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.

Collectin-11 detects stress-induced L-fucose pattern to trigger renal epithelial injury

“…It was reported that interchain disulphide bonds held together the CL-10 and CL-11 single chains, implying that such heterotrimers can only form within a cell that synthesized both components (34). So far, the only known cell in which CL-11 and CL-10 are coexpressed is the hepatocyte.…”

Heterocomplex Formation between MBL/Ficolin/CL-11–Associated Serine Protease-1 and -3 and MBL/Ficolin/CL-11–Associated Protein-1

“…We are aware that the novel CL CL-10 (also known as CL-L1) could be a possible candidate in the family comprising circulating MASP binding partners (31); however, we assume that depletion of CL-11 also will include depletion of CL-10 because both CLs reportedly bind to mannose (32). Moreover, it has recently been shown that CL-10 and CL-11 peptide chains presumably form complexes, thus depletion of one of the molecules will lead to depletion of the other (33). It should be mentioned that depletion was verified in ELISA assays using lower serum concentrations than the concentration applied for complex measurements because higher serum concentrations would exceed the limit for these assays.…”

The pattern recognition molecule collectin-L1 in critically ill children

“…CL-L1 is encoded by the COLEC10 gene and is primarily expressed in the liver, placenta, and adrenal glands (18). Initially, CL-L1 was identified as a cytosolic protein but has now been found in the circulation, where it complexes with MBL-associated serine proteases (MASPs), the enzymes responsible for activation of complement through the lectin pathway (21,22,26). In healthy individuals, CL-L1 levels appear to be present at near adult levels at birth and show low variation (22).…”

“…Nevertheless, a limitation of our study is that we only showed associations, with no evidence of causality. Secondly, the measurements we performed are primarily of Articles hetero-oligomers between CL-L1 and CL-K1 polypeptide chains, two collectins that have most likely evolved from the same ancestral gene by gene duplication (21,26,29). We have observed that there is a tight correlation between the amount of CL-L1 and CL-K1 in plasma but no one has studied in detail whether both molecules can be present separately at different sites in the body and whether such proteins appear in plasma at extreme conditions (24,26,29,30).…”