COLEC11

COLEC11 (CL-K1/CL-11) is a secreted, oligomeric C-type lectin collectin that functions as a recognition molecule of the lectin complement pathway and as a developmental guidance cue (PMID:20956340, PMID:21258343). It circulates in plasma as disulfide-linked oligomers in association with MASP-1/3, and recognizes microbial surfaces—bacteria, fungi, and viruses including influenza A—through Ca2+-dependent binding of L-fucose and D-mannose (PMID:20956340, PMID:22475410). In parallel, it engages DNA and apoptotic cells presenting extracellular DNA through a high-affinity, Ca2+-independent site distinct from its carbohydrate-recognition domain, with oligomerization required for binding (PMID:23954398). Upon engaging either microbial carbohydrate or DNA ligands, CL-11 drives MASP-2-dependent C4b deposition, activating the lectin pathway (PMID:23954398, PMID:30323815). It circulates and acts in heteromeric complexes with the paralogous collectin CL-10/CL-L1, whose co-expression at peripheral epithelial and secretory tissues supports local heterocomplex assembly (PMID:30108587, PMID:30323815). Beyond innate immunity, CL-K1 serves as a guidance cue for neural crest cell migration during embryogenesis, and loss-of-function mutations in COLEC11 cause the developmental disorder 3MC syndrome (PMID:21258343).

1. 2006 Medium

   Establishing that CL-K1 is a secreted protein with defined Ca2+-dependent sugar specificity answered the basic question of what class of molecule it is and what it recognizes.

   Evidence cDNA cloning, CHO cell expression, and sugar-binding assays

   PMID:17179669

   Open questions at the time

   • No physiological ligand or downstream pathway identified
   • Single lab, founding characterization
   • No oligomeric or complex partner defined
2. 2007 Medium

   Mapping CL-K1 tissue distribution addressed where the protein is produced and likely acts, implicating hepatic synthesis with secretion into blood and broad epithelial expression.

   Evidence Immunohistochemistry and real-time PCR across murine tissues

   PMID:18040075

   Open questions at the time

   • Localization without direct functional consequence
   • Does not establish secretion mechanism or circulating form
3. 2010 High

   Demonstrating physical association with MASP-1/3 and oligomerization placed CL-11 within the lectin complement pathway and connected its carbohydrate recognition to an effector module.

   Evidence Co-purification, ELISA, mass spectrometry, and in vitro microbial binding assays

   PMID:20956340

   Open questions at the time

   • Did not demonstrate direct C4b deposition/complement activation
   • MASP-1 vs MASP-3 functional roles not resolved
4. 2011 High

   Identifying COLEC11 loss-of-function as the cause of 3MC syndrome and a neural crest guidance role established a developmental function distinct from immunity.

   Evidence Human genetic sequencing across 11 families, murine embryo expression, zebrafish morpholino knockdown, and neural crest migration assay

   PMID:21258343

   Open questions at the time

   • Molecular receptor/signaling for neural crest guidance not defined
   • Relationship between immune and developmental functions unresolved
5. 2012 Medium

   Distinguishing CL-11 (serum) from its cytosolic paralog CL-L1 and detailing CRD specificity clarified which collectin operates extracellularly in circulation.

   Evidence Structural/specificity characterization, binding assays, and co-purification

   PMID:22475410

   Open questions at the time

   • Consolidation paper, limited new primary data
   • Heterocomplex stoichiometry not defined
6. 2013 High

   Showing high-affinity, Ca2+-independent DNA binding via a site separate from the CRD, coupled to MASP-2-driven C4b deposition, revealed a second ligand class linking CL-11 to apoptotic-cell handling and complement activation.

   Evidence Surface plasmon resonance, competition/domain-separation binding studies, apoptotic cell binding, and in vitro C4b deposition assay

   PMID:23954398

   Open questions at the time

   • DNA-binding site not mapped at residue level
   • In vivo relevance of DNA-triggered complement activation not established
7. 2018 Medium

   Defining CL-11/CL-10 heterocomplexes and their tissue co-expression established the physiological circulating and local assembly state of the protein and confirmed MASP-2-dependent activation on microbial surfaces.

   Evidence Size exclusion chromatography, ELISA, IHC/mRNA localization, and in vitro C4b deposition on zymosan

   PMID:30108587 PMID:30323815

   Open questions at the time

   • Functional difference between homo- and heterocomplexes not quantified
   • Single lab biochemistry

• How CL-K1 transduces neural crest guidance and whether this developmental role intersects with its complement-activating function remains unresolved.
• No neural crest receptor identified
• No structural model of ligand discrimination
• Mechanistic basis of 3MC pathology unexplained