Table 2. .
Functions of animal and human lectinsa
| Activity | Example of lectin |
|---|---|
| Recognition of stem region of N-glycans, a signal for ubiquitin conjugation when accessible in incorrectly folded glycoproteins | F-box proteins Fbs1 and Fbs2, which comprise the ligand-specific part of SCFb ubiquitin ligase complexes |
| Molecular chaperones with dual specificity for Glc2/Glc1Man9GlcNAc2 and protein part of nascent glycoproteins in the ER | malectin/ribophorin I complex, calnexin, calreticulin |
| Targeting of misfolded glycoproteins with Man8-5GlcNAc2 as carbohydrate ligand to ER-associated degradation (ERAD) | EDEM1,2c/Mnl1 (Htm1) (α1,2-mannosidases; in mammals active as lectins), Yos9p (MRHd domain) in yeast, erlectin (XTP3-Be) and OS-9f in mammals |
| Intracellular transport of glycoproteins and vesicles, e.g. in apical, axonal and lysosomal routing | comitin, ERGIC53g and VIP36h (probably also ERGLi and VIPLj), galectins-3, -4 and -9, P-type lectins |
| Intracellular transport and extracellular assembly | non-integrin 67 kDa elastin/laminin-binding protein |
| Enamel formation and biomineralization | amelogenin |
| Inducer of membrane superimposition and zippering (formation of Birbeck granules) |
langerin (CD207) |
| Molecular glue for high-order (glyco)protein association (packing) | eye lens-specific galectin (GRIFIN) |
| Cell type-specific endocytosis | cysteine-rich domain (β-trefoil) of the dimeric form of mannose receptor for GalNAc-4-SO4-bearing glycoprotein hormones in hepatic endothelial cells, dendritic cell and macrophage C-type lectins (mannose receptor family members (tandem-repeat type) and single-CRDk lectins such as trimeric langerin/CD207 or tetrameric DC-SIGNl/CD209), hepatic and macrophage asialoglycoprotein receptors, HAREm, P-type lectins |
| Recognition of foreign glycans (β1,3-glucans, β1,2-mannosides, cell wall peptidoglycan, LOSn and LPSo), mycobacterial glycolipid or host-like epitopes |
CR3p (CD11b/CD18, Mac-1 antigen), C-type lectins such as collectins, DC-SIGN, dectin-1, Mincle and RegIIIγ (murine)q or HIP/PAP (human), ficolins, galectins, immulectins, intelectins, Limulus coagulation factors C and G, siglecs, tachylectins |
| Recognition of foreign or aberrant glycosignatures on cells (including endocytosis or initiation of opsonization or complement activation) and of apoptotic/necrotic cells (glycans or peptide motifs) |
collectins, C-type macrophage and dendritic cell lectins, CR3 (CD11b/CD18, Mac-1 antigen), α/θ defensins, ficolins, galectins, pentraxins (CRP, limulin), RegIIIγ (HIP/PAP), siglecs, tachylectins |
| Targeting of enzymatic activity in multimodular proteins | acrosin, Limulus coagulation factor C, laforin, β-trefoil fold ((QxW)3
domain) of GalNAc-Tsr involved in mucin-type O-glycosylation—often found in microbial glycosylhydrolases for plant cell wall polysaccharides, then termed carbohydrate-binding modules |
| Induction or suppression of effector release (H2O2, cytokines etc.) | chitinase-like YKL-40, galectins, I-type lectins (e.g. CD33 (siglec-3), siglecs-7 and -9), selectins and other C-type lectins such as CD23, BDCA2 and dectin-1, Toll-like receptor 4 |
| Modulation of enzymatic activities in modular proteins/receptor endocytosis via lattice formation |
mannan-binding lectin (acting on meprins), galectins |
| Coordination of autophagy/repair mechanisms by sensing endomembrane damage and ‘calling for help’ | galectins-3, -8 and -9 |
| Cell growth control, induction of apoptosis/anoikis and axonal regeneration, anti- and pro-inflammatory regulation with/without modulating gene expression |
amphoterin and other heparin-binding proteins, cerebellar soluble lectin, chitinase-like lectins, C-type lectins, galectins, hyaluronic acid-binding proteins, siglecs (e.g. CD22 and CD33) |
| Cell migration and routing | galectins, hyaluronic acid-binding proteins (CD44, hyalectans/lecticans, RHAMMs), I-type lectins, selectins and other C-type lectins |
| Cell–cell interactions | galectins, gliolectin, I-type lectins (e.g. siglecs, N-CAMt, P0 or L1), selectins and other C-type lectins such as DC-SIGN or macrophage mannose receptor |
| Cell–matrix interactions | calreticulin, discoidin I, galectins, heparin- and hyaluronic acid-binding lectins including hyalectans/lecticans |
| Matrix network assembly | galectins (e.g. galectin-3/hensin), non-integrin 67 kDa elastin/laminin-binding protein, proteoglycan core proteins (C-type CRD and G1 domain of hyalectans/lecticans) |
aAdapted from [68], extended and modified; bSkp-1-Cul1-F-box protein complex; cER degradation enhancing α-mannosidase-like protein; dmannose-6-phosphate receptor homology; eXTP3-transactivated gene B precursor; fosteosarcoma 9; gER-Golgi intermediate compartment protein (lectin) (MW: 53 kDa); hvesicular-integral (membrane) protein (lectin) (MW: 36 kDa); iERGIC-53-like protein; jVIP-36-like protein; kcarbohydrate recognition domain; ldendritic cell-specific ICAM-3-grabbing nonintegrin; mhyaluronan receptor for endocytosis; nlipooligosaccharide; olipopolysaccharide; pcomplement receptor type 3; qmember of regenerating (reg) gene family of secreted proteins; rUDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases; sreceptor for hyaluronan-mediated motility; tneural cell adhesion molecule.