Fig. 3 | Nature Communications

Fig. 3

From: Chitin-based barrier immunity and its loss predated mucus-colonization by indigenous gut microbiota

Fig. 3

Protein components of the Ciona barrier membrane. a Domain structure of the membrane-attack complex/perforin family protein, Ci-MACPF1 (951 amino acid residue [aa]). Ci-MACPF1 consists of a signal peptide, 10 thrombospondin type 1 repeats (TSR) domains (cyan), an MACPF domain (yellow) and an epidermal growth factor (EGF)-like domain (magenta). MACPF domains are essential for cytolytic activities, as in human complement factor 6 (Hs-C6) and human perforin (Hs-Perforin). For details, see Supplementary Figure 5. b Domain structure of the variable-region containing chitin-binding protein, VCBP-C (349 aa). VCBP-C consists of a signal peptide, two variable-type immunoglobulin (Ig-V) domains and a chitin-binding domain (CBD) of carbohydrate-binding module family 14. Horizontal lines denote the regions corresponding to N-terminally His-tagged recombinant proteins: Wt, ΔC, and ΔV. c Upper panels show that VCBP-C binds to chitin beads using CBD. Recombinant proteins are visualized with chromogenic detection of His-tag (purple). Lower panels show that Wt tethers Ciona-gut derived bacilli on chitin beads. Recombinant proteins and bacilli were visualized with confocal laser scanning microscopy using fluorophore-conjugated anti-His tag antibody (blue) and a nuclear staining reagent, TO-PRO-3 (red), respectively. d Domain structure of the gel-forming mucin, Ci-GFM1 (2880 aa). Ci-GFM1 is a mosaic protein composed of 30 domains of 13 types. It shares core organization with human von Willebrand factor (Hs-VWF, 2813 aa) and human GFM (Hs-MUC2, 5179 aa). Common scaffolding consists of D1 (cyan), D2 (yellow), D`D3 (magenta), and D4 (green) assemblies, two von Willebrand C (VWC) domains and a C-terminal cystine knot (CK) domain (blue). Each protein has additional domains with specific functions. For example, CBD for chitin-binding in Ci-GFM1, von Willebrand A (VWA) domain for platelet binding in Hs-VWF and proline–threonine–serine-rich (PTS) domain for hyper glycosylation in Hs-MUC2. FN fibronectin type II domain, VWD von Willebrand D domain, C8 cysteine 8 domain, TIL trypsin inhibitor-like domain, E E domain. e Intermolecular disulfide bonds in D`D3 (magenta) and CK (blue) are essential for the multimeric structures, concatenating rope of Hs-VWF (left) and flat hexagonal net of Hs-MUC2 (right), which are the structural bases of the physiological functions of these molecules18, 19. Scale bars c 100 μm

Back to article page