title: Interaction properties of human mannan-binding lectin (MBL)-associated serine proteases-1 and -2, MBL-associated protein 19, and MBL.
abstract: The mannan-binding lectin (MBL) activation pathway of complement plays an important role in the innate immune defense against pathogenic microorganisms. In human serum, two MBL-associated serine proteases (MASP-1, MASP-2) and MBL-associated protein 19 (MAp19) were found to be associated with MBL. With a view to investigate the interaction properties of these proteins, human MASP-1, MASP-2, MAp19, as well as the N-terminal complement subcomponents C1r/C1s, Uegf, and bone morphogenetic protein-1-epidermal growth factor (CUB-EGF) segments of MASP-1 and MASP-2, were expressed in insect or human kidney cells, and MBL was isolated from human serum. Sedimentation velocity analysis indicated that the MASP-1 and MASP-2 CUB-EGF segments and the homologous protein MAp19 all behaved as homodimers (2.8-3.2 S) in the presence of Ca(2+). Although the latter two dimers were not dissociated by EDTA, their physical properties were affected. In contrast, the MASP-1 CUB-EGF homodimer was not sensitive to EDTA. The three proteins and full-length MASP-1 and MASP-2 showed no interaction with each other as judged by gel filtration and surface plasmon resonance spectroscopy. Using the latter technique, MASP-1, MASP-2, their CUB-EGF segments, and MAp19 were each shown to bind to immobilized MBL, with K:(D) values of 0.8 nM (MASP-2), 1.4 nM (MASP-1), 13.0 nM (MAp19 and MASP-2 CUB-EGF), and 25.7 nM (MASP-1 CUB-EGF). The binding was Ca(2+)-dependent and fully sensitive to EDTA in all cases. These data indicate that MASP-1, MASP-2, and MAp19 each associate as homodimers, and individually form Ca(2+)-dependent complexes with MBL through the CUB-EGF pair of each protein. This suggests that distinct MBL/MASP complexes may be involved in the activation or regulation of the MBL pathway.
authors: Laboratoire d'Enzymologie Moléculaire, Institut de Biologie Structurale Jean-Pierre Ebel (Commissariat à l'Energie Atomique-Centre National de la Recherche Scientifique), Grenoble, France. thielens@ibs.fr
authors: N M
authors: NM
authors: Thielens
authors: S
authors: S
authors: Cseh
authors: S
authors: S
authors: Thiel
authors: T
authors: T
authors: Vorup-Jensen
authors: V
authors: V
authors: Rossi
authors: J C
authors: JC
authors: Jensenius
authors: G J
authors: GJ
authors: Arlaud
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D037222:Collectins; D003173:Complement C1s / Q000235:genetics; D019281:Dimerization; D004815:Epidermal Growth Factor / Q000235:genetics; D016326:Extracellular Matrix Proteins / Q000235:genetics; D006801:Humans; D037102:Lectins / Q000378:metabolism*; D008351:Mannans / Q000378:metabolism; D050606:Mannose-Binding Protein-Associated Serine Proteases; D010446:Peptide Fragments / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D017463:Receptors, Complement 3b / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D018411:Spodoptera / Q000235:genetics; D020349:Surface Plasmon Resonance
chemical_list: D002352:Carrier Proteins; D002413:Cations, Divalent; D037222:Collectins; D016326:Extracellular Matrix Proteins; D037102:Lectins; D008351:Mannans; D010446:Peptide Fragments; D017463:Receptors, Complement 3b; D011994:Recombinant Proteins; C062354:fibropellin protein, sea urchin; D004815:Epidermal Growth Factor; C105296:MASP2 protein, human; D050606:Mannose-Binding Protein-Associated Serine Proteases; D012697:Serine Endopeptidases; D003173:Complement C1s; D002118:Calcium