The SEC receptor recognizes a pentapeptide neodomain of alpha 1-antitrypsin-protease complexes.
Formation of the covalently stabilized alpha 1-antitrypsin (alpha 1-AT)-neutrophil elastase complex, the archetype of serpin-enzyme complexes, results in a structurally rearranged alpha 1-AT molecule that possesses chemo-attractant activities, mediates an increase in synthesis of alpha 1-AT by mononuclear phagocytes and hepatocytes, and is more rapidly cleared from the circulation than is the native alpha 1-AT molecule. We have recently identified an abundant, high affinity cell surface receptor on human hepatoma HepG2 cells and human monocytes that binds alpha 1-AT-elastase complexes, mediates endocytosis and lysosomal degradation of alpha 1-AT-elastase complexes, and induces an increase in synthesis of alpha 1-AT. We have referred to this receptor as the serpin-enzyme complex, or SEC, receptor because it also recognizes complexes of serpins antithrombin III, alpha 1-antichymotrypsin, and C1 inhibitor with their cognate enzymes. In the current study, we show that a pentapeptide domain in the carboxyl terminal fragment of alpha 1-AT (amino acids 370-374, FVFLM) is sufficient for binding to the SEC receptor. A synthetic analog of this pentapeptide (peptide 105C, FVYLI) blocks binding and internalization of alpha 1-AT-125I-trypsin complexes by HepG2 cells. 125I-Peptide 105C binds specifically and saturably to HepG2 cells, and its binding is blocked by alpha 1-AT-trypsin or alpha 1-AT-elastase complexes. Alterations of this sequence introduced into synthetic peptides (mutations, deletions, or scrambling) demonstrate that binding of the pentapeptide domain is sequence-specific. Comparisons with the sequences of other serpins in the corresponding region indicate that this pentapeptide neodomain is highly conserved.
Joslin
G
G
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110.
Fallon
R J
RJ
Bullock
J
J
Adams
S P
SP
Perlmutter
D H
DH
D000595:Amino Acid Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D019272:Leukocyte Elastase; D008969:Molecular Sequence Data; D010196:Pancreatic Elastase / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis / Q000494:pharmacology; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000378:metabolism*; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
D010455:Peptides; D011956:Receptors, Cell Surface; D000515:alpha 1-Antitrypsin; C064184:serpin-enzyme complex receptor; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase