Ultrastructure of alpha 2-macroglobulins

Delain, Etienne; François, Patrice; Barray, Martine; Leuven, Freddy Van

doi:10.1016/0892-0354(92)90012-f

Cited by 47 publications

(34 citation statements)

References 215 publications

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“…The changes in the front and the back parts are probably not very large, as indicated by the similar overall architecture of the reconstructed native ␣ 2 M and the crystallographic structure of ␣ 2 M-MA. If this simulation is correct, the mechanism for the conformational change from native to transformed ␣ 2 M would be considerably simpler than those considered earlier (3,26,35,37).…”

Section: Discussionmentioning

confidence: 99%

“…Structure of ␣ 2 M-MA at 10 Å Resolution-Previous EM studies have discussed the shape of ␣ 2 M-MA on the basis of its three major orientations on EM grids or in vitreous ice, the H-view, the L-view (here called the X-view), and the End-view (3,31,33). While ␣ 2 M-MA in the H-view (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In a three-dimensional reconstruction of native ␣ 2 M, the dimensions of the molecule were estimated to be 200 and 140 Å (35) with an internal cavity of cross-section 40 and 60 Å. In addition, molecules probably representing intermediates in the transition from native to transformed ␣ 2 M have been observed (3,37,38). The proteinase(s) in the ␣ 2 M-proteinase complex appear to partially fill a large elongated cavity (27,28,31,33), which seems to be empty in ␣ 2 M-MA (28 -30, 33).…”

mentioning

confidence: 99%

“…Receptor recognition sites are located at the tip of each of the arms of the H (27,34). When studied by EM, native ␣ 2 M has various shapes, which among others resemble a twisted cross (3,26), a doughnut (25), and a padlock (26,35). It has recently been shown that all of these shapes correspond to one single structure (36).…”

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confidence: 99%

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Low Resolution X-ray Structure of Human Methylamine-treated α2-Macroglobulin

Andersen

Koch

Dolmer

et al. 1995

Journal of Biological Chemistry

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The structure of methylamine-treated human ␣ 2 -macroglobulin (␣ 2 M-MA), a 720-kDa tetrameric inactivated proteinase inhibitor from plasma, has been determined to a resolution of 10 Å. Data were collected with synchrotron radiation at 120 K, and phases were calculated by multiple isomorphous replacement and solvent flattening. A novel feature of the structure of ␣ 2 M is present in its proteinase-binding cavity, dividing it into two compartments. The potential sites for proteinase entrapment in these compartments are sterically restricted. The positions of the thiol groups appearing from the functional important thiol esters upon their cleavage have been determined. They are found at the walls of the compartments at the center of the structure. The overall structure of ␣ 2 M-MA is much more sphere-like than previously inferred from electron microscopy studies. However, several aspects of the structure are well described by recent three-dimensional reconstructions. Possible models for the monomer, the disulfide bridged dimer, and native ␣ 2 M are discussed.1 is the best studied member of the class of proteinase-binding ␣-macroglobulins (for reviews, see Refs. 1-3). One subunit of ␣ 2 M contains 1451 residues of which eight are glycosylated. This subunit has a mass of 180 kDa (4). Two subunits form disulfide bridged dimers (5). Two such dimers make noncovalent contacts to form the 720-kDa functional tetramer.The native form of ␣ 2 M can form complexes with various proteinases. This complex formation is initiated by specific limited proteolysis of the bait region (6) found at residues 667-705 (7). The cleavage of the bait region initiates a series of conformational changes in the ␣ 2 M subunits resulting in entrapment of the attacking proteinase inside the tetramer. The final result of these changes is the transformed form of ␣ 2 M. The native and transformed forms of ␣ 2 M appear in electrophoresis as the slow and fast forms of ␣ 2 M (6, 8). The native form of ␣ 2 M contains internal ␤-Cys-␥-Glu thiol esters, formed from Cys-949 and Glu-952 in each subunit. During complex formation, these thiolesters become activated, and this activation results in covalent binding of the proteinase primarily through ⑀-Lys(proteinase)-␥-Glu(␣ 2 M) cross-links (9 -11). The bound proteinase is still active, but it is only accessible to small substrates and inhibitors. Two small proteinase molecules the size of chymotrypsin, but only one large proteinase like plasmin, can be bound to ␣ 2 M (12). A final result of the conformational change is that sites in the C-terminal domains (residues 1314 -1451) (13-15) become exposed for interaction with the cellular receptor for ␣ 2 M-proteinase complexes. This receptor has been found to be identical to the low density lipoprotein receptor-related protein (16 -18). Incubation of ␣ 2 M with methylamine also leads to thiol ester cleavage and covalent binding of methylamine (9,19). The conformation of the resulting molecule, ␣ 2 M-MA, resembles that of the fast form ␣ 2 M-proteinase complex (20, ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Low Resolution X-ray Structure of Human Methylamine-treated α2-Macroglobulin

Andersen

Koch

Dolmer

et al. 1995

Journal of Biological Chemistry

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“…Proteinases first cleave the "bait region" of native ␣ 2 M exposing the internal ␥-glutamyl-␤-cysteinyl thioester bond. Reaction of the thioester bond with a free amino lysyl residue on the surface of the proteinase results in bond rupture and a major conformational change in native ␣ 2 M. The resulting molecule is much more compact as evidenced by faster migration on a native acrylamide gel (3), electron microscopy (4,5), sedimentation behavior (6), and circular dichroism (7). Consequently the receptor-recognition site is exposed.…”

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confidence: 99%

The Binding of Receptor-recognized α2-Macroglobulin to the Low Density Lipoprotein Receptor-related Protein and the α2M Signaling Receptor Is Decoupled by Oxidation

Boyer

Pizzo

1997

Journal of Biological Chemistry

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1 is a highly conserved, homotetrameric, 720-kDa glycoprotein found in high concentration in the plasma (2-4 mg/ml). It has the unique ability to inhibit all mechanistic classes of proteinases by "entrapping" the proteinase and thereby sterically blocking the access of high molecular weight substrates (reviewed in Refs. 1 and 2). Proteinases first cleave the "bait region" of native ␣ 2 M exposing the internal ␥-glutamyl-␤-cysteinyl thioester bond. Reaction of the thioester bond with a free amino lysyl residue on the surface of the proteinase results in bond rupture and a major conformational change in native ␣ 2 M. The resulting molecule is much more compact as evidenced by faster migration on a native acrylamide gel (3), electron microscopy (4, 5), sedimentation behavior (6), and circular dichroism (7). Consequently the receptor-recognition site is exposed. Small amine nucleophiles, such as methylamine, can initiate this reaction by directly attacking the thioester bond generating the conformational change and the exposure of the receptor-recognition site without bait region cleavage. Receptor-recognized ␣ 2 M (␣ 2 M*) can rapidly eliminate the "entrapped" proteinase from the circulation by binding to a cell surface clearance receptor, the low density lipoprotein receptor-related protein (LRP) (8, 9). LRP is a multiligand receptor that binds to a wide variety of unrelated ligands (reviewed in Ref. 10). Binding of all ligands to LRP can be effectively competed by receptor-associated protein (RAP), which co-purifies with LRP. Prior investigation of ␣ 2 M* binding to LRP has shown that the binding mechanism involves a cluster of positively charged residues on ␣ 2 M* interacting with the second complement-like repeat on LRP, which contains clusters of negatively charged residues (11). Analysis of the receptor-binding site on ␣ 2 M* using monoclonal antibody (12, 13) and recombinantly expressed protein (14, 15) demonstrates that the carboxyl terminus of ␣ 2 M* is involved in receptor binding.Although LRP is the only ␣ 2 M* receptor identified to date, some important cellular regulatory functions ascribed to ␣ 2 M* suggest that an alternate receptor must exist. ␣ 2 M*, but not native ␣ 2 M, suppresses the production of superoxide anion (16), enhances the release of prostaglandin E 2 (17, 18) and platelet activating factor (19), and stimulates the proliferation of vascular smooth muscle cells (20). Moreover, our laboratory has characterized a novel signaling cascade and found that it does not appear to be LRP-mediated (21-23). Furthermore, we have identified two classes of ␣ 2 M* binding sites on peritoneal macrophages and human trabecular meshwork cells, both of which demonstrate activation of signaling cascades after exposure to ␣ 2 M* (24). The lower affinity binding site is 10 times more abundant than the high affinity binding site and has clearly been identified as LRP (25,26). The identity of the signaling receptor remains elusive; however, using site-directed mutagenesis, we have found that a lysine residue (13...

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Binding of rat α1-inhibitor-3-methylamine to the α2-macroglobulin signaling receptor induces second messengers

1996

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Binding of receptor-recognized forms of tetrameric human alpha 2-macroglobulin (alpha 2M*) to a macrophage signaling receptor induces cAMP synthesis, increases in inositol 1,4,5-triphosphate (IP3) synthesis, and a concomitant rise in cytosolic free calcium ([Ca2+]i). The alpha 2M* signaling receptor is coupled to a pertussis-toxin insensitive G protein. Binding of alpha 2M* also occurs to the low density lipoprotein receptor-related protein/alpha 2M receptor (LRP/alpha 2MR), but this binding does not induce signal transduction. Rat alpha 1-inhibitor-3 (alpha 1I3) is a monomeric member of the alpha-macroglobulin/complement superfamily. Like alpha 2M, it can react with proteinases or methylamine which induces a conformational change causing activated alpha 1I3 to bind to LRP/alpha 2MR. We now report that alpha 1I3-methylamine binds to the macrophage alpha 2M* signaling receptor inducing a rapid rise in the synthesis of IP3 with a subsequent 1.5- to 3-fold rise in [Ca2+]i. alpha 1I3-methylamine binding to macrophages also caused a statistically significant elevation in cAMP. Native alpha 1I3, like alpha 2M, was unable to induce signal transduction. alpha 1I3 forms a complex with alpha 1-microglobulin, which has a distinct conformation from alpha 1I3 and is recognized by LRP/alpha 2MR. This complex also induces an increase in [Ca2+]i comparable to the effect of alpha 1I3-methylamine on macrophages. It is concluded that activation of alpha 1I3 by methylamine or binding of alpha 1-microglobulin causes similar conformational changes in the inhibitor, exposing the receptor recognition site for the alpha 2M* signaling receptor, as well as for LRP/alpha 2MR.

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Ultrastructure of alpha 2-macroglobulins

Cited by 47 publications

References 215 publications

Low Resolution X-ray Structure of Human Methylamine-treated α2-Macroglobulin

Low Resolution X-ray Structure of Human Methylamine-treated α2-Macroglobulin

The Binding of Receptor-recognized α2-Macroglobulin to the Low Density Lipoprotein Receptor-related Protein and the α2M Signaling Receptor Is Decoupled by Oxidation

Binding of rat α1-inhibitor-3-methylamine to the α2-macroglobulin signaling receptor induces second messengers

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