A Versatile Magnetic\nNanoplatform for Plug-and-Play\nFunctionalization: Genetically Programmable Cargo Loading to Bacterial\nMagnetosomes by SpyCatcher “Click Biology”

Bacterial magnetosomes (“MAGs”) represent\na promising\nclass of magnetic iron oxide nanoparticles with exceptional material\ncharacteristics and high application potential in the biomedical and\nbiotechnological field. For the surface functionalization of MAGs\nwith different protein cargos, their enveloping membrane can be addressed\nby genetic means. However, the expression of foreign polypeptides\nas translational fusion to magnetosome membrane proteins is still\nlaborious and lacks versatility as the generated particles are monospecific\nand thus restricted to predetermined functions. Utilizing the SpyTag-SpyCatcher\n(ST-SC) bioconjugate system, we here establish a flexible platform\nfor the targeted nanoassembly of multifunctional MAGs that combines\nthe rapidity of chemical coupling (e.g., by cross-linking reactions)\nand the unmatched selectivity and controllability of <i>in vivo</i> functionalization. MAGs genetically\nengineered to display either SC- or ST-connectors are shown to efficiently\nbind a variety of complementary tagged (protein) cargo. Specifically,\nwe cover a broad spectrum of representative functional moieties and\nforeign cargo (such as enzymes, antibodies, fluorophores, and silica\nbeads) with relevance in biotechnology and biomedicine and demonstrate\nthe interchangeability of the MAGs-adapted ST-SC system. For the controlled\ngeneration of artificial shells surrounding the particles, SC-MAGs\nare effectively coated by protein-corona proteins. The potential of\nthe here-provided toolkit is even more enhanced by using SC-MAGs as\nan affinity tool for selective protein pulldown <i>in vitro</i> and <i>in vivo</i>. Overall, this innovative technology\nturns bacterial MAGs into a flexible magnetic nanoscaffold for the\ntargeted <i>plug-and-play</i> display of virtually unlimited\nadditional functionalities, thereby generating a multitude of magnetic\nhybrid materials that can be used in many applications.