Preparation of Bacterial Magnetosomes for Proteome Analysis

MamF-like proteins are distant Tic20 homologs involved in organelle assembly in bacteria

Organelle-specific protein translocation systems are essential for organelle biogenesis and maintenance in eukaryotes but thought to be absent from prokaryotic organelles. Here, we demonstrate that MamF-like proteins are crucial for the formation and functionality of bacterial magnetosome organelles. Deletion of mamF-like genes in the Alphaproteobacterium Magnetospirillum gryphiswaldense results in severe defects in organelle positioning, biomineralization, and magnetic navigation. These phenotypic defects result from the disrupted targeting of a subset of magnetosomal proteins that contain C-terminal glycine-rich integral membrane domains. Phylogenetic analyses reveal an ancient evolutionary link between MamF-like proteins and plastidial Tic20. Our findings redefine the molecular roles of MamF-like proteins and suggest that organelle-specific protein targeting systems also play a role in bacterial organelle formation.

A Versatile Magnetic Nanoplatform for Plug-and-Play Functionalization: Genetically Programmable Cargo Loading to Bacterial Magnetosomes by SpyCatcher "Click Biology"

Bacterial magnetosomes ("MAGs") represent a promising class of magnetic iron oxide nanoparticles with exceptional material characteristics and high application potential in the biomedical and biotechnological field. For the surface functionalization of MAGs with different protein cargos, their enveloping membrane can be addressed by genetic means. However, the expression of foreign polypeptides as translational fusion to magnetosome membrane proteins is still laborious and lacks versatility as the generated particles are monospecific and thus restricted to predetermined functions. Utilizing the SpyTag-SpyCatcher (ST-SC) bioconjugate system, we here establish a flexible platform for the targeted nanoassembly of multifunctional MAGs that combines the rapidity of chemical coupling (e.g., by cross-linking reactions) and the unmatched selectivity and controllability of in vivo functionalization. MAGs genetically engineered to display either SC- or ST-connectors are shown to efficiently bind a variety of complementary tagged (protein) cargo. Specifically, we cover a broad spectrum of representative functional moieties and foreign cargo (such as enzymes, antibodies, fluorophores, and silica beads) with relevance in biotechnology and biomedicine and demonstrate the interchangeability of the MAGs-adapted ST-SC system. For the controlled generation of artificial shells surrounding the particles, SC-MAGs are effectively coated by protein-corona proteins. The potential of the here-provided toolkit is even more enhanced by using SC-MAGs as an affinity tool for selective protein pulldown in vitro and in vivo. Overall, this innovative technology turns bacterial MAGs into a flexible magnetic nanoscaffold for the targeted plug-and-play display of virtually unlimited additional functionalities, thereby generating a multitude of magnetic hybrid materials that can be used in many applications.

Green nanomedicine: the path to the next generation of nanomaterials for diagnosing brain tumors and therapeutics?

Introduction: Current brain cancer treatments, based on radiotherapy and chemotherapy, are sometimes successful, but they are not free of drawbacks.Areas covered: Traditional methods for the treatment of brain tumors are discussed here with new solutions presented, among which the application of nanotechnology has demonstrated promising results over the past decade. The traditional synthesis of nanostructures, which relies on the use of physicochemical methodologies are discussed, and their associated concerns in terms of environmental and health impact due to the production of toxic by-products, need for toxic catalysts, and their lack of biocompatibility are presented. An overview of the current situation for treating brain tumors using nanotechnological-based approaches is introduced, and some of the latest advances in the application of green nanomaterials (NMs) for the effective targeting of brain tumors are presented.Expert opinion: Green nanotechnology is introduced as a potential solution to toxic NMs through the application of environmentally friendly and cost-effective protocols using living organisms and biomolecules. The current status of this field, such as those involving clinical trials, is included, and the possible limitations of green-NMs and potential ways to avoid those limitations are discussed so that the field can potentially evolve.

Single-step transfer of biosynthetic operons endows a non-magnetotactic Magnetospirillum strain from wetland with magnetosome biosynthesis

The magnetotactic lifestyle represents one of the most complex traits found in many bacteria from aquatic environments and depends on magnetic organelles, the magnetosomes. Genetic transfer of magnetosome biosynthesis operons to a non-magnetotactic bacterium has only been reported once so far, but it is unclear whether this may also occur in other recipients. Besides magnetotactic species from freshwater, the genus Magnetospirillum of the Alphaproteobacteria also comprises a number of strains lacking magnetosomes, which are abundant in diverse microbial communities. Their close phylogenetic interrelationships raise the question whether the non-magnetotactic magnetospirilla may have the potential to (re)gain a magnetotactic lifestyle upon acquisition of magnetosome gene clusters. Here, we studied the transfer of magnetosome gene operons into several non-magnetotactic environmental magnetospirilla. Single-step transfer of a compact vector harbouring >30 major magnetosome genes from M. gryphiswaldense induced magnetosome biosynthesis in a Magnetospirillum strain from a constructed wetland. However, the resulting magnetic cellular alignment was insufficient for efficient magnetotaxis under conditions mimicking the weak geomagnetic field. Our work provides insights into possible evolutionary scenarios and potential limitations for the dissemination of magnetotaxis by horizontal gene transfer and expands the range of foreign recipients that can be genetically magnetized.