title: Localisation of the major reactive lysine residue involved in the self-crosslinking of proteinase-activated Limulus alpha 2-macroglobulin.
abstract: When alpha 2-macroglobulin (alpha 2M) from the American horseshoe crab, Limulus polyphemus, reacts with proteinases, its thiol esters, like those of other alpha-macroglobulins, become activated, leading to the formation of covalently crosslinked species that can be detected as high molecular weight bands in reducing SDS-PAGE. While other alpha-macroglobulins extensively form crosslinks to the reacting proteinase, Limulus alpha 2M does not. It rather becomes internally crosslinked. It was found from N-terminal sequence analysis of purified [14C]carboxymethylated peptides from Limulus alpha 2M-trypsin complexes that an isopeptide bond formed in approx. 60% yield from the thiol esterified Gln-1002 specifically to Lys-254 in the opposing monomer of the disulphide bridged dimer is the main cause of the internal crosslinking.
authors.affiliation: Department of Molecular and Structural Biology, University of Aarhus, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Dolmer
authors.forename: L B
authors.initials: LB
authors.lastname: Husted
authors.forename: P B
authors.initials: PB
authors.lastname: Armstrong
authors.forename: L
authors.initials: L
authors.lastname: Sottrup-Jensen
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents; D010450:Endopeptidases / Q000378:metabolism*; D006737:Horseshoe Crabs; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D000511:alpha-Macroglobulins; D010450:Endopeptidases; D014357:Trypsin; D008239:Lysine