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|Figure 1 : Refolding of a denatured protein to create a native protein using a nanochannel in the organic nanotube gel|
- Nanochannels in organic nanotubes act as space for restoration of the activity of denatured proteins.
- The organic nanotube can protect the restored protein from heat and chemicals.
- Efficient preparation of high-purity proteins and applications in nanoreactors and enzyme sensors are expected.
Naohiro Kameta (Researcher), Organic Nanotube Material Team, the Nanotube Research Center (Director: Sumio Iijima) of the National Institute of Advanced Industrial Science and Technology (AIST; President: Tamotsu Nomakuchi), has developed organic nanotube gels that restore the activity of denatured proteins by folding them into the native three-dimensional structure (refolding). The organic nanotube gels can protect proteins from heat and chemicals.
This technology has been realized by forming organic nanotube gels in which the inner and outer surface structures and diameter of the nanochannel are precisely controlled for the protein of interest. The denatured proteins are encapsulated in the process of the organic nanotube gel formation and are then recovered from the gel by using a change in pH. In this way, only proteins with restored activity can be obtained at high purity. Use of the organic nanotubes as the gel media has the benefit of allowing easy removal of the denaturant by water washing and easy separation and recovery of the protein of interest; these can be achieved without filtration or centrifugal separation. In addition, when proteins are encapsulated in the nanochannel of the organic nanotube, the activity of the proteins is not inactivated by heating or by adding a high concentration of denaturant. Expected applications of this technology include efficient preparation of high-purity proteins and use in nanoreactors and enzyme sensors by combining an enzyme with the organic nanotube.
Details of the results will be published online in ACS Nano, a scientific journal of the American Chemical Society, on May 23, 2012 (JST).
Social Background of Research
From a green innovation perspective, enzymes that promote chemical reactions in the body in a specific and highly selective manner with a high yield are attracting substantial attention as energy-efficient, low-environmental-impact catalysts in chemical industrial processes. An enzyme, which is a protein, is folded into a specific three-dimensional structure by the interaction of amino acids (protein components) and exhibits catalytic activity that is based on the structure. Recombinant technology using Escherichia coli is commonly used in the industrial production of proteins. However, an enzyme considerably changes its structure from the native three-dimensional one in the expression of a recombinant protein and aggregates of denatured proteins with no catalytic activity are formed. The restoring efficiency of proteins with a native three-dimensional structure and original catalytic activity from the aggregate is very low. Consequently, various additives to help suppress protein aggregation or to encourage protein refolding into the native three-dimensional structure have been developed. However, the additives have low yield and versatility.
In the body, there is a protein group called molecular chaperones that have nanospaces to encapsulate denatured proteins for isolation and to help with protein refolding. In recent years, porous inorganic materials and polymer nanoparticles that can mimic molecular chaperones have attracted attention. However, an additive is required for desorption of proteins from the porous inorganic materials or polymer nanoparticles and both the additive and incompletely refolded proteins contaminate the aimed protein. Therefore, a complex separation process is required and such a process may cause redenaturation of the protein.
History of Research
Over more than 10 years, AIST has been working to develop fibrous organic nanomaterials and tubular ones (i.e. organic nanotubes) formed by self-organization in solvents of amphiphilic molecules synthesized from renewable, natural products, such as sugars, amino acids, nucleic acids, and fatty acids. In recent years, AIST has established a process for mass production of organic nanotubes and has been developing various applications of these organic nanotubes.
The outer surface of conventional bilayer-membrane organic nanotubes has the same structure as the inner surface on the nanochannel side. Recently, by using molecular design and molecular arrangement control, AIST has created monolayer-membrane organic nanotubes with an inner-surface structure that differs from that of the outer surface. Providing the nanochannel-side surface with a structure that allows interaction with drugs, protein, DNA, and nanoparticles (called "guests"), the nanotube can encapsulate guests efficiently and selectively. Storage and release of the guests can be regulated by externally controlling the interaction.
The researcher formed organic nanotube gels in which the surface structure and the diameter of the nanochannel were precisely controlled to enable denatured protein molecules to be encapsulated as guests. He also aimed to develop new functions, such as the promotion of protein refolding and the protection of protein activity.
The researcher intends to create organic nanotube gels in which the surface structure and nanochannel diameter are controlled appropriately for a variety of proteins with different properties. He aims to develop an artificial molecular chaperone system through collaborative research, including provision of samples. He will also apply enzyme-conjugated organic nanotubes to nanoreactors and enzyme sensors.
The National Institute of Advanced Industrial Science and Technology (AIST), led by President Nomakuchi, is a public research institution funded by the Japanese government to a large extent. The present AIST is a rather new research organization established in 2001. However, AIST and its predecessor organizations have been contributing to society through continuous advancement in technologies and support of Japanese industries since 1882.
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