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Developmental biology — Proteins|
When proteins shake hands
In spider silk, in wood, in tendons, in healing small wounds, even in the spaces between cells, protein fibres are virtually everywhere. Small protein fibres, protein nanofibres, often are very stable, can be decomposed easily by microorganisms, and may have an antibacterial effect that kills or inhibits bacteria. But, artificially creating protein fibres is not easy.
However now, fibres with new properties are being successfully created by materials scientists at the Friedrich Schiller University Jena (FSUJ), Jenna, Germany. Reported in the latest issue of the journal ACS NANO, the work was done in collaboration with a team from the Leibnitz Institute of Photonic Technology (IPHT) also in Jena, Germany.
"Protein fibres consist of several natural protein macromolecules. Nature builds nanomaterials, whose diameter is roughly a 1,000 times smaller than that of a human hair, by a process of self-assembly. What presents little difficulty for nature with its millions of years of experience is usually not that easy to create in the laboratory."
Prof. Jandt's team in recent years has succeeded in creating protein nanofibres from two natural proteins fibrinogen and fibronectin, even controlling their size and structure as in linear or branched.
Protein nanofibres with defined properties
Jandt's group wants to define specific protein nanofibres to be used in biosensors for drug delivery, in optical probes, or in bone cement. To do this, Jena researchers came up with the idea of combining two unique proteins into a self-assembling new nano fibre. Jandt and team used the protein albumin, which controls the osmotic pressure in blood, with haemoglobin, the protein making red pigment in blood and transports oxygen through blood. The scientists dissolved both proteins in ethanol and then heated them to 65 °C. Over several stages, the process resulted in the formation of a new hybrid protein nanofibre containing both proteins.
For the very first time a so-called handshake existed between the two proteins in a new fibre.
"Proving these new hybrid protein nanofibres indeed contain both proteins was not easy as they are so tiny, there are hardly any microscopy methods able to see their details", explains Klaus Jandt adding: "We were provided decisive support for this proof by Prof. Deckert and his team at the Leibniz Institute of Photonic Technology."
Dr Volker Deckert and his team found optical signals coming from the new hybrid nanofibres, which are as typical for albumin and haemoglobin as a fingerprint is for a person. They relied on so-called tip-enhanced Raman spectroscopy (TERS) for this result. "The method's extreme sensitivity allowed us to identify the different proteins even without special markers, permitting their unambiguous classification," explained Prof. Deckert.
Biomimetic principles for materials of the future
The scientists from Jena look at this brand new fibre creation as a breakthrough. Such innovative fibres perhaps can be used to construct larger fibre structures with properties not created in nature. Now, perhaps networks of these nanofibres can help in regenerating bone and cartilage.
Professor Jandt: "This has opened the door for a completely new generation of functional materials for medical engineering, nanoelectronics, sensors, or optics, all based on natural substances and construction principles. These biomimetic principles will have a decisive effect on the materials of the future." Scientists from Jena are confident that this new self-organization approach can be successfully transferred to other proteins that feature identical amino acid sequences.
Creating and establishing proof of hybrid protein nanofibers (hPNFs), i.e., PNFs that contain more than one protein, is a currently unsolved challenge in bioinspired materials science. Such hPNFs could serve as universal building blocks for the bottom-up preparation of functional materials with bespoke properties. Here, inspired by the protein assemblies occurring in nature, we introduce hPNFs created via a facile self-assembly route and composed of human serum albumin (HSA) and human hemoglobin (HGB) proteins. Our circular dichroism results shed light on the mechanism of the proteins’ self-assembly into hybrid nanofibers, which is driven by electrostatic/hydrophobic interactions between similar amino acid sequences (protein handshake) exposed to ethanol-triggered protein denaturation. Based on nanoscale characterization with tip-enhanced Raman spectroscopy (TERS) and immunogold labeling, our results demonstrate the existence and heterogenic nature of the hPNFs and reveal the high HSA/HGB composition ratio, which is attributed to the fast self-assembling kinetics of HSA. The self-assembled hPNFs with a high aspect ratio of over 100 can potentially serve as biocompatible units to create larger bioactive structures, devices, and sensors.
Authors: Christian Helbing, Tanja Deckert-Gaudig, Izabela Firkowska-Boden, Gang Wei, Volker Deckert, and Klaus D. Jandt.
Keywords: AFM; hemoglobin; protein nanofibers; self-assembly; serum albumin; TERS
This project was supported by the German Research Foundation DFG under the project name "Novel functional materials based on self-assembled protein nanofibers: creating and understanding nanofibers".
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Klaus D. Jandt's group wanted to combine specific properties of protein nanofibres for use as components in biosensors, for drug delivery, within optical probes, even in bone cement. To do this, researchers devised a method to combine two proteins into a nanofibre. Image credit: Izabela Firkowska-Boden/FSUJ