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L Sottrup-Jensen

Publications and source records attributed to L Sottrup-Jensen.

At least 109 records · Page 6Linked to original sources
PubMed1986

Domain structure of human alpha 2-macroglobulin. Characterization of a receptor-binding domain obtained by digestion with papain.

Digestion of methylamine-treated alpha 2-macroglobulin (alpha 2M X MA) with catalytic amounts of papain at pH 4.5 has been investigated. Cleavage of Lys(1313)-Glu resulted in two major products, which could be separated by gel chromatography: a large disulfide bridged fragment set nearly the size of intact alpha 2M X MA, and an 18 kDa fragment, constituting the carboxy-terminal domain of alpha 2M. This domain contained the receptor recognition site, exposed as a result of cleavage of the internal beta-cysteinyl-gamma-glutamyl thiol esters in alpha 2M. Compared with alpha 2M-trypsin complex the apparent affinity for binding to rat hepatocyte receptors was 0.1 and 2% at 4 and 37 degrees C, respectively. The receptor-binding domain presumably forms a compact globular beta-barrel-type structure, stable at pH 2.5-9.0. Chemical modification experiments suggest that receptor binding is contributed by a determinant formed by the precise folding of the polypeptide chain.

Animals↗
PubMed1986

The receptor-binding domain of human alpha 2-macroglobulin. Isolation after limited proteolysis with a bacterial proteinase.

Limited proteolysis of human alpha 2-macroglobulin (alpha 2M) by a novel bacterial proteinase resulted in the isolation of a soluble 20-kDa domain. The isolated fragment contained the receptor recognition site, expressed on alpha 2M complexes, as it competed effectively with alpha 2M-trypsin for binding to the receptor on skin fibroblasts. The fragment also reacted with two monoclonal antibodies which define epitopes that are part of the receptor recognition site. Characterization of the 20-kDa domain showed it to contain an intact disulfide bridge, while its susceptibility to N-glycanase and reaction with concanavalin A indicated the presence of N-linked carbohydrate. The NH2-terminal sequence (Glu-Glu-Phe-Pro-Phe-Ala-Leu-Gly-Val-Glu-Thr-Leu-Pro-Glu-Thr-Cys-Asp-Glu -Pro) proved this fragment to constitute the COOH terminus of human alpha 2M. Proteolysis occurred at Lys1313-Glu which together with the observation that tosyllysine chloromethyl ketone was an effective inhibitor of the bacterial proteinase, would indicate the latter to hydrolyze preferentially peptide bonds carboxyl-terminal to lysine residues.

Amino Acid Sequence↗
PubMed1985

Characterization of human pregnancy zone protein. Comparison with human alpha 2-macroglobulin.

Native human pregnancy zone protein (PZP), a close homolog of alpha 2-macroglobulin (alpha 2M), can be obtained in approximately 20% yield from pooled late pregnancy plasma or serum by a combination of polyethylene glycol precipitation, euglobulin precipitation, DEAE-Sephacel chromatography, zinc-chelate affinity chromatography, and negative affinity chromatography on insolubilized antibodies against human serum proteins. Both proteins are similarly organized as disulfide-bridged dimers of 360 kDa containing 180-kDa subunits. These dimers constitute the proteinase-binding units of PZP, and in contrast to alpha 2M, they appear to be only loosely associated, indicating a subtle difference in the quaternary structure of these alpha-macroglobulins. The preparations contain functionally intact beta-cysteinyl-gamma-glutamyl thiol esters, located in the same nonapeptide sequence as found in alpha 2M, and form complexes with a variety of proteinases in which a large fraction of the proteinase is bound covalently. Proteinases bound to PZP are still active and poorly accessible to reaction with large inhibitors like alpha 1-proteinase inhibitor. The structural and functional features of PZP indicate that PZP and alpha 2M, although extremely similar, may have different yet overlapping sets of proteinases as targets. It is possible that PZP mainly controls the activity of cellular proteinases released under conditions of increased cellular turnover and that PZP could be the human equivalent to the acute phase alpha-macroglobulins known in other species.

Chemical Precipitation↗
PubMed1985

Uptake of rat and human alpha 2-macroglobulin-trypsin complexes into rat and human cells.

Uptake of rat and human alpha 2-macroglobulin-trypsin complexes was measured in rat hepatocytes, rat and human adipocytes and human fibroblasts. Uptake and degradation of 125I-labelled rat complex were about one-third of that of the human complex in the various isolated cell types. In rat hepatocytes, the apparent Km for cell association of the rat complex was about 16 nM as compared to about 6 nM for the human complex. The Vmax values were similar, about 1 X 10(4) molecules X cell-1 X min-1. Thus, rat alpha 2-macroglobulin (an acute-phase protein) complexed with trypsin follows the same pathways of uptake as the human homologue, although with a somewhat lower affinity for the uptake system.

Adipose Tissue↗
PubMed1985

Common evolutionary origin of alpha 2-macroglobulin and complement components C3 and C4.

A comparison of the sequence of the subunit of human alpha 2-macroglobulin (alpha 2M; 1451 amino acid residues) with that of murine complement component pro-C3 (1639 amino acid residues) reveals eight extended regions of sequence similarity. These regions contain between 19% and 31% identically placed residues and account for 75% and 67%, respectively, of the polypeptide chains of alpha 2M and pro-C3. Published sequence data for complement component C4 show that segments of this protein match well with corresponding stretches in alpha 2M and pro-C3. It is proposed that alpha 2M, C3 and C4, which all contain a unique activatable beta-cysteinyl-gamma-glutamyl thiol ester, have a common evolutionary origin and are homologous proteins. Several larger regions of low sequence similarity indicate the presence of structural domains in each of these proteins that specifically modify an underlying common gross structure. The quartets of basic residues in pro-C3 and pro-C4, at which cleavage takes place to produce the mature subunits of these proteins, and most of the residues forming the anaphylatoxin peptides of C3 and C4 (C3a and C4a) are absent in alpha 2M. In addition, C3 and C4 contain large portions, which extend beyond the COOH terminus of alpha 2M.

Amino Acid Sequence↗
PubMed1984

Mechanism of alpha 2-macroglobulin-proteinase interactions. Studies with trypsin and plasmin.

The time course of the interactions of alpha 2-macroglobulin with trypsin and with plasmin was studied by measuring the generation of thiol groups, the concentration of alpha 2-macroglobulin subunits cleaved at the bait regions, and the change in intrinsic protein fluorescence of alpha 2-macroglobulin-enzyme reaction mixtures as functions of time. The interaction of alpha 2-macroglobulin with trypsin was found to be very fast but could be studied in the presence of benzamidine, a rather strong competitive inhibitor of trypsin. The results obtained indicate that alpha 2-macroglobulin-proteinase reactions, known to involve specific limited proteolysis of the bait regions, gross conformational changes, and cleavage of the internal beta-cysteinyl-gamma-glutamyl thiol esters of native alpha 2-macroglobulin, may proceed via at least two different reaction pathways determined by the nature of or the concentration of the reacting proteinase. After initial cleavage of one bait region at high proteinase activity the next step presumably is a fast cleavage of a second bait region before any substantial rearrangements leading to generation of thiol groups and the final incorporation of the proteinase occur. At low proteinase activity no further bait region cleavages occur and only the two thiol groups of half of the alpha 2-macroglobulin molecule are generated in the final 1:1 complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Identification of molecular forms of plasminogen and plasmin-inhibitor complexes in urokinase-activated human plasma.

Urokinase-activated human plasma was analysed by acetic acid/urea/polyacrylamide-gel electrophoresis. The bands representing plasminogen, the plasmin-alpha 2-plasmin inhibitor and plasmin-alpha 2-macroglobulin complexes were identified by immunoprecipitation with specific antibodies and by comparison with purified components. Plasminogen and the plasmin-inhibitor complexes were isolated from plasma or thrombin-clotted plasma containing 125I-labelled Glu-plasminogen (residues 1-790) and urokinase. The plasma was kept at 37 degrees C for 0.5 and 10 times the lysis time of the clotted plasma, the clotted plasma until lysis. The plasmin heavy chain from the plasmin-inhibitor complexes was subsequently prepared. Only in one case could a low-grade proteolytic conversion of Glu- forms into Lys/Met/Val-forms (residues 77-790, 68-790 and 78-790 respectively) during the preparations be detected. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and N-terminal sequence analysis of the purified plasminogen and plasmin heavy chain showed the following. The plasminogen in plasma was on the Glu- form. Glu-plasmin constituted 0.74 and 0.58 of the plasmin bound to the alpha 2-plasmin inhibitor in plasma after brief and prolonged activation respectively. The rest was Lys/Met/Val-plasmin. The clotted plasma contained about equal amounts of Glu-plasminogen and Lys/Met/Val-plasminogen, and predominantly Lys/Met/Val-plasmin complexed to alpha 2-plasmin inhibitor and alpha 2-macroglobulin. The results of the analysis of the purified material substantiated the identity of radioactive protein bands in the gel after acetic acid/urea/polyacrylamide-gel electrophoresis.

Amino Acid Sequence↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. I. Isolation of the 26 CNBr fragments, amino acid sequence of 13 small CNBr fragments, amino acid sequence of methionine-containing peptides, and alignment of all CNBr fragments.

The isolation of the 26 CNBr fragments from the identical Mr = 180,000 subunits of human alpha 2-macroglobulin is described. The fragments have been purified by combinations of gel chromatography, ion-exchange chromatography, high voltage paper electrophoresis, paper chromatography, and high performance liquid chromatography. The complete amino acid sequences of 13 small CNBr fragments have been determined. These fragments include CB1 (residues 1-9), CB3 (residues 79-98), CB4 (residues 99-128), CB9 (residues 442-477), CB10 (residues 478-497), CB13 (residues 644-650), CB14 (residues 651-665), CB15 (residues 666-674), CB16 (residues 675-690), CB19 (residues 937-945), CB20 (residues 946-954), CB24 (residues 1356-1362), and CB25 (residues 1363-1375). The fragments determined account for 200 of the 1451 residues of the subunits of alpha 2-macroglobulin. Most likely, Cys-6 of CB9 is bound to the corresponding residue in CB9 from another subunit, thus forming an interchain disulfide bridge in alpha 2-macroglobulin. Cys-1 of CB15 is bound to Cys-35 of CB12. CB15 contains a pair of Gln residues that can react covalently with amines in a factor XIIIa-catalyzed process (Gln-5 and Gln-6). CB16 contains the primary cleavage sites for proteinases in the bait region of alpha 2-macroglobulin (-Arg7-Val-Gly-Phe-Tyr-Glu-). CB20 contains the residues which in native alpha 2-macroglobulin presumably form an internal reactive beta-cysteinyl-gamma-glutamyl thiol ester (Cys-4 and Glx-7). Partial NH2- and COOH-terminal sequence data are given for the 13 large CNBr fragments. Complete or partial sequence determination of 19 methionine-containing peptides or variants thereof allow the alignment of all the CNBr fragments.

Amino Acid Sequence↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. II. Primary structure of eight CNBr fragments located in the NH2-terminal half of alpha 2-macroglobulin, accounting for 603 amino acid residues.

The amino acid sequence has been determined for eight medium-sized CNBr fragments from the NH2-terminal part of human alpha 2-macroglobulin. The fragments are: CB2 (10-78), CB5 (129-223), CB6 (224-295), CB7 (296-392), CB8 (393-441), CB11 (498-584), CB12 (585-643), and CB17 (691-775). These fragments account for 603 of the 1451 residues of the subunits of alpha 2-macroglobulin. CB2 contains two glucosamine-based carbohydrate groups attached to Asn-23 and Asn-38, and one internal disulfide bridge connecting Cys-16 with Cys-54. CB6 contains one glucosamine-based carbohydrate group attached to Asn-1 and two internal disulfide bridges (Cys-5 bound to Cys-53 and Cys-23 bound to Cys-41, respectively); Cys-32 is bound to Cys-16 in CB8. CB7 contains two glucosamine-based carbohydrate groups attached to Asn-78 and Asn-92, CB8 contains 1 Cys residue (Cys-16), bridged to Cys-32 of CB6. CB11 contains 1 Cys residue (Cys-75), bridged to Cys-58 of CB17. CB12 contains 1 Cys residue (Cys-35), bridged to Cys-1 of CB15. CB17 contains 1 Cys residue (Cys-58), bound to Cys-75 of CB11.

Amino Acid Sequence↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. III. Primary structure of three large disulfide-bridged CNBr fragments, located in the COOH-terminal part of alpha 2-macroglobulin and accounting for 301 residues.

The amino acid sequences have been determined for three CNBr fragments of human alpha 2-macroglobulin which form a disulfide-bridged Mr = 40,000 fragment set. The fragments are located in the COOH-terminal part of alpha 2-macroglobulin (CB18, residues 776-936; CB23, residues 1292-1355; and CB26, residues 1376-1451). CB18 contains one glucosamine-based carbohydrate group attached to Asn-71 and two internal disulfide bridges (Cys-23 bound to Cys-51 and Cys-49 bound to Cys-85, respectively). Cys-123 is disulfide bridged to Cys-7 of CB23. Cys-38 of CB23 is disulfide bridged to Cys-69 of CB26. CB26, which contains one glucosamine-based carbohydrate group attached to Asn-26, is the COOH-terminal CNBr fragment. CB18, CB23, and CB26 account for 301 of the 1451 residues of the subunit of alpha 2-macroglobulin.

Amino Acid Sequence↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. IV. Primary structure of two large CNBr fragments, located in the COOH-terminal part and accounting for 337 residues.

The amino acid sequences have been determined for two CNBr fragments of human alpha 2-macroglobulin which, due to the presence of an uncleaved Hse-Thr bond, form an Mr = 40,000 fragment. These fragments are located in the COOH-terminal part of alpha 2-macroglobulin (CB21, residues 955-1185 and CB22, residues 1186-1291). CB21 contains one glucosamine-based carbohydrate group attached to Asn-14 and one internal disulfide bridge (Cys-102 bound to Cys-150). CB21 and CB22 account for 337 of the 1451 residues of the subunit of alpha 2-macroglobulin.

Amino Acid Sequence↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. V. The complete structure.

The primary structure of the tetrameric plasma glycoprotein human alpha 2-macroglobulin has been determined. The identical subunits contain 1451 amino acid residues. Glucosamine-based oligosaccharide groups are attached to asparagine residues 32, 47, 224, 373, 387, 846, 968, and 1401. Eleven intrachain disulfide bridges have been placed (Cys25-Cys63, Cys228-Cys276, Cys246-Cys264, Cys255-Cys408, Cys572-Cys748, Cys619-Cys666, Cys798-Cys826, Cys824-Cys860, Cys898-Cys1298, Cys1056-Cys1104, and Cys1329-Cys1444). Cys-447 probably forms an interchain bridge with Cys-447 from another subunit. The beta-SH group of Cys-949 is thiol esterified to the gamma-carbonyl group of Glx-952, thus forming an activatable reactive site which can mediate covalent binding of nucleophiles. A putative transglutaminase cross-linking site is constituted by Gln-670 and Gln-671. The primary sites of proteolytic cleavage in the activation cleavage area (the "bait" region) are located in the sequence: -Arg681-Val-Gly-Phe-Tyr-Glu-. The molecular weight of the unmodified alpha 2-macroglobulin subunit is 160,837 and approximately 179,000, including the carbohydrate groups. The presence of possible internal homologies within the alpha 2-macroglobulin subunit is discussed. A comparison of stretches of sequences from alpha 2-macroglobulin with partial sequence data for complement components C3 and C4 indicates that these proteins are evolutionary related. The properties of alpha 2-macroglobulin are discussed within the context of proteolytically regulated systems with particular reference to the complement components C3 and C4.

Amino Acid Sequence↗
PubMed1984

Appendix. Structural predictions on alpha 2-macroglobulin from the amino acid sequence.

The composite result from three different methods predicts that alpha 2-macroglobulin has a predominant pattern of alternating beta-strands and turns. Only scattered pieces of alpha-helix are present throughout its sequence. Predicted beta-strands constitute 43.8% and helices 8.6%, in fair agreement with circular dichroism spectra. Circular dichroism spectra and sequence data suggest that the tertiary structure of complement component C3b is similar to that of the alpha 2 macroglobulin monomer. At present, the beta-barrel configuration of prealbumin seems to be a better model than those of soybean trypsin inhibitor, serine proteases, and immunoglobulins. A repetitive pattern of disulfide loops could indicate structural units of about 200 residues in size, but this is not supported by amino acid sequence homology. The hydropathic pattern of the sequence reveals numerous examples of predicted immunogenic peptides and detects an approximately 100-residue hydrophobic core region, which could constitute parts of the tentatively assigned consecutive activation cleavage and thiol ester domains. This core is an obvious candidate of rearrangement transfer between the highly exposed bait region and the partly shielded thiol ester site. The presumed intersubunit half-cystine is moderately buried and has two nearby patches of high charge density which could guide the dimeric assembling.

Amino Acid Sequence↗
PubMed1984

Partial primary structure of human pregnancy zone protein: extensive sequence homology with human alpha 2-macroglobulin.

Human pregnancy zone protein (PZP) is a major pregnancy-associated protein. Its quaternary structure (two covalently bound 180-kDa subunits, which are further non-covalently assembled into a tetramer of 720 kDa) is similar to that of human alpha 2-macroglobulin (alpha 2M). Here we show, from the results of complete or partial sequence determination of a random selection of 38 tryptic peptides covering 685 residues of the subunit of PZP, that PZP and alpha 2M indeed are extensively homologous. In the stretches of PZP sequenced so far, the degree of identically placed residues in the two proteins is 68%, indicating a close evolutionary relationship between PZP and alpha 2M. Although the function of PZP in pregnancy is largely unknown, its close structural relationship to alpha 2M suggests analogous proteinase binding properties and a potential for being taken up in cells by receptor-mediated endocytosis. In this regard our studies indicate a bait region in PZP significantly different from that present in alpha 2M. PZP could be the human equivalent of the acute-phase alpha-macroglobulins (e.g., rat alpha 2M and rabbit alpha 1M) described earlier.

Amino Acid Sequence↗
PubMed1983

Enzymatic properties of alpha 2-macroglobulin-proteinase complexes. Apparent discrimination between covalently and noncovalently bound trypsin by reaction with soybean trypsin inhibitor.

The binding of trypsin to alpha 2-macroglobulin, the appearance of free beta-cysteinyl thiol groups of the formed complexes, the steady-state kinetics of their enzymic hydrolysis of carbobenzoxy-L-valyl-glycyl-L-arginyl-4-nitroanilide and finally their reactions with soybean trypsin inhibitor leading to the formation of ternary alpha 2-macroglobulin-trypsin-soybean trypsin inhibitor complexes were investigated. Each alpha 2-macroglobulin molecule binds two trypsin tightly; the dissociation constants were found to be unmeasureably small, but the extent of formation of 1:1 and 1:2 complexes at different molar ratios of alpha 2-macroglobulin to trypsin as determined from the appearance of thiol groups clearly indicated that binding of trypsin to alpha 2-macroglobulin shows negative cooperativity. Binding of the first trypsin makes the access of the second less easy. The kinetic results showed a decrease of the kc/Km value of hydrolysis of the tripeptide substrate by approx. 4-fold compared to that of free trypsin for each alpha 2-macroglobulin-bound trypsin. Here no differences were seen between the bound trypsins. The analysis of the reactions between the alpha 2-macroglobulin-trypsin complexes and soybean trypsin inhibitor shows that ternary complexes do form, although slowly, and that two processes occur, not only when 1:2 complexes but also when 1:1 complexes react with soybean trypsin inhibitor. Soybean trypsin inhibitor apparently discriminates between two distinct binding modes of trypsin to alpha 2-macroglobulin, the covalently and the noncovalently alpha 2-macroglobulin-bound trypsins.

Animals↗
PubMed1983

Cell association and degradation of alpha 2-macroglobulin-trypsin complexes in hepatocytes and adipocytes.

125I-Labelled alpha 2-macroglobulin-trypsin complex (125I-labelled alpha 2-macroglobulin X trypsin) was associated to isolated rat adipocytes and hepatocytes with a half-time of about 60 min at 37 degrees C. The association of 0.5 micrograms/ml 125I-labelled alpha 2-macroglobulin X trypsin was inhibited by unlabelled alpha 2-macroglobulin X trypsin with a half-inhibition constant of about 8 micrograms/ml (11 nM). 125I-Labelled alpha 2-macroglobulin became cell-associated to a smaller extent (10-40% of that of alpha 2-macroglobulin X trypsin) and the half-inhibition constant was about 35 micrograms/ml in adipocytes. The cell association of 125I-labelled alpha 2-macroglobulin X trypsin was markedly inhibited by dansylcadaverine, bacitracin, omission of Ca2+ from the medium or pretreatment of the cells with trypsin. After incubation for 180 min more than 60% of the cell-associated 125I-labelled alpha 2-macroglobulin X trypsin was not removed by treatment of the cells with trypsin-EDTA and represented probably internalized material. 125I-Labelled alpha 2-macroglobulin X trypsin was degraded to trichloroacetic acid-soluble fragments by suspensions of both cell types but only to a negligible extent by incubation media preincubated with these cells. The rate of degradation of 0.5 micrograms/ml 125I-labelled alpha 2-macroglobulin was approx. 40% of that of 125I-labelled alpha 2-macroglobulin X trypsin. Degradation of 125I-labelled alpha 2-macroglobulin X trypsin was abolished by a high concentration (0.5 mg/ml) of alpha 2-macroglobulin X trypsin. It is concluded that alpha 2-macroglobulin X trypsin by a specific and saturable mechanism is bound to, internalized and degraded by isolated rat adipocytes and hepatocytes.

Adipose Tissue↗
PubMed1983

Partial primary structure of bovine plasma fibronectin: three types of internal homology.

Approximately one-half of the amino acid sequence (911 amino acid residues out of 1,880 expected) for bovine plasma fibronectin (cold-insoluble globulin) has been determined. Three types of internal homology were identified, showing that a number of partial gene duplications (multiplications) have occurred during the evolution of this protein. Digestion of fibronectin with plasmin results in major fragments with molecular masses of 29, 170, 23, and 6 kilodaltons (kDal). The NH(2)-terminal 29-kDal fragment consists of 259 residues ordered as five mutually homologous domains (type I homology) with two disulfide bonds in each domain. The 170-kDal fragment shows two to three bands after NaDodSO(4) gel electrophoresis, indicating heterogeneity. This fragment contains the gelatin binding site and the strong heparin binding site present in fibronectin. Digestion of the 170-kDal fragment with chymotrypsin liberates a 45-kDal fragment that also binds to gelatin. This fragment contains at least one domain of type I homology and two domains of type II homology. Further digestion of the 170-kDal fragment with chymotrypsin results in the formation of a 30-kDal fragment that retains the heparin binding activity. This fragment contains sequences constituting type III homology. The 23-kDal fragment consists of 178 residues having three domains of type I homology. The 6-kDal fragment consists of two identical peptides of 26 residues, and these two peptides are linked to each other by two disulfide bonds that form the interchain bridges. Another one of the peptides for which the sequence was determined links the COOH-terminus of the 29-kDal fragment to the NH(2)-terminus of the 170-kDal fragment. This and the fact that the COOH-terminal residue of the 6-kDal fragment is a glutamic acid residue order the four plasmin-digestion fragments as 29-, 170-, 23-, and 6-kDal in the intact fibronectin molecule.

Amino Acid Sequence↗