Fig. 8: Experimental validation of the inhibitory role of nematode SPI-I8 in host inflammation.

a Structural modelling and docking of MKRN1 and RACK1, Haemonchus contortus SPI-I8B, MKRN1 and RACK1 in silico. Nematode SPI-I8 protects RACK1 from MKRN1-mediated polyubiquitination on the lysine residues K183 and K185 by competing the space for physical interaction. K183 and K185 residues are indicated in red. The amino acid residues closest to these two residues are shown in black, and the distances has been measured. b Effect of recombinant Nippostrongylus brasiliensis SPI-I8 (rNb-SPI-I8; peritoneal injection) on the colon length of mice administrated with dextran sulfate sodium (DSS)-induced colitis. Four groups were set, and five C57BL/6 mice were included in each group. The bottles indicate DSS administration through water by drinking freely. The blue injectors mean peritoneal injection of rNb-SPI-I8 (50 µg per mouse). Seven days post treatment, colons of treated mice were collected and measured at autopsy. The length of each colon from mice was recorded. Student t-test analysis is used to indicate the significance of difference. ** p < 0.01; **** p < 0.0001; ns, not significant. c Effect of rNb-SPI-I8 on the survival of mice peritoneally injected with endotoxic lipopolysaccharide (LPS)-induced systemic inflammation. Ten C57BL/6 mice were pre-treated with 50 µg SPI-I8 (the former blue injector) by intraperitoneal injection every day for three days, then treated with 150 µg SPI-I8 (the later blue injector) and 50 mg LPS (red injector) by tail vein injection on day 4. Mice (n = 10) treated with the same volume of PBS and 50 mg LPS (red injector) on day 4 to serve as positive control.