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. 2023 Sep 20;11(9):1506. doi: 10.3390/vaccines11091506

Figure 2.

Figure 2

Chemical display of the SpyTag/SpyCatcher plug-and-display construction and reaction mechanism. The SpyTag-decorated VLPs with amine group are produced by fusing 13 aa SpyTag sequence with structural protein DNA sequence and are expressed in a chosen vector. Meanwhile, the SpyCatcher (138 aa) is fused with the target antigen and expressed separately in a selected vector. The SpyTag/SpyCatcher can induce spontaneous and robust protein chemistry between Lysine (Lys) and Aspartic acid (Asp) to form a covalent amide bond (dashed circles). Carrier Type I uses homogenic Xtag/XCatcher, while Carrier Type II uses heterogenic Xtag/Xcatcher. The locations of the SpyTag and SpyCatcher are flexible and should be designed and verified in a protein-dependent manner. The intermolecular isopeptide bond is formed by amide bond formation between the SpyTag/SpyCatcher-antigen and VLP, resulting in antigen display on the surface of VLP. X indicates Spy/Snoop. (Figure was created in Figdraw: https://www.figdraw.com, accessed on 7 October 2022).