Bispecific CD8 Treg modulators regulate a novel regulatory CD8 T cell network and eliminate pathogenic CD4 T cells in live cell co-culture system

INTRODUCTION

Others have described a subset of CD8 T cells (CD8 Treg) with immunosuppressive characteristics in inflammatory disease settings. CD8 Treg activation through canonical T cell receptors results in their oligoclonal expansion and perforin dependent elimination of pathogenic CD4 T cells. We have described the CD8 Treg network in Celiac patients and its potential to eliminate pathogenic CD4 T cells. Here we describe bispecific CD8 Treg modulators that activate CD8 Tregs, resulting in pathogenic CD4 T cell death.

METHODS

Novel bispecific CD8 Treg modulators were tested for target specificity by Octet and cell binding. The functional impact of CD8 Treg modulators was evaluated using flow and Luminex assays, and in a live cell co-culture system using Celiac patient derived CD8 Tregs and gliadin activated CD4 T cell targets. CD8 Treg modulators with specific molecular formats were then ranked for functional efficacy.

RESULTS

We tested a panel of bispecific CD8 Treg modulators with monovalent binding affinities in the low nanomolar range that selectively bind the CD8 Treg subset. Within 48 hours of CD8 Treg modulator addition to T cell co-cultures, CD8 Tregs had a rapid increase of cytolytic markers and degranulation in response to CD4 T cell targets. We observed a concomitant increase of activated CD4 T cell death and decrease of pro-inflammatory cytokines.

CONCLUSIONS

Our results indicate that a targeted approach to engage and activate CD8 Treg reduces pathogenic CD4 T cells. As this newly described CD8 Treg cell network is observed in many autoimmune diseases, we postulate that bispecific CD8 T cell modulators may represent a novel, selective and broadly applicable therapeutic approach for the treatment of human autoimmune diseases.

The engineered CD80 variant fusion therapeutic davoceticept combines checkpoint antagonism with conditional CD28 costimulation for anti-tumor immunity

Despite the recent clinical success of T cell checkpoint inhibition targeting the CTLA-4 and PD-1 pathways, many patients either fail to achieve objective responses or they develop resistance to therapy. In some cases, poor responses to checkpoint blockade have been linked to suboptimal CD28 costimulation and the inability to generate and maintain a productive adaptive anti-tumor immune response. To address this, here we utilize directed evolution to engineer a CD80 IgV domain with increased PD-L1 affinity and fuse this to an immunoglobulin Fc domain, creating a therapeutic (ALPN-202, davoceticept) capable of providing CD28 costimulation in a PD-L1-dependent fashion while also antagonizing PD-1 - PD-L1 and CTLA-4–CD80/CD86 interactions. We demonstrate that by combining CD28 costimulation and dual checkpoint inhibition, ALPN-202 enhances T cell activation and anti-tumor efficacy in cell-based assays and mouse tumor models more potently than checkpoint blockade alone and thus has the potential to generate potent, clinically meaningful anti-tumor immunity in humans.

ICOSL+ plasmacytoid dendritic cells as inducer of graft-versus-host disease, responsive to a dual ICOS/CD28 antagonist

Acute graft-versus-host disease (aGVHD) remains a major complication of allogeneic hematopoietic cell transplantation (HCT). CD146 and CCR5 are proteins that mark activated T helper 17 (Th17) cells. The Th17 cell phenotype is promoted by the interaction of the receptor ICOS on T cells with ICOS ligand (ICOSL) on dendritic cells (DCs). We performed multiparametric flow cytometry in a cohort of 156 HCT recipients and conducted experiments with aGVHD murine models to understand the role of ICOSL⁺ DCs. We observed an increased frequency of ICOSL⁺ plasmacytoid DCs, correlating with CD146⁺CCR5⁺ T cell frequencies, in the 64 HCT recipients with gastrointestinal aGVHD. In murine models, donor bone marrow cells from ICOSL-deficient mice compared to those from wild-type mice reduced aGVHD-related mortality. Reduced aGVHD resulted from lower intestinal infiltration of pDCs and pathogenic Th17 cells. We transplanted activated human ICOSL⁺ pDCs along with human peripheral blood mononuclear cells into immunocompromised mice and observed infiltration of intestinal CD146⁺CCR5⁺ T cells. We found that prophylactic administration of a dual human ICOS/CD28 antagonist (ALPN-101) prevented aGVHD in this model better than did the clinically approved belatacept (CTLA-4-Fc), which binds CD80 (B7-1) and CD86 (B7-2) and interferes with the CD28 T cell costimulatory pathway. When started at onset of aGVHD signs, ALPN-101 treatment alleviated symptoms of ongoing aGVHD and improved survival while preserving antitumoral cytotoxicity. Our data identified ICOSL⁺-pDCs as an aGVHD biomarker and suggest that coinhibition of the ICOSL/ICOS and B7/CD28 axes with one biologic drug may represent a therapeutic opportunity to prevent or treat aGVHD.

Abstract LB-085: ALPN-202 combines checkpoint inhibition with conditional T cell costimulation to overcome T cell suppression by M2c macrophages and improve the durability of engineered T cell anti-tumor responses

Background: Despite significant clinical benefit of checkpoint inhibitors (CPI) in some settings, unfortunately, the majority of patients still fail to respond and/or develop resistance. This is likely due to a complex set of factors including, but not limited to, the presence of immunosuppressive myeloid cells and/or T cell exhaustion due to chronic TCR activation in the absence of sufficient costimulation. ALPN-202, a variant CD80 vIgD™-Fc fusion protein that mediates PD-L1-dependent CD28 costimulation and blocks PD-L1 and CTLA-4, was designed to overcome several of these suppressive mechanisms. The objective of these studies was to measure effects of ALPN-202 on the suppression of T cell activation by M2c macrophages and to determine in vivo effects of ALPN-202 on T cell exhaustion in an adoptively transferred human TCR transgenic tumor model. Methods: M2c macrophages differentiated from primary monocytes with M-CSF and IL-10 were cocultured for 72hr with T cells, anti-CD3 and a titration of ALPN-202, anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibodies. Cytokine concentrations in the culture media were measured at 24 and 72 hrs, and T cells and macrophages characterized at 72 hrs by flow cytometry. To measure its anti-tumor activity and effect on T cell exhaustion in vivo, ALPN-202 was evaluated in a humanized model using anti-HPV E6 TCR-transduced human T cells transferred into immunodeficient NSG mice bearing HPV+ SCC152 squamous cell tumors stably expressing PD-L1. Tumor volume was measured twice weekly and on day 38 tumors were harvested, digested, and intratumoral T cells characterized for expression of exhaustion markers. Results: In the in vitro coculture assay, ALPN-202 increased T cell proliferation and production of IL-2, IFNγ, TNFα, GM-CSF, IL-6, and IL-21 significantly more potently than CPI alone. Additionally, the M2c macrophages in the presence of ALPN-202 displayed a dose-dependent elevation of MHC II, CD80, and CD86, indicative of a more pro-inflammatory, M1-like phenotype. In the SCC152 tumor model, ALPN-202 induced a more robust anti-tumor response than CPI while the intratumoral T cells expressed lower levels of exhaustion markers. Conclusions: As a dual checkpoint inhibitor and conditional CD28-costimulator, ALPN-202 induced robust and selective T cell costimulation in vitro which overcame M2c macrophage-mediated suppression more potently than CPI alone. Intriguingly, not only were T cells vigorously activated, but M2c macrophages transitioned to a more M1-like proinflammatory phenotype. In a humanized tumor model, ALPN-202 treatment resulted in potent anti-tumor activity with reduced signs of T cell exhaustion in the TME. The data suggest that by combining CD28 costimulation with CPI, ALPN-202 may provide a more robust and persistent anti-tumor T cell response compared to CPI alone.

Citation Format: Mark F. Maurer, Siddarth Chandrasekaran, Katherine Lewis, Sherri Mudri, Kayla Kleist, Fariha Ahmed-Qadri, Chelsea Gudgeon, Steven D. Levin, Stacey R. Dillon, Kristine M. Swiderek, Stanford L. Peng. ALPN-202 combines checkpoint inhibition with conditional T cell costimulation to overcome T cell suppression by M2c macrophages and improve the durability of engineered T cell anti-tumor responses [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-085.

Abstract P1-20-03: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Dillon SR, Evans LS, Rickel E, Lewis KE, Swanson R, Levin SD, Wolfson M, Peng SL, Swiderek KM. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-20-03.

Partial efficacy of a broadly neutralizing antibody against cell-associated SHIV infection

Broadly neutralizing antibodies (BnAbs) protect macaques from cell-free simian/human immunodeficiency virus (SHIV) challenge, but their efficacy against cell-associated SHIV is unclear. Virus in cell-associated format is highly infectious, present in transmission-competent bodily fluids, and potentially capable of evading antibody-mediated neutralization. The PGT121 BnAb, which recognizes an epitope consisting of the V3 loop and envelope glycans, mediates antibody-dependent cellular cytotoxicity and neutralization of cell-to-cell HIV-1 transmission. To evaluate whether a BnAb can prevent infection after cell-associated viral challenge, we infused pigtail macaques with PGT121 or an isotype control and challenged animals 1 hour later intravenously with SHIV_SF162P3-infected splenocytes. All five controls had high viremia 1 week after challenge. Three of six PGT121-infused animals were completely protected, two of six animals had a 1-week delay in onset of high viremia, and one animal had a 7-week delay in onset of viremia. The infused antibody had decayed on average to 2.0 μg/ml by 1 week after infusion and was well below 1 μg/ml (range, <0.1 to 0.8 μg/ml) by 8 weeks. The animals with a 1-week delay before high viremia had relatively lower plasma concentrations of PGT121. Transfer of 22 million peripheral blood mononuclear cells (PBMCs) stored at weeks 1 to 4 from the animal with the 7-week delayed onset of viremia into uninfected macaques did not initiate infection. Our results show that HIV-1-specific neutralizing antibodies have partial efficacy against cell-associated virus exposure in macaques. We conclude that sustaining high concentrations of bioavailable BnAb is important for protecting against cell-associated virus.

Immunological considerations for developing antibody therapeutics for Influenza A

Influenza infection can give rise to serious illness leading to complications and hospitalization of patients. The efficacy of current standard of care is very limited and provides little relief for patients hospitalized with serious flu. Human monoclonal antibodies (mAb) against influenza are being developed as new treatment options for this patient population. When developing antibody therapeutics, it is important to consider all possible immunologic effects of the antibodies on viral infection and disease progression including those other than the postulated therapeutic mechanisms. An area of concern is the potential of antibody-dependent enhancement (ADE) of illness. ADE of viral infections has been extensively described for Dengue virus (DENV) but not for influenza. Recently, preliminary results from clinical viral challenge studies of anti-HA-stalk mAbs suggested the possibility of enhanced viral shedding, raising concerns for ADE when utilizing mAbs as therapeutic intervention for influenza although viral shedding was not enhanced in the clinical viral challenge of anti-M2 mAb TCN-032. We herein discuss the known mechanisms of ADE and their relevance to developing mAbs such as anti-HA and anti-M2 for influenza disease.

Abstract 870: Derivation and characterization of antibodies from immune checkpoint blockade treated cancer patients

The IgG+ memory B cell repertoire of cancer patients demonstrating durable responses to immune checkpoint blockade therapy has been interrogated to identify tumor specific antibodies. Matched serum and PBMC samples have been collected from 10 melanoma patients with durable responses to treatment with ipilimumab. A panel of 7 well characterized melanoma cell lines with a diverse set of oncogenic driver mutations has been employed to assess durable responder patient serum reactivity to cell surface determinants in a live-cell flow cytometry assay. IgG+ memory B cells obtained from several prioritized durable responder melanoma patients have been plated out on 384 well plates at monoclonal density. The memory B cells have been activated in a short term culture system optimized to expand the clonal B cells and induce secretion of IgG. Antibodies secreted from clonally expanded B cells have been screened using live cell high throughput multiplex flow cytometry assays against a panel of melanoma cell lines. A prioritized subset of antibodies, selected on the basis of tumor cell line binding profiles and antibody v-region sequences, has been cloned and expressed as recombinant IgG1. A cell surface target for a prioritized antibody has been identified and the in vitro analysis and characterization of the antibody including functional activity and immunohistochemistry staining on tumor and normal tissues has been carried out in preparation for in vivo testing of efficacy.

Citation Format: Mark Branum, Laura Smith, Heather Brett, Paul Algate, Brad Greenfield, William Brown, Kristine M. Swiderek. Derivation and characterization of antibodies from immune checkpoint blockade treated cancer patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 870.

Efficacy and safety of treatment with an anti-m2e monoclonal antibody in experimental human influenza

BACKGROUND

The efficacy of TCN-032, a human monoclonal antibody targeting a conserved epitope on M2e, was explored in experimental human influenza.

METHODS

Healthy volunteers were inoculated with influenza A/Wisconsin/67/2005 (H3N2) and received a single dose of the study drug, TCN-032, or placebo 24 hours later. Subjects were monitored for symptoms, viral shedding, and safety, including cytokine measurements. Oseltamivir was administered 7 days after inoculation.

RESULTS

Although the primary objective of reducing the proportion of subjects developing any grade ≥2 influenza symptom or pyrexia, was not achieved, TCN-032-treated subjects showed 35% reduction (P = .047) in median total symptom area under the curve (days 1-7) and 2.2 log reduction in median viral load area under the curve (days 2-7) by quantitative polymerase chain reaction (P = .09) compared with placebo-treated subjects. TCN-032 was safe and well tolerated with no additional safety signals after administration of oseltamivir. Serum cytokine levels (interferon γ, tumor necrosis factor α, and interleukin 8 and 10) were similar in both groups. Genotypic and phenotypic analyses showed no difference between virus derived from subjects after TCN-032 treatment and parental strain.

CONCLUSIONS

These data indicate that TCN-032 may provide immediate immunity and therapeutic benefit in influenza A infection, with no apparent emergence of resistant virus. TCN-032 was safe with no evidence of immune exacerbation based on serum cytokine expression. Clinicaltrials.gov registry number. NCT01719874.

Physiological effects of unassembled chaperonin Cct subunits in the yeast Saccharomyces cerevisiae

Eukaryotic chaperonins, the Cct complexes, are assembled into two rings, each of which is composed of a stoichiometric array of eight different subunits, which are denoted Cct1p-Cct8p. Overexpression of a single CCT gene in Saccharomyces cerevisiae causes an increase of the corresponding Cct subunit, but not of the Cct complex. Nevertheless, overexpression of certain Cct subunits, especially CCT6, suppresses a wide range of abnormal phenotypes, including those caused by the diverse types of conditional mutations tor2-21, lst8-2 and rsp5-9 and those caused by the concomitant overexpression of Sit4p and Sap155p. The examination of 73 altered forms of Cct6p revealed that the cct6-24 mutation, containing GDGTT --> AAAAA replacements of the conserved ATP-binding motif, was unable to suppress any of these traits, although the cct6-24 allele was completely functional for growth. These results provide evidence for functional differences among Cct subunits and for physiological properties of unassembled subunits. We suggest that the suppression is due to the competition of specific Cct subunits for activities that normally modify various cellular components. Furthermore, we also suggest that the Cct subunits can act as suppressors only in certain states, such as when associated with ATP.

Functional interaction of heterogeneous nuclear ribonucleoprotein C with poliovirus RNA synthesis initiation complexes

We had previously demonstrated that a cellular protein specifically interacts with the 3' end of poliovirus negative-strand RNA. We now report the identity of this protein as heterogeneous nuclear ribonucleoprotein (hnRNP) C1/C2. Formation of an RNP complex with poliovirus RNA was severely impaired by substitution of a lysine, highly conserved among vertebrates, with glutamine in the RNA recognition motif (RRM) of recombinant hnRNP C1, suggesting that the binding is mediated by the RRM in the protein. We have also shown that in a glutathione S-transferase (GST) pull-down assay, GST/hnRNP C1 binds to poliovirus polypeptide 3CD, a precursor to the viral RNA-dependent RNA polymerase, 3D(pol), as well as to P2 and P3, precursors to the nonstructural proteins. Truncation of the auxiliary domain in hnRNP C1 (C1DeltaC) diminished these protein-protein interactions. When GST/hnRNP C1DeltaC was added to in vitro replication reactions, a significant reduction in RNA synthesis was observed in contrast to reactions supplemented with wild-type fusion protein. Indirect functional depletion of hnRNP C from in vitro replication reactions, using poliovirus negative-strand cloverleaf RNA, led to a decrease in RNA synthesis. The addition of GST/hnRNP C1 to the reactions rescued RNA synthesis to near mock-depleted levels. Furthermore, we demonstrated that poliovirus positive-strand and negative-strand RNA present in cytoplasmic extracts prepared from infected HeLa cells coimmunoprecipitated with hnRNP C1/C2. Our findings suggest that hnRNP C1 has a role in positive-strand RNA synthesis in poliovirus-infected cells, possibly at the level of initiation.

A tenascin-C aptamer identified by tumor cell SELEX: systematic evolution of ligands by exponential enrichment

The targeting of molecular repertoires to complex systems rather than biochemically pure entities is an accessible approach that can identify proteins of biological interest. We have probed antigens presented by a monolayer of tumor cells for their ability to interact with a pool of aptamers. A glioblastoma-derived cell line, U251, was used as the target for systematic evolution of ligands by exponential enrichment by using a single-stranded DNA library. We isolated specifically interacting oligonucleotides, and biochemical strategies were used to identify the protein target for one of the aptamers. Here we characterize the interaction of the DNA aptamer, GBI-10, with tenascin-C, an extracellular protein found in the tumor matrix. Tenascin-C is believed to be involved in both embryogenesis and oncogenesis pathways. Systematic evolution of ligands by exponential enrichment appears to be a successful strategy for the a priori identification of targets of biological interest within complex systems.

Cell proteins TIA-1 and TIAR interact with the 3' stem-loop of the West Nile virus complementary minus-strand RNA and facilitate virus replication

It was reported previously that four baby hamster kidney (BHK) proteins with molecular masses of 108, 60, 50, and 42 kDa bind specifically to the 3'-terminal stem-loop of the West Nile virus minus-stand RNA [WNV 3'(-) SL RNA] (P. Y. Shi, W. Li, and M. A. Brinton, J. Virol. 70:6278-6287, 1996). In this study, p42 was purified using an RNA affinity column and identified as TIAR by peptide sequencing. A 42-kDa UV-cross-linked viral RNA-cell protein complex formed in BHK cytoplasmic extracts incubated with the WNV 3'(-) SL RNA was immunoprecipitated by anti-TIAR antibody. Both TIAR and the closely related protein TIA-1 are members of the RNA recognition motif (RRM) family of RNA binding proteins. TIA-1 also binds to the WNV 3'(-) SL RNA. The specificity of these viral RNA-cell protein interactions was demonstrated using recombinant proteins in competition gel mobility shift assays. The binding site for the WNV 3'(-) SL RNA was mapped to RRM2 on both TIAR and TIA-1. However, the dissociation constant (K(d)) for the interaction between TIAR RRM2 and the WNV 3'(-) SL RNA was 1.5 x 10(-8), while that for TIA-1 RRM2 was 1.12 x 10(-7). WNV growth was less efficient in murine TIAR knockout cell lines than in control cells. This effect was not observed for two other types of RNA viruses or two types of DNA viruses. Reconstitution of the TIAR knockout cells with TIAR increased the efficiency of WNV growth, but neither the level of TIAR nor WNV replication was as high as in control cells. These data suggest a functional role for TIAR and possibly also for TIA-1 during WNV replication.

Sera from children with type 1 diabetes mellitus react against a new group of antigens composed of lysophospholipids

Several autoantibodies related to Type 1 diabetes mellitus and their corresponding autoantigens have been previously identified. While peptide antigens are more widely recognized, lipid antigens like sulfatides and gangliosides are also known epitopes for the diabetic humoral immune response. Islet cell antibodies (ICA) in Type 1 diabetes are heterogeneous immunoglobulins directed against selected antigens in the islets of Langerhans. Moreover, ICA may be the best predictive marker of disease in family members of patients with Type 1 diabetes. The aims of this study were: (1) to purify lipids from porcine pancreas that contain ICA epitopes; (2) to characterize these lipid antigens, and (3) to use the purified lipids in an assay to detect antibodies in patients with Type 1 diabetes. A unique family of 4 lysophospholipids, 1 fully characterized as lysophosphatidylmyoinositol, partially inhibited ICA staining, and therefore, were considered to be candidate antigens for an ICA immunoassay. Using a dot blot immunoassay, we detected antibodies directed against these phospholipids in 28 out of 46 (61%) diabetic sera, while detecting only 1 false positive out of 28 nondiabetic sera (3.6%; p < 0.0001 comparing diabetic vs. nondiabetic serum). Therefore, lysophospholipid immunoassay positivity is present in sera of Type 1 diabetic patients. Furthermore, we detected 15 out of 23 ICA-negative diabetic sera (65.2%), showing that our phospholipid immunoassay does not correlate with ICA positivity.

Cloning of the mspA gene encoding a porin from Mycobacterium smegmatis

Porins form channels in the mycolic acid layer of mycobacteria and thereby control access of hydrophilic molecules to the cell. We purified a 100 kDa protein from Mycobacterium smegmatis and demonstrated its channel-forming activity by reconstitution in planar lipid bilayers. The mspA gene encodes a mature protein of 184 amino acids and an N-terminal signal sequence. MALDI mass spectrometry of the purified porin revealed a mass of 19 406 Da, in agreement with the predicted mass of mature MspA. Dissociation of the porin by boiling in 80% dimethyl sulphoxide yielded the MspA monomer, which did not form channels any more. Escherichia coli cells expressing the mspA gene produced the MspA monomer and a 100 kDa protein, which had the same channel-forming activity as whole-cell extracts of M. smegmatis with organic solvents. These proteins were specifically detected by a polyclonal antiserum that was raised to purified MspA of M. smegmatis. These results demonstrate that the mspA gene encodes a protein of M. smegmatis, which assembles to an extremely stable oligomer with high channel-forming activity. Database searches did not reveal significant similarities to any other known protein. Southern blots showed that the chromosomes of fast-growing mycobacterial species contain homologous sequences to mspA, whereas no hybridization could be detected with DNA from slow growing mycobacteria. These results suggest that MspA is the prototype of a new class of channel-forming proteins.

Hepatitis A virus capsid protein VP1 has a heterogeneous C terminus

Hepatitis A virus (HAV) encodes a single polyprotein which is posttranslationally processed into the functional structural and nonstructural proteins. Only one protease, viral protease 3C, has been implicated in the nine protein scissions. Processing of the capsid protein precursor region generates a unique intermediate, PX (VP1-2A), which accumulates in infected cells and is assumed to serve as precursor to VP1 found in virions, although the details of this reaction have not been determined. Coexpression in transfected cells of a variety of P1 precursor proteins with viral protease 3C demonstrated efficient production of PX, as well as VP0 and VP3; however, no mature VP1 protein was detected. To identify the C-terminal amino acid residue of HAV VP1, we performed peptide sequence analysis by protease-catalyzed [18O]H2O incorporation followed by liquid chromatography ion-trap microspray tandem mass spectrometry of HAV VP1 isolated from purified virions. Two different cell culture-adapted isolates of HAV, strains HM175pE and HM175p35, were used for these analyses. VP1 preparations from both virus isolates contained heterogeneous C termini. The predominant C-terminal amino acid in both virus preparations was VP1-Ser274, which is located N terminal to a methionine residue in VP1-2A. In addition, the analysis of HM175pE recovered smaller amounts of amino acids VP1-Glu273 and VP1-Thr272. In the case of HM175p35, which contains valine at amino acid position VP1-273, VP1-Thr272 was found in addition to VP1-Ser274. The data suggest that HAV 3C is not the protease responsible for generation of the VP1 C terminus. We propose the involvement of host cell protease(s) in the production of HAV VP1.

Isolation and comparison of natural and recombinant human CENP-A autoantigen

Anticentromere antibodies (ACA) are associated with systemic sclerosis (scleroderma) patients exhibiting the more benign or so called limited manifestation of the disease (lSSc). ACA reactivity is directed against multiple polypeptide targets, the smallest of which is designated CENP-A. CENP-A is not an abundant cellular constituent; therefore to maximize recovery, we developed a protocol with a minimum of steps to isolate CENP-A from a human cell line. The trace cellular amount of this protein clearly dictated the production of its recombinant counterpart to facilitate determination of the role of the CENP-A antigen in scleroderma pathogenesis. Here we describe the eukaryotic expression of CENP-A cDNA using baculovirus-mediated infection of insect cells. The non-fusion recombinant protein spans the natural residues of the human CENP-A protein and rCENP-A followed the same chromotographic sequence for purification as did the natural source. The availability of the bona fide antigen provided a critical standard upon which to document authenticity of the recombinant polypeptide. The two forms of this antigen have been compared and shown to exhibit similar physical and antigenic properties.

Solid-phase synthesis and characterization of carcinoembryonic antigen (CEA) domains

Carcinoembryonic antigen (CEA), a 180,000 dalton cell surface glycoprotein expressed on tumors of the colon, breast, ovary, and lung, has seven predicted immunoglobulin-like domains (N-A1-B1-A2-B2-A3-B3), most of which are recognized by distinct monoclonal antibodies. To study the individual domains, we have prepared several of the domains (N, A3, B3, and A3-B3) by solid-phase peptide synthesis. The syntheses were performed by the Fmoc method using single couplings, elevated temperatures for both the coupling and deblocking reactions, and a flexible solvent system for the coupling reactions. The syntheses were accomplished on an in-house built synthesizer which allowed for temperature control and flexible solvent control during the course of the coupling reactions. Due to the large size of the peptides (84-184 residues), it was anticipated that the overall purity of the final product would not exceed 60% even for an average coupling yield of 99.5%. Therefore, several of the peptides were synthesized with a His6 "tail" at the amino terminus, allowing for purification on a Ni-NTA chelate column. For the most part, the purified peptides exhibited single sharp peaks by RP-HPLC, migrated at their expected molecular weights by gel permeation chromatography, gave correct masses by electrospray ionization or matrix-assisted laser desorption ionization time of flight mass spectrometry, gave the expected amino acid analyses, N-terminal sequences, and tryptic maps, and bound their appropriate monoclonal antibodies. The N-domain was extremely hydrophobic, requiring 6M guanidinium hydrochloride for solubilization, the A3 domain was soluble in dilute acid, and the B3 domain had an intermediate solubility. The affinity constants of the A3 domain and several mutants (also made by peptide synthesis) are reported, along with characterization of the 178 amino acid two-domain peptide, A3-B3. Although there is no evidence for proper folding of these domains by NMR, their ability to bind monoclonal antibodies with high affinity suggests that this is a plausible approach for producing individual domains of CEA.

Selenium-dependent glutathione peroxidase-GI is a major glutathione peroxidase activity in the mucosal epithelium of rodent intestine

Gpx2 mRNA, encoding a selenium-dependent glutathione peroxidase (GPX-GI), has been found to be highly expressed in the gastrointestinal tract (GI) mucosal epithelium. In this study, we show that GPX-GI is produced in the mucosal epithelium of the adult rat GI tract and that the activity levels are comparable to that from GPX-1. Post-mitochondrial supernatant GPX activity from the mucosal epithelium of the complete length of the small intestine was partially purified. A sample enriched for putative GPX-GI was fractionated by SDS-polyacrylamide gel electrophoresis. Polypeptides of 21 kDa and 22 kDa were digested with trypsin. After resolving the tryptic peptides by high pressure liquid chromatography (HPLC), the major peaks were analyzed for their amino acid sequence by Microflow-HPLC-Tandem Mass Spectrometry and automated Edman degradation sequencing. Both methods revealed that the 21-kDa sample contained rat GPX-GI determined by the sequence homology with the deduced mouse GPX-GI polypeptide sequence. Rat GPX-1 was also detected in the samples. AntiGPX-GI and antiGPX-1 antibodies were used to determine the distribution of the respective isoenzyme activities along the length of the intestine and with respect to the crypt to villus axis in rats. GPX-GI and GPX-1 activities were uniformly distributed in the middle and lower GI tract and with respect to the crypt to villus axis. GPX-GI activity accounted nearly the same percentage of the total GPX activity as GPX-1 in all of the these compartments. Studies on the distal ileum segment of wildtype and Gpx1 gene knockout mice showed that GPX-GI activity was also at parity with GPX-1 in the mucosal epithelium of this segment.

MgATP binding to the nucleotide-binding domains of the eukaryotic cytoplasmic chaperonin induces conformational changes in the putative substrate-binding domains

The eukaryotic cytosolic chaperonins are large heterooligomeric complexes with a cylindrical shape, resembling that of the homooligomeric bacterial counterpart, GroEL. In analogy to GroEL, changes in shape of the cytosolic chaperonin have been detected in the presence of MgATP using electron microscopy but, in contrast to the nucleotide-induced conformational changes in GroEL, no details are available about the specific nature of these changes. The present study identifies the structural regions of the cytosolic chaperonin that undergo conformational changes when MgATP binds to the nucleotide binding domains. It is shown that limited proteolysis with trypsin in the absence of MgATP cleaves each of the eight subunits approximately in half, generating two fragments of approximately 30 kDa. Using mass spectrometry (MS) and N-terminal sequence analysis, the cleavage is found to occur in a narrow span of the amino acid sequence, corresponding to the peptide binding regions of GroEL and to the helical protrusion, recently identified in the structure of the substrate binding domain of the archeal group II chaperonin. This proteolytic cleavage is prevented by MgATP but not by ATP in the absence of magnesium, ATP analogs (MgATPyS and MgAMP-PNP) or MgADP. These results suggest that, in analogy to GroEL, binding of MgATP to the nucleotide binding domains of the cytosolic chaperonin induces long range conformational changes in the polypeptide binding domains. It is postulated that despite their different subunit composition and substrate specificity, group I and group II chaperonins may share similar, functionally-important, conformational changes. Additional conformational changes are likely to involve a flexible helix-loop-helix motif, which is characteristic for all group II chaperonins.

The identification of peptide modifications derived from gel-separated proteins using electrospray triple quadrupole and ion trap analyses

Microspray tandem mass spectrometry (MS/MS) in combination with database search routines has become a powerful tool for the identification of proteins from femtomole amounts of material following gel electrophoresis and in-gel digestion procedures. However, artifactual modification of susceptible residues can arise during gel electrophoresis, leading to unexpected peptide mass shifts during mass analysis. Consequently, collision-induced dissociation (CID) spectra generated from these derivatized peptides can defy direct interpretation by automated database search routines and remain unidentified. Here, we evaluate the MS/MS spectra of peptides carrying oxidized derivatives of tryptophane and methionine residues, and various modifications of cysteine. We demonstrate that certain of these modifications generate characteristic fragmentation patterns or "fingerprints", during CID analysis, the knowledge of which can facilitate the interpretation of the spectra. We will show that these signature fragment ions are predominantly produced during the CID analysis of singly charged ions although they can be observed in the MS/MS spectra of the doubly charged species as well. In other cases, the CID spectrum lacks a characteristic fingerprint and the modification remains silent. However, CID spectra of related peptides, differing only by their modifications, are similar and all or part of the fragment ion spectra will have shifted by a discreet mass, which facilitates the identification of the modified residue. At the same time, the comparison of related spectra can prevent misinterpretations such as the assignment of a residue mass to the wrong amino acid or a neutral loss fragment ion to a gamma- or b-ion.

Identification of a steroidogenic neurohormone in female mosquitoes

In the female mosquito, Aedes aegypti, neurohormones are released from the brain in response to a blood meal and stimulate the ovaries to secrete ecdysteroid hormones, which modulate yolk protein synthesis in the fat body. Neuropeptides with this bioactivity were isolated from head extracts, and partial sequences from these peptides when aligned gave a 31-residue sequence at the amino terminus. Oligonucleotide primers for this sequence were used to amplify with the polymerase chain reaction a genomic DNA product that hybridized to a clone from a head cDNA library. The cDNA encodes a 149-residue preprohormone that is processed into an 86-residue peptide, as indicated by the mass value obtained from the native peptide, with the expected amino-terminal sequence. After modification, the cDNA for the putative neurohormone was expressed in a bacterial system, and the purified peptide had high specific activity in bioassays, thus confirming that it is a steroidogenic gonadotropin, the first to be identified for invertebrates.

A novel retinal pigment epithelial protein suppresses neutrophil superoxide generation. II. Purification and microsequencing analysis

In the preceding communication, a novel protein was reported. This protein is secreted by retinal pigment epithelial (RPE) cells, and inhibits generation of superoxide by activated neutrophils in vitro. This protein is synthesized endogenously by RPE cells. The mechanism of inhibition is not by scavenging of the released superoxide; rather the protein intervenes the activation sequence of the neutrophils and, therefore, the consequential release of superoxide. In this study, the novelty of this RPE protein is further established by structural characterization. The supernatant proteins from rabbit RPE cultures were initially separated by a conventional, high capacity, DEAE Sepharose CL-6B anion exchange chromatography. The inhibitory activity on neutrophil superoxide generation was displayed in one fraction. This fraction was further purified either by microseparation anion exchange-high performance liquid chromatography or by microcapillary reversed phase-high performance liquid chromatography. Sodium dodecyl sulfate gel electrophoresis was used in every step of the purification to monitor the homogeneity of the protein. The final purification gave a doublet of 69/75 kDa without other contaminating bands. The microsequencing analysis was carried out by the Edman degradation. Both N-termini were found to be blocked, and the 'on membrane' internal trypsin digestion was carried out. Secondary ion mass spectrometry was used to assess the purity of the tryptic fragments before sequencing analysis. From both the 69 and 75 kDa bands, a total of eight polypeptide sequences were obtained. Three of these sequences share some degree of homology with transferrin family proteins; and the other five sequences did not match any sequence in the database. Therefore, this RPE secretory protein appears to be novel, both in the primary amino acid sequence and in its function. No RPE secretory protein has been reported to display the superoxide inhibitory capability. If this function is also operative in vivo, it could suppress neutrophil-mediated tissue damage in inflammation.

The peptide pQFYRFamide is encoded on the FMRFamide precursor of the snail Helix aspersa but does not activate the FMRFamide-gated sodium current

The complete sequence of the FMRFamide precursor cDNA from Helix aspersa is reported here. Since the 5' end of this cDNA is identical to that of the precursor that encodes the heptapeptide analogs of FLRFamide, the two transcripts are probably derived by alternative RNA splicing. A novel pentapeptide, Glp-Phe-Tyr-Arg-Phe-NH2 (pQFYRFamide), predicted from the cDNA sequence, was purified from extracts of H. aspersa ganglia and identified by mass spectroscopy. Partial gene sequences for the FMRFamide precursors of two closely related pulmonate species-Cepaea nemoralis and Polydontes acutangula-were also determined and compared with the cDNA sequence of H. aspersa and a partial gene sequence previously determined from H. pomatia. Not only are the FMRFamide-related sequences and proteolytic processing sites conserved, but the linear arrangement of these landmarks is also retained. Synthetic pQFYRFamide has some effects on the isolated heart and on neuronal potassium currents in H. aspersa that are similar to those of FMRFamide, but it does not activate the neuronal FMRFamide-gated sodium channel.

Poly(rC) binding protein 2 binds to stem-loop IV of the poliovirus RNA 5' noncoding region: identification by automated liquid chromatography-tandem mass spectrometry

The 5' noncoding region of poliovirus RNA contains an internal ribosome entry site (IRES) for cap-independent initiation of translation. Utilization of the IRES requires the participation of one or more cellular proteins that mediate events in the translation initiation reaction, but whose biochemical roles have not been defined. In this report, we identify a cellular RNA binding protein isolated from the ribosomal salt wash of uninfected HeLa cells that specifically binds to stem-loop IV, a domain located in the central part of the poliovirus IRES. The protein was isolated by specific RNA affinity chromatography, and 55% of its sequence was determined by automated liquid chromatography-tandem mass spectrometry. The sequence obtained matched that of poly(rC) binding protein 2 (PCBP2), previously identified as an RNA binding protein from human cells. PCBP2, as well as a related protein, PCBP1, was over-expressed in Escherichia coli after cloning the cDNAs into an expression plasmid to produce a histidine-tagged fusion protein. Specific interaction between recombinant PCBP2 and poliovirus stem-loop IV was demonstrated by RNA mobility shift analysis. The closely related PCBP1 showed no stable interaction with the RNA. Stem-loop IV RNA containing a three nucleotide insertion that abrogates translation activity and virus viability was unable to bind PCBP2.

A critical proteolytic cleavage site near the C terminus of the yeast retrotransposon Ty1 Gag protein

Cleavage of the Gag and Gag-Pol polyprotein precursors is a critical step in proliferation of retroviruses and retroelements. The Ty1 retroelement of Saccharomyces cerevisiae forms virus-like particles (VLPs) made of the Gag protein. Ty1 Gag is not obviously homologous to the Gag proteins of retroviruses. The apparent molecular mass of Gag is reduced from 58 to 54 kDa during particle maturation. Antibodies raised against the C-terminal peptide of Gag react with the 58-kDa polypeptide but not with the 54-kDa one, indicating that Gag is proteolytically processed at the C terminus. A protease cleavage site between positions 401 and 402 of the Gag precursor was defined by carboxy-terminal sequencing of the processed form of Gag. Certain deletion and substitution mutations in the C terminus of the Gag precursor result in particles that are two-thirds the diameter of the wild-type VLPs. While the Ty1 protease is active in these mutants, their transposition rates are decreased 20-fold compared with that of wild-type Ty1. Thus, the Gag C-terminal portion, released in the course of particle maturation, probably plays a significant role in VLP morphogenesis and Ty1 transposition.

Data-controlled automation of liquid chromatography/tandem mass spectrometry analysis of peptide mixtures

The structural characterization of proteins and peptides isolated in minute quantities requires the most efficient use of available sample. A mass spectrometer data system was programmed to continuously evaluate incoming liquid chromatography/mass spectrometry data against a user-defined array of information. The resulting conclusions were used to automatically set and modify acquisition parameters in real time to collect collision-induced dissociation spectra for selected ions (tandem mass spectrometry). This approach has provided a mechanism to target specific subsets of masses in a complex mixture and/or to discriminate selectively against masses that are known or not of interest. Masses of contaminants or peptide masses derived from known proteins can be automatically recorded and removed from further consideration for collision-induced dissociation analysis. Once recorded, these "libraries" of masses can be used across multiple analyses. This technique directs the mass spectrometer data system to focus on the analysis of masses significant to the user, even if their signal intensities are well below the intensities of contaminating masses. When combined with a database search program to correlate tandem mass spectra to known protein sequences, the identity of the protein can be established unequivocally by using less than 100 fmol of sample.

Definition of the full extent of glycosylation of the 45-kilodalton glycoprotein of Mycobacterium tuberculosis

Chemical evidence for the true glycosylation of mycobacterial proteins was recently provided in the context of the 45-kDa MPT 32 secreted protein of Mycobacterium tuberculosis (K. Dobos, K. Swiderek, K.-H. Khoo, P. J. Brennan, and J. T. Belisle, Infect. Immun. 63:2846-2853, 1995). However, the full extent and nature of glycosylation as well as the location of glycosylated amino acids remained undefined. First, to examine the nature of the covalently attached sugars, the 45-kDa protein was obtained from cells metabolically labeled with D-[U-14C] glucose and subjected to compositional analysis, which revealed mannose as the only covalently bound sugar. Digestion of the protein with the endoproteinase subtilisin and analysis of products by liquid chromatography-electrospray-mass spectrometry on the basis of fragments demonstrating neutral losses of hexose (m/z 162) or pentose (m/z 132) revealed five glycopeptides, S7, S18, S22, S29, and S41 among a total of 50 peptides, all of which produced only m/z 162 fragmentation ion deletions. Fast atom bombardment-mass spectrometry, N-terminal amino acid sequencing, and alpha-mannosidase digestion demonstrated universal O glycosylation of Thr residues with a single alpha-D-Man, mannobiose, or mannotriose unit. Linkages within the mannobiose and mannotriose were all alpha 1-2, as proven by gas chromatography-mass spectrometry of oligosaccharides released by beta-elimination. Total sequences of many of the glycosylated and nonglycosylated peptides combined with published information on the deduced amino acid sequence of the entire 45-kDa protein demonstrated that the sites of glycosylation were located in Pro-rich domains near the N terminus and C terminus of the polypeptide backbone. Specifically, the Thr residues at positions 10 and 18 were substituted with alpha-D-Manp(1-->2)alpha-D-Manp, the Thr residue at position 27 was substituted with a single alpha-D-Manp, and Thr-277 was substituted with either alpha-D-Manp, alpha-D-Manp(1-->2)alpha-D-Manp, or alpha-D-Manp(1--> 2)alpha-D-Manp(1-->2)alpha-D-Manp. This report further corroborates the existence of true prokaryotic glycoproteins, defines the complete structure of a mycobacterial mannoprotein and the first complete structure of a mannosylated mycobacterial protein, and establishes the principles for the study of other mycobacterial glycoproteins.

Amino acid sequence of CAP2b, an insect cardioacceleratory peptide from the tobacco hawkmoth Manduca sexta

The primary structure of a novel insect neuropeptide, Cardioacceleratory Peptide 2b (CAP2b), from the tobacco hawkmoth Manduca sexta has been established using a combination of mass spectroscopy, Edman degradation microsequencing, amino acid analysis, and biological assays. The sequence of CAP2b, pyroGlu-Leu-Tyr-Ala-Phe-Pro-Arg-Val-amide, has a molecular weight of 974.6 and is blocked at both the amino and carboxyl ends. Examination of several national computer protein data bases failed to reveal other peptides or proteins with any sequence homology to CAP2b indicating that this is likely to be a novel insect neuropeptide. This peptide may be a general activator of insect viscera since it causes an increase in heart rate in Manduca and in Drosophila, and has also been implicated in the regulation of fluid secretion by the Malphigian tubules of Drosophila.

Determination of disulphide bridges in PG-2, an antimicrobial peptide from porcine leukocytes

We determined the cysteine connectivity of protegrin PG-2, a leukocyte-derived antimicrobial peptide, by performing sequential enzyme digestions with chymotrypsin and thermolysin, and monitoring each digest by direct liquid chromatography-electrospray mass spectrometric analysis. This approach resolved the disulphide pairing pattern unambiguously with only picomolar amounts of PG-2. The inferred cysteine connectivity was confirmed by traditional amino acid composition analyses using nanomolar amounts of the protegrin. The results suggest that protegrins will assume a tachyplesin-like, disulphide-stabilized anti-parallel beta-sheet configuration in solution.

Prophenin-1, an exceptionally proline-rich antimicrobial peptide from porcine leukocytes

We purified and characterized an unusual antimicrobial peptide, prophenin-1 (PF-1), from porcine leukocytes. The peptide had a mass of 8,683 and contained 79 residues, including 42 (53.2%) prolines and 15 (19.0%) phenylalanines. Its N-terminal 60 residues consisted of three perfect and three nearly perfect repeats of a decamer, FPPPNFPGPR. Prophenin-1 was encoded on a cathelin-containing precursor and showed substantially more activity against E. coli, a Gram-negative bacterium, than against Listeria monocytogenes, a Gram-positive organism, in vitro.

Gallinacins: cysteine-rich antimicrobial peptides of chicken leukocytes

We purified three homologous antimicrobial peptides ('gallinacins') from chicken leukocytes, examined their antimicrobial activity in vitro, and established their primary sequences by a combination of gas phase microsequencing and on-line LC-ESI-MS analysis of endo- and exoprotease peptide digests. The peptides contained 36-39 amino acid residues, were relatively cationic due to their numerous lysine and arginine residues, and each contained 3 intramolecular cystine disulfide bonds. Gallinacins showed primary sequence homology to the recently delineated beta-defensin family, heretofore found only in the respiratory epithelial cells and neutrophils of cattle, suggesting that beta-defensins originated at least 250 million years ago, before avian and mammalian lineages diverged. The 9 invariant residues (6 cysteines, 2 glycines and 1 proline) common to avian gallinacins and bovine beta-defensins are likely to constitute the essential primary structural motif of this ancient family of host-defense peptides.

A two-domain structure for the two subunits of NAD(P)H:quinone acceptor oxidoreductase

NAD(P)H:quinone acceptor oxidoreductase (EC 1.6.99.2) (DT-diaphorase) is a FAD-containing reductase that catalyzes a unique 2-electron reduction of quinones. It consists of 2 identical subunits. In this study, it was found that the carboxyl-terminal portion of the 2 subunits can be cleaved by various proteases, whereas the amino-terminal portion cannot. It was also found that proteolytic digestion of the enzyme can be blocked by the prosthetic group FAD, substrates NAD(P)H and menadione, and inhibitors dicoumarol and phenindione. Interestingly, chrysin and Cibacron blue, 2 additional inhibitors, cannot protect the enzyme from proteolytic digestion. The results obtained from this study indicate that the subunit of the quinone reductase has a 2-domain structure, i.e., an amino-terminal compact domain and a carboxyl-terminal flexible domain. A structural model of the quinone reductase is generated based on results obtained from amino-terminal and carboxyl-terminal protein sequence analyses and electrospray mass spectral analyses of hydrolytic products of the enzyme generated by trypsin, chymotrypsin, and Staphylococcus aureus protease. Furthermore, based on the data, it is suggested that the binding of substrates involves an interaction between 2 structural domains.

Electrospray ionization mass spectrometry as a mechanistic tool: mass of human leucocyte elastase and a beta-lactam-derived E-I complex

We have utilized liquid chromatography electrospray ionization mass spectrometry (ESI-MS) to probe the nature of the covalent E-I complex of human leucocyte elastase (HLE) and a beta-lactam. The mass spectrum of HLE isozyme 4 displayed one major and two minor components with masses of 25,202, 25,043, and 24,522 Da, respectively. Isozyme 3 displayed three components, with masses of 25,180, 24,030, and 24,523 Da. These data suggest that the isozymes differ in the type and not the content of carbohydrate. The minor components represent decreases in carbohydrate content. Inactivation of isozyme 4 with trans-4-(ethoxycarbonyl)-3-ethyl-1-[(4-nitrophenyl)sulfonyl]-azetidin -3-one increased the mass of the three components by that of the parent compound. Similar results were obtained with the mixture of HLE isozymes. These observations demonstrate that HLE does not catalyze the beta-elimination of p-nitrophenylsulfinate as Firestone et al. [(1990) Tetrahedron 46, 2255) suggested. In addition, it suggests that a "double hit" of both the active-site serine and histidine is not required to form a stable acyl-enzyme. Noncovalent complexes between HLE and either the tight-binding secretory leucoprotease inhibitor (SLPI) or a slow tight-binding peptide difluoroketone inhibitor were not observed by ESI-MS. SLPI displayed a mass of 11,710 Da in the absence and presence of HLE. These data demonstrate the utility of ESI-MS to probe the mechanism of inhibition of enzymes by mechanism-based inhibitors.

Structure-function studies of human aromatase

Site-directed mutagenesis experiments have been carried out to determine the structure-function relationship of human aromatase. By sequence comparison, the region in aromatase that corresponds to the distal helix of cytochrome P-450cam has been identified to be Gln-298 to Val-313. Eight aromatase mutants with changes in this region, i.e. C299A, E302L, P308F, D309N, D309A, T310S, T310C, and S312C, have been generated using a mammalian cell stable-expression system. The results from site-directed mutagenesis studies indicate that the region containing Gln-298 to Val-313 is indeed a very important part of the active site of aromatase. The catalytic properties of P308F, D309N, and D309A have been examined in detail and are discussed. Active site-directed labeling is also an important approach to investigate the structure-function relationship of aromatase. HPLC-linked electrospray mass spectrometry is indicated as a useful technique for the characterization of active site-directed probe-modified enzyme. The mass spectral analysis of aromatase suggests that aromatase is glycosylated.

Calmodulin is a subunit of nitric oxide synthase from macrophages

A central issue in nitric oxide (NO) research is to understand how NO can act in some settings as a servoregulator and in others as a cytotoxin. To answer this, we have sought a molecular basis for the differential regulation of the two known types of NO synthase (NOS). Constitutive NOS's in endothelium and neurons are activated by agonist-induced elevation of Ca2+ and resultant binding of calmodulin (CaM). In contrast, NOS in macrophages does not require added Ca2+ or CaM, but is regulated instead by transcription. We show here that macrophage NOS contains, as a tightly bound subunit, a molecule with the immunologic reactivity, high performance liquid chromatography retention time, tryptic map, partial amino acid sequence, and exact molecular mass of CaM. In contrast to most CaM-dependent enzymes, macrophage NOS binds CaM tightly without a requirement for elevated Ca2+. This may explain why NOS that is independent of Ca2+ and elevated CaM appears to be activated simply by being synthesized.

Purification and characterization of PSP-I and PSP-II, two major proteins from porcine seminal plasma

Two major glycoproteins, designated PSP-I and PSP-II, were purified from porcine seminal plasma by ammonium sulfate fractionation, CM-cellulose chromatography, gel filtration on Sephadex G-75 (superfine), and reverse phase high performance liquid chromatography. These two proteins exist in several forms differing mainly in the carbohydrate moiety. The complete amino acid sequence of PSP-I has been determined by automated Edman degradation of peptides generated by proteolytic digestion and cyanogen bromide cleavage. The protein is 109 residues long and has a single glycosylation site at the asparagine residue at position 47. In addition, the N-terminal sequence of PSP-II has also been determined. PSP-I is a unique protein; a sequence homology search using the protein data base did not reveal any significant homology with other proteins. PSP-II shares 50% sequence homology with a family of zona pellucida-binding glycoproteins at the N-terminus.

Cloning and characterization of inducible nitric oxide synthase from mouse macrophages

Nitric oxide (NO) conveys a variety of messages between cells, including signals for vasorelaxation, neurotransmission, and cytotoxicity. In some endothelial cells and neurons, a constitutive NO synthase is activated transiently by agonists that elevate intracellular calcium concentrations and promote the binding of calmodulin. In contrast, in macrophages, NO synthase activity appears slowly after exposure of the cells to cytokines and bacterial products, is sustained, and functions independently of calcium and calmodulin. A monospecific antibody was used to clone complementary DNA that encoded two isoforms of NO synthase from immunologically activated mouse macrophages. Liquid chromatography-mass spectrometry was used to confirm most of the amino acid sequence. Macrophage NO synthase differs extensively from cerebellar NO synthase. The macrophage enzyme is immunologically induced at the transcriptional level and closely resembles the enzyme in cytokine-treated tumor cells and inflammatory neutrophils.

P-type calcium channels blocked by the spider toxin omega-Aga-IVA

Voltage-dependent calcium channels mediate calcium entry into neurons, which is crucial for many processes in the brain including synaptic transmission, dendritic spiking, gene expression and cell death. Many types of calcium channels exist in mammalian brains, but high-affinity blockers are available for only two types, L-type channels (targeted by nimodipine and other dihydropyridine channel blockers) and N-type channels (targeted by omega-conotoxin). In a search for new channel blockers, we have identified a peptide toxin from funnel web spider venom, omega-Aga-IVA, which is a potent inhibitor of both calcium entry into rat brain synaptosomes and of 'P-type' calcium channels in rat Purkinje neurons. omega-Aga-IVA will facilitate characterization of brain calcium channels resistant to existing channel blockers and may assist in the design of neuroprotective drugs.

Antagonism of synaptosomal calcium channels by subtypes of omega-agatoxins

Venom of the funnel web spider Agelenopsis aperta inhibits the binding of 125I-omega-conotoxin GVIA (omega-CgTx) to calcium channels in chick brain synaptosomal membranes. Fractionation of the venom by liquid chromatography shows that this inhibitory activity is associated primarily with a diverse class of peptide toxins called omega-agatoxins (omega-Aga). Using binding inhibition as an assay, we purified and identified the novel, 76-amino acid toxin, omega-Aga-IIIA. Inhibition of 125I-omega-CgTx binding to chick synaptosomal membranes by omega-Aga-IIIA and omega-Aga-IIA is correlated with block of potassium-stimulated 45Ca entry into synaptosomes; omega-Aga-IA neither inhibits 125I-omega-CgTx binding nor 45Ca entry under identical conditions. omega-Aga-IIA and omega-Aga-IIIA are 20-30-fold more potent than omega-CgTx as antagonists of synaptosomal calcium channels. However, whereas omega-CgTx completely blocks 45Ca entry into synaptosomes at saturating concentrations, the omega-agatoxins maximally block only 60-70% of 45Ca entry. Pretreatment of synaptosomes with omega-Aga-IIIA occludes block of 45Ca entry by omega-CgTx. The results indicate that, while the omega-agatoxins bind to the entire population of omega-CgTx-sensitive calcium channels in chick synaptosomal membranes, they exert only a partial block of 45Ca flux. Such block could occur via two distinct mechanisms. Toxin binding may alter the kinetics of a homogeneous population of channels, resulting in lower overall conductance upon depolarization. Alternatively, the omega-agatoxins may bind to two distinct channel subtypes, only one of which is blocked as a result of toxin occupation.

Molecular cloning and expression of the regulatory (RG1) subunit of the glycogen-associated protein phosphatase

DNA clones encoding the glycogen-binding (RG1) subunit of glycogen-associated protein phosphatase were isolated from rabbit skeletal muscle lambda gt11 cDNA libraries. Overlapping clones provided an open reading frame of 3327 nucleotides that predicts a polypeptide of 1109 amino acids with a molecular weight of 124,257. Northern hybridization of rabbit RNA identified a major mRNA transcript of 7.5 kilobases present in skeletal, diaphragm, and cardiac muscle, but not in brain, kidney, liver, and lung. Southern analysis of rabbit genomic DNA digested with various restriction endonucleases gave rise to a single hybridizing fragment, suggesting that a single gene is present. Expression of the complete RG1 subunit coding sequence in Escherichia coli generated a protein of apparent molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of approximately 160,000, similar to the size of the polypeptide detected by Western immunoblot in rabbit skeletal muscle extracts. The RG1 subunit shares significant homology with the Saccharomyces cerevisiae GAC1 gene product which is involved in activation of glycogen synthase and glycogen accumulation. The homology with GAC1 substantiates the role of this enzyme in control of glycogen metabolism. Hydropathy analysis of the RG1 subunit amino acid sequence revealed the presence of a hydrophobic region in the COOH terminus, suggesting a potential association with membrane. This result suggests that the same phosphatase regulatory component may be involved in targeting the enzyme both to membranes and to glycogen.