Proteins are the building blocks of cells, tissues, and the larger creations of life (such as humans), which makes them important. That doesn’t make them easy to understand. In fact, studies such as one about the protein ferritin, just released by researchers at Nanyang Technological University (Singapore) in the Journal of Biological Chemistry, tend to increase the knowledge of how complicated protein structures can be, while leaving open questions about how they get that way.
Ferritin is a protein molecule that regulates the distribution of iron within cells and tissues. It’s composed of 24 proteins that configure themselves into a spherical shape with a hollow core. The word that is often applied to protein structure is nanoarchitecture, meaning that the architecture (or configuration) of proteins is mostly at the nano scale (that is, only a few atoms in size). At this scale, the center of a ferritin molecule is called a nanocage. That implies caging something, which happens to be correct. Ferritin stores ions of iron, which though quite active and sometimes harmful chemically, are safely reserved for use within the cell by the structure of ferritin.
For molecular biologists perhaps the most interesting thing about structures such as ferritin is that they are self assembling, that is, when the right amino acid and protein components are available in the presence of the right enzymes – the components of ferritin simply follow specific chemical pathways (pathways = processes) until the structure is formed. It’s a process scientists would love to duplicate, but in most areas of molecular biology (and nanotechnology) there hasn’t been a great deal of success. That’s largely because scientists don’t fully understand the process(es) of self assembly. The chemistry, especially in such tiny molecular reactions, is mostly understood in outline.
For the Singapore team, led by assistant professor Brendan Orner, understanding the ferritin nanocage – its shape, origin, and chemical properties – means, potentially, being able to use it for developing and storing man-made nanostructures. Specifically they were interested in growing nanoparticles of precise dimensions inside the ferritin cage.
“Slight deviations in size or shape can radically change nanoparticles’ properties, particularly in the case of metals and semiconductors,” Orner said. “Our ferritin proteins are hollow, so, when we grow mineral or metal clusters inside them, the growth stops when the nanoparticles reach the limits of the protein shell.”
By studying the rules that control the folding and assembly of such a protein in nature, Orner said, the investigators hope to be able to manipulate them one day to create new proteins with novel sizes and shapes and, therefore, generate nanoparticles of novel sizes and shapes inside them.
[Source: Nanotechnology Today]
The research thus far has been able to determine the ‘hot spots’ (read: chemically most active) for the formation of the ferritin nanocage, and the identification of the amino acids critical for the formation. These amino acids turned out to be located (mostly) in side-chains (like appendages to the main molecule formation). Removing some of the side-chains usually affected the shape, but surprisingly, the effect could be balanced by removing additional side-chains.
Ferritin is but one of many proteins and protein complexes under study. The field of proteomics (the study of proteins, their structures and functions) is young and (like this study) incomplete.