Induction of cytotoxic T lymphocyte activity by fusion-active peptide-containing virosomes.

Priming of cytotoxic T lymphocyte (CTL) activity with exogenous antigen requires introduction of the antigen into the MHC class I presentation pathway of antigen-presenting cells. In the present study, we used fusogenic reconstituted envelopes (virosomes), derived from influenza virus, as a carrier system for delivery of a synthetic soluble peptide corresponding to a major murine CTL epitope of the influenza virus nucleoprotein (NP). Virosomes containing encapsulated NP-peptide efficiently sensitized target cells for recognition by influenza-specific CTLs generated through priming of mice with infectious virus. Intramuscular immunization of mice with peptide-containing virosomes induced a potent class I MHC-restricted CTL response against influenza-infected target cells. By contrast, an equal dose of NP-peptide encapsulated in fusion-inactivated virosomes did not induce CTL activity, indicating an essential role of the membrane fusion activity of the virosomes in the induction of the response. Likewise, NP-peptide encapsulated in liposomes, NP-peptide mixed with empty virosomes and NP-peptide in IFA failed to induce a CTL response. These results demonstrate that fusion-active virosomes represent a promising delivery system for induction of class I MHC-restricted CTL activity with non-replicating viral antigens.

Crystal structure of a murine alpha-class glutathione S-transferase involved in cellular defense against oxidative stress.

Glutathione S-transferases (GSTs) are ubiquitous multifunctional enzymes which play a key role in cellular detoxification. The enzymes protect the cells against toxicants by conjugating them to glutathione. Recently, a novel subgroup of alpha-class GSTs has been identified with altered substrate specificity which is particularly important for cellular defense against oxidative stress. Here, we report the crystal structure of murine GSTA4-4, which is the first structure of a prototypical member of this subgroup. The structure was solved by molecular replacement and refined to 2.9 A resolution. It resembles the structure of other members of the GST superfamily, but reveals a distinct substrate binding site.

X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa.

The three-dimensional structure of antistasin, a potent inhibitor of blood coagulation factor Xa, from the Mexican leech Haementeria officinalis was determined at 1.9 A resolution by X-ray crystallography. The structure reveals a novel protein fold composed of two homologous domains, each resembling the structure of hirustasin, a related 55-residue protease inhibitor. However, hirustasin has a different overall shape than the individual antistasin domains, it contains four rather than two beta-strands, and does not inhibit factor Xa. The two antistasin domains can be subdivided into two similarly sized subdomains with different relative orientations. Consequently, the domain shapes are different, the N-terminal domain being wedge-shaped and the C-terminal domain flat. Docking studies suggest that differences in domain shape enable the N-terminal, but not C-terminal, domain of antistasin to bind and inhibit factor Xa, even though both have a very similar reactive site. Furthermore, a putative exosite binding region could be defined in the N-terminal domain of antistasin, comprising residues 15-17, which is likely to interact with a cluster of positively charged residues on the factor Xa surface (Arg222/Lys223/Lys224). This exosite binding region explains the specificity and inhibitory potency of antistasin towards factor Xa. In the C-terminal domain of antistasin, these exosite interactions are prevented due to the different overall shape of this domain.

A novel rat mesangial matrix protein, MMP-50/100, involved in mesangial glomerulopathies.

BACKGROUND: Within the glomerular extracellular matrix, the glomerular basement membrane and the mesangial matrix have different compositions, presumably related to their different functions. In this study, a novel mesangial matrix protein is recognized by mAb ED5 and KiM4R, which were originally selected for reactivity with follicular dendritic cells of rat lymphoid organs. EXPERIMENTAL DESIGN: Distribution of this mesangial matrix protein (MMP-50/100) was studied in normal Wistar rat kidneys by indirect immunofluorescence and immunoelectron microscopy. For partial immunobiochemical characterization, ED5-affinity-purified glomerular matrices were subjected to SDS-PAGE analysis. Expression of MMP-50/100 was additionally studied in kidneys of rats depleted for complement and in kidneys of rats depleted for resident macrophages. Functional significance of MMP-50/100 was studied in kidneys of rats with mesangial glomerulopathies. RESULTS: Immunoelectron microscopy showed that MMP-50/100 is located in the extracellular matrix of the rat renal mesangium between mesangial cells and the basement membrane and on the mesangial cell membrane. SDS-PAGE analysis of affinity-purified glomerular matrices indicated that MMP-50/100 is a polypeptide glycoprotein with chains of apparent molecular weights of 50 and 100 kDa. Both in vivo and in vitro results indicate that MMP-50/100 does not appear to be a complement factor, or an Fc or complement receptor. In rats partially depleted for resident macrophages, the expression of MMP-50/100 was similar to that in control rats. In rats with BSA-induced chronic serum sickness nephritis, in rats with anti-Thy-1 nephritis, and in rats with uninephrectomy-induced focal glomerular sclerosis, the mesangial expression of MMP-50/100 was significantly increased. In the first model, double-label immunofluorescence demonstrated identical localization of MMP-50/100 with mesangial immune complex deposits. CONCLUSIONS: We conclude that MMP-50/100 is an intrinsic component of the mesangial matrix, presumably related to the "classic" mesangial cell. Expression of MMP-50/100 is increased in expanded mesangial matrices during development of glomerular disease. Furthermore, MMP-50/100 appears to be involved in the handling of mesangial immune complexes.

Crystallization and preliminary crystallographic characterization of endo-polygalacturonase II from Aspergillus niger.

The endo-polygalacturonase II from Aspergillus niger has been crystallized from an ammonium sulfate solution by the hanging drop method. The crystals belong to the monoclinic space group P2(1), with cell dimensions a = 69.6 A, b = 152.6 A, c = 74.0 A and beta = 91.2 degrees with four molecules per asymmetric unit. The crystals diffract to at least 2.8 A resolution and are suitable for X-ray analysis.

Crystallization and preliminary crystallographic analysis of antistasin, a leech-derived inhibitor of blood coagulation factor Xa.

The salivary gland of the Mexican leech Haementeria officinalis contains a 15 kDa protein which is a potent and selective inhibitor of factor Xa. It inhibits not only blood coagulation, but also metastasis. A gene, coding for a sequence similar to published antistasin sequences, has been synthesized and expressed in Chinese hamster ovary (CHO) cells. The recombinant protein was purified and crystallized at pH 6.0, using 31% ammonium sulfate as a precipitant. The crystals diffract at least to 2.8 A. The spacegroup is I422 with a = b = 77.7 A and c = 88.4 A. The crystals contain 42% solvent and one protein molecule in the asymmetric unit. A search for heavy atom derivatives is in progress.

Crystallization of porcine liver ribonuclease inhibitor a member of the family of proteins containing leucine-rich repeats.

Single crystals of the RNase inhibitor from porcine liver have been obtained from 30 to 34% saturated ammonium sulphate solutions at pH 6.0 to 7.2, containing 20 mM dithiothreitol, at room temperature over a period of two to three weeks. Because the inhibitor contains 30 1/2-cystinyl residues, all of which occur in the free thiol form, crystallization experiments were carried out in a desiccator under a nitrogen atmosphere. The crystals belong to the tetragonal space group I4, with cell dimensions a = b = 134.76 A and c = 83.65 A. The asymmetric part of the unit cell contains two molecules with a molecular mass of 49,093 Da, as could be shown with a self-rotation function calculated in the resolution range 10.0 to 3.2 A. The crystals diffract to at least 3.2 A resolution and are suitable for an X-ray structure determination.