Origami from peptides
Scientists have folded protein origami tetrahedra in mouse liver cells
Daria Spasskaya, N+1
Biochemists managed to put together three-dimensional structures of a given shape from a polypeptide chain. To do this, scientists have constructed protein spirals that fold together in a certain way when amino acid residues interact. Proteins consisting of spirals with specified properties are capable of forming structures in the form of tetrahedra, pyramids and prisms both in solution and in living cells. A new type of self-assembled protein nanoparticles, by analogy with DNA origami, can be used both in biomedicine, for example, for drug delivery, and in other applications. The work is published in Nature Biotechnology.
Geometric shapes assembled from amino acid spirals
Drawings from an article in Nature Biotechnology
The ability of biological polymers to form secondary and tertiary structures attracts bioengineers who try to use rational design to make DNA and proteins fold in the right way. The formation of given structures by nucleic acids due to the complementarity property is known as DNA origami and has been successfully used for various tasks for a long time. For example, DNA molecules assembled in the right way were used to create molecular nanomobiles, deliver drugs to cancer cells, and even to create electronic microchips.
DNA consists of only four structural blocks (A,T,G,C) that interact with each other in a strictly limited way (A "pairs" with T, and G with C). Protein chains consist of 20 amino acids that can interact with each other in a much wider spectrum through electrostatic and hydrophobic interactions. Thanks to this, natural proteins form several dozen specific tertiary structures, and scientists have shown that this is far from the limit. Researchers from several institutes in Ljubljana, in collaboration with colleagues from other European universities, managed to create an algorithm that allows designing the design of new particles with a given three-dimensional structure based on the spiral protein domains existing in nature. To demonstrate the algorithm's work, the authors made proteins in the form of a tetrahedron, a tetrahedral pyramid and a triangular prism. These proteins turned out to be soluble, folded well in bacteria, eukaryotic cells and even in liver cells of a live mouse. The self-assembling structures are based on coiled-coil spiral protein domains (they can be called "superspiral", although there is no established term for them in Russian). Such domains are often used in nature to interact proteins with each other.
DNA consists of only four structural blocks (A,T,G,C), which interact with each other in a strictly limited way (A "pairs" with T, and G with C). Protein chains consist of 20 amino acids that can interact with each other in a much wider spectrum through electrostatic and hydrophobic interactions. Thanks to this, natural proteins form several dozen specific tertiary structures, and scientists have shown that this is far from the limit.
Researchers from several institutes in Ljubljana, in collaboration with colleagues from other European universities, managed to create an algorithm that allows designing the design of new particles with a given three-dimensional structure based on the spiral protein domains existing in nature. To demonstrate the work of the algorithm, the authors made proteins in the form of a tetrahedron, a tetrahedral pyramid and a triangular prism. These proteins turned out to be soluble, folded well in bacteria, eukaryotic cells and even in liver cells of a live mouse.
The self-assembling structures are based on coiled-coil spiral protein domains (they can be called "superspiral", although there is no established term for them in Russian). Such domains are often used in nature for proteins to interact with each other.
The design scheme of nanoparticles in the form of geometric shapes of protein spirals. Coiled-coil domains form the edges of the figure and are encoded as part of a single polypeptide chain, which automatically forms the desired structure when folded
In the experiment, one polypeptide chain, that is, one protein, formed one geometric shape. The largest polypeptide chain in the experiment consisted of more than 700 amino acids. The edges of the figure were the same "super spirals" that were formed by the interaction of hydrophobic and charged amino acid residues in the composition of individual spirals. The individual domains were separated by flexible linkers, allowing corners to be formed. The shape of the particles obtained in vitro, the researchers confirmed using electron microscopy and a number of physical methods.
To demonstrate the applicability of the obtained protein nanoparticles in living systems, the authors of the work first expressed protein tetrahedra in bacteria and showed that, unlike the proteins obtained in previous studies, such particles are well folded in cells and at the same time soluble, that is, they are contained in the cytoplasm in the right form.
At the next stage, tetrahedra were expressed in human cells. In order to confirm the correct assembly of the structure inside the cell, the authors "sewed" halves of the reporter protein to different ends of the protein molecule. If the protein chain formed into the desired structure, a whole reporter capable of glowing was assembled from the halves. It turned out that the figures were assembled correctly both in the cell line and in the mouse liver cells, where the researchers delivered the genetic constructs encoding tetrahedra. Additionally, scientists have confirmed that such protein particles, although not found in nature, do not activate intracellular defense reactions and do not cause an immune response in the body.
The scheme of the experiment of checking the self-assembly of structures in mouse liver cells (left). Halves of the reporter protein are suspended at different ends of the polypeptide chain, which, if properly assembled, is capable of oxidizing the fluorescent substrate. Origami tetrahedra are correctly folded in the mouse liver (right), which demonstrates the glow of cells.
Self-assembled protein particles with a given shape, according to the researchers, can be used in various fields of molecular therapy. Such proteins can be used not only as a means of delivery (by analogy with DNA structures), but also, for example, to create genetically encoded vaccines, with the help of which nanoparticles containing antigens on their surface are synthesized in the body.
We wrote that earlier scientists managed to create hybrid nanoparticles consisting of DNA and protein. Protein "staples" improved the ability of DNA structures to self-assemble.
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