Comparative aspects of prothrombin activation

The activation of the purified prothrombins from human, bovine, and chicken species have been studied. Chicken prothrombin activation, similar to bovine prothrombin, resulted in the formation of a 161 residue prothrombin fragment 1, a 113 residue prothrombin fragment 2, and chicken thrombin with a 49 residue A chain and a B chain of approximately 260 residues. When human prothrombin is converted to thrombin, the resulting thrombin is shorter from the amino-terminus of the A chain by 13 residues (human prothrombin fragment 3). The vitamin K-dependent regions of all three species are very similar in sequence (33 of 46 residues identical for all three species). The regions of internal homology observed within the human and bovine fragments are apparently also present within the chicken fragments, indicating that the partial gene duplication which resulted in the evolution of a prothrombin molecule of greater size than the other vitamin K-dependent coagulation proteins occurred prior to the divergence of birds and mammals over 300 million years ago.

Crystallization of hemoglobins II and III of the symbiont-harboring clam Lucina pectinata

Diffraction data to 2.7 A resolution were measured on crystals of the homotetramers of components II and III of the cytoplasmic hemoglobin of the symbiont-harboring clam Lucina pectinata. Even though the crystallization conditions are different and the sequence homology of the two hemoglobins is only 63%, the crystals are isomorphous to each other and to the heterotetramer Hb II/III, implying that the residues primarily involved in the intermolecular interactions and responsible for crystal cohesion may be invariant.

A hierarchy of disulfide-bonded subunits: the quaternary structure of Eudistylia chlorocruorin

The quaternary structure of the cysteine-rich, approximately 3500-kDa chlorocruorin (Chl) from the marine polychaete Eudistylia vancouverii was investigated using maximum entropy deconvolution of the electrospray ionization mass spectra (ESIMS). The native Chl provided two groups of peaks, at approximately 25 and approximately 33 kDa, and one peak at approximately 66 kDa. ESIMS of the reduced and reduced and carbamidomethylated Chl and of its subunits obtained by HPLC provided the complete subunit composition of the Chl. Two groups of nonglobin linker chains were observed: L1a-f (25 000.4, 25 017.9, 25 039.6, 25 057.0, 25 074.4 and 25 096.8 Da) and L2a-d (25 402.7, 25 446.0, 25 461.6 and 25 478.3Da) (+/-2.5 Da), with relative intensities L1:L2 = 5:2. Six globin chains were found, a1, a2, and b1-4, with reduced masses of 16 051.5, 16 172.4, 16 853.5, 17 088.9, 17 161.2 and 17 103.6 (+/-1.0 Da) and relative intensities of 8:4:1:4:2:1, respectively. Disulfide-bonded dimers and a tetramer of globin chains were identified: D1 = a1 + b3 at 33 207.1; D2 at 33 374.1, which had a cysteinylated Cys (a2 + b2 + Cys); and D3 = a1 + b4 at 33 149.4 Da (+/-3.0 Da), with relative intensities D1:D2:D3 = 5:4:1 and T = a1 + a2 + b1 + b2 at 66 154.8 +/- 4.0 Da. A 206-kDa dodecamer subunit obtained by dissociation of the Chl in 4 M urea [Qabar, A. N., et al. (1991) J. Mol. Biol. 222, 1109-1129], was found to consist only of tetramers T. A model was proposed for the Chl, based on a dimer:tetramer ratio of 2:1: four 206-kDa dodecamers (trimer of tetramers) and 48 dimers tethered to a framework of 30 L1 and 12 L2 linker chains. The 144 globin chains (2480 kDa) and 42 linker chains (1059 kDa) provide a total mass of 3539 kDa, in good agreement with the 3480 +/- 225 kDa determined previously by STEM mass mapping. The hierarchy of disulfide-bonded globin subunits observed for Eudistylia Chl provides a built-in heterogeneity of hexagonal bilayer structures.

Electrospray ionization mass spectrometric study of the multiple intracellular monomeric and polymeric hemoglobins of Glycera dibranchiata

The intracellular hemoglobin (Hb) of the marine polychaete Glycera dibranchiata is comprised of two groups of globins differing in their primary structures and state of aggregation. About six electrophoretically and chromatographically distinct monomeric Hbs which have Leu as the distal residue, and an equal number of polymeric Hbs which have the usual distal His, have been identified to date. Deconvolution of the electrospray ionization mass spectra (ESI-MS) of the Hbs and of their carbamidomethylated, reduced, and reduced/carbamidomethylated forms, using a maximum entropy-based approach (MaxEnt), showed the presence of at least 18 peaks attributable to monomer Hbs (14,500-15,200 Da) and an approximately equal number of polymer Hb peaks (15,500-16,400 Da). Although the ratio of the monomer to polymer components in pooled Hb preparations remained constant at 60:40, Hb from individuals had generally less than 6 monomer and 6 polymer components; -2 of the 19 individuals appeared to be deficient in polymer Hbs. Taking into account possible fragmentations of the known monomeric and polymeric globin sequences, we estimate conservatively that there are 10 monomeric and an equal number of polymeric Hbs, the majority comprising a single free Cys. Surprisingly, the calculated mass of the sequence deduced from the high-resolution monomer Hb crystal structures does not correspond to any of the observed masses. ESI-MS of the monomer Hb crystal revealed 11 components, of which 5, accounting for 67% of total, were related to the three major sequences GMG2-4. These findings underline the need for routine mass spectrometric characterization of all protein preparations. The complete resolution of the Glycera Hb ESI-MS using MaxEnt processing illustrates the power of this method to resolve complex protein mixtures.

Expression of thrombospondin 1 on the surface of activated platelets mediates their interaction with the heavy chains of human kininogens through Lys 244-Pro 254

Platelet thrombospondin (TSP1) forms a complex with high (HK) and low (LK) molecular weight kininogens. We isolated a proteolytic fragment from HK and LK heavy chains (12 kDa) recognized by TSP1 with a N-terminal sequence, K244ICVGCPRDIP254. Lys244-Pro254 oxidized to cyclic form prevented binding of 125I-LK to TSP1. This effect was abolished by reduction and alkylation. Oxidized peptide KICVGCPRDIP (100 microM) reversed the known inhibitory effects of LK or HK (1 microM), on thrombin-induced platelet activation, suggesting this peptide forms part of the cell binding site on HK and LK for activated platelets. KICVGCPRDIP completely inhibited the binding of 125I-LK to activated platelets. However, the peptide only partially inhibited binding of 125I-HK to platelets, suggesting an additional binding site on the HK light chain. Fluorescein-labeled KICVGCPRDIP bound directly and specifically to activated platelets. A monoclonal antibody directed to TSP1 partially inhibited the binding of 125I-HK to activated but not inactivated platelets. We conclude residues Lys244-Pro254 on kininogen heavy chain is responsible for binding to thrombospondin on the surface of activated platelets.

Molecular symmetry of the dodecamer subunit of Lumbricus terrestris hemoglobin

The principal functional subunit of the approximately 3500 kDa extracellular Lumbricus terrestris hemoglobin is a 213 kDa dodecamer of four chemically distinct globin chains, consisting of a non-covalent complex of three trimer submits (disulfide-bonded chains a, b and c) and three monomer subunits (chain d). X-ray diffraction of crystals of the dodecamer grown at neutral pH, were found to be monoclinic, with the unit cell dimensions: a = 112.3 A, b = 190.0 A, c = 69.6 A, beta = 102.0 degrees with h + k + l = 2n + 1 absent, characteristic of space group I121. In addition, these crystals exhibit a pseudo trigonal P321 symmetry with unit cell dimensions a = 190.5 A, b = 190.5 A, c = 69.5 A, gamma = 120.0 degrees. Assuming that the assymetric unit contains an entire dodecamer, a model of the latter was constructed that satisfies the symmetry of the trigonal pseudo cell and is consistent with the symmetry of the I121 crystallographic cell. The resulting model has strong implications concerning the hexagonal bilayer structure of the native hemoglobin.

Electron spin resonance and fluorescence studies of the conformational environment of the thiol groups of thrombospondin: interactions with thrombin

The free thiols of platelet thrombospondin (TSP) were modified with thiol-specific spin labels and fluorescence probes. The conformational effects of thrombin complexation with TSP were monitored by thiol-specific spin labels covalently attached to TSP and active site specific spin labels on thrombin. The results provide evidence supporting speculations that the thiols of the three polypeptide chains in TSP are not conformationally identical. Studies on the effects of Ca2+ and temperature confirm that TSP exists in multiple conformations which are under dynamic equilibrium. The ESR spectra of spin-labeled TSP are sensitive to the proteolytic effects of thrombin in the presence and absence of calcium. Phenylsulfonyl fluoride spin labels specific for the active site of thrombin are excellent indicators of thrombin: TSP complex formation in the absence of calcium. The anticoagulant thrombin inhibitor hirudin competes with TSP for the same binding locus on thrombin (which includes the requirement of an intact anion exosite). The results suggest that the species observed here is the noncovalent complex formed during the first step of the TSP--thrombin interaction, showing also that thrombin activity is not essential for complex formation. ESR and fluorescence studies of thiol-labeled TSP indicate that the sulfhydryls are not affected in the noncovalent thrombin: TSP complex, although they must be playing a major role in the second step, i.e., formation of the covalent complex, through intermolecular thiol exchange.

Solid tumor cells express functional "tethered ligand" thrombin receptor

Previous work demonstrated that alpha-thrombin promoted tumor cell adhesion to endothelium and extracellular matrix as well as enhanced the metastatic capacity of tumor cells. This study was initiated to investigate whether the thrombin effect on tumor cells is mediated through the "tethered ligand" thrombin receptor. RT-PCR analysis using primers based on the human thrombin receptors detected mRNA in human colon adenocarcinoma cells (clone A), whose authenticity was confirmed by Southern hybridization. The presence of thrombin receptor mRNA in rat (W256 carcinosarcoma) and mouse (melanoma) tumor cells was demonstrated by RT-PCR/Southern blotting using species-specific PCR primers. Sequencing of the PCR fragment of clone A cells revealed complete homology with the reported human cDNA sequence. Subsequently, tumor cells derived from three species, i.e., human, rat, and mouse, were found to express the thrombin receptor protein as revealed by immunoblotting using ligand peptide-derived mAb ATAP138, whose reactivity towards the M(r) approximately 66,000, potential thrombin receptor was blocked by preincubating the antibody with the immunogen peptide SFLLRNPNDKYEPF (TRP 14). Finally, peptides TRP 14 and TRP 7 (SFLLRNP), but not TRP 5 (FLLRN), were found to mimic alpha-thrombin in stimulating tumor cell adhesion to fibronectin, suggesting that the thrombin receptors expressed on solid tumor cells are biologically functional.

Platelet thrombospondin interactions with human high and low molecular weight kininogens

Multifunctional proteins, e.g. high molecular weight kininogen (HK, 120 kDa) and the homotrimer, thrombospondin (TSP, 540 kDa), which have more than one domain on a single polypeptide chain, are particularly well-suited to be structural elements of extracellular matrices because of their ability to bind to several macromolecules. We now demonstrate that 125I-high molecular weight kininogen (HKa) cleaved by purified kallikrein forms a complex with purified intact platelet TSP (540 kDa). HK also complexed with a proteolytic fragment (450 kDa) of TSP, lacking its three identical heparin-binding domains (HBD, 30 kDa), but failed to bind to a more extensively proteolysed molecule (210 kDa) lacking the C-terminal globular domain indicating that the binding on TSP-450 kDa is confined to the C-terminus. The binding of HK to intact TSP and to its 450 kDa fragment was of high affinity (Kd = 17-52 nM), specific, concentration dependent and saturable. Furthermore, we found both forms of the light chain (LC) of HK (56 and 46 kDa) resulting from cleavage by plasma kallikrein bound to both intact TSP and HBD independent of the presence of calcium ions. However, neither the epitope recognized by monoclonal antibody (MAb) C11C1 on domain 5 nor the prekallikrein binding site on domain 6 are involved, suggesting that the intervening proline-rich region may be the site of interaction. The heavy chain (HC) of HK required ionized calcium to bind to intact TSP or its 450 kDa homotrimer fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of prothrombin: isolation and characterization of the cDNAs encoding chicken and hagfish prothrombin

The cDNA sequences of chicken and hagfish prothrombin have been determined. The sequences predict that prothrombin from both species is synthesized as a prepro-protein consisting of a putative Gla domain, two kringle domains, and a two-chain protease domain. Chicken and hagfish prothrombin share 51.6% amino acid sequence identity (313/627 residues). Both chicken and hagfish prothrombin are structurally very similar to human, bovine, rat, and mouse prothrombin and all six species share 41% amino acid sequence identity. Amino acid sequence alignments of human, bovine, rat, mouse, chicken, and hagfish prothrombin suggest that the thrombin B-chain and the propeptide-Gla domain are the regions most constrained for the common function(s) of vertebrate prothrombins.

The role of thrombin in tumor cell metastasis

The relationship between malignancy and thrombosis and hemostasis has long been recognized but is poorly understood. The interaction of tumor cells and the proteins and cells of coagulation is symbiotic and complex. Selected cancers have been known to respond to antithrombotic and anticoagulant therapies such as warfarin, heparin and most recently, hirudin. The identification of the functional 'tethered ligand' thrombin receptor on platelets, other cells and recently tumor cells has provided additional opportunities to examine and control the course of tumor proliferation. Thrombin, at concentrations which precede fibrin formation, is a potent inducer of tumor cell expression of various integrin receptors and tumor cell adhesion to the matrix and other activated cells. New strategies based on specifically controlling the action of thrombin may be beneficial in arresting the proliferation of these cells.

Purification and properties of the hemoglobins of the platyhelminth Isoparorchis hypselobagri (Trematoda: Isoparorchidae) and its host Wallagu attu (catfish)

1. The hemoglobins of the trematode Isoparorchis hypselobagri and of its host Wallagu attu (catfish) were isolated and purified. 2. SDS-polyacrylamide gel electrophoresis showed both to consist of single, 15-17 kDa chains, having different electrophoretic mobilities. 3. Isoelectric focusing showed the trematode hemoglobin to be homogeneous with a pI of 4.2 and the host hemoglobin to consist of several components. 4. Gel filtration of freshly prepared trematode hemoglobin revealed one peak corresponding to M(r) approximately 17 kDa; gel filtration of a preparation which had been stored for 2-3 months demonstrated the presence of two peaks, whose elution volumes corresponded to M(r) of ca 35 and 17 kDa, respectively. 5. Reversed-phase chromatography of carboxymethylated 35 and 17 kDa peaks on a C8 column, gave a single peak a and two peaks b and c, respectively. 6. Edman degradation of peaks a, b and c obtained provided identical sequences of 27 amino acid residues for peaks a and c and another sequence differing at 10 of the 27 positions, for peak b. Edman degradation of the freshly prepared Isoparorchis hemoglobin provided the first 15 amino acid residues found for peaks a and c. The host hemoglobin gave an N-terminal sequence completely different from the trematode sequences. 7. Since gel filtration of the 35 and 17 kDa peaks showed no sign of an interconversion equilibrium, it appears that the 35 kDa peak and peak a represent a disulfide-bonded dimer of a monomer globin chain which shares the 27 N-terminal residues with chain c, the major monomer globin component of the 17 kDa peak.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of recombinant polymeric hemoglobin P1 of Glycera dibranchiata

The apoprotein of component P1 of the polymeric fraction of the intracellular hemoglobin of the marine polychaete Glycera dibranchiata has been expressed at a high level in Escherichia coli. The expressed globin was reconstituted with heme and purified. The N-terminal sequence of the recombinant P1 is identical to the cDNA-derived sequence of cloned P1 (Zafar et al., Biochem. Biophys. Acta, 1041, 117-123, 1990). Gel filtration, SDS-PAGE, optical spectra over the range 200-650 nm, and circular dichroism over the range 200-250 nm of the purified recombinant P1 were very similar to the polymeric fraction of native Glycera hemoglobin. The molar ellipticity at 222 nm provided an estimate of 77% for the alpha-helical content of the recombinant P1, in excellent agreement with that calculated from the crystal structure of Glycera monomeric component M-II. Although the oxygen binding affinity of the recombinant P1 is higher than that of the polymeric fraction of Glycera hemoglobin (3-4 torr vs 7-13 torr), which consists of at least six different single-chain hemoglobins, the Hill coefficient is lower (1.0-1.2 vs 1.2-1.4).

Adventitious variability? The amino acid sequences of nonvertebrate globins

1. The more than 140 amino acid sequences of non-vertebrate hemoglobins (Hbs) and myoglobins (Mbs) that are known at present, can be divided into several distinct groups: (1) single-chain globins, containing one heme-binding domain; (2) truncated, single-chain, one-domain globins; (3) chimeric, one-domain globins; (4) chimeric, two-domain globins; and (5) chimeric multi-domain globins. 2. The crystal structures of eight nonvertebrate Hbs and Mbs are known, all of them monomeric, one-domain globin chains. Although these molecules represent plants, prokaryotes and several metazoan groups, and although the inter-subunit interactions in the dimeric and tetrameric molecules differ from the ones observed in vertebrate Hbs, the secondary structures of all seven one-domain globins retain the characteristic vertebrate "myoglobin fold". No crystal structures of globins representing the other four groups have been determined. 3. Furthermore, a number of the one-, two- and multi-domain globin chains participate in a broad variety of quaternary structures, ranging from homo- and heterodimers to highly complex, multisubunit aggregates with M(r) > 3000 kDa (S. N. Vinogradov, Comp. Biochem. Physiol. 82B, 1-15, 1985). 4. (1) The single-chain, single-domain globins are comparable in size to the vertebrate globins and exhibit the widest distribution. (A) Intracellular Hbs include: (i) the monomeric and polymeric Hbs of the polychaete Glycera; (ii) the tetrameric Hb of the echiuran Urechis; (iii) the dimeric Hbs of echinoderms such as Paracaudina and Caudina; and (iv) the dimeric and tetrameric Hbs of molluscs, the bivalves Scapharca, Anadara, Barbatia and Calyptogena. (B) Extracellular Hbs include: (i) the multiple monomeric and dimeric Hbs of the larva of the insect Chironomus; (ii) the Hbs of nematodes such as Trichostrongylus and Caenorhabditis; (iii) the globin chains forming tetramers and dodecamers and comprising approximately 2/3 of the giant (approximately 3600 kDa), hexagonal bilayer (HBL) Hbs of annelids, e.g. the oligochaete Lumbricus and the polychaete Tylorrhynchus and of the vestimentiferan Lamellibrachia; and (iv) the globin chains comprising the ca 400 kDa Hbs of Lamellibrachia and the pogonophoran Oligobrachia. (C) Cytoplasmic Hbs include: (i) the Mbs of molluscs, the gastropods Aplysia, Bursatella, Cerithedea, Nassa and Dolabella and the chiton Liolophura; (ii) the three Hb of the symbiont-harboring bivalve Lucina; (iii) the dimeric Hb of the bacterium Vitreoscilla; and (iv) plant Hbs, including the Hbs of symbiont-containing legumes (Lgbs), the Hbs of symbiont-containing non-leguminous plants and the Hbs in the roots of symbiont-free plants.(ABSTRACT TRUNCATED AT 400 WORDS)

Thrombin increases the metastatic potential of tumor cells

Initial arrest of tumor cells in the microvasculature and their attachment to the endothelium and subendothelial matrix (SEM) are essential prerequisites for metastasis to occur. Factors mediating these interactions are viewed as important determinants of the tumor-cell metastatic phenotype. In this work we have studied the effects of thrombin, its analogs and its precursors on the adhesive properties and metastatic potential of tumor cells. We show that alpha-thrombin, the native form of the key coagulation enzyme, is capable of enhancing tumor-cell adhesion to both the endothelium and SEM components represented by fibronectin. Subclotting, physiological concentrations of alpha-thrombin produced a 2- to 5-fold increase in tumor-cell adhesion. A bell-shaped dose-response curve was observed, with maximal effect at 0.1 U/ml. Maximum effect occurred when cells were exposed to the agonist for 15 min and exposure for up to 4 hr resulted in enhanced tumor-cell adhesion. Prolonged incubation with thrombin resulted in a decline in the thrombin-enhanced adhesion which reached unstimulated control levels by 24 hr. Thrombin precursors and active-site-inhibited thrombin analogs only had minimal adhesion-enhancing activity; nitro- and exosite-alpha-thrombin, which retain a functional active site, mimicked, although to a lesser degree, the action of alpha-thrombin. Tumor-cell incubation with thrombin resulted in an upregulated cell-surface expression of the alpha11b beta 3 integrin, a receptor mediating interactions between tumor cells and endothelial cells, and between tumor cells and SEM. Antibodies against alpha 11b beta 3 integrin effectively inhibited thrombin-enhanced tumor-cell adhesion. Thrombin effects on tumor cells involved the PKC signal transduction pathway as thrombin-enhanced adhesion was inhibited by pre-incubation with PKC inhibitors and a transient PKC translocation from cytosol to membrane was observed following thrombin challenge. In vivo, thrombin-treated tumor cells demonstrated a 2-fold increase in their lung-colonizing ability. In contrast to the adhesion results, the metastasis-enhancing effects of alpha-thrombin were mimicked by a thrombin precursor (prothrombin) and thrombin analogs.

The amino acid sequence of hemoglobin III from the symbiont-harboring clam Lucina pectinata

The cytoplasmic hemoglobin III from the gill of the symbiont-harboring clam Lucina pectinata consists of 152 amino acid residues, has a calculated Mm of 18,068, including heme, and has N-acetyl-serine as the N-terminal residue. Based on the alignment of its sequence with other vertebrate and nonvertebrate globins, it retains the invariant residues Phe45 at position CD1 and His98 at the proximal position F8, as well as the highly conserved Trp16 and Pro39 at positions A12 and C2, respectively. The most likely candidate for the distal residue at position E7 is Gln66. Lucina hemoglobin III shares 95 identical residues with hemoglobin II (J. D. Hockenhull-Johnson et al., J. Prot. Chem. 10, 609-622, 1991), including Tyr at position B10, which has been shown to be capable of entering the distal heme cavity and placing its hydroxyl group within a 2.8 A of the water molecule occupying the distal ligand position, by modeling the hemoglobin II sequence using the crystal structure of sperm whale metmyoglobin. The amino acid sequences of the two Lucina globins are compared in detail with the known sequences of mollusc globins, including seven cytoplasmic and 11 intracellular globins. Relative to 75% homology between the two Lucina globins (counting identical and conserved residues), both sequences have percent homology scores ranging from 36-49% when compared to the two groups of mollusc globins. The highest homology appears to exist between the Lucina globins and the cytoplasmic hemoglobin of Busycon canaliculatum.

Organization of non-vertebrate globin genes

The organization of non-vertebrate globin genes exhibits substantially more variability than the three-exon, two-intron structure of the vertebrate globin genes. (1) The structures of genes of the single-domain globin chains of the annelid Lumbricus and the mollusc Anadara, and the globin gene coding for the two-domain chains of the clam Barbatia, are similar to the vertebrate plan. (2) Genes for single-domain chains exist in bacteria and protozoa. Although the globin gene is highly expressed in the bacterium Vitreoscilla, the putative globin gene hmp in E. coli, which codes for a chimeric protein whose N-terminal moiety of 139 residues contains 67 residues identical to the Vitreoscilla globin, may be either unexpressed or expressed at very low levels, despite the presence of normal regulatory sequences. The DNA sequence of the globin gene of the protozoan Paramecium, determined recently by Yamauchi and collaborators, appears to consist of two exons separated by a short intron. (3) Among the lower eukaryotes, the yeasts Saccharomyces and Candida have chimeric proteins consisting of N-terminal globin and C-terminal flavoprotein moieties of about the same size. The structure of the gene for the chimeric protein of Saccharomyces exhibits no introns. According to Riggs, the presence of chimeric proteins in E. coli and other prokaryotes, such as Alcaligenes and Rhizobium, as well as in yeasts, suggests a previously unrecognized evolutionary pathway for hemoglobin, namely that of a multipurpose heme-binding domain attached to a variety of unrelated proteins with diverse functions. (4) The published globin gene sequences of the insect larva Chironomus have an intron-less structure and are present as clusters of multiple copies; the expression of the globin genes is tissue and developmental stage-specific. Furthermore, the expression of many of these genes has not yet been demonstrated despite the presence of apparently normal regulatory sequences in the two flanking regions. Unexpectedly, Bergtrom and collaborators have recently shown that at least three Ctt globin II beta genes contain putative introns. (5) Pohajdak and collaborators have found a seven-exon and six-intron structure for the globin gene of the nematode Pseudoterranova which codes for a two-domain globin chain. Although the second and fourth introns of the N-terminal domain correspond to the two introns found in vertebrate globin genes, the position of the third intron is close to that of the central intron in plant hemoglobins.(ABSTRACT TRUNCATED AT 400 WORDS)

Thrombin enhances tumor cell adhesive and metastatic properties via increased alpha IIb beta 3 expression on the cell surface

The association between blood coagulation and cancer growth and metastatic dissemination is not yet completely understood. In this study we demonstrate that thrombin is capable of enhancing tumor cell adhesive properties and thereby increases tumor cell metastatic potential. Following exposure to alpha-thrombin, Walker 256 carcinosarcoma cells and B16 amelanotic melanoma cells became more adherent to both endothelial cell monolayers and the subendothelial matrix component, fibronectin. Preincubation of W256 and B16a cells with doses of alpha-thrombin from 0.01 to 10.0 U/ml produced a bell shape dose-response curve with the maximal effect (a 2-5-fold increase in adhesion) observed at 0.1 U/ml (corresponding to 0.8 nM). Complexes of alpha-thrombin with its inhibitors, hirudin and antithrombin III-heparin, diminished its effect on tumor cell adhesion. The effect of thrombin on tumor cell adhesion may be mediated by the alpha IIb beta 3 integrin as thrombin increased cell surface expression of the alpha IIb beta 3 complex. The significance of the in vitro observations was further substantiated by results of in vivo studies. Pretreatment of B16a cells with alpha-thrombin resulted in a 2-fold increase in the number of metastatic lung colonies in an experimental metastasis model. The data indicate a new role for thrombin in the metastatic spread of cancer.

Thrombospondin as a mediator of cancer cell adhesion in metastasis

Thrombospondin (TSP) is a 450 kDa adhesive glycoprotein. It is present in high concentrations in the platelet alpha-granule and can readily be secreted following platelet activation where local concentrations can be increased by 3-4 orders of magnitude. TSP is also synthesized by a variety of other cells and is incorporated into their extracellular matrix. TSP is a homotrimer with a number of functional domains, at least four of which might serve as receptor recognizing regions. The amino-terminal heparin binding domain interacts with heparin, other glycosaminoglycans and glycolipids and likely recognizes specific cell surface proteoglycans. The central disulfide cross-linked region, 210 kDa non-reduced and 70 kDa reduced, contains a peptide motif CSVTCG which is apparently responsible for binding to glycoprotein IV (CD36) with high affinity. Immediately adjacent to the calcium binding region of TSP, which undergoes considerable molecular relaxation in the absence of calcium, is an RGDA sequence. TSP has been demonstrated to bind to integrins of the alpha v beta 3 and alpha IIb beta 3 class. The carboxy-terminal region of TSP also contains at least one binding epitope for a cell receptor. There are 2 well characterized genes for TSP and truncated forms of TSP have been detected which have inhibitory effects on angiogenesis. Finally, TSP can interact with fibrinogen and fibronectin, perhaps on cellular surfaces, which might serve as secondary receptor-like mechanisms for TSP binding and subsequent mediation of cell adhesion.

Localization of two binding domains for thrombospondin within fibronectin

Thrombospondin is a major glycoprotein of the platelet alpha-granule and is secreted during platelet activation. Several protease-resistant domains of thrombospondin mediate its interactions with components of the extracellular matrix including fibronectin, collagen, heparin, laminin, and fibrinogen. Thrombospondin, as well as fibronectin, is composed of several discretely located biologically active domains. We have characterized the thrombospondin binding domains of plasma fibronectin and determined the binding affinities of the purified domains; fibronectin has at least two binding sites for thrombospondin. Thrombospondin bound specifically to the 29-kDa amino-terminal heparin binding domain of fibronectin as well as to the 31-kDa non-heparin binding domain located within the larger 40-kDa carboxy-terminal fibronectin domain generated by chymotrypsin proteolysis. Platelet thrombospondin interacted with plasma fibronectin in a specific and saturable manner in blot binding as well as solid-phase binding assays. These interactions were independent of divalent cations. Thrombospondin bound to the 29-kDa fibronectin heparin binding domain with a Kd of 1.35 x 10(-9) M. The Kd for the 31-kDa domain of fibronectin was 2.28 x 10(-8) M. The 40-kDa carboxy-terminal fragment bound with a Kd of 1.65 x 10(-8) M. Heparin, which binds to both proteins, inhibited thrombospondin binding to the amino-terminal domain of fibronectin by more than 70%. The heparin effect was less pronounced with the non-heparin binding carboxy-terminal domain of fibronectin. By contrast, the binding affinity of the thrombospondin 150-kDa domain, which itself lacked heparin binding, was not affected by the presence of heparin. Based on these data, we conclude that thrombospondin binds with different affinities to two distinct domains in the fibronectin molecule.

Evidence for the existence of O-linked sugar chains consisting of glucose and xylose in bovine thrombospondin

We have recently discovered unusual sugar chains [xylose-glucose and (xylose)2-glucose] linked to a serine residue in the first epidermal growth factor (EGF)-like domains of human and bovine coagulation factors VII, IX, and protein Z. The sequence surrounding this serine residue has a common -Cys-X-Ser-X-Pro-Cys- structure. Since one (residues 533-538) of the three EGF-like domains found in human thrombospondin contains the conserved sequence, we examined the presence of such O-linked sugar chains in bovine thrombospondin (bTSP) and its 210-kDa fragment. Component sugar analysis after pyridylamination (PA) of the acid hydrolysates of the S-aminoethylated proteins revealed that the proteins contain glucose (Glc) and xylose (Xyl). The oligosaccharide moieties released from intact bTSP by hydrazinolysis followed by pyridylamination were separated into two PA-oligosaccharides by high performance liquid chromatography (HPLC). Component sugar analysis of these PA-oligosaccharides indicated that they consist of Glc and Xyl in molar ratios of 1:1 and 1:2 (or 1:3). The reducing ends of both PA-sugar chains were found to be PA-Glc, as judged from the retention time of the HPLC peak of their hydrolysates. The presence of these PA-sugar chains in bTSP was confirmed by HPLC mapping with two different columns, using standard PA-di- or PA-trisaccharide derived from coagulation factors. From these results, we concluded that bTSP contains O-linked sugar chains consisting of Glc and Xyl in one of its three EGF-like domains.

Comparison of the hemoglobins of the platyhelminths Gastrothylax crumenifer and Paramphistomum epiclitum (Trematoda: Paramphistomatidae)

1. Gastrothylax crumenifer and Paramphistomum epiclitum parasitize the water buffalo Bubalus bubalis. 2. Gastrothylas hemoglobin consisted of two fractions of ca 30,000 and ca 18,000 by gel filtration. SDS-electrophoresis showed both to be single, ca 15,000 chains. 3. Paramphistomum hemoglobin was ca 16,000 by both gel filtration and SDS-electrophoresis. 4. Reversed-phase chromatography of carboxymethylated trematode and buffalo globins gave single peaks and two peaks, respectively. Although Paramphistomum hemoglobin provided and N-terminal sequence, Gastrothylax hemoglobin did not, suggesting blocked N-terminals. The buffalo sequences were found to be identical to the sequences of the alpha and beta chains of bovine hemoglobin. 5. Although Paramphistomum hemoglobin consists of only one chain, Gastrothylax hemoglobin consists either of one chain which aggregates to a dimer or of two different chains, only one of which aggregates to a dimer.

Hierarchy of globin complexes. The quaternary structure of the extracellular chlorocruorin of Eudistylia vancouverii

The molecular dimensions of the extracellular, hexagonal bilayer chlorocruorin of the polychaete Eudistylia vancouverii, determined by scanning transmission electron microscopy (STEM) of negatively stained specimens, were diameter of 27.5 nm and height of 18.5 nm. STEM mass measurements of unstained, freeze-dried specimens provided a molecular mass (Mm) of 3480 +/- 225 kDa. The chlorocruorin had no carbohydrate and its iron content was 0.251 +/- 0.021 wt%, corresponding to a minimum Mm of 22.4 kDa. Mass spectra and nuclear magnetic resonance spectra of the prosthetic group confirmed it to be protoheme IX with a formyl group at position 3. SDS/polyacrylamide gel electrophoresis, reversed-phase chromatography and N-terminal sequencing suggested that the chlorocruorin consists of at least three chains of approximately 30 kDa and five chains of approximately 16 kDa; the two types of subunits occur in the ratio 0.26:0.74(+/- 0.08). Complete dissociation of the chlorocruorin at neutral pH in the presence of urea or guanidine hydrochloride, followed by gel filtration, produced elution profiles consisting of three peaks, B, C and D. Fractions B and C consisted of the approximately 16 kDa chains and fraction D consisted of the approximately 30 kDa subunits. Mass measurements of particles in STEM images of unstained, freeze-dried fractions B and C provided Mm of 208 +/- 23 kDa and 65 +/- 12 kDa, respectively, in agreement with 191 +/- 13 kDa and 67 +/- 5 kDa obtained by gel filtration. Particles with Mm = 221 +/- 21 kDa were also observed in STEM images of unstained, freeze-dried chlorocruorin. These results imply that the chlorocruorin structure, in addition to the approximately 30 kDa linker subunits that have 0.26 to 0.47 heme groups/chain, comprises approximately 65 kDa tetramers and approximately 200 kDa dodecamers (trimers of tetramers) of globin chains. The stoichiometry of the tetramer and linker subunits calculated from molar amino acid compositions was 34 +/- 4 and 43 +/- 9. The complete dissociation of the chlorocruorin was accompanied by a 50 to 75% loss of the 55 +/- 14 Ca2+/mol protein, and was decreased to approximately 35% by the presence of 10 to 25 mM-Ca2+. Reassociation of dissociated chlorocruorin was maximal in the presence of 2.5 to 5 mM-Ca2+. The dodecamer and/or tetramer subunits in the absence or presence of Ca2+ exhibited very limited (less than 10%) reassociation into hexagonal bilayer structures, only in the presence of the linker subunit.(ABSTRACT TRUNCATED AT 400 WORDS)

Crystallization of a complex of hemoglobin components II and III of the symbiont-harboring clam Lucina pectinata

Diffraction data to 3.1 A resolution were collected on crystals of a complex of components II and III of the cytoplasmic hemoglobin of the symbiont-harboring clam Lucina pectinata. The crystal system is tetragonal, a = 76.3 A, c = 153.1 A and the space group is P42212. The asymmetric unit probably contains a dimer of the tetrameric complex.

The amino acid sequence of hemoglobin II from the symbiont-harboring clam Lucina pectinata

The cytoplasmic hemoglobin II from the gill of the clam Lucina pectinata consists of 150 amino acid residues, has a calculated Mm of 17,476, including heme and an acetylated N-terminal residue. It retains the invariant residues Phe 44 at position CD1 and His 65 at the proximal position F8, as well as the highly conserved Trp 15 at position A12 and Pro 38 at position C2. The most likely candidate for the distal residue at position E7, based on the alignment with other globins, is Gln 65. However, optical and EPR spectroscopic studies of the ferri Hb II (Kraus, D. W., Wittenberg, J. B., Lu, J. F., and Peisach, J., J. Biol. Chem. 265, 16054-16059, 1990) have implicated a tyrosinate oxygen as the distal ligand. Modeling of the Lucina Hb II sequence, using the crystal structure of sperm whale aquometmyoglobin, showed that Tyr 30 substituting for the Leu located at position B10 can place its oxygen within 2.8 A of the water molecule occupying the distal ligand position. This structural alteration is facilitated by the coordinate mutation of the residue at position CD4, from Phe 46 in the sperm whale myoglobin sequence to Leu 47 in Lucina Hb II.

HLA-DR is a procoagulant

Numerous incidents of thromboembolic complications have been documented in cancer patients and in recipients of mismatched organ transplants. Tumor procoagulants have also been implicated in the process of metastasis. Two protein bands of 35,000 and 28,000 daltons isolated from human ovarian carcinoma possessed procoagulant activity. The 35,000 dalton protein had an amino terminal sequence identical to that of the major histocompatibility antigen HLA-DR. Further, isolation of the protein using immunoaffinity column chromatography with monoclonal antibody to HLA-DR resulted in the isolation of procoagulant activity. The immunoaffinity purified protein enhanced thrombin generation in recalcified normal plasma approximately 20- fold. HLA-DR procoagulant activity was completely inhibited by Staphylococcal enterotoxin A. We propose that the procoagulant nature of HLA-DR may contribute to thrombotic disorders in several cancers and in association with graft rejection. The ability of enterotoxin A to inhibit this procoagulant may lead to development of future therapeutic strategies.

1H-NMR studies of bovine platelet factor 4: histidine assignments and interactions with heparin

1H-NMR spectroscopy has been used to assign and to characterize the two histidine C2H resonances of the heparin binding protein, bovine platelet factor 4. One histidine has a pKa value of 6.51 at 27 degrees C; the second histidine exhibits 2 pKa values of 5.52 and 5.66 at 27 degrees C. The two histidine resonances have been assigned by an analysis of their deuterium exchange kinetics. Both resonances are solvent accessible with half-times of exchange at pH 8.8 of 3.3 and 4.0 days. These two resonances have been assigned by digesting partially deuterated protein with Staphylococcus aureus V-8 proteinase, separating and purifying the resulting peptides, and determining their relative and residual hydrogen content by NMR. The results indicate that His-38 has the lower pKa value and the slower deuterium exchange rate, whereas His-50 has the higher pKa value and the faster deuterium exchange rate at pH 8.8. The 1H-NMR resonance of His-38 of bovine platelet factor 4 is preferentially perturbed by the introduction of heparin. This observation and the presence of His-38 within the belt of positively charged residues around the platelet factor 4 tetramer supports the model of the platelet factor 4-heparin complex in which the polysaccharide crosses over each of the 2 alpha-helices of the 2 dimers at right angles.

beta-NGF-endopeptidase: structure and activity of a kallikrein encoded by the gene mGK-22

Mouse nerve growth factor (NGF) is cleaved at a histidine-methionine bond to release an NH2-terminal octapeptide (NGF1-8). The enzyme responsible, beta-NGF-endopeptidase, is structurally and functionally similar to gamma-NGF and epidermal growth factor-binding protein (EGF-BP) and cleaves mouse low molecular weight kininogen to produce bradykinin-like activity. These data have suggested that, like gamma-NGF and EGF-BP, beta-NGF-endopeptidase is a mouse glandular kallikrein. Evidence for a physiological role for NGF1-8 encouraged studies to further characterize the structure and function of this enzyme. Purified beta-NGF-endopeptidase migrated as a single band on isoelectric focusing and reducing SDS-polyacrylamide gels. As was expected, it removed NGF1-8 from NGF. Interestingly, enzymatic activity on an artificial substrate, and on NGF, was inhibited by NGF1-8 and by bradykinin. These studies further supported the view that beta-NGF-endopeptidase acts on both NGF and kininogen. The first 30 NH2-terminal amino acids of beta-NGF-endopeptidase were sequenced. This analysis demonstrated that the enzyme is encoded by the gene designated mGK-22 (Evans et al., 1987). The sequence of this gene corresponds to that of EGF-BP type A (Anundi et al., 1982; Drinkwater et al., 1987), and so studies were performed to determine whether or not beta-NGF-endopeptidase participates in EGF complex formation. Chromatographic and kinetic data gave no evidence that beta-NGF-endopeptidase is an EGF-binding protein. Our studies suggest that contamination of high molecular weight (HMW) EGF preparations with beta-NGF-endopeptidase erroneously led to earlier designation of the product of mGK-22 as an EGF-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotactic activity and receptor binding of neutrophil attractant/activation protein-1 (NAP-1) and structurally related host defense cytokines: interaction of NAP-2 with the NAP-1 receptor

Neutrophil attractant/activation protein-1 (NAP-1) has sequence similarity to platelet factor-4 (PF-4) and to NAP-2 (a truncated from of connective tissue activating protein-III [CTAP-III(des 1-15)]. We compared chemotactic activity for neutrophils of these related proteins. We also included for comparison CTAP-III, CTAP-III(des 1-13), the C-terminal dodecapeptide of PF-4 [PF-4(59-70)], and C5a. Chemotactic potency (EC50) was highest for NAP-1 and C5a. Although chemotactic efficacy (peak percentage of neutrophils migrating) was comparable for C5a, NAP-1, and NAP-2, the NAP-2 response occurred only at concentrations 100-fold higher than the NAP-1 EC50 of 10(8) M. Data for the CTAP-III proteins confirmed that CTAP-III is not an attractant and that chemotactic activity appears as a result of cleavage of residues at the N-terminus to make CTAP-III(des 1-13) or NAP-2 [CTAP-III(des 1-15)]. Chemotactic activity of PF-4 was low and variable, with no significant response by neutrophils from six of nine subjects. In contrast, PF-4(59-70) regularly induced high chemotactic responses, although the EC50 of 1.6 x 10(5)M was 1,000-fold greater than that of NAP-1. The binding of fluoresceinated NAP-1 to neutrophils was inhibited by unlabeled NAP-1 or NAP-2 but not by PF-4 or PF-4 (59-70). This suggests that NAP-2 interacts with the neutrophil NAP-1 receptor. Despite the low chemotactic potency of NAP-2, it is a potential attractant at sites of injury because of the relatively large amounts of the parent CTAP-III released from platelets, as indicated by a serum concentration of approximately 10(-6) M.

Heterogeneity of the subunits of Lumbricus terrestris extracellular hemoglobin dissociated at alkaline pH

1. The gel filtration profiles of dissociated extracellular hemoglobin of Lumbricus terrestris obtained in 0.1 M borate buffers at pH greater than 9, using columns of Sephadex G100, Sephacryl S200 and Ultragel AcA 44, consist of at least two peaks A and B. 2. SDS-PAGE of several fractions across the complete elution profile demonstrates that only the fractions under the right hand portion of peak B are homogenous and consist of the monomer (M) subunit (Mr = 17,000). 3. The fractions under the first peak contain the remaining subunits, a disulfide-bonded trimer (T) subunit (Mr = 50,000) and of two subunits (D1 and D2) of ca 30,000. 4. Densitometry of the SDS-PAGE patterns suggests that the proportions of these subunits vary across the two peaks, implying that peak A does not consist of a complex of fixed stoichiometry of the T and D1 and D2 subunits. 5. Furthermore, the D1 and D2 subunits overlap the M subunit in the trough between peaks A and B and are present in the left hand portion of peak B, probably because of the self-association of the M subunit. 6. In addition, SDS-PAGE experiments with a single fraction of peak A, where the load and the duration of staining were varied, suggests that the relative proportions of the subunits are independent of these two variables.

Iron and heme contents of the extracellular hemoglobins and chlorocruorins of annelids

1. A survey of the literature on the extracellular hemoglobins and chlorocruorins of over 30 species of annelids, covering the last 30 years, shows that the range of iron content is 0.211-0.265 wt.% (mean = 0.228 +/- 0.013, N = 28) and the range of the heme content is 1.83-3.64 wt.% (mean = 2.60 +/- 0.38, N = 29). 2. There is relatively little scatter in the values of the experimental iron contents and only one of the 28 values is clearly outside the standard deviation range. 3. The values of heme contents are much more scattered, with seven values, clearly outside the standard deviation limits. 4. The aberrant cases are discussed and it is noted that the mean heme content of 2.60 wt.% corresponds to an iron content of 0.236 wt.% in excellent agreement with the mean iron content of 0.228 wt.%. 5. This result suggests strongly that experimental values of iron and heme contents outside the ranges of 0.211-0.243 and 2.3-2.7 wt.%, respectively, corresponding to a minimum molecular mass outside the range 23,000-26,000, should be regarded with caution.

The cDNA sequences encoding two components of the polymeric fraction of the intracellular hemoglobin of Glycera dibranchiata

The intracellular hemoglobin of the polychaete Glycera dibranchiata consists of several components, some of which self-associate into a "polymeric" fraction. The cDNA library constructed from the poly(A+) mRNA of Glycera erythrocytes (Simons, P. C., and Satterlee, J. D. (1989) Biochemistry 28, 8525-8530) was screened with two oligodeoxynucleotide probes corresponding to the amino acid sequences MEEKVP and AMNSKV. Each of the two probes identified a full-length positive insert; these were sequenced using the dideoxynucleotide chain termination method. One clone was 630 bases long and contained 36 bases of 5'-untranslated RNA, a reading frame of 441 bases coding for the 147 amino acids of globin P2 including the residues MEEKVP, and a 3'-untranslated region of 153 bases. The other clone was 540 bases long and contained 24 bases of 5'-untranslated RNA, an open reading frame of 441 bases coding for globin P3 including the residues AMNSKV, and a 3'-untranslated region of 75 bases. The inferred amino acid sequences of the two globins were in agreement with the partial amino acid sequences obtained by chemical methods. The P2 and P3 globin sequences, together with the previously determined P1 sequence of a complete insert and partial sequences P4, P5, and P6 obtained from partial inserts (Zafar, R. S., Chow, L. H., Stern, M. S., Vinogradov, S. N., and Walz, D. A. (1990) Biochim. Biophys. Acta, in press) suggest that there are at least six components in the polymeric fraction of Glycera hemoglobin, which is in agreement with the results of polyacrylamide gel electrophoresis in Tris/glycine buffer, pH 8.3, 6 M urea. Nothern and dot blot analyses of Glycera erythrocyte poly(A+) mRNA using the foregoing two cDNA probes clearly demonstrated the presence of mature messages encoding both types of globins. Comparison of the polymeric sequences P1, P2, and P3 with the "monomeric" globins M-II and M-IV using the alignment and templates of Bashford et al. (Bashford, D., Chothia, C., and Lesk, A. M. (1987) J. Mol. Biol. 196, 199-216) showed that all five globins have identical residues at 39 positions. At 44 positions, the three polymeric globins share identical residues that differ from the identical residues at the corresponding locations in the monomeric sequences M-II and M-IV including position E7, where the latter have leucine instead of the distal histidine. At 15 positions, there occurs an alteration from polar to nonpolar or from a small nonpolar to a larger nonpolar residue in going from the monomeric to the polymeric globins.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino acid sequence of the monomer subunit of the giant extracellular hemoglobin of the aquatic oligochaete, Tubifex tubifex

The extracellular hemoglobin of the aquatic oligochaete Tubifex tubifex consists of four subunits: a monomer of 16.5 kDa, a disulfide-bonded trimer of about 50 kDa and at least two subunits of about 30 kDa. The complete amino acid sequence of the monomeric subunit was determined: it consists of 141 amino acid residues and has a molecular mass of 16,286 Da including a heme group. 39 residues (28%) were found to be identical with those in the corresponding positions in the monomeric globin chains from Lumbricus terrestris, Pheretima sieboldi, and Tylorrhynchus heterochaetus. Tubifex and Lumbricus are most similar, with 75 amino acid identities (53%). There are eight invariant residues amongst these monomeric globins and the intracellular monomeric globin of Glycera and the human beta-globin. The monomeric globin from Tubifex aligns best with those of group A, globins which have a Cys in their second position and an invariant Lys-Val-Lys at positions 9-11 [Gotoh et al. (1987) Biochem. J. 241, 441-445]. The two cysteine residues, at positions 2 and 131, appear to be disulfide-bonded.

The heterogeneity of the polymeric intracellular hemoglobin of Glycera dibranchiata and the cDNA-derived amino acid sequence of one component

The erythrocytes of the marine polychaete Glycera dibranchiata contain a number of different, single-chain hemoglobins, some of which self-associate into a 'polymeric' fraction. An oligodeoxynucleotide probe was synthesized based on partial amino acid sequences determined by chemical methods, and used to screen a cDNA library constructed from the poly(A+)mRNA of Glycera erythrocytes (Simons, P.C. and Satterlee, J.D. (1989) Biochemistry 28, 8525-8530). The longest positive inserts found were sequenced using the dideoxy nucleotide chain termination method. One complete clone was obtained: clone 5A, 816 bases long, contained 59 bases of 5'-untranslated RNA, an open reading frame of 441 bases coding for 147 amino acids and a 3'-untranslated region of 316 bases. The derived amino acid sequence of Glycera globin P1 was in agreement with the partial amino acid sequences obtained by chemical methods. Three additional inserts obtained in the screening were also sequenced: the inferred amino acid sequences proved to be partial globin sequences which were different from each other and from the sequence of P1. Thus, the 'polymeric' fraction of the intracellular hemoglobin of Glycera probably consists of at least four different globin chains much like the 'monomeric' fraction. Comparison of the 'polymeric' sequence with the two known 'monomeric' sequences, M-II and M-IV, shows that they share 54 identical residues. At 74 positions, the identical residues in M-II and M-IV differ from the corresponding residue in P1, including at E-7, where P1 has a distal His, in contrast to Leu in M-II and M-IV. The alignment of Bashford et al. ((1987) J. Mol. Biol. 196, 199-216) and their templates were used to examine the principal differences between the two types of Glycera globin sequences. They appear to consist of uncommon surface amino acid residues at positions C6 (Phe vs. Ala), E10 (Val vs. Lys), E17 (Lys vs. Val), G1 (Arg vs. Lys), G10 (Met vs. Ala) and H5 (Arg vs. Lys). One or more of these residues could be responsible for the self-association exhibited by the 'polymeric' Glycera globins.

Connective tissue activation. XXXIV: Effects of proteolytic processing on the biologic activities of CTAP-III

Microheterogeneity of connective tissue activation peptide III (CTAP-III) was revealed by preparative and analytical isoelectric focusing. Proteolytic activities in human platelet preparations resulted in four cleavage products of platelet-derived CTAP-III. Three isoforms (CTAP-III des 1-13, des 1-14, and des 1-15/NAP-2) stimulate [14C]glycosaminoglycan synthesis; two isoforms also promote [3H]DNA synthesis in human fibroblast cultures. Elastase (from porcine pancreas) cleavage of human platelet-derived CTAP-III and rCTAP-III-Leu-21 to the des 1-15 isoforms was associated with either preservation of specific anabolic biologic activity or an actual increase in specific activity. Nonenzymatic glycosylation of lysyl residues and deamination of the NH2-terminal asparagine of platelet-derived CTAP-III were commonly present, but did not correlate with the biologic activities that were measured. Protein sequence homology shows CTAP-III and its isoforms to be members of a family of proteins (including NAP-1/II-8, MGSA, and platelet factor-4) known to be associated with growth, wound repair, inflammation, and neoplasia. The consequences of proteolytic processing reported here for CTAP-III may be characteristic of the other proteins in this group.

Quaternary structure of the giant extracellular hemoglobin of the leech Macrobdella decora

The molecular dimensions of the extracellular hemoglobin of the leech Macrobdella decora, determined by scanning transmission electron microscopy were 29.8 nm x 19.5 nm (diameter x height) for negatively stained specimens. Measurements of molecular mass (Mm) of unstained specimens with the microscope gave Mm = 3560 +/- 160 kDa. Small-angle X-ray scattering measurements gave a diameter of 28.0(+/- 0.5) nm, radius of gyration 10.5(+/- 0.2) nm and volume 7500(+/- 300) nm3. The hemoglobin had no carbohydrate and its iron content was found to be 0.23(+/- 0.02)% (w/w), corresponding to a minimum Mm of 24,000(+/- 1300) kDa. SDS/polyacrylamide gel electrophoresis of the unreduced hemoglobin showed that it consisted of three subunits, which have apparent Mm values of 12 (1), 25 (2) and 29 kDa (3). The reduced hemoglobin consisted of four subunits, I (12 kDa), II (14 kDa), III (26 kDa) and IV (30 kDa). Subunit 1 corresponded to subunit I, subunit 2 to subunits III and IV and subunit 3 to subunit II. Partial N-terminal sequences were obtained for subunit 1, the two chains of subunit 2 and one of the two chains of subunit 3, suggesting that the hemoglobin consists of at least five different polypeptide chains. The percentage fraction of the three unreduced subunits was determined by densitometry of SDS/polyacrylamide gel patterns and quantitative determination of Coomassie R-250 dye bound to the individual bands in reduced and unreduced patterns to be, monomer (subunit I) : non-reducible subunit (subunit 2) : reducible dimer (subunit 3) = 0.35 : 0.29 : 0.35 (S.D. = +/- 0.05). This corresponded to a stoichiometry of 74 +/- 11 : 37 +/- 5 : 38 +/- 6, assuming the molecular masses to be 17 kDa, 30 kDa and 34 kDa, taking into account the anomalously high mobility of annelid globins in SDS-containing gels. The stoichiometry calculated from the amino acid compositions of the hemoglobin and the three subunits was 82 +/- 12 : 29 +/- 4 : 40 +/- 8. Gel filtration of the hemoglobin at pH 9.8, at neutral pH subsequent to dissociation at pH 4 and at neutral pH in the presence of urea and Gu.HCl provided no evidence for the existence of a putative 1/12 of the whole molecule (Mm approx. 300 kDa). Furthermore, the largest subunits obtained had Mm of 60 to 100 kDa and had a much decreased content of subunit 2, suggesting that the hemoglobin was not a simple multimeric protein. Three-dimensional reconstruction from microscope images provided a model of Macrobdella hemoglobin that is very similar to the reconstruction of Lumbricus hemoglobin: the radial mass distribution curves are virtually superimposable.(ABSTRACT TRUNCATED AT 400 WORDS)

A possible receptor-binding function for the N-terminus of connective tissue activating peptide III

Connective tissue activating peptide III (CTAP-III) is an 85-residue peptide which has been purified from platelets and shown to possess mitogenic activity toward a variety of fibroblastic cell lines. beta-Thromboglobulin (beta TG) is an 81-residue peptide which is derived from CTAP-III by cleavage of the N-terminal tetrapeptide Asn-Leu-Ala-Lys which results in the loss of mitogenic activity. The near-UV CD spectra for the two proteins indicated that the conformations as well as the electronic environments of the two disulfide bonds, and also of the single aromatic tyrosine residue, were similar in CTAP-III and beta TG. However, differences in the far-UV CD spectra of these proteins indicated a substantial decrease in alpha-helical content for beta TG (29%) as compared to CTAP-III (38%). Structure prediction analysis also suggested that the longer N-terminal segment of CTAP-III may form an alpha-helix. The N-terminal region of beta TG, which lacks this tetrapeptide, was predicted to be in an unordered, or possibly a turn, conformation. This predicted structural difference appears to be due to the high helix-forming potential of the N-terminal tetrapeptide Asn-Leu-Ala-Lys in CTAP-III. These results suggest a possible structural role for the N-terminal region of CTAP-III in the expression of the biologic activities of this protein. On the basis of these studies, a reasonable hypothesis to account for the difference in mitogenic activity between beta TG and CTAP-III is that the N-terminal region must be helical for receptor binding to occur.

Human alpha- to zeta-thrombin cleavage occurs with neutrophil cathepsin G or chymotrypsin while fibrinogen clotting activity is retained

Human neutrophil cathepsin G or bovine chymotrypsin proteolytically cleaved human alpha-thrombin at the B-chain Trp148-Thr149 bond generating a new form, zeta-thrombin. While incubation of alpha-thrombin with cathepsin G at pH 7.4 and 37 degrees C resulted in a partial loss of fibrinogen clotting activity, 86 +/- 13% of the clotting activity and 99 +/- 16% of the active sites titratable with p-nitrophenyl p-guanidinobenzoate were retained upon controlled passage of alpha-thrombin through chymotrypsin-Sepharose 4B at pH 6.2 or 7.4 and 24 degrees C (n = 15). Kinetic parameters for H-D-hexahydrotyrosyl-Ala-Arg p-nitroanilide were Km = 1.52 +/- 0.60 vs 1.32 +/- 0.18 microM and kcat = 51.9 +/- 2.9 vs 35.8 +/- 6.4 s-1 with alpha-thrombin vs chymotrypsin-prepared zeta-thrombin (n = 4 vs 3), respectively (I = 0.15 M, pH 7.4, and 24 degrees C). Some 95% of the clotting activity was lost when zeta-thrombin was passed through trypsin-Sepharose 4B under conditions for converting alpha- to nonclotting beta- and subsequently gamma-thrombin. The resulting gamma-like thrombins eluted bimodally with 260 and 310 mM NaCl when applied to Amberlite CG-50 resin [cross-linked poly(methylacrylic acid)] developed with a linear salt gradient in 50 mM Tris at pH 7.4 and 24 degrees C. These elution peaks correspond to 240, 330, and 350 mM NaCl for gamma-, alpha-, and zeta-thrombin, respectfully, implying that the anion-binding exosite is partially destroyed in gamma-like thrombins but is intact in zeta-thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombospondin binding to specific sequences within the A alpha- and B beta-chains of fibrinogen

Thrombospondin is a multifunctional adhesive glycoprotein which binds to the surface of resting and activated platelets. Thrombospondin also binds to a variety of proteins, including fibrinogen. The interactions between platelet-bound thrombospondin and fibrinogen are thought to facilitate irreversible platelet aggregation. Both the A alpha- and B beta-chains of fibrinogen specifically bind to thrombospondin. Cyanogen bromide cleavage products of the fibrinogen A alpha- and B beta-chains, and synthetic peptides corresponding to specific regions of these cleavage products were utilized to identify the regions of the fibrinogen A alpha- and B beta-chains which bind to thrombospondin. Cyanogen bromide fragments of the A alpha- and B beta-fibrinogen chains, resolved by gel filtration and reversed-phase chromatography, were examined for thrombospondin binding activity. Thrombospondin specifically bound to the A alpha-chain fragment encompassing residues 92-147 and the B beta-chain fragment encompassing residues 243-305. Analyses of the binding characteristics of two series of overlapping synthetic peptides revealed that peptides corresponding to residues 113-126 of the A alpha-chain and residues 243-252 of the B beta-chain retained thrombospondin binding activity. Separate bovine serum albumin conjugates of the active A alpha-chain and B beta-chain peptides inhibited platelet aggregation. These studies reveal that fibrinogen possesses at least two unique sequences which are recognized by thrombospondin and that such interaction may affect platelet aggregation.

Connective tissue activation. XXXIII. Biologically active cleavage products of CTAP-III from human platelets

Evidence for three new isoforms of CTAP-III from human platelets is presented; two NH2-terminal cleavage products were identified, CTAP-III (des 1-13) and CTAP-III (des 1-15). CTAP-III (des 1-13) has a pI of 8.6 and is a relatively stable proteolytic cleavage product that retains the capacity to stimulate [14C]GAG synthesis in human synovial cell cultures. CTAP-III (des 1-15) appears to be an elastase or chymotrypsin cleavage product and identical to NAP-2, an entity thought to have neutrophil activating properties.

Thrombospondin interaction with plasminogen. Evidence for binding to a specific region of the kringle structure of plasminogen

Platelet thrombospondin interacts with plasminogen in a specific and saturable manner. Thrombospondin was found to specifically bind to plasminogen and the nonenzyme chain of plasmin. Preincubation of 125I-labeled thrombospondin with 30 mmol/L lysine was without effect in the binding of thrombospondin to immobilized plasminogen; preincubation of 125I-labeled plasminogen with 30 mmol/L lysine, on the other hand, significantly reduced the binding of plasminogen to immobilized thrombospondin, suggesting that the interaction of thrombospondin with plasminogen is not the direct result of the lysine binding sites of plasminogen. Arginine and benzamidine, ligands known to specifically bind to the kringle 5 domain of plasminogen, blocked the binding of thrombospondin to plasminogen. Limited elastase proteolysis of plasminogen and plasmin resulted in the generation of two distinct thrombospondin binding domains, one of which was retained on lysine-agarose. The isolation and amino-terminal analysis of these domains following elastase proteolysis of plasminogen identified them, respectively, as a domain containing kringle structures 4 and 5 and plasmin and the other domain consisting of kringle 5-plasmin. A 16-residue synthetic peptide, which represents the amino acids linking kringle 4 to kringle 5 (residues 435-450 of native plasminogen), was without effect in either binding to thrombospondin or blocking the binding of thrombospondin to plasminogen. Plasminogen, therefore, possesses a single thrombospondin interactive site that is independent of, but influenced by, the lysine binding site containing kringle structures and most likely is located within the kringle 5 domain.

The three-dimensional structure of bovine platelet factor 4 at 3.0-A resolution

Platelet factor 4 (PF4), which is released by platelets during coagulation, binds very tightly to negatively charged oligosaccharides such as heparin. To date, six other proteins are known that are homologous in sequence with PF4 but have quite different functions. The structure of a tetramer of bovine PF4 complexed with one Ni(CN)4(2-) molecule has been determined at 3.0 A resolution and refined to an R factor of 0.28. The current model contains residues 24-85, no solvent, and one overall temperature factor. Residues 1-13, which carried an oligosaccharide chain, were removed with elastase to induce crystallization; residues 14-23 and presumably 86-88 are disordered in the electron density map. Because no heavy atom derivative was isomorphous with the native crystals, the complex of PF4 with one Ni(CN)4(2-) molecule was solved using a single, highly isomorphous Pt(CN)4(2-) derivative and the iterative, single isomorphous replacement method. The secondary structure of the PF4 subunit, from amino- to carboxyl-terminal end, consists of an extended loop, three strands of antiparallel beta-sheet arranged in a Greek key, and one alpha-helix. The tetramer contains two extended, six-stranded beta-sheets, each formed by two subunits, which are arranged back-to-back to form a "beta-bilayer" structure with two buried salt bridges sandwiched in the middle. The carboxyl-terminal alpha-helices, which contain lysine residues that are thought to be intimately involved in binding heparin, are arranged as antiparallel pairs on the surface of each extended beta-sheet.

Human pepsinogen C (progastricsin) polymorphism: evidence for a single locus located at 6p21.1-pter

A series of six clones containing the entire human pepsinogen C gene (PGC) was identified in a cosmid vector library by using cDNA and oligonucleotide probes. The 10.7-kb PGC gene includes nine exons and exhibits a high degree of sequence identity (60%) with the functionally related pepsinogen A genes. The predicted amino acid sequence was identical with the partial amino-terminal and carboxyl-terminal sequences of purified pepsinogen C. An informative restriction fragment length polymorphism was detected with several restriction enzymes and involved an insertion or deletion of 100 bp of intron sequence located between exons 7 and 8. Evidence that there is only a single PGC gene in humans is presented. The PGC gene and the prolactin gene were regionally localized to 6p21.1-pter by analysis of mouse X human somatic cell hybrids.

Platelet membrane glycoprotein V: characterization of the thrombin-sensitive glycoprotein from human platelets

Human platelets contain a single membrane glycoprotein which is susceptible to thrombin proteolysis, glycoprotein V. We have purified 1 mg of glycoprotein V from 10(13) platelets using a combination of gel filtration, hydroxylapatite and ion-exchange chromatographies. Glycoprotein V has a blocked amino-terminus. Following proteolysis by human alpha-thrombin, a major fragment, termed glycoprotein Vf1, had the sequence Gly-Pro-Phe-X-Arg-Pro-Ala-Ala-Asp-Glu-Ser-Val-Glu-Ala-Pro-Val-Asn-Gln-Al a-Glu- Ala-Pro-. The purified glycoprotein was not a substrate for human gamma-thrombin. Glycoprotein V contained 17.5% carbohydrate, with the majority of the carbohydrate consisting of neutral hexoses. Deglycosylated glycoprotein V had a molecular weight of 57.5 kDa compared to the glycosylated protein's 82 kDa and the deglycosylated protein was recognized by polyclonal antibodies raised against glycoprotein V. Immunoelectrophoresis of human and rat platelets and megakaryocytes gave a single immunoreactive band, with the rat glycoprotein having a slightly larger molecular mass. Glycoprotein V is most likely an integral membrane protein.

The complete amino acid sequence of porcine gastrotropin, an ileal protein which stimulates gastric acid and pepsinogen secretion

The stomach is stimulated by an enterooxyntin factor in a delayed response to feeding, resulting in an increase in both gastric acid and pepsinogen secretion. We have previously reported on the identity of such a factor from the porcine ileum (Wider, M. D., Vinik, A. I., and Heldsinger, A. (1984) Endocrinology 115, 1484-1491). This protein, termed gastrotropin, is localized to the distal region of the ileum where it constitutes less than 0.1% of the cytosolic protein. We have completed the primary structure of porcine gastrotropin by Edman degradation and mass spectrometry. Gastrotropin (Mr = 14,054) contains 127 amino acid residues and has a blocked (acetylated) alanine at its NH2 terminus. The sequence of porcine gastrotropin is similar to rat liver fatty acid-binding protein (FABP), with 44 of 127 residues being identical (35%). Homology with other members of the FABP family is significantly less apparent, with the order of similarity being liver FABP greater than heart FABP greater than retinol-binding protein greater than intestine FABP. The sequences of the NH2-terminal regions of these proteins account for virtually all of the homology; there are 9 conserved residues common to all five proteins. Gastrotropin represents the first member of the FABP family which has an extracellular function.

Immunological relatedness of annelid extracellular hemoglobins and chlorocruorins

1. The immunological relatedness of several annelid extracellular hemoglobins and chlorocruorins was investigated using ELISAs and Western blotting to determine the binding of purine polyclonal and monoclonal antibodies to Lumbricus terrestris hemoglobin with the hemoglobins of Tubifex tubifex, Tylorrhynchus heterochaetus, Arenicola marina and Macrobdella decora and the chlorocruoins of Myxicola infundibulum and Eudistylia vancouverii. 2. Polyclonal antibodies to Lumbricus terrestris hemoglobin bound to all the other hemoglobins and chlorocruorins. However, the titers were in all cases one to several orders of magnitude smaller than with Lumbricus terrestris hemoglobin. 3. Polyclonal antibodies to Eudistylia vancouverii chlorocruorin bound to the hemoglobins of Lumbricus terrestris, Tubifex tubifex, Arenicola marina, Tylorrhynchus heterochaetus and Macrobdella decora. 4. Of the nine monoclonal antibodies to Lumbricus terrestris hemoglobin isolated, two (No. 24 and No. 26) bound to the other hemoglobins and to Myxicola chlorocruorin, but the binding was again weaker than with Lumbricus hemoglobin. Antibody No. 26 also bound to Eudistylia chlorocruorin. Although antibody No. 24 appears to recognize a conformation-dependent epitope, antibody No. 26 recognizes a common epitope in each of the four subunits M, D1, D2, and T of unreduced Lumbricus hemoglobin. 4. An additional two monoclonal antibodies to Lumbricus hemoglobin (No. 21 and No. 25) bound also only to Tubifex hemoglobin. Antibody No. 21 recognizes subunits D1 and M of Lumbricus hemoglobin and No. 25 appears to recognize a conformation-dependent epitope.

Connective tissue activation. XXXII. Structural and biologic characteristics of mesenchymal cell-derived connective tissue activating peptide-V

Connective tissue activating peptide-V (CTAP-V) is a single-chain, mesenchymal cell-derived anionic protein with large and small molecular forms (Mr of 28,000 and 16,000, respectively), as defined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The proteins have similar specific activities with respect to stimulation of hyaluronic acid and DNA formation in human synovial fibroblast cultures. S-carboxymethylation or removal of sialic acid residues did not modify CTAP-V biologic activity. Rabbit antibodies raised separately against each of the purified CTAP-V proteins reacted, on immunodiffusion and on Western blot, with each antigen and neutralized mitogenic activity. The amino-terminal amino acid sequence of the CTAP-V proteins, determined by 2 laboratories, confirmed their structural similarities. The amino-terminal sequence through 37 residues was demonstrated for the smaller protein. The first 10 residues of CTAP-V (28 kd) were identical to the N-terminal decapeptide of CTAP-V (16 kd). The C-terminal sequence, determined by carboxypeptidase Y digestion, was the same for both CTAP-V molecular species. The 2 CTAP-V peptides had similar amino acid compositions, whether residues were expressed as a percent of the total or were normalized to mannose. Reduction of native CTAP-V protein released sulfhydryl groups in a protein:disulfide ratio of 1:2; this suggests that CTAP-V contains 2 intramolecular disulfide bonds. Clearly, CTAP-V is a glycoprotein. The carbohydrate content of CTAP-V (16 kd) and CTAP-V (28 kd) is 27% and 25%, respectively. CTAP-V may have significance in relation to autocrine mechanisms for growth regulation of connective tissue cells and other cell types.