blot analyses suggest that Dictyostelium possesses another myosin that is very closely related to Myo J.

Amino acid preferences in the octapeptide subunit of the major histocompatibility complex class I heterotrimer H-2Ld

Major histocompatibility complex class I (MHC-I) molecules are heterotrimers composed of polymorphic alpha-chains, monomorphic beta-chains, and peptides of eight or nine amino acids. The peptides are derived from various intracellularly occurring proteins and are very heterogeneous. They are essential for a stable conformation of the MHC-I protein at physiological temperature. This study presents results from stabilization experiments that were designed to determine the impact of the amino acids in every sequence position of octapeptides on the thermal stability of the mouse MHC-I molecule H2-Ld. OX7 octapeptide libraries with one defined and seven randomized positions were employed as they allow the effects of individual amino acids to be determined. The results confirm the importance of the motif amino acids proline and leucine for positions 2 and 8, respectively, of octapeptides. They are among the most efficient amino acids for these positions. However, with a few exceptions, all amino acids are permitted in all eight sequence positions. Hydrophobic amino acids are generally favored. Charged amino acids, especially aspartic acid and glutamic acid, are disfavored. Stabilization indices were defined as measures for the MHC stabilization power of the amino acids. These indices can serve to predict the efficiency of peptide binding to H-2Ld and can guide the design of T-cell epitopes.

Structures of lantibiotics studied by NMR

During the last decade, Nuclear Magnetic Resonance has played an important role in the unravelling of the primary and tertiary structures of lantibiotics. A short overview of these studies, together with typical spatial structures obtained, is presented.

Protein engineering of lantibiotics

Whereas protein engineering of enzymes and structural proteins nowadays is an established research tool for studying structure-function relationships of polypeptides and for improving their properties, the engineering of posttranslationally modified peptides, such as the lantibiotics, is just coming of age. The engineering of lantibiotics is less straightforward than that of unmodified proteins, since expression systems should be developed not only for the structural genes but also for the genes encoding the biosynthetic enzymes, immunity protein and regulatory proteins. Moreover, correct posttranslational modification of specific residues could in many cases be a prerequisite for production and secretion of the active lantibiotic, which limits the number of successful mutations one can apply. This paper describes the development of expression systems for the structural lantibiotic genes for nisin A, nisin Z, gallidermin, epidermin and Pep5, and gives examples of recently produced site-directed mutants of these lantibiotics. Characterization of the mutants yielded valuable information on biosynthetic requirements for production. Moreover, regions in the lantibiotics were identified that are of crucial importance for antimicrobial activity. Eventually, this knowledge will lead to the rational design of lantibiotics optimally suited for fighting specific undesirable microorganisms. The mutants are of additional value for studies directed towards the elucidation of the mode of action of lantibiotics.

Engineering of a novel thioether bridge and role of modified residues in the lantibiotic Pep5

Pep5 is a 34-amino-acid antimicrobial peptide, produced by Staphylococcus epidermidis 5, that contains the thioether amino acids lanthionine and methyllanthionine, which form three intramolecular ring structures. In addition, two didehydrobutyrines are present in the central part of the lantibiotic and an oxobutyryl residue is located at the N terminus. All rare amino acids are introduced by posttranslational modifications of a ribosomally made precursor peptide. To elucidate the function of the modified residues for the antimicrobial action of Pep5, mutant peptides, in which single modified residues had been eliminated, were produced by site-directed mutagenesis. All of these peptides showed a reduced antimicrobial activity. In addition, those peptides from which the ring structures had been deleted became susceptible to proteolytic digest. This demonstrates that the ring structures serve as stabilizers of conformations essential for activity, e.g., amphiphilicity, as well as for protecting Pep5 against proteases of the producing strains. In addition, residues that could serve as precursors of new modified amino acids in lantibiotics were introduced into the Pep5 precursor peptide. This way, a novel methyllanthionine and a didehydroalanine were inserted into the flexible central part of Pep5, demonstrating that biosynthesis of modified amino acids is feasible by protein engineering and use of the lantibiotic modification system.

A 'mixed' self-assembled monolayer for an impedimetric immunosensor

A synthetic peptide with the amino acid sequence 135-154 of the capsid protein VP1 of the foot-and-mouth-disease virus was modified with omega-hydroxyundecanethiol and applied together with non-derivatised omega-hydroxyundecanethiol for consecutive adsorption onto gold electrodes according to self-assembling procedures. The binding of a specific antibody to prepared recognition layers could be monitored by measurement of impedance or capacitance. In order to avoid non-specific effects, all measurements were performed in the presence of BSA. The complex between the antigenic peptide and the antibody was split by applying 6 M urea solution. The gold electrodes were mounted into an optimised flow-through system in order to perform capacitance-time measurements. The immobilised peptide can be recognised repeatedly by specific antibodies.

Synthetic peptides coupled to the lipotripeptide P3CSS induce in vivo B and Thelper cell responses to HIV-1 reverse transcriptase

To evaluate the ability of the lipotripeptide P3CSS to increase peptide-specific immune responses in vivo, we immunized mice from different inbred strains (BALB/c, C3H/HeJ, C57BL/6) with the 22-mer lipopeptide conjugates P3CSS-[RT-(522-543)] and P3CSS-[RT-(528-549)] of HIV-1 reverse transcriptase (RT) which included an immunodominant Th epitope [i.e. RT-(528-543)] characterized previously. Analysis of T and B cell responses to these lipopeptide conjugates indicated that specific Th responses could be readily induced in vivo. The peptide segments could also efficiently prime mice for secondary recognition of native RT. The use of shorter peptides permitted a delineation of the minimal T cell recognition site of this RT C-terminal region [i.e. RT-(528-540)]. Close to this T cell epitope we identified a B cell determinant containing the motif EQVD [RT-(546-549)] which was recognized in three different strains of mice (H-2b, H-2d and H-2k). A comparison with X-ray analysis of the C-terminal region of HIV-1 reverse transcriptase indicated exposed positions of these Th and B cell epitopes. Both the presence of T and B cell sites and its limited polymorphism make the region RT-(528-549) a promising candidate for vaccine design. The use of the P3CSS adjuvant/carrier principle as a nontoxic adjuvant may be of major importance in the development of vaccines applicable to humans.

Structure activity studies of mast cell activation and hypotension induced by neuropeptide Y (NPY), centrally truncated and C-terminal NPY analogues

1. Neuropeptide-induced histamine release is thought to occur via receptor-independent mechanisms, with net charge and lipophilicity being important factors. 2. In this study, the histamine releasing ability of neuropeptide Y (NPY), two C-terminal segments of NPY and 13 centrally truncated NPY analogues was examined. These results were compared with the ability of the peptides to bind to the Y2 receptor in the rabbit kidney membrane model and with their hypotensive actions in the anaesthetized-rat model. 3. All analogues tested, with the exception of [Glu4,25,33,35]-NPY(1-4)-Ahx-(25-36) and [Asp4,25,33,35]NPY(1-4)-Ahx-(25-36) which were devoid of histamine releasing activity, evoked a dose-dependent histamine release but there were marked differences between the peptides. The native peptide was the least active. 4. Histamine release was not linked to the ability of the peptides to displace NPY from Y2 receptors. There was a statistical correlation between the hypotensive effects expressed as ED10 values (mumol kg-1, which induced a blood pressure decrease of 10 mmHg) and the EC25 for histamine release (r = 0.62, P = 0.04), although histamine release may not be the sole determinant of the alterations in blood pressure. 5. There was a strong negative correlation between EC25 for histamine release and net positive charge (r = -0.93, P = 5.7 x 10(-7), i.e. increasing the net positive charge caused greater histamine release. However, there was a 12 fold difference in activity amongst the most positively charged analogues (+5). Helicity did not correlate with histamine releasing ability. 6. In the development of NPY-related drugs the avoidance of compounds with net positive charge is recommended.

Crystallographic studies on the binding modes of P2-P3 butanediamide renin inhibitors

The binding modes of three peptidomimetic P2-P3 butanediamide renin inhibitors have been determined by x-ray crystallography. The inhibitors are bound with their backbones in an extended conformation, and their side chains occupying the S5 to S1' pockets. A (2-amino-4-thiazolyl)methyl side chain at the P2 position shows stronger hydrogen-bonding and van der Waals interactions with renin than the His side chain, which is present in the natural substrate. The ACHPA-gamma-lactam transition state analog has similar interactions with renin as the dihydroxyethylene transition state analog.