The α-Macroglobulin Bait Region

Posttranslational folding of alpha 1-inhibitor 3. Evidence for a compaction process

alpha 1-inhibitor 3 (alpha 1 I3) is a rodent-specific proteinase inhibitor of about 190 kDa belonging to the alpha 2-macroglobulin family. It consists of five globular domains, three of which are connected by disulfide bridges, and contains an intramolecular thiol ester which can react with attacking proteinases. To explore the folding of newly synthesized alpha 1 I3, we have used rat hepatocytes and pulsechase experiments. In one of the analyses, the radiolabeled protein was isolated from cell lysates by immunoprecipitation and its Asp-Pro bonds cleaved by treatment with formic acid. The size of the major fragment, as assessed by electrophoresis under nonreducing conditions, was found to increase from 100 to 150 kDa upon the chasing. This result, together with knowledge of the positions of the cleavage sites and the disulfide arrangement, indicates that one of the interdomain disulfide bonds is formed after the synthesis of the polypeptide. Analysis of the same material by limited proteolysis and by velocity centrifugation showed that the folded regions became larger and that the protein became more compact; the thiol ester was found to be formed after these conformational changes. These results suggest that the domains of alpha 1 I3 are only partially developed directly after the synthesis of the polypeptide and that they acquire their final structure as the protein condenses and the domains interact with one another.

Crystallisation and preliminary X-ray analysis of the receptor-binding domain of human and bovine alpha 2-macroglobulin

The receptor-binding domains (RBDs) of human and bovine alpha 2-macroglobulin (alpha 2M) have been isolated after limited proteolysis of methylamine-treated alpha 2M with papain. Single crystals of the RBDs have been grown by vapour diffusion. Crystals of human RBD are very thin plates unsuited for data collection. However, crystals of RBD from bovine alpha 2M give diffraction patterns suitable for X-ray analysis, and a complete dataset with a maximum resolution of 2.3 A has been collected with synchrotron radiation at cryogenic temperature. The crystals belong to spacegroup P3(1)21 or P3(2)21 with cell parameters a = b = 106.8 A, c = 72.2 A.

Mannan-binding protein forms complexes with alpha-2-macroglobulin. A protein model for the interaction

We report that alpha-2-macroglobulin (alpha 2M) can form complexes with a high molecular weight porcine mannan-binding protein (pMBP-28). The alpha 2M/pMBP-28 complexes was isolated by PEG-precipitation and affinity chromatography on mannan-Sepharose, protein A-Sepharose and anti-IgM Sepharose. The occurrence of alpha 2M/pMBP-28 complexes was further indicated by crossed immunoelectrophoresis and by use of an anti-alpha 2M affinity column and chelating Sepharose loaded with Zn2+. The eluates from these affinity columns showed alpha 2M subunits (94 and 180 kDa) and pMBP subunits (28kDa) in SDS-PAGE, which reacted with antibodies against alpha 2M and pMBP-28, respectively, in Western blotting. Furthermore, alpha 2M/pMBP-28 complexes were demonstrated by electron microscopy. Fractionation of pMBP-containing D-mannose eluate from mannan-Sepharose on Superose 6 showed two protein peaks which reacted with anti-C1 s antibodies in ELISA, one of about 650-800 kDa, which in addition contained pMBP-28 and anti-alpha 2M reactive material, the other with an M(r) of 100-150 kDa. The latter peak revealed rhomboid molecules (7 x 15 nm) in the electron microscope and a 67 kDa band in SDS-PAGE under reducing conditions. This band was also seen in eluates from the anti-alpha 2M and chelating Sepharose columns. Based on these observations and previous findings by other investigators of a serine protease with about 67 kDa subunits which copurifies with human MBP we propose a model for the interaction of pMBP-28 with alpha 2M.

Very low density lipoprotein receptor binds and mediates endocytosis of urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex

Very low density lipoprotein receptor (VLDL-R) was found to be expressed in bovine mammary gland and the human breast carcinoma cell line MCF-7 as an M(r) 105,000 variant, and in Chinese hamster ovary (CHO) cells transfected with human VLDL-R cDNA as an M(r) 130,000 variant. The receptor was purified by ligand affinity chromatography with immobilized M(r) 40,000 receptor-associated protein (RAP). The purified receptor was found to bind urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex (u-PA.PAI-1), while there was no or very weak binding of active site blocked u-PA (DFP-u-PA), PAI-1 or u-PA-type-2 plasminogen activator inhibitor complex. The binding of u-PA.PAI-1 was blocked by RAP. The transfected CHO cells had an efficient, RAP-sensitive endocytosis of u-PA.PAI-1, severalfold higher than non-transfected parental CHO cells. u-PA.PAI-1 endocytosis was partially inhibited by DFP-u-PA, which blocks binding of the complex to the u-PA receptor. RAP and DFP-u-PA sensitive u-PA.PAI-1 endocytosis was also observed in MCF-7 cells, which were without detectable levels of other RAP-binding endocytosis receptors. These results show that VLDL-R represents a novel endocytosis mechanism for u-PA receptor-bound u-PA.PAI-1.

Alpha 2-macroglobulin bait region variants. A role for the bait region in tetramer formation

To test the hypothesis that a large portion of the bait region of human alpha 2-macroglobulin (alpha 2M) can be removed without adversely affecting the protein's structural and functional properties, we expressed two human alpha 2M variants with truncated bait regions and examined whether these variants folded normally and functioned as proteinase inhibitors. Each variant contains sites that are normal bait region cleavage sites in wild-type alpha 2M, including the primary trypsin cleavage site. The truncated bait regions are shorter by 23 and 27 residues, respectively, and lack the C-terminal portion as well as different parts of the N-terminal section of the bait region. We found that such bait region truncation permitted normal folding of the monomers as well as formation of the thiol ester and dimerization by disulfide cross-linking, although the resulting species bound 6-(p-toluidino)-2-naphthalenesulfonic acid in a manner more like thiol ester-cleaved alpha 2M than native alpha 2M. The variants' thiol esters reacted with nucleophiles at rates identical to wild-type alpha 2M. Surprisingly, however, the truncations prevented the noncovalent association of the covalent 360-kDa dimers that normally gives tetrameric alpha 2M, decoupled bait region cleavage from thiol ester activation, and resulted in the inability of the two variants to "trap" proteinase. This was despite apparent cleavage of the bait region by proteinase, albeit at very much reduced rates relative to wild-type tetrameric alpha 2M. The kinetics of thiol ester cleavage-dependent protein conformational changes also changed from sigmoidal to exponential. These findings indicate that residues in the bait region appear to be necessary for noncovalent association of 360-kDa disulfide-linked dimers to give tetrameric alpha 2M and suggest a role for the bait region in normal alpha 2M in coupling bait region cleavage to the sequence of conformational changes that result in thiol ester activation and ultimately proteinase trapping.

Alpha 2-macroglobulin-mediated clearance of proteases from the plasma of the American horseshoe crab, Limulus polyphemus

Because proteases free in the body are damaging to the tissues, animals have evolved various agents for their inactivation and clearance. Mammals, for instance, have a diverse array of active site protease inhibitors in the plasma. In addition, mammals have alpha 2-macroglobulin (alpha 2M), which binds active proteases, and the alpha 2M-protease complex is then cleared from the plasma by a receptor-mediated endocytotic process. alpha 2M is also present in the plasma of many invertebrates, and in the American horseshoe crab, Limulus polyphemus, it is the only protease inhibitor in the plasma. To search for a clearance process for proteases in Limulus, fluorescein isothiocyanate (FITC)-labeled proteins were injected into the blood, and the fluorescence in the plasma and associated with the blood cells was determined. FITC-labeled trypsin was cleared with an initial mixing period (0-10 min) and a rapid clearance period (10-30 min), followed by the reappearance of FITC in the plasma (45-90 min). Before and during the clearance process, the labeled trypsin was associated with a complex having a molecular mass identical to that of Limulus alpha 2M, and that was precipitated by antibodies directed against Limulus alpha 2M. The fluoresceinated material that reappeared in the plasma after 45 min was of low molecular mass (< 10 kDa) and thus appears to have experienced degradation. The clearance of trypsin requires its protease activity, since phenylmethylsulfonyl fluoride-inactivated, FITC-labeled trypsin was cleared only very slowly if at all (t1/2 > 180 min). FITC-labeled, trypsin-reacted Limulus alpha 2M was cleared rapidly from the plasma of Limulus, whereas FITC-labeled, native Limulus alpha 2M persisted undiminished in excess of 400 min. The blood cells of Limulus bound FITC-labeled trypsin-reacted Limulus alpha 2M, and the peak of recovery from the blood cells coincided with the minimum concentration of FITC-labeled protein in the plasma, suggesting that the blood cells participate in the clearance of alpha 2M-protease complex from the plasma. Thus, we have demonstrated the existence of a clearance pathway in Limulus that operates selectively on enzymatically active proteases and have shown that Limulus alpha 2M is the probable agent for protease clearance. This is the first documentation of a protease clearance pathway in invertebrates and represents the first identified physicological function for alpha 2M in invertebrates.

Binding of transforming growth factor-beta (TGF-beta) to pregnancy zone protein (PZP). Comparison to the TGF-beta-alpha 2-macroglobulin interaction

Pregnancy zone protein (PZP) is quantitatively the most important pregnancy-associated plasma protein and it has strong similarity to alpha 2-macroglobulin. Since alpha 2-macroglobulin is a binding protein for transforming growth factors-beta (TGF-beta), it was of interest to test whether the related protein, PZP, also binds to these growth-regulatory proteins. Using affinity-labelling methods, we demonstrate that PZP binds both TGF-beta 1 and TGF-beta 2 and that the binding characteristics are similar to those of the TGF-beta-alpha 2-macroglobulin interaction. TGF-beta 2 and TGF-beta 1 bind to PZP in a predominantly noncovalent manner in vitro. TGF-beta 1 and TGF-beta 2 bind to both the dimeric and tetrameric forms of PZP. Our studies also indicate that PZP binds TGF-beta 2 with higher affinity than TGF-beta 1. Finally, we demonstrate that PZP inhibits the binding of TGF-beta 1 and TGF-beta 2 to their cell surface receptors. The increased level of PZP during pregnancy may affect the action of TGF-beta by regulating the distribution, clearance and/or general availability of TGF-beta. The preferential binding of TGF-beta 2 over TGF-beta 1 by PZP implies that PZP may differentially regulate the action of TGF-beta 1 and TGF-beta 2.

Amino acid sequence of hen ovomacroglobulin (ovostatin) deduced from cloned cDNA

The complete amino acid sequence of the hen ovomacroglobulin (ovostatin) subunit has been determined from cDNA and partial peptide sequence analysis. Ovostatin is a tetrameric member of the alpha-macroglobulin (alpha M) family of proteins. The 4715 nt ovostatin cDNA encodes a 36- or a 16-residue signal peptide and a 1437-residue mature protein (162.2 kDa). At the protein level the overall score of sequence identity between ovostatin and mammalian alpha Ms is 39-44%, indicating an early divergence from the line leading to the mammalian alpha Ms. Ovostatin contains 56 mol glucosamine per mol subunit, and 12 of its Asn-residues are likely to be N-glycosylated. Including carbohydrate, the size of the ovostatin subunit is approx. 185 kDa. The ovostatin subunit is predicted to contain 12 intrachain disulfide bridges, and two subunits are predicted to be disulfide bound by two interchain bridges. One Cys residue may be unpaired or participate in dimer formation as a third interchain disulfide bridge. Ovostatin contains a unique 40-residue bait region. In contrast to other alpha Ms, ovostatin contains no internal beta-Cys-gamma-Glu thiol ester, as a result of a Cys-to-Asn replacement (TGC or TGT to AAT), but the Gln-moiety of the thiol ester is preserved. By comparing the sequences of the receptor binding domain in alpha Ms with the corresponding region of ovostatin possible determinants for receptor recognition of mammalian alpha Ms are proposed.

The isolation and partial characterization of alpha 2-macroglobulin from the serum of the ostrich (Struthio camelus

1. alpha 2-Macroglobulin (alpha 2M) activity is present in the serum of the ostrich, Struthio camelus. The chromogenic synthetic peptide substrates BAPNA and ATNA were hydrolysed by trypsin and chymotrypsin, respectively, in the presence of ostrich serum and the alpha 2 M in ostrich serum protected trypsin from being inhibited by soybean trypsin inhibitor. Ostrich alpha 2M proved to be a potent inhibitor of bovine pancreatic trypsin and chymotrypsin. 2. alpha 2M was purified to apparent homogeneity by PEG precipitation, DEAE-Toyopearl 650M, Bio-Gel A-5m and Zn(2+)-affinity chromatography. 3. Ostrich alpha 2M migrated as a single band (M(r) 779,000 during non-denaturing gradient gel electrophoresis and showed increased mobility after reaction with trypsin. Denaturation dissociated ostrich alpha 2M into half-molecules. Denaturation with reduction further dissociated the protein into quarter-subunits. 4. Isoelectric focusing revealed a pI of 5.3. 5. The amino acid composition of ostrich alpha 2M is typical of an alpha 2M, comparing favourably with those of other animal species. The carbohydrate composition of the purified protein, in percentage dry weight of the molecule, was galactose: mannose (1:1), 4.55; N-acetylglucosamine 2.35; N-acetylneuraminic acid, 0.58; and fucose, 0.77. 6. alpha 2M was assessed immunologically by Ouchterlony double-diffusion and Western blot analysis with polyvalent antisera directed against ostrich alpha 2M. 7. Ostrich alpha 2M seems to show many physical, chemical and kinetic properties similar to those of other known alpha 2M(s), but is expected to differ from other alpha Ms when considering the primary structure of the bait region, the area differing among alpha Ms from different species and determining its specificity.

Probing different conformational states of pregnancy-zone protein. Fluorescence studies utilizing the binding of 4,4'-bis(8-anilino-1-naphthalenesulphonate)

The binding of the fluorescence probe 4,4'-bis(8-anilino-1-naphthalenesulphonate) (bis-ANS) to the human proteinase inhibitor pregnancy-zone protein (PZP) and its complexes with methylamine and chymotrypsin were investigated. The existence of dimeric PZP-chymotrypsin complex was demonstrated and both the dimeric and the tetrameric PZP-chymotrypsin complexes could be studied separately. The fluorescence data indicate that bis-ANS binds to two different sites on PZP and its complexes. The values of the dissociation constant, Kd1, for the binding to the high-affinity site were determined to be 231 +/- 14, 220 +/- 28, 114 +/- 15 and 49 +/- 1 nM, for the binding to native PZP, PZP-methylamine and dimeric and tetrameric PZP-chymotrypsin, respectively. An 11-30-fold decrease was observed in the affinity for the second site, the corresponding values of the dissociation constant, Kd2, being 1.5-2.8 +/- 1.0 microM, which are not significantly different for PZP and its derivatives. The results suggest that the probe bis-ANS discriminates between the different conformational states of PZP and that while the conformation of the complex with methylamine does not differ much from that of the native protein, there is a significant change in conformation when chymotrypsin cleaves the bait region. This is substantiated by a 30%-45% decrease in the maximum enhancement of fluorescence intensity when PZP is treated with chymotrypsin. Although the dimeric and tetrameric forms of PZP-chymotrypsin complexes differ in Kd1 values, the difference in the maximum enhancement of the fluorescence of bis-ANS by the two forms is not significant. This indicates that dimer-dimer interaction in the tetrameric form does not involve hydrophobic sites. The necessity of bait-region cleavage for extensive conformational changes in PZP distinguishes it from alpha 2-macroglobulin, the other alpha-macroglobulin in human plasma.

Matrix metalloproteinases: a review

Matrix metalloproteinases (MMPs) are a family of nine or more highly homologous Zn(++)-endopeptidases that collectively cleave most if not all of the constituents of the extracellular matrix. The present review discusses in detail the primary structures and the overlapping yet distinct substrate specificities of MMPs as well as the mode of activation of the unique MMP precursors. The regulation of MMP activity at the transcriptional level and at the extracellular level (precursor activation, inhibition of activated, mature enzymes) is also discussed. A final segment of the review details the current knowledge of the involvement of MMP in specific developmental or pathological conditions, including human periodontal diseases.

Differences in the proteinase inhibition mechanism of human alpha 2-macroglobulin and pregnancy zone protein

Different conformational states of human alpha 2-macroglobulin (alpha 2M) and pregnancy zone protein (PZP) were investigated following modifications of the functional sites, i.e. the 'bait' regions and the thiol esters, by use of chymotrypsin, methylamine and dinitrophenylthiocyanate. Gel electrophoresis, mAb (7H11D6 and alpha 1:1) and in vivo plasma clearance were used to describe different molecular states in the proteinase inhibitors. In alpha 2M, in which the thiol ester is broken by binding of methylamine and the 'trap' is closed, cyanylation of the liberated thiol group from the thiol ester modulates reopening of the 'trap' and the 'bait' regions become available for cleavage again. The trapping of proteinases in the cyanylated derivative indicates that the trap functions as in native alpha 2M. In contrast, cyanylation has no effect on proteinase-treated alpha 2M. As demonstrated by binding to mAb, the methylamine and dinitrophenylthiocyanate-treated alpha 2M exposes the receptor-recognition site, but the derivative is not cleared from the circulation in mice. The trap is not functional in PZP. In native PZP and PZP treated with methylamine, the conformational states seem similar. The receptor-recognition sites are not exposed and removal from the circulation in vivo is not seen for these as for the PZP-chymotrypsin complex. Tetramers are only formed when proteinases can be covalently bound to the PZP. Conformational changes are not detected in PZP derivatives in which the thiol ester is treated with methylamine and dinitrophenylthiocyanate. The results suggest that the conformational changes in alpha 2M are generated by mechanisms different to these in PZP. The key structure gearing the conformational changes in alpha 2M is the thiol ester, by which the events 'trapping' and exposure of the receptor-recognition site can be separated. In PZP, the crucial step for the conformational changes is the cleavage of the 'bait' region, since cleavage of the thiol ester does not lead to any detectable conformational changes by the methods used.

The primary sequence and the subunit structure of mouse alpha-2-macroglobulin, deduced from protein sequencing of the isolated subunits and from molecular cloning of the cDNA

Mouse plasma alpha-2-macroglobulin (m alpha 2M) was isolated and the N-terminal amino-acid sequences determined after separation of the 165-kDa and 35-kDa subunits. These sequences were compared to the protein sequence predicted by the cDNA, which was cloned from a mouse liver library and sequenced. From these data it is evident that both subunits are encoded by one mRNA of approximately 5 kb expressed predominantly in liver. The smaller subunit, with the N-terminal sequence DLSSSDLT, comprises the C-terminal 257 residues of m alpha 2M and is derived from a single-chain precursor probably by proteolytic processing at an arginine residue in the sequence PTRDLSS. Analysis of the predicted protein further showed all the salient features of a proteinase inhibitor of the macroglobulin family: a bait region that deviates from all known sequences in this family, a very conserved internal thiolester site and conserved cysteine residues and putative N-glycosylation sites. The synthesis of m alpha 2M in adult liver was demonstrated by Northern blotting and in fetal liver by in-situ hybridization. Transient transfection of COS cells with the cDNA under control of a viral promoter demonstrated the secretion and partial processing of m alpha 2M in the culture medium. In plasma the level of m alpha 2M was found to be stable as expected for the murine counterpart of human plasma alpha-2-macroglobulin. The possibilities of using the mouse as a genetic model to study this proteinase inhibitor in vivo are discussed.

Interaction between bovine trypsin and a synthetic peptide containing 28 residues of the bait region of human alpha 2-macroglobulin

The time course of the interaction between trypsin and a synthetic peptide corresponding to a segment (residues 676-703) of the bait region (residues 666-706) of human alpha 2-macroglobulin (alpha 2M) was studied by measuring the generation of cleavage products as a function of time by HPLC. Three primary cleavage sites for trypsin were present in the synthetic peptide. The fastest cleavage occurred at the bond corresponding to Arg696-Leu in alpha 2M with an estimated kcat/Km = 1-2 x 10(6) M-1.s-1. This value is of the same magnitude as that characterizing the interaction of alpha 2M and trypsin when taking into account the fact that alpha 2M is a tetramer, kcat/Km = 5 x 10(6) M-1.s-1 [Christensen, U. & Sottrup-Jensen, L. (1984) Biochemistry 23, 6619-6626]. The values of kcat/Km for cleavage at bonds corresponding to Arg681-Val and Arg692-Gly in alpha 2M were 1.5 x 10(5) M-1.s-1 and 1.3 x 10(5) M-1.s-1, respectively. Cleavage of intermediate product peptides was slower, with kcat/Km in the range 13-1.3 x 10(6) M-1.s-1. The value of Km determined for fast cleavage in the synthetic peptide was 8-10 microM. 1H-NMR spectroscopy indicated no ordered structure of the peptide. Hence, the very fast cleavage of the peptide is compatible with a loose structure that readily adopts a conformation favorable for recognition and cleavage by trypsin.

Proteinase inhibitory activity in the plasma of a mollusc: evidence for the presence of alpha-macroglobulin in Biomphalaria glabrata

1. A methylamine-sensitive inhibitor was present in the plasma of B. glabrata. 2. This inhibitor decreased trypsin activity against a protein substrate, however trypsin retained activity against a low molecular weight substrate in the presence of the inhibitor. 3. Snail plasma protected trypsin from inhibition by soybean trypsin inhibitor. 4. The results give evidence for an alpha-macroglobulin proteinase inhibitor in the plasma of this gastropod mollusc.

Structure of the human alpha-2 macroglobulin gene and its promotor

The human alpha 2-macroglobulin gene was isolated in five overlapping clones. The gene spans approx. 48 kb and consists of 36 exons, from 21 to 229 bp in size and with consensus splice sites. Intron sizes range from 145 bp to 7.5 kb. The alpha 2M gene is a single copy gene in the human genome. A sequence polymorphism within the bait domain, coding for an Arg to His substitution within the primary cleavage site for trypsin, was identified in 1 of 132 individuals tested so far. Three transcription initiation sites have been identified in liver by primer extension and RNase protection assays. The most proximal, major site (+1) is preceded by a TATA-like structure (ATAAA) at -26 bp. Only 2 mRNA species were found in uterus and in cultured lung fibroblasts, while alpha 2M is not expressed to a detectable level in skin fibroblasts. The far distal transcription initiation site which is preceded by an intact TATA box and a potential HP-1 binding site is thus specific for liver.

Inhibition of adrenocortical steroidogenesis by alpha 2-macroglobulin is caused by associated transforming growth factor beta

alpha 2-Macroglobulin (alpha 2M) is the major protein secreted by bovine adrenocortical cells in primary culture and its synthesis is stimulated by transforming growth factor beta (TGF beta). We investigated here the effects of alpha 2M on adrenocortical steroidogenesis. We observed that commercial preparations of bovine plasma alpha 2M were able to mimic the inhibitory action of TGF beta on adrenocortical cortisol production, with the same specificity of action directed at the steroid 17 alpha-hydroxylation step. This inhibition was time-dependent and dose-dependent (50% inhibition observed with 2 mg/ml alpha 2M). Acid/ethanol extracts of alpha 2M appeared to retain the full inhibitory activity of alpha 2M. Anti-TGF beta antibodies could reverse the inhibition caused by the acid/ethanol extract but not that caused by native alpha 2M. Taken together, these results indicate that the inhibition of adrenocortical steroidogenesis induced by alpha 2M is caused by associated TGF beta. We estimated that 2 mg of alpha 2M contained approximately 0.1 ng of TGF beta, corresponding to a molar ratio of 1/700,000 between TGF beta and alpha 2M. These results also clearly indicate that the alpha 2M-TGF beta complexes are biologically active on adrenocortical cells, suggesting that these cells possess the enzymatic equipment that can activate the latent alpha 2M-TGF beta complexes.

alpha 2-Macroglobulin is cleaved by HIV-1 protease in the bait region but not in the C-terminal inter-domain region

alpha 2-Macroglobulin is cleaved by human immunodeficiency virus-1 protease. The cleavage site is the Phe684-Tyr685 bond in the "bait region", an exposed part of alpha 2-macroglobulin, creating the "F-form". The methylamine derivative of alpha 2-macroglobulin is also cleaved at the same bond. The homologous chicken ovomacroglobulin does not form an F-form structure with the protease, although, F-form generation by other enzymes is known. This is possibly due to the lack of a suitable cleavage sequence in the corresponding region of ovomacroglobulin. In human alpha 2-macroglobulin, the interdomain segment between the main part of the molecule and the receptor-binding C-terminal domain is not cleaved by the HIV protease although typical cleavage sequences occur. In AIDS, therefore, HIV protease from infected cells in unlikely to interfere with receptor-binding of alpha 2-macroglobulin.

Differential regulation of the two mRNA species of the rodent negative acute phase protein alpha 1-inhibitor 3

Screening of two rat liver cDNA libraries, one of which was constructed using an alpha 1-inhibitor 3 (alpha 1-13) specific primer, yielded overlapping cDNA clones which correspond to the full length cDNA for alpha 1-13 mRNA. On the basis of sequence microheterogeneity existing throughout the cDNA sequence we identified two alpha 1-13 mRNA species whose sequences are so grossly different in their bait regions that the amino acid homology therein is only 30%. Using oligonucleotide probes derived from their respective bait regions we investigated the regulation of the two alpha 1 I3 mRNA species and demonstrated that only one of them, alpha 1-I3 variant I, is regulated pretranslationally following experimentally induced inflammation.

Detection of endopeptidase activity and analysis of cleavage specificity using a radiometric solid-phase enzymatic assay

A radiometric procedure to detect the presence of proteolytic enzymes and analyze their substrate specificity is described. The enzymatic activity is first measured by the release into solution of a radiolabeled reporter group from an immobilized peptidyl substrate. Two peptidyl substrates encompassing multiple cleavage sites, a derivative of Leu-enkephalin and a peptide related to the bait region of human alpha 2-macroglobulin, are prepared and linked via a spacer molecule to an insoluble support. The labeled peptides released are then separated by high-performance liquid chromatography. The position of the released peptides upon chromatography allows direct identification of the sites of cleavage. The assay, using a radioactive iodinated tyrosine residue as reporter group, is extremely sensitive (less than 0.02 pg/ml of trypsin), reproducible, and easy to perform while yielding unambiguous identification of the sites of cleavage. This assay can be used to detect the presence of enzymatic activities and/or of enzyme inhibitors. Furthermore, it can be easily adapted to detect from a variety of sources all four classes of enzymes known by using appropriate peptidyl substrate sequences, buffer, pH, and incubation conditions.

Primary structure of pregnancy zone protein. Molecular cloning of a full-length PZP cDNA clone by the polymerase chain reaction

A full-length cDNA clone of the human pregnancy zone protein (PZP) was cloned from the hepatocellular carcinoma cell line Hep3B. Based on the exon sequences of the PZP gene (Devriendt et al. (1989) Gene 81, 325-334; Marynen et al., unpublished data), primer pairs were designed to amplify six overlapping fragments of the PZP cDNA. The obtained cDNA is 4609 bp long and contains an open reading frame coding for 1482 amino acids, including a signal peptide of 25 amino acid residues. Comparison with the published partial PZP amino acid sequence (Sottrup-Jensen et al. (1984) Proc. Natl. Acad. Sci. USA 81, 7353-7357) and the PZP genomic sequences confirmed the identity as a PZP cDNA. 71% of the corresponding amino acid residues in PZP and human alpha 2-macroglobulin (alpha 2M) are identical and all cysteine residues are conserved. A typical internal thiol ester site and a bait domain were identified. A Pro/Thr polymorphism was identified at amino acid position 1180, and an A/G nucleotide polymorphism at bp 4097.

alpha2-Macroglobulin from hemolymph of the freshwater crayfish Astacus astacus

1. A high mol. wt proteinase inhibitor has been purified from the haemolymph of the freshwater crayfish Astacus astacus. 2. The protein is a disulphide-bonded dimer (Mr 390,000) of two identical polypeptide chains (Mr 185,000). 3. The inhibitor displays a broad specificity and protects trypsin from inhibition by soybean trypsin inhibitor and thus is similar to vertebrate alpha 2-macroglobulin. 4. The alpha 2-macroglobulin-like inhibitor from Astacus interacts with bovine trypsin in an equimolar stoichiometry thereby decreasing tryptic hydrolysis of N-benzoyl-L-arginine-ethylester to 50% residual activity. In contrast, the activity of Astacus protease, a digestive zinc proteinase from crayfish toward succinyl-alanyl-alanyl-alanyl-4-nitroanilide is inhibited almost completely. 5. Sensitivity of the inhibitor to methylamine and autolytic cleavage suggests the presence of an internal thioester bond. 6. The N-terminal amino acid sequence of Astacus alpha 2-macroglobulin is strongly related to the alpha 2-macroglobulins from Pacifastacus leniusculus (91% identity) and from the lobster Homarus americanus (72% identity). In contrast, only 25% of the residues are identical with the alpha 2-macroglobulin from the horseshoe crab Limulus polyphemus. There is also a faint similarity to human complement protein C3 and human alpha 2-macroglobulin.

Kinetics and mechanism of proteinase-binding of pregnancy zone protein (PZP). Appearance of sulfhydryl groups in reactions with proteinases

Proteinase binding by pregnancy zone protein (PZP), an alpha-macroglobulin involves bait region cleavages, association of dimeric-PZP into tetrameric and reaction of internal gamma-glutamyl-beta-cysteinyl thiol esters of PZP with proteinase side chains. The product is an equimolar enzyme-PZP(tetramer) covalently linked complex with four free sulfhydryl groups. The kinetics of the appearances of sulfhydryl groups during the reaction of PZP with chymotrypsin has been investigated using stopped-flow and conventional mixing techniques over a broad concentration range. Thiol ester cleavages followed double exponential decays corresponding with two steps. The faster one resulted in the appearance of three sulfhydryl groups with an observed rate constant, k(obs) = k1.1 + k1.2 delta E, dependent on the excess concentration of chymotrypsin, delta E, and k1.1 = 0.03 s-1 and k1.2 = 4 x 10(4) M-1 s-1. The last sulfhydryl group appeared in a slower step, with similar concentration dependence and k2.1 approximately 0.003 s-1 and k2.2 approximately 5 x 10(3) M-1s-1. Covalent binding of the enzyme apparently was simultaneous with the faster thiol ester cleavage step. Based on these and previous results a model of the reaction mechanism of the proteinase binding reaction of PZP is proposed. It consists of four major steps: (i) Bait region cleavage of PZP-dimers by the enzyme, (ii) fast association of enzyme-PZP(dimer) species with native PZP or with another enzyme-PZP(dimer) compound resulting in release of one of the associated enzyme molecules (iii) reaction of an average of three thiol esters of the enzyme-PZP(tetramer) intermediate with the associated internal enzyme molecule or with an external one. In this step one enzyme molecule becomes covalently linked to the PZP-(tetramer), three sulfhydryl groups appear and the enzymic activity of the bound enzyme molecule decreases to the level of that of the final complex. (iv) Hydrolysis of the last thiol ester and in the presence of excess enzyme, degradation of enzyme-PZP(tetramer) complexes and formation of fragments some of which are the size of PZP(dimer) with enzyme bound.

Amino acid sequences of ovomucoid third domain from 25 additional species of birds

Ovomucoids were isolated from 25 avian species other than the 101 studied in Laskowski et al. (1987, Biochemistry 26, 202-221). These were subjected to limited proteolysis with an appropriate enzyme, and connecting peptide extended ovomucoid third domains were isolated and sequenced to the end in a protein sequencer. Of the 25 new sequences, 13 duplicate ones were already known, and 12 are unique. Probably the most striking findings are a Pro14----Ser14 replacement in weka, an Ala14----Thr15 replacement in Bulwer's pheasant, the discovery of two additional amino acid residues Ile18 and Gly18 at the P1 reactive site position in Kalij pheasant and tawny frogmouth, respectively, and the first finding of a negative (Glu34) rather than positive (Lys34 or Arg34) amino acid residue at the NH2 terminus of the alpha helix in caracara ovomucoid third domain. These results complete the determination of all the sequences of ovomucoid third domains in the four species genus Gallus, in the five species genus Syrmaticus, and in the two species genera Aix and Pavo.