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Distribution of plasma kallikrein between C-1 inactivator and alpha 2-macroglobulin in plasma utilizing a new assay for alpha 2-macroglobulin-kallikrein complexes.

We have previously described an enzyme-linked immunosorbent assay for the quantification of C-1 inactivator-kallikrein complexes in plasma (Lewin, M. F., Kaplan, A. P., and Harpel, P. C. (1983) J. Biol. Chem. 258, 6415-6421). We have now developed an immunoimmobilization-enzyme assay for alpha 2-macroglobulin-kallikrein complexes. In this assay these complexes are removed from plasma by immunoabsorption with the IgG fraction of rabbit anti-alpha 2-macroglobulin antiserum coupled to an agarose gel. The immobilized alpha 2-macroglobulin-kallikrein complex hydrolyzes the fluorogenic substrate D-Ser-Pro-Phe-Arg-7-amino-4-trifluoromethyl coumarin, and this activity is proportional to the concentration of complexes in the plasma. Using these assays we have studied the distribution of plasma kallikrein between its inhibitors under several different experimental conditions. When kallikrein is added to plasma, about 57% binds to C-1 inactivator and 43% to alpha 2-macroglobulin. When prekallikrein is activated endogenously in plasma by the addition of kaolin or Hageman factor fragment, approximately 84% of kallikrein is now bound to C-1 inactivator and 16% to alpha 2-macroglobulin. Temperature dramatically affects the distribution of kallikrein. The binding of kallikrein to alpha 2-macroglobulin in plasma is inversely related to temperature, whereas the binding to C-1 inactivator is directly related: 85% of the kallikrein is bound to alpha 2-macroglobulin at 4 degrees C, whereas at 37 degrees C, only 33% is bound. The total amount of kallikrein bound to the two inhibitors is similar at each temperature. These studies thus provide new insight concerning kallikrein formation and regulation in plasma.

Complement C1 Inactivator Proteins↗

Effects of injury on the concentration of alpha1-macroglobulin and alpha2-macroglobulin in the plasmas of male and remale rats.

The effects of injury on the concentration of alpha1-macroglobulin and alpha2-macroglobulin in the plasmas of male and remale rats has been investigates. At 5 days after injury to the male rats the alpha1-macroglobulin concentration increased to 131% of its preinjury value. The alpha2-macroglobulin concentration increased more rapidly to a maximum of 86 times its initial value. In the female rats alpha2-macroglobulin increased only slightly and alpha1-macroglobulin not at all.

Animals↗

Production of conformation-specific monoclonal antibodies against alpha 2 macroglobulin and their use for quantitation of total and transformed alpha 2 macroglobulin in human blood.

Monoclonal antibodies against the human proteinase inhibitor, alpha 2 macroglobulin, have been produced by immunizing BALB/c mice with alpha 2 macroglobulin reacted with methylamine. Two antibodies have been characterized in detail with respect to their binding to native alpha 2 macroglobulin and to different derivatives of the inhibitor. The antibody alpha-1 was found to recognize only those forms of the inhibitor which were transformed by reaction with different proteinases or with methylamine. Binding of alpha-1 was mapped to a specific epitope localized within a distance of 138 amino acid residues from the C terminal end of alpha 2 macroglobulin. The C terminal end is assumed to be exposed during the transformation of the inhibitor and harbours the receptor recognition site. The monoclonal antibody alpha-11 was found to bind to all forms of the inhibitor indicating that its epitope is located in a region not involved in major conformational changes of the inhibitor. On the basis of the different reactivity patterns of alpha-1 and alpha-11 two enzyme-linked immunosorption assays were established for quantitation of total and transformed alpha 2 macroglobulin in human blood. The concentration of the two forms have been determined in a population of 114 healthy individuals giving values of 254 +/- 6.6 mg/dl (mean +/- SEM) of total alpha 2 macroglobulin and 1.07 +/- 0.05 mg/dl (mean +/- SEM) of the transformed inhibitor.

Animals↗

Time-course levels of alpha 2-macroglobulin and albumin in cow colostrum and milk and alpha 2-macroglobulin levels in mastitic cow milk.

Time-course levels of alpha 2-macroglobulin and albumin in cow's colostrum and milk during lactation were investigated in order to obtain data that could help to elucidate the biological role of alpha 2-macroglobulin in mammary secretions. Levels of these proteins were also studied in mastitic cow milk and were related to the degree of mastitis, which could allow its use as a mastitis marker. The highest concentration of alpha 2-macroglobulin was found in the first milking (386.7 micrograms/ml). This value decreased very rapidly during the colostral period, attaining its definitive value during the 2nd wk postpartum (4.5 micrograms/ml). The albumin/alpha 2-macroglobulin ratio increased by 6.8 in the first milking to 44.4 at 2 wk postpartum, indicating that the increase of alpha 2-macroglobulin was greater than that of albumin. In mastitic cow's milk, the concentration of alpha 2-macroglobulin (48.1, 71.4, and 89.0 microgram/ml) was also higher than that in normal milk. This increase was found to be related to the degree of mastitis as determined by the California Test.

Animals↗

Evolution of alpha 2-macroglobulin. The structure of a protein homologous with human alpha 2-macroglobulin from plaice (Pleuronectes platessa L.) plasma.

The plaice (Pleuronectes platessa L.) papain-binding protein previously demonstrated to be homologous with human alpha(2)-macroglobulin, and designated plaice alpha(2)-macroglobulin homologue or alphaMh, was shown to be a glycoprotein of s(20,w) 11.86S. In polyacrylamide-gel pore-limit electrophoresis under non-denaturing conditions plaice alphaMh migrated to the same position as half-molecules of human alpha(2)-macroglobulin, and treatment with methylamine or a proteinase caused no change in its electrophoretic properties. Either denaturation in urea (4m) or mild reduction by dithiothreitol (1mm) partially dissociated plaice alphaMh into half-molecules. Denaturation with reduction further dissociated the protein into quarter-subunits. In sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under reducing conditions plaice alphaMh dissociated into subunits of M(r) 105000 (I) and 90000 (II). Approximately equal amounts of each subunit were formed, and peptide ;mapping' showed subunits I and II to be distinct polypeptide chains. Under alkaline denaturing conditions, a proportion of the I chains of alphaMh were cleaved into fragments of M(r) about 60000 and 40000. This cleavage was favoured by reducing conditions and prevented by prior inactivation of the alphaMh with methylamine. [(14)C]Methylamine allowed to react with alphaMh became covalently linked to subunit I. These properties suggested the existence of an autolytic site on subunit I analogous to the autolytic site of human alpha(2)-macroglobulin. Reaction of alphaMh with a proteinase resulted in cleavage of a fragment of M(r) 10000-15000 from subunit I. A proportion of the proteinase molecules trapped by alphaMh became covalently linked to the inhibitor. A scheme is proposed for the evolution of human alpha(2)-macroglobulin and plaice alphaMh from a common ancestral protein, which may also have been an ancestor of complement components C3 and C4.

Amino Acid Sequence↗

Identification of residues in alpha-macroglobulins important for binding to the alpha2-macroglobulin receptor/Low density lipoprotein receptor-related protein.

Variants of the receptor binding domain of both human alpha2-macroglobulin and the corresponding domain of hen egg white ovomacroglobulin have been expressed in Escherichia coli and refolded in vitro. Competition experiments with methylamine-treated alpha2-macroglobulin for binding to the multifunctional alpha2-macroglobulin receptor identify two Lys residues (residues 1370 and 1374 in human alpha2-macroglobulin) spaced by three amino acid residues as crucial for receptor binding. From this result and mutational evidence from other ligands for the alpha2-macroglobulin receptor, a tentative sequence motif for receptor binding is proposed.

Amino Acid Sequence↗

Sequence of rat alpha 1-macroglobulin, a broad-range proteinase inhibitor from the alpha-macroglobulin-complement family.

The alpha-macroglobulin-complement family of plasma proteins includes at least three different alpha-macroglobulins in rats, alpha 2-macroglobulin (alpha 2M), alpha 1 inhibitor III (alpha 1I3), and alpha 1-macroglobulin (alpha 1M). These high molecular weight polypeptides (Mr 160,000 to 200,000) are broad-range proteinase inhibitors. They utilize an internal thiolester function to trap proteinases that cleave their bait regions. The amino acid sequences of alpha 2M and two variants of alpha 1I3 are known. The isolation of alpha 1M cDNA clones and the determination of their cDNA and derived amino acid sequences are reported here. Alpha 1M shares 57.2% and 53.0% overall amino acid sequence identity with alpha 2M and alpha 1I3, respectively, but differs significantly from both in its bait region, suggesting that each inhibitor addresses a different spectrum of proteinases. The disulfide bridge structure of alpha 1M was deduced from its sequence and showed extensive similarities with the experimentally determined structures of other alpha-macroglobulins, suggesting similar overall tertiary structures. Alpha 1M mRNA was detected in 13 different rat tissues tested, whereas alpha 2M and alpha 1I3 mRNAs showed a far more restricted tissue distribution. While alpha 2M and alpha 1I3 mRNA and protein concentrations are significantly altered during acute and chronic inflammations, alpha 1M plasma concentrations are changed only twofold. Thus, in contrast with alpha 2M and alpha 1I3, the functions provided by alpha 1M may be ubiquitously and constitutively required in a broad range of tissues.

Amino Acid Sequence↗

Synthesis of alpha 2-macroglobulin in human gingiva: a study of the concentration of macroglobulin and albumin in gingival fluid and serum.

Albumin and alpha 2-macroglobulin were analysed in gingival fluid collected by filter paper strips from 6 volunteers before, during and after 10 days of dental plaque accumulation. The two proteins were also determined in samples of venous blood at the beginning of abstention from tooth brushing and 10 days later. A nephelometric technique was used for the analysis of albumin, but alpha 2-macroglobulin was determined by ELISA. The plaque and gingival indices, as well as the flow of gingival fluid, increased significantly during the period of plaque accumulation and then returned to baseline values. The concentrations of the two proteins in blood remained within normal limits. In gingival fluid, however, the concentration of albumin increased about two-fold at the peak of inflammation, while that of alpha 2-macroglobulin increased as much as 6 times. The enhanced passage of alpha 2-macroglobulin into the gingival sulcus in comparison to the entirely plasma-derived albumin was consistent with the concept that the greater excretion of globulin during inflammation must be due to an increased local synthesis.

Adult↗

Zonal distribution of receptor binding of trypsin-activated alpha 2-macroglobulin, alpha 2-macroglobulin receptor-associated protein, lactoferrin and transferrin on rat liver parenchymal cells.

Periportal and perivenous rat liver parenchymal cells were isolated according to the digitonin-collagenase perfusion method. Affinities and maximal specific binding of a conjugate of glutathione S-transferase and the alpha 2-macroglobulin receptor-associated protein (GST-39kDaP), of lactoferrin and of transferrin to freshly isolated periportal parenchymal cells in vitro were not significantly different from values obtained with perivenous cells. It is concluded that the receptors for these three ligands show a zonally homogeneous expression in rat liver. The zonal homogeneity in binding observed for GST-39kDaP is at variance with the 1.5-fold higher periportal over perivenous binding of trypsin-activated alpha 2-macroglobulin. Since GST-39kDaP as well as trypsin-activated alpha 2-macroglobulin are ligands for the alpha 2-macroglobulin receptor/low-density lipoprotein receptor-related protein, it is suggested that GST-39kDaP can bind to (an) additional receptor(s) with a higher perivenous expression. The zonal homogeneity observed with lactoferrin, an inhibitor of ligand binding to the lipoprotein remnant receptor, may indicate zonal homogeneity of the lipoprotein remnant receptor. The observed zonal homogeneity of the transferrin receptor suggests an equal and essential need for iron by parenchymal cells across the rat liver acinus in vivo.

Animals↗

Evidence of an alpha 2-macroglobulin-like molecule in plasma of Salamandra salamandra. Structural and functional similarity with human alpha 2-macroglobulin.

A high-Mr (Mr 750,000) alpha 1-macroglobulin, obtained from Salamandra salamandra, is described. Salamander alpha 1-macroglobulin is composed of two monomers of equal Mr, which are composed of two polypeptide chains, each of Mr 180,000, linked by disulfide bonds. The molecular parameters of this protein, its binding to trypsin and inactivation by methylamine suggest that salamander alpha 1-macroglobulin is closely related to human alpha 2-macroglobulin and to other related proteins described in the animal kingdom.

Animals↗

Expression in mouse embryos and in adult mouse brain of three members of the amyloid precursor protein family, of the alpha-2-macroglobulin receptor/low density lipoprotein receptor-related protein and of its ligands apolipoprotein E, lipoprotein lipase, alpha-2-macroglobulin and the 40,000 molecular weight receptor-associated protein.

We have analysed by northern blotting and by in situ hybridization the expression patterns of eight different genes during the second half of mouse embryonic development and in adult mouse brain: we compared the messenger RNA levels of amyloid precursor protein and of the two amyloid precursor protein-like proteins 1 and 2 and we have analysed expression of apolipoprotein E and of its main receptor in brain, the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and three other ligands: the proteinase inhibitor alpha-2-macroglobulin, the modifying enzyme lipoprotein lipase and the 44,000 molecular weight heparin binding protein, a ligand of unknown function. During embryogenesis the temporal expression pattern differs considerably for the three members of the amyloid precursor proteins. Total embryo messenger RNA levels of amyloid precursor protein and amyloid precursor protein-like protein 2 increased progressively, while amyloid precursor protein-like protein 1 messenger RNA showed a burst of synthesis between days 10 and 13 post-coitum. Significantly, expression of the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and of its associated protein, the 44,000 molecular weight heparin binding protein, exhibited their most important increase very similar to that of amyloid precursor protein-like protein 1, between days 10 and 13 post-coitum. Apolipoprotein E, lipoprotein lipase and alpha-2-macroglobulin messenger RNA levels in total embryos increased progressively, beginning most pronounced at days 13, 15 and 17, respectively. In mouse embryos, in situ hybridization established amyloid precursor protein, amyloid precursor protein-like protein 2 and alpha-2-macroglobulin/low density lipoprotein receptor-related protein messenger RNA to be expressed in most organs, with the notable exception of the liver, while expression of the other studied proteins was much more restricted. Among adult mouse tissues, the genes investigated were expressed very prominently in brain, except for lipoprotein lipase and for the complete absence of alpha-2-macroglobulin messenger RNA. In adult mouse brain, the cortex and hippocampus exhibited strong signals for most genes analysed. Exceptions are lipoprotein lipase and apolipoprotein E messenger RNAs, and the absent alpha-2-macroglobulin messenger RNA. Several interesting features, similarities as well as differences, between brain tissue sections hybridized with probes for amyloid precursor protein, amyloid precursor protein-like proteins 1 and 2 and between alpha-2-macroglobulin/low density lipoprotein receptor-related protein and heparin binding protein-44 were observed and are described. The results are further discussed in view of the known or anticipated physiological functions of the proteins examined and of their possible role in the etiology of Alzheimer's disease.

Amyloid beta-Protein Precursor↗

Purification of alpha2-macroglobulin and the construction of immunogenic alpha2-macroglobulin-peptide complexes for use as cancer vaccines.

A simple method for purification of immunogenic alpha2-macroglobulin from murine serum is described. Also described is a method for creating alpha2-macroglobulin-antigen complexes using purified alpha2-macroglobulin and peptides derived from tumor cell lysates. The application of such alpha2-macroglobulin-antigen complexes for eliciting cancer immunity is discussed.

Animals↗

Purification and characterization of a "half-molecule" alpha 2-macroglobulin from the southern grass frog: absence of binding to the mammalian alpha 2-macroglobulin receptor.

An alpha-macroglobulin (alpha 2M), which is a dimer consisting of two non-disulfide-bonded subunits, was identified and purified from frog plasma by Ni2+ chelate affinity chromatography. This frog "half-molecule" alpha-macroglobulin migrated as an alpha 2-globulin in cellulose-acetate electrophoresis rather than as the previously described frog alpha 1M, which exists as a tetramer formed by the noncovalent association of disulfide-bonded pairs. A molecular weight of approximately 380 000 was obtained by gel-filtration high-pressure liquid chromatography, and in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) the protein migrated as a single band of Mr approximately 180 000 before and after reduction. No evidence was obtained for association of this protein to a higher molecular weight species. After the preparation was heated, additional bands were obtained in SDS-PAGE with Mr approximately 60 000 and 12 000. The additional bands were not obtained after heating methylamine-treated preparations. The circular dichroic spectrum of frog alpha 2M exhibits negative ellipticity over the region 205-250 nm with a minimum at 216 nm. After reaction with proteinase, a decrease in the absolute mean residue rotation was obtained. Amino acid analysis demonstrated that frog alpha 2M and alpha 1M are similar in composition to avian and mammalian alpha-macroglobulins; however, there are sufficient differences in the composition of these two amphibian alpha-macroglobulins to support the conclusion that they are distinct proteins. Frog alpha 2M bound approximately 0.5 mol of trypsin/mol of inhibitor. This binding was abolished by pretreatment with methylamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

Differential scanning calorimetry of alpha 2-macroglobulin and alpha 2-macroglobulin-proteinase complexes.

Differential scanning calorimetry is shown to detect substantial structural alterations occurring on the association of proteinases with the serum glycoprotein alpha 2-macroglobulin. At pH 7.5, the thermally induced unfolding of the macroglobulin occurs at approx. 60 degrees C with a transition enthalpy of 17 J/g. Association of active thermolysin, trypsin and papain shifts the transition temperature to 77 degrees C (transition enthalpy 5 J/g), indicating that a substantial conformational change accompanies the binding event. The stoicheiometry of the thermolysin--alpha 2-macroglobulin association producing this change appears to be unity, implying the presence of co-operative subunit interactions in the mechanism of association. The calorimetric method provides a novel approach for the evaluation of conformational variants induced on protein-protein association or pre-existing in the purified macroglobulin.

Calorimetry, Differential Scanning↗

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse.

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

Animals↗

Comparison of the binding of chicken alpha-macroglobulin and ovomacroglobulin to the mammalian alpha 2-macroglobulin receptor.

Chicken alpha-macroglobulin (alpha M) and ovomacroglobulin were purified by Ni+2 chelate chromatography. These proteins had similar subunit structure as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Chicken alpha M bound 1.0 mol and ovomacroglobulin bound 0.8 mol 125I-trypsin per mol inhibitor, respectively. Ovomacroglobulin cleared rapidly from the circulation of mice, and the clearance was inhibited by asialoorosomucoid, but native chicken alpha M cleared slowly (t 1/2 greater than 1 h). After reaction with trypsin, this alpha-macroglobulin cleared rapidly (t 1/2 = 3 min), and this clearance was inhibited by a 1000-fold molar excess of human alpha 2M-methylamine. Ovomacroglobulin-trypsin did not inhibit the binding of 0.2 nM 125I-labeled human alpha 2M-methylamine to mouse peritoneal macrophages in vitro, but chicken alpha M reacted with trypsin inhibited the binding by 50% at 1.9 nM. A kappa I of 1.1 nM was calculated for the binding of chicken alpha M-trypsin to the mammalian alpha-macroglobulin receptor. This affinity is comparable to that obtained with human and bovine alpha 2M.

Amino Acids↗

Electron microscope studies of human alpha 2-macroglobulin-chymotrypsin complex: demonstration that the two structures assigned to native and proteolyzed alpha 2-macroglobulin represent two views of the proteolyzed molecule.

Electron microscope studies of native and protease-bound human alpha 2-macroglobulin have led to two contradictory models for these two structures. One viewpoint maintains that the native structure has the shape of )+(, which contracts on binding of the protease to the shape of ([). An opposing view proposes that the native structure has the shape of a padlock and that )+( and ([) are the side and end views of the proteolyzed molecule. In this investigation, electron microscope studies of the alpha-chymotrypsin-treated alpha 2-macroglobulin utilizing a tilt stage have shown that the two shapes [)+( and ([)] interconvert. This demonstrates that these two shapes represent the side and end views of the proteolyzed alpha 2-macroglobulin which are related by a 90 degree rotation of the prototype molecule.

Chymotrypsin↗

Subunit and primary structure of a mouse alpha-macroglobulin, a human alpha 2-macroglobulin homologue.

A mouse alpha-macroglobulin (AMG), a homologue of human alpha 2-macroglobulin (alpha 2 M), has been purified to homogeneity. In contrast to human and acute-phase rat alpha 2 M which contains subunits of about Mr 190 000, the mouse protein contains two major (Mr 163000 and 35000) and one minor (Mr 185000) subunits. Also unlike human alpha 2 M, which can be broken down into about 85000-dalton subunits when reacted with an endopeptidase, the native AMG is cleaved by trypsin into multiple components (Mr 86000, 63000, 61000 and 33000). Two-dimensional peptide map analysis of these various 125I-labeled subunit components reveals that the 185000- and 163000-dalton components are homologous proteins but only the 185000-dalton protein contains the 35000-dalton component. The 163000-dalton protein is cleaved by trypsin into 86000- and 63000-dalton components, and the 86-kDa component in turn can be broken down into 61000- and 33000-dalton fragments. Since the 35000-dalton component is serologically related to AMG but does not share any tryptic peptides with both the 163000- and 33000-dalton components, it is neither a copurified impurity nor a cleavage product of the major (163000-dalton) subunit. AMG, therefore, is composed of covalently linked subunits of Mr 163000 and 35000, and the 185000-dalton protein may be a variant subunit of AMG. Trypsin treatment of the [14C]methylamine-labeled AMG and alpha 2 M also sequentially generate subunit patterns indistinguishable from those of the unlabeled macroglobulins. The methylamine-sensitive site(s) of AMG is localized in the 63000-dalton peptide, which is rather resistant to trypsin digestion and to staining by Coomassie brillant blue. We conclude from this study that the mouse homologue has a subunit composition and primary structure distinctly different from those of human and rat alpha 2 M.

Amino Acid Sequence↗