The composition of protein-nanoparticle complexes can be studied using technologies that allow the investigation of the interactions of biological molecules with inorganic compounds. A recent study published in the journal ACS Applied Bio Materials examined the structural characteristics of protein nanoparticle complexes using single-particle cryoelectron microscopy (cryo-EM).
Study: Determination of the complex structure of protein-nanoparticles by cryoelectron microscopy. Image credit: Volodymyr Dvornyk / Shutterstock.com
What are protein-nanoparticle complexes?
The combination of nanoparticles with proteins is of considerable interest due to the incredible potential of their complexes, which combine the nanoparticle characteristics of nanoparticles with the particular structure and functionality of different proteins.
Both natural and artificial biological processes are able to control the production and development of inorganic nanoparticles in terms of size, structure, and functionality.
Particularly valuable are nanoparticle and protein complexes in the area of nanobioscience development such as biomedicine, drug development systems, and biosensors. Nanoparticles with sizes equivalent to biological cells can enter and act within the cell. Therefore, for these applications it is required to study the interactions of nanoparticles with various protein complexes.
Limitations of the methods of determining the current structure
Currently, there is very little high-resolution research on biomolecules that explicitly interact with a synthetic nanocomposite. The most widely used structural determination techniques, X-ray crystallization and nuclear magnetic resonance (NMR), are generally inadequate for the determination of the structure of biomolecules coupled to inorganic substrates.
Methods such as solid-state NMR and sum-frequency vibrational spectrometry (SFG) have been used effectively to investigate the interactions of smaller biomineralizing protein complexes with inorganic materials.
Although these approaches provide extremely valuable data, they are currently limited to smaller proteins and several additional procedures are needed to evaluate structural information.
Cryoelectron microscopy (cryo-EM): a new technique for analyzing structures
Research into the region of the biomolecule-inorganic interface, as well as the topic of biomaterials, will greatly benefit from better functional and structural analytical techniques. One such method, cryoelectron microscopy (cryo-MS), has transformed molecular biology in recent years.
In this study, the researchers wanted to show how single-particle cryo-MS approaches can be used to analyze protein nanomaterial compounds. In the study, two compounds of protein nanomaterials, GroEL bound to platinum nanoparticles (GroEL-PtNP) and ferritin bound to iron oxide nanoparticles were used as model materials.
Key developments in the study
It was shown that cryo-EM could be used to identify high-resolution protein structures and nanoscale materials in the case of a combination of GroEL and platinum nanoparticles (PtNP). GroEL is a 60 kDa protein that helps fold various proteins and is necessary for cell survival. GroEL has been found to help create stable PtNPs in addition to its crucial functions in protein folding.
The researchers then used ferritin bound to iron oxide nanoparticles (HuLF-FeNP) to see if complexes of additional protein nanomaterials could be studied using normal cryo-MS methods.
Ferritins are a kind of biomineralizing protein that plays an important role in preserving iron levels within molecules. Ferritin concentrations in the body change in various chronic diseases.
Ferritins have various uses in biotechnology, including the directed production of organic semiconductors, neuroimaging, and biomolecule-based water filtration systems, in addition to their vital function in iron homeostasis.
The accuracy of cryo-EM was substantially worse in the case of HuLF-FeNPs and no definite structure and composition could be determined. Although cryo-EM data did not provide adequate calibration of the atomic model for HuLF, iron oxide nanoparticles could still be seen on the inner surfaces of the HuLF shell.
Future perspective on Cryo-EM and its applications
It can be concluded from the findings that single-particle cryo-MS has shown great promise for studying the structural properties of protein-nanomaterial interactions. However, further advances will be needed to produce high-resolution models of protein-inorganic interfaces.
Although the data obtained were used to create a structure using fairly typical techniques, there are several workflow improvements that could improve the end results. Future research on HuLF-FeNPs and GroEL-PtNPs should focus on improving masking processes in order to increase the quality and resolution of 3D data produced from these samples.
Future advances in cryo-MS data collection and processing techniques are expected to increase the clarity of the models and provide new vital details of structural function on how organic substances approach inorganic compounds.
Reference
Sen, S. et al. (2022). Determination of the structure of the protein-nanoparticle complex by cryoelectron microscopy. Applied biomaterials ACS. Available at: https://pubs.acs.org/doi/10.1021/acsabm.2c00130
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