A unique interhelical insertion in plasminogen activator inhibitor-2 contains three glutamines, Gln83, Gln84, Gln86, essential for transglutaminase-mediated cross-linking

Plasminogen activator inhibitor type 2 (PAI-2) prevents fibrinolysis by blocking plasminogen activators. It is expressed principally by trophoblast cells and macrophages. PAI-2 in trophoblast membranes has been found cross-linked to large complexes apparently catalyzed by trophoblast transglutaminase (Jensen, P. H., Lorand, L., Ebbesen, P., and Gliemann, J. (1993) Eur. J. Biochem. 214, 141-146). Recombinant human PAI-2 was labeled with [14C]putrescine catalyzed by guinea pig liver transglutaminase. The [14C]putrescine-labeled PAI-2 was digested with cyanogen bromide and trypsin, and the peptides were purified by reverse-phase high performance chromatography. Amino acid sequencing and plasma desorption mass spectrometry of the labeled peptides revealed [14C]putrescine incorporation at Gln83, Gln84, and Gln86. These residues are present in a PAI-2-specific region of 33 amino acids that is inserted between helices C and D and which probably represents a unique solvent-exposed domain. A PAI-2 mutant lacking this insertion was determined not to be a substrate for transglutaminase by [14C]putrescine incorporation and could not form transglutaminase-catalyzed polymers. Thus, the unique PAI-2 insertion represents a functional domain that, by virtue of its transglutaminase acceptor sites, allows participation in binding reactions without affecting the inhibitory function of PAI-2.

The isolation of activin from ovine amniotic fluid

During a study of the levels of inhibin and follistatin in ovine amniotic fluid, we noted that although detectable levels of immunoactive inhibin and follistatin were found throughout gestation, the addition of amniotic fluid to a rat anterior pituitary cell culture resulted in a stimulation, rather than the expected suppression, of FSH concentrations. These data suggested the possibility that activin was present in amniotic fluid. We, therefore, set out to isolate the molecules responsible for this activin-like activity and determine their structure. Amniotic fluid, collected from pregnant sheep between 120-140 days gestation, was used as starting material in the purification and diluted in parallel to a human activin-A standard in the activin RIA employed to monitor the purification. A total pool of 7.4 liters amniotic fluid was processed by dye affinity chromatography, hydrophobic interactive chromatography, gel filtration, and a series of reverse phase HPLC steps. Polyacrylamide gel electrophoresis of fractions from the final HPLC step, which showed both activin immunoactivity and bioactivity, revealed a band with a mol wt of 25.3 kilodaltons (kDa), which reduced to 15.8 kDa, and a minor band of 45 kDa, which reduced to 25 kDa. NH2-terminal amino acid sequences of several active fractions from the same region were identical to the known sequence of ovine activin-A. The identification of immunoactive activin, follistatin, and inhibin in amniotic fluid raises the question of the sites of production of these proteins and their interactions and role in fetal physiology.

Comparative study of the T cell response to two allelic forms of a malarial vaccine candidate protein

T cell responses to two allelic forms of the merozoite surface Ag 2 (MSA2) of Plasmodium falciparum were mapped in mice using the rMSA2 proteins, Ag 1609 which has the sequence of the FCQ27/PNG strain and Ag 1615 which has the sequence of the Indochina 1 strain. Lymph node cells of BL/10 and B10.BR mice immunized with either Ag 1609 or Ag 1615 responded to both Ag in in vitro proliferation assays. Lymph node cells of BALB/c mice did not respond. The T cell determinants recognized by the responder strains were mapped to conserved and variant regions of these Ag using overlapping synthetic peptides. The determinants recognized by each mouse strain were distinct. Marked difference in sequence between the central regions of the two rMSA2 proteins did not affect antigenic processing of the conserved N and C terminal regions. Hence lymph node cells of BL/10 mice immunized with either Ag 1615 or Ag 1609 recognized an immunodominant T cell determinant at the highly conserved N terminal end within the sequence YSNTFINNAYNMSIR (peptide 3b) and B10.BR mice similarly immunized recognized an immunodominant determinant at the highly conserved C terminal within the sequence CTDGNKENCGAATSL (peptide 23). Several peptides identified as containing immunodominant T cell determinants specific to BL/10 mice induced peptide-specific T cells in both BL/10 and B10.BR mouse strains when used as immunogens. However, the ability of the peptide-primed T cells to proliferate in response to the rMSA2 proteins was confined to BL/10 mice. An example of this was observed with peptides 3b and N (KNESKYSNTFINNAYNMSIRRSMAN). Peptide N was able to prime B10.BR and BL/10 mice for an enhanced antibody response when these mice were subsequently immunized with Ag 1615 even though Ag 1615-specific T cell proliferation was not detected in B10.BR mice primed with N. The study concluded that 1) conserved sequences such as peptide N when used in vaccines may give rise to MSA2-specific memory Th cells amenable to boosting by subsequent exposure to all parasite strains and 2) peptide priming may be a useful pathway for inducing defined memory Th cells in a wider population and for preferentially inducing T dependent over T independent responses to some malarial Ag.

Comparative study of the T cell response to two allelic forms of a malarial vaccine candidate protein

T cell responses to two allelic forms of the merozoite surface Ag 2 (MSA2) of Plasmodium falciparum were mapped in mice using the rMSA2 proteins, Ag 1609 which has the sequence of the FCQ27/PNG strain and Ag 1615 which has the sequence of the Indochina 1 strain. Lymph node cells of BL/10 and B10.BR mice immunized with either Ag 1609 or Ag 1615 responded to both Ag in in vitro proliferation assays. Lymph node cells of BALB/c mice did not respond. The T cell determinants recognized by the responder strains were mapped to conserved and variant regions of these Ag using overlapping synthetic peptides. The determinants recognized by each mouse strain were distinct. Marked difference in sequence between the central regions of the two rMSA2 proteins did not affect antigenic processing of the conserved N and C terminal regions. Hence lymph node cells of BL/10 mice immunized with either Ag 1615 or Ag 1609 recognized an immunodominant T cell determinant at the highly conserved N terminal end within the sequence YSNTFINNAYNMSIR (peptide 3b) and B10.BR mice similarly immunized recognized an immunodominant determinant at the highly conserved C terminal within the sequence CTDGNKENCGAATSL (peptide 23). Several peptides identified as containing immunodominant T cell determinants specific to BL/10 mice induced peptide-specific T cells in both BL/10 and B10.BR mouse strains when used as immunogens. However, the ability of the peptide-primed T cells to proliferate in response to the rMSA2 proteins was confined to BL/10 mice. An example of this was observed with peptides 3b and N (KNESKYSNTFINNAYNMSIRRSMAN). Peptide N was able to prime B10.BR and BL/10 mice for an enhanced antibody response when these mice were subsequently immunized with Ag 1615 even though Ag 1615-specific T cell proliferation was not detected in B10.BR mice primed with N. The study concluded that 1) conserved sequences such as peptide N when used in vaccines may give rise to MSA2-specific memory Th cells amenable to boosting by subsequent exposure to all parasite strains and 2) peptide priming may be a useful pathway for inducing defined memory Th cells in a wider population and for preferentially inducing T dependent over T independent responses to some malarial Ag.

Immunization of owl monkeys with the ring-infected erythrocyte surface antigen of Plasmodium falciparum

Aotus nancymai were immunized with the 4-mer, 8-mer, and 11-mer repeat peptides of the ring-infected erythrocyte surface antigen molecule of Plasmodium falciparum conjugated to diphtheria toxoid with muramyl dipeptide (MDP) as adjuvant. Immunization failed to induce protective immunity against the Uganda Palo Alto strain of P. falciparum as judged by maximum levels of parasitemia of immunized monkeys relative to those of controls. The fused polypeptide FPAg632, when combined with MDP, also failed to induce protective immunity. However, the maximum level of parasitemia and serologic response to the 11-mer peptide were inversely correlated. The safety of the use of MDP was evident.

Plasminogen activator inhibitor 2 (PAI-2) is not inactivated by exposure to oxidants which can be released from activated neutrophils

Purified recombinant human monocyte plasminogen activator inhibitor 2 (PAI-2) retained inhibitory activity after exposure to a number of oxidants, including hypochlorite anion (OCl-), chloramine-T (CT) and hydrogen peroxide (H2O2). Analysis of PAI-2 exposed to oxidants by gel filtration chromatography and SDS-PAGE indicated that although the protein could no longer be detected by silver staining, this was not due to fragmentation of the PAI-2 molecule. The sensitivity of a number of serine protease inhibitors (serpins), (eg. alpha 1 proteinase inhibitor (alpha 1PI) and plasminogen activator inhibitor 1 (PAI-1] to oxidative inactivation has been attributed to oxidation of reactive site methionine residues and/or tertiary structural modifications. The relevance of these phenomena and the potential for PAI-2 to be used as a therapeutic inhibitor of urokinase (uPA)-dependent proteolysis during inflammation and tumour metastasis is discussed.

The alpha-chain of murine CD8 lacks an invariant Ig-like disulfide bond but contains a unique intrachain loop instead

The CD8 Ag is a cell surface heterodimer which demarcates predominantly cytotoxic T cells which are restricted by class I MHC Ag. The disulfide bonds within the murine structure were assigned in this study and the alpha-beta-interchain bond involves one or more cysteine residues located in each chain proximal to the plasma membrane or included within it. The location of the intrachain disulfide loop within the CD8 beta-chain confirms its proposed structural homology to an IgV domain but no corresponding disulfide loop is present within the alpha-chain. The invariant IgV disulfide loop has been replaced by a unique, short loop involving an unusual cysteine which is conserved in the CD8 alpha-chains of man, mouse, and rat. Despite its lack of precedent in other Ig-related structures, this unusual disulfide loop can be parsimoniously accommodated into a modified domain which has retained the major features of the Ig structural motif.

The alpha-chain of murine CD8 lacks an invariant Ig-like disulfide bond but contains a unique intrachain loop instead

The CD8 Ag is a cell surface heterodimer which demarcates predominantly cytotoxic T cells which are restricted by class I MHC Ag. The disulfide bonds within the murine structure were assigned in this study and the alpha-beta-interchain bond involves one or more cysteine residues located in each chain proximal to the plasma membrane or included within it. The location of the intrachain disulfide loop within the CD8 beta-chain confirms its proposed structural homology to an IgV domain but no corresponding disulfide loop is present within the alpha-chain. The invariant IgV disulfide loop has been replaced by a unique, short loop involving an unusual cysteine which is conserved in the CD8 alpha-chains of man, mouse, and rat. Despite its lack of precedent in other Ig-related structures, this unusual disulfide loop can be parsimoniously accommodated into a modified domain which has retained the major features of the Ig structural motif.