title: Heteromeric complexes of native collectin kidney 1 and collectin liver 1 are found in the circulation with MASPs and activate the complement system.
abstract: The complement system is an important part of the innate immune system. The complement cascade may be initiated downstream of the lectin activation pathway upon binding of mannan-binding lectin, ficolins, or collectin kidney 1 (CL-K1, alias CL-11) to suitable microbial patterns consisting of carbohydrates or acetylated molecules. During purification and characterization of native CL-K1 from plasma, we observed that collectin liver 1 (CL-L1) was copurified. Based on deglycosylation and nonreduced/reduced two-dimensional SDS-PAGE, we detected CL-K1 and CL-L1 in disulfide bridge-stabilized complexes. Heteromeric complex formation in plasma was further shown by ELISA and transient coexpression. Judging from the migration pattern on two-dimensional SDS-PAGE, the majority of plasma CL-K1 was found in complex with CL-L1. The ratio of this complex was in favor of CL-K1, suggesting that a heteromeric subunit is composed of one CL-L1 and two CL-K1 polypeptide chains. We found that the complex bound to mannan-binding lectin-associated serine proteases (MASPs) with affinities in the nM range in vitro and was associated with both MASP-1/-3 and MASP-2 in plasma. Upon binding to mannan or DNA in the presence of MASP-2, the CL-L1-CL-K1 complex mediated deposition of C4b. In favor of large oligomers, the activity of the complex was partly determined by the oligomeric size, which may be influenced by an alternatively spliced variant of CL-K1. The activity of the native heteromeric complexes was superior to that of recombinant CL-K1. We conclude that CL-K1 exists in circulation in the form of heteromeric complexes with CL-L1 that interact with MASPs and can mediate complement activation.
authors.affiliation: Department of Cancer and Inflammation Research, Institute of Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark;
authors.forename: Maiken L
authors.initials: ML
authors.lastname: Henriksen
authors.forename: Jette
authors.initials: J
authors.lastname: Brandt
authors.forename: Jean-Piere
authors.initials: JP
authors.lastname: Andrieu
authors.forename: Christian
authors.initials: C
authors.lastname: Nielsen
authors.forename: Pia H
authors.initials: PH
authors.lastname: Jensen
authors.forename: Uffe
authors.initials: U
authors.lastname: Holmskov
authors.forename: Thomas J D
authors.initials: TJ
authors.lastname: Jorgensen
authors.forename: Yaseelan
authors.initials: Y
authors.lastname: Palarasah
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Thielens
authors.forename: Soren
authors.initials: S
authors.lastname: Hansen
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D037222:Collectins / Q000097:blood* / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology; D015935:Complement C4b / Q000378:metabolism*; D037582:Complement Pathway, Mannose-Binding Lectin; D004247:DNA / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D008351:Mannans / Q000276:immunology; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000502:physiology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D046912:Multiprotein Complexes; D010446:Peptide Fragments / Q000737:chemistry; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: C445459:COLEC10 protein, human; C518521:Colec11 protein, human; D037222:Collectins; D008351:Mannans; D046912:Multiprotein Complexes; D010446:Peptide Fragments; D011994:Recombinant Proteins; D015935:Complement C4b; D004247:DNA; C084067:MASP1 protein, human; C105296:MASP2 protein, human; D050606:Mannose-Binding Protein-Associated Serine Proteases