A conserved region in alpha-macroglobulins participates in binding to the mammalian alpha-macroglobulin receptor.
Efforts to characterize the receptor recognition domain of alpha-macroglobulins have primarily focused on human alpha 2-macroglobulin (alpha 2M). In the present work, the structure and function of the alpha-macroglobulin receptor recognition site were investigated by amino acid sequence analysis, plasma clearance, and cell binding studies using several nonhuman alpha-macroglobulins: bovine alpha 2M, rat alpha 1-macroglobulin (alpha 1M), rat alpha 1-inhibitor 3 (alpha 1I3), and proteolytic fragments derived from these proteins. Each alpha-macroglobulin bound to the murine peritoneal macrophage alpha-macroglobulin receptor with comparable affinity (Kd approximately 1 nM). A carboxyl-terminal 20-kDa fragment was isolated from each of these proteins, and this fragment bound to alpha-macroglobulin receptors with Kd values ranging from 10 to 125 nM. The amino acid identity between the homologous carboxyl-terminal 20-kDa fragments of human and bovine alpha 2M was approximately 90%, while the overall sequence homology between all carboxyl-terminal fragments studied was 75%. The interchain disulfide bond present in the human alpha 2M carboxyl-terminal 20-kDa fragment was conserved in bovine alpha 2M and rat alpha 1I3, but not in rat alpha 1M. The clearance of each intact alpha-macroglobulin-proteinase complex was significantly retarded following treatment with cis-dichlorodiammineplatinum(II) (cis-DDP). cis-DDP treatment, however, did not affect receptor recognition of purified carboxyl-terminal 20-kDa fragments of these alpha-macroglobulins. A carboxyl-terminal 40-kDa subunit, which can be isolated from rat alpha 1M, bound to the murine alpha-macroglobulin receptor with a Kd of 5 nM.(ABSTRACT TRUNCATED AT 250 WORDS)
Enghild
J J
JJ
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710.
Thøgersen
I B
IB
Roche
P A
PA
Pizzo
S V
SV
D000595:Amino Acid Sequence; D006801:Humans; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D011971:Receptors, Immunologic / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D010446:Peptide Fragments; D011971:Receptors, Immunologic; D000511:alpha-Macroglobulins