title: The chaperone and potential mannan-binding lectin (MBL) co-receptor calreticulin interacts with MBL through the binding site for MBL-associated serine proteases.
abstract: The chaperone calreticulin has been suggested to function as a C1q and collectin receptor. The interaction of calreticulin with mannan-binding lectin (MBL) was investigated by solid-phase binding assays. Calreticulin showed saturable and time-dependent binding to recombinant MBL, provided that MBL was immobilized on a solid surface or bound to mannan on a surface. The binding was non-covalent and biphasic with an initial salt-sensitive phase followed by a more stable salt-insensitive interaction. For plasma-derived MBL, known to be complexed with MBL-associated serine proteases (MASPs), no binding was observed. Interaction of calreticulin with recombinant MBL was fully inhibited by recombinant MASP-2, MASP-3 and MAp19, but not by the MASP-2 D105G and MAp19 Y59A variants characterized by defective MBL binding ability. Furthermore, MBL point mutants with impaired MASP binding showed no interaction with calreticulin. Comparative analysis of MBL with complement component C1q, its counterpart of the classical pathway, revealed that they display similar binding characteristics for calreticulin, providing further indication that calreticulin is a common co-receptor/chaperone for both proteins. In conclusion, the potential MBL co-receptor calreticulin binds to MBL at the MASP binding site and the interaction may involve a conformational change in MBL.
authors.affiliation: Department of Autoimmunology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Rasmus
authors.initials: R
authors.lastname: Pagh
authors.forename: Karen
authors.initials: K
authors.lastname: Duus
authors.forename: Inga
authors.initials: I
authors.lastname: Laursen
authors.forename: Paul R
authors.initials: PR
authors.lastname: Hansen
authors.forename: Julie
authors.initials: J
authors.lastname: Mangor
authors.forename: Nicole
authors.initials: N
authors.lastname: Thielens
authors.forename: Gérard J
authors.initials: GJ
authors.lastname: Arlaud
authors.forename: Leif
authors.initials: L
authors.lastname: Kongerslev
authors.forename: Peter
authors.initials: P
authors.lastname: Højrup
authors.forename: Gunnar
authors.initials: G
authors.lastname: Houen
mesh_terms: D001665:Binding Sites; D019921:Biotinylation; D037282:Calreticulin / Q000378:metabolism*; D037222:Collectins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D015151:Immunoblotting; D037601:Mannose-Binding Lectin / Q000378:metabolism*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D037282:Calreticulin; D037222:Collectins; D037601:Mannose-Binding Lectin; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D050606:Mannose-Binding Protein-Associated Serine Proteases