Characterization and expression of protein(s) involved in gold nanoparticle formations by Thermus scotoductus SA-01

[摘要] English: Developments in the biosynthesis of nanoparticles have increased significantly during the last few years as a result of the growing interest in the unique properties displayed by nanoparticles. These particles are extremely small in size and have a large surface to volume ratio, giving them unique physical and chemical properties at this scale that differs considerably from when they are used in larger form. These exceptional properties are used in a wide variety of applications, ensuing nanotechnology to become a multidisciplinary field. Research into application structure types are extended daily and as a result, the next few years will be crucial as applications for nanomaterials in the industry are most likely to be increased. Gold nanoparticles is receiving more and more attention because of its wide variety of uses in optical, electronic, magnetic, catalytic, and biomedical applications, but even more due to them being the most stable of all the metal nanoparticles. Several methods are used to produce these metal nanoparticles, but are mostly making use of toxic chemicals in the synthesis protocol, which are harmful to the environment and human health. To overcome this problem, researchers are making use of more 'greener alternatives through the use of biological systems and microorganisms in nanoscience and nanotechnology. These microorganisms have unique potential in producing nanoparticles that are environmentally friendly and display different shapes, sizes and distributions. Among the different microorganisms used, bacteria have received the most attention in the nanoparticle production process, but have not been as successful as chemical synthesis to produce monodisperse noble metal nanoparticles. In this study, successful gold reduction and nanoparticle formation with different shapes, sizes and distribution was obtained; however, these particles were not monodisperse. This was achieved with a thermostable protein of ± 70 kDa that was identified as an ABC transporter, peptide-binding protein and which was purified from Thermus scotoductus SA-01; an extremophile and thermophilic bacterium that was isolated from groundwater samples from Mponeng (a deep South African gold mine in the Witwatersrand Supergroup operated by AngloGold Ashanti) at a depth of 3.2 km with ambient rock temperature of 60ºC. The protein was expressed in Escherichia coli and Thermus thermophilus HB27, a mesophilic and a thermophilic expression host respectively. It was found that the expression host might have an influence on the way the protein is folded and therefore influence nanoparticle formation. Expression studies was also done on the protein that either included or excluded Histidine-Tags and a leader peptide, but it was found that neither the His-Tags nor the leader peptide had any influence on the nanoparticles produced. Gold reduction and nanoparticle formation was obtained through reduction of a surface exposed disulphide bond in the ABC transporter, peptide-binding protein, using sodium dithionite as electron donor and reducing agent. In general it was found that nanoparticle formation was dependant on environmental parameters but control of this process was not complete. Chemical reduction did influence the nanoparticle formation process in some instances, but overall it could be seen that the presence of the protein played a significant role in slowing down the reaction rate, yielding a level of control over the nanoparticles produced and ensuring a more environmentally friendly, biological process for the production of gold nanoparticles.

[发布机构] University of the Free State