Table 1 Key receptor proteins involved in phagocytosisa
Protein family; a representative (GI) | Detection in proteomic studies (number of species, out of 5 studied) | Role in phagocytosis | Domain architecture (with CDD IDs)band structural features (N-C)c | Range of orthologs in eukaryotes | Prokaryotic homologs | References |
|---|---|---|---|---|---|---|
Fcγ 204121 | 1 (mouse) | Fcγ binds IgG- opsonized particles and initiates assembly of protein complexes inside the macrophage | Two tandem immunoglobulin domains (cl00093); one membrane-spanning domain | This domain architecture is present only in Mammalia; immunoglobulin domains are found in all animals | Only distantly related immunoglobulin domains in some bacteria | [66] |
Complement receptor C3 (CR3) (αMβ2 integrin) | Binds C3bi- opsonized particles, initiates intracellular signal cascade leading to particle uptake (macrophages) |  |  |  | ||
αM integrin 88501734 | 2 (mouse, Drosophila) |  | Von Willebrand factor type A (vWA) domain (cd014690), two Integrin alpha (beta-propellor repeats) domains (smart00191), Integrin alpha domain (pfam08441); a transmembrane domain | All animals | No orthologs, but vWA domain is common in both archaea and bacteria; integrin alpha repeats are found in some bacteria |  |
β2 integrin 124056465 | 2 (mouse, Drosophila) |  | vWA domain (cl000057), Integrin beta tail domain (pfam07965), transmembrane region; Integrin beta cytoplasmic domain (pfamo8725) | All animals | Integrin beta chain-like proteins are present in cyanobacteria (e.g., 113475558); vWA domains are present in many archaea and bacteria. |  |
epidermal growth factor (EGF) receptor 6478868 | 0 | growth factors enhance macropinocytosis in some mammalian cell lines | A tandem repeat of a unit containing Receptor l domain (pfam01030) and Furin-like cysteine rich region (pfam00757); a transmembrane region; cytoplasmic Protein Tyrosine Kinase domain (cd001920). | All animals | No orthologs but Protein Tyrosine Kinase domain is common in archaea and bacteria. | |
Mannose receptor 109895388 | 1 (mouse) | Mannose receptor is the main phagocytic receptor of human alveolar macrophages that perform opsonin-independent phagocytosis. Mannose receptor is required for phagocytosis in dinoflagellates (Oxyrrhis marina), T. vaginalis, and microglia | Carbohydrate-binding domain RICIN (cd00161); Fibronectin Type II domain (cd00062); eight C-type lectin-like domains (CLECT; cd00037); a transmembrane domain | This domain architecture is conserved inl Chordata. Other animals, plants, Choanoflagellida, Kinetoplastida, and green algae have various arrangements of CLECT domains, from single domain to tandem arrays of 11 domains (S. purpuratus). | No orthologs; CLECT domain is also present in some bacteria | |
CED-1/MEGF-10/Draper/LRP1 12597465 | 0 | The main receptor in apoptotic cell (AC) phagocytosis | EMI domain, a cysteine-rich domain of EMILINs and other extracellular proteins; multiple EGF-like motifs (cl02497); a transmembrane domain | All animals. Although putative homolog of MEGF10/CED-1 is present in Entamoeba [148], our screening did not reveal it, perhaps due to lack of sequence similarity. | None | [67] |
SibA-SibD of Dictyostelium 60465670 | 0 | Adhesion receptor with structural and functional similarities to metazoan integrin beta chains. | vWA domain; four bacterial-like repeats (RTX family/adhesion- like protein); a transmembrane domain | Dictyostelium only | Partial: RTX family protein, adhesin like protein in various bacteria | [75] |
Transmembrane 9 (TM9) proteins/Phg1 74859302 | 1 (Drosophila) | Membrane proteins essential for cellular adhesion and phagocytosis | Endomembrane protein 70 (pfam02990): N-terminal signal peptide followed by a large extracellular domain and 9 transmembrane domains | All except for Giardia and Entamoeba | None | |
SadA 60465074 | 0 | Involved in phagocytosis of Dictyostelium, possibly, as an adhesion receptor. | Three EGF-like repeats (pfam07974); nine transmembrane domains | Dictyostelium only; EGF repeats of SadA are similar to corresponding regions of tenascins and integrins. | None | [77] |