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Description

Technological advances in the field of bioengineering have led to the development of functional biomaterials with applications in the areas of drug delivery, diagnosis and bioenergy. Currently, computational approaches are used to guide design of proteins that form nanostructures with high accuracy at atomic levels. Alternatively, research has shown that fused protein-peptides are promising candidates for the formation of assemblies such as nanoparticles and large-cage structures with biocatalytic applications. In line with these advances, a convenient technique that allows easy control of the size of protein nanoparticles is therefore highly desirable. Recent studies have demonstrated the formation of gels by self-assembly of designed peptides by altering pH, or addition of metal ions such as calcium and potassium, and spherical protein−polymer micelles triggered by change in temperature. However, regardless of such progress, it is still difficult to control the assembled structures, in part, due to the lack of a fundamental understanding of protein self-assembly into nanomaterials.

Recently, a team of researchers at Monash University: Dr. Bhuvana K. Shanbhag (Postdoctoral fellow), Mr. Chang Liu (PhD candidate), A/Professor Victoria S. Haritos, and led by Dr. Lizhong He from the Department of Chemical Engineering explored the factors that affect protein nanoparticle formation using an enzyme−peptide system. In particular, they designed their enzyme−peptide system which incorporated bovine carbonic anhydrase (BCA) linked with a P114 peptide which could be readily produced from a single DNA construct using the bacterium Escherichia coli in high yield. Their work is currently published in the research journal, ACS Nano.

In brief, the research commenced with a detailed cross-examination of the effects of pH and specific cations and anions at varying concentrations on formation of protein nanoparticles. Next, the intermolecular protein−peptide contacts within nanoparticles were identified by cross-linking followed by mass spectrometry. The researchers then studied an alternative self-assembly trigger mechanism where magnesium ions were used as the initiators. Lastly, they tested whether the presence of other biomolecules affected assembly of protein nanoparticles and the controlled dis-assembly of the nanoparticles.

The authors observed that both pH and magnesium ion concentration could be varied independently or in combination to control nanoparticle size. In addition, they noted that the formation of protein nanoparticles did not affect the enzyme activity of proteins within the nanoparticles formed under a broad range of assembly conditions. Furthermore, the protein nanoparticles were observed to remain stable to the change in conditions once they were formed, and retained their size over long periods of storage.

In a nutshell, the study by Monash University scientists demonstrated the controlled formation of protein nanoparticles driven by a self-assembly peptide linked to the protein, in lowered pH conditions within buffered solutions or metal ion Mg²⁺ as two independent modulating parameters. In general, their work elucidated the key peptide−peptide and protein−peptide interactions that were affected by the two solution conditions. Altogether, the study offered vital information that enables the convenient formation and tailoring of protein nanoparticles without changing amino acid sequence.