Structure of a rat α₁‐macroglobulin receptor‐binding domain dimer

Abstract

Abstracta-Macroglobulin inhibits a broad spectrum of proteinases by forming macromolecular cages inside which proteinases are cross-linked and trapped. Upon formation of a complex with proteinase, a-macroglobulin undergoes a large conformational change that results in the exposure of its receptor-binding domain~RBD!. Engagement of this domain by a-macroglobulin receptor permits clearance of the a-macroglobulin: proteinase complex from circulation. The crystal structure of rat a 1 -macroglobulin RBD has been determined at 2.3 Å resolution. The RBD is composed of a nine-stranded b-sandwich and a single a-helix that has been implicated as part of the receptor binding site and that lies on the surface of the b-sandwich. The crystallographic asymmetric unit contains a dimer of RBDs related by approximate twofold symmetry such that the putative receptor recognition sites of the two monomers are contiguous. By gel filtration and ultracentrifugation, it is shown that RBD dimers form in solution with a dissociation constant of ;50 mM. The structure of the RBD dimer might mimic a conformation of transformed a-macroglobulin in which the proposed receptor binding residues are exposed on one face of the dimer. A pair of phenylalanine residues replaces a cystine that is conserved in other members of the macroglobulin family. These residues participate in a network of aromatic side-chain interactions that appears to stabilize the dimer interface.

Proteomics study of neuropathic and nonneuropathic dorsal root ganglia: altered protein regulation following segmental spinal nerve ligation injury

“…After cleavage of its bait region by a target proteinase, macroglobulin entraps the proteinase for clearance from the circulation through a cell surface receptor (144). Although rat ␣1-macroglobulin is a Ϸ170-kDa protein, two spots of ␣1-macroglobulin observed on our gels were proteolytic fragments of the COOH terminus containing the receptor binding domain (144). The patterns of the pI variants exhibiting MW of Ϸ36 kDa and pI of Ϸ5 on our gels (Fig.…”

“…Interestingly, the protein was reported to enhance nerve growth factor-promoted neurite outgrowth (69). After cleavage of its bait region by a target proteinase, macroglobulin entraps the proteinase for clearance from the circulation through a cell surface receptor (144). Although rat ␣1-macroglobulin is a Ϸ170-kDa protein, two spots of ␣1-macroglobulin observed on our gels were proteolytic fragments of the COOH terminus containing the receptor binding domain (144).…”

Structure of a bacterial α2-macroglobulin reveals mimicry of eukaryotic innate immunity

“…2) and could serve a local stabilizing role (see below). It is of note that MG10 is structurally reminiscent of the C-terminal, receptor-binding domain of eukaryotic alpha-macroglobulin 35,36 (r.m.s.d. ¼ 3.54 Å over 120 C-alpha atoms), but its involvement in protease clearance is to date unclear.…”

High Affinity Binding of the Receptor-associated Protein D1D2 Domains with the Low Density Lipoprotein Receptor-related Protein (LRP1) Involves Bivalent Complex Formation

“…Interestingly, cell-based experiments reveal that the LRP1-mediated uptake of ␣ 2 M requires CR modules from both cluster I and cluster II (48). Structural analysis of the dimeric receptor binding domain from rat ␣ 2 M reveals that the critical lysine residues are located 18 Å apart (49), implying that CR modules in LRP1 that have this spacing are likely binding sites.…”