Part:BBa_K4195025

Biology

INPNC

INPNC is a truncated form of ice nucleation protein (INP) consisting of N- and C-terminal domains (1). It is a membrane protein commonly used to target protein onto the cell membrane.

rFET

rFET is a truncated form of the A chain of mouse fetuin-B (residues 141-169). Vertebrate fetuins are multi-domain plasma-proteins of the cystatin-superfamily (2). It was reported that mouse fetuin-B shows high inhibition effect to the toxin PirB (3). We used the ClusPro (4) to evaluate the affinity of mouse fetuin-B to PirA and PirB. The results showed that the 141-169 residues of the A chain of mouse fetuin-B have higher affinity to PirA and PirB than the complete A chain of mouse fetuin-B. What’s more, there is no glycosylation site in rFET sequence, so the expression of recombinant rFET by engineered E. coli can be available and functional. In summary, we chose the 141-169 residues of the A chain of mouse fetuin-B as the functional inhibitor and named it rFET (BBa_K4195009).
The rFET can be displayed on the surface of the engineered bacteria and OMVs (outer membrane vesicles) due to the localization of INPNC. The OMVs with rFET displayed is more stable in the environment than rFET and is a better choice for binding to toxins. This part has one more His-tag (6×His) than BBa_K4195024, which allows it to be used to verify the function of the surface display system.

Usage and design

Engineering outer membrane vesicles (OMVs) for treating and preventing AHPND caused by the pathogen V. parahaemolyticus are a significant part of OMEGA project (Operable Magic to Efficiently Getting over AHPND). Based on the efforts of our previous projects in 2020 (AnTea-Glyphosate) and 2021 (SALVAGE), we further developed the surface display system on the OMVs released by the engineered bacteria. The usage of cargo proteins was no more limited to enzymes that are usually utilized to catalyze series bio-chemical reactions, since some receptors or ligands involved in complex protein-protein interaction (PPI) were selected as the cargo candidates. This year, we chose two classic anchor proteins, ClyA and INPNC, to construct the display cassette with various cargo proteins including rFET (receptor), rLvAPN1 (receptor), TTPA (ligand) and TTPB (ligand) (Fig. 1). On one hand, with the receptors displayed, OMVs will gain the function of neutralizing toxins secreted by V. parahaemolyticus. On the other hand, with the assistance of ligands displayed on the surface, OMVs will become a special vector to deliver antimicrobials for the specific pathogen. In summary, we have taken a step closer to the collections of extracellular functional elements (EFE), combining the OMVs, secretion systems and surface display systems which we have been dedicated to since 2020. Learn more information from our Designpage.

Fig. 1 Graphic description of the expression gene circuits for display cassette designed in OMEGA project.
For this part (INPNC-rFET-his), rFET-his was fused to the C-terminal of INPNC to verify the function of surface display system INPNC. Arabinose-inducible system was used in the expression circuit of this part in pSB1C3 then composite part BBa_K4195126 was obtained. We transformed the constructed plasmid into E. coli BL21(DE3) for further verification of its location on the surface of E. coli.

Characterization

Identification

When constructing this circuit, colony PCR and gene sequencing were used to verify that the transformants were correct. Target bands (2505 bp) can be observed at the position between 2000 bp and 3000 bp (Fig. 2).

Fig. 2 DNA gel electrophoresis of the colony PCR products of BBa_K4195126_pSB1C3.

2. Ability of displaying heterologous protein on the surface of engineered bacteria

We used BBa_I0500 promoter and RBS (BBa_B0034) to express INPNC-rFET-his protein in E. coli BL21(DE3). The arabinose-induced overnight culture was then incubated with FITC-labeled anti-His-tag antibody to test whether the rFET was displayed on the surface of engineered bacteria or not.

Fig. 3 The results of immunofluorescence to characterize the function of INPNC surface display system (p = 0.0199).</br> The ratio of fluorescence intensity (λ_Ex = 492 nm, λ_Em = 518 nm) to OD₆₀₀ of positive control (bacteria with surface display system INPNC) is higher than that of negative control (bacteria without surface display system INPNC) (Fig. 3), which indicates that our surface display system works well that the rFET is successfully located on the surface on the surface of bacteria.

Reference

1. E. van Bloois, R. T. Winter, H. Kolmar, M. W. Fraaije, Decorating microbes: surface display of proteins on Escherichia coli. Trends Biotechnol. 29, 79-86 (2011).
2. K. Karmilin et al., Mammalian plasma fetuin-B is a selective inhibitor of ovastacin and meprin metalloproteinases. Sci. Rep. 9, 546 (2019).
3. M. Victorio-De Los Santos et al., The B Subunit of PirABvp Toxin Secreted from Vibrio parahaemolyticus Causing AHPND Is an Amino Sugar Specific Lectin. Pathogens. 9, 182 (2020).
4. D. Kozakov et al., The ClusPro web server for protein-protein docking. Nat. Protoc. 12, 255-278 (2017).