Why is structural biology important?
Mostly, biological research can be considered as an indirect science. It often relies on measurements of factors that are a result of a particular activity, they very infrequently directly portray the fundamental cellular processes.
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A common scenario is to measure the consequences of a stimulus, and in some cases, the stimulus is unknown.
The growing field of in-cell structural biology is providing a solution to generating the missing detail of the direct processes of the cell. It is a tool that is vital to observing the fine details of the activities that underly all of life’s processes.
While we have been able to look into the structures of the cell since the invention of the microscope, technological advancements, although steady, they have been slow. This has meant that for many years these imaging techniques have been limited by the technology’s capabilities in resolution, magnification, and focus.
Now, as developments in structural biology gain speed, scientists are being able to determine the molecular and macromolecular structure within cells.
The main aim of in-cell structural biology is to build an image of the inner structures of the cell to help determine how the cell’s physical attributes relate to its function.
As a result, scientists hope to create dynamic images of cells, where the molecular relationships can be understood in terms of how they relate to key cell processes, such as those fundamental to reproduction, aging, and death.
Structural biology often focuses on proteins as they are built from a genetic template, and the complex structure of amino acids that build the protein dictates how it will interact with other structures, and therefore, how it will influence biological functions.
Visualizing proteins is already helping to build an in-depth understanding of how cells work. It’s allowing the numerous molecules existent within cells to be put into context with the rest on the intracellular environment.
Overall, in-cell structural biology is important because it is deepening our understanding of how cells function. It is allowing us to understand how function arises from the structure, which is especially important in uncovering the role that biological macromolecules play in disease.
While many methods have been established for investigating in-cell structural biology, an overview of these methods is beyond the scope of this article. Instead, below we focus on the likely future applications of the broad sector of in-cell structural biology that may arise from the current research taking place.
Recently, research has led to advances in cryo-electron tomography (cryo-ET) technology. It has established itself as a key tool for imaging the molecular architecture of macromolecular protein complexes within the cellular settings in which they are native.
The method of cryo-ET involves recording projection images along with intervals of tilt angles in two dimensions. Three-dimensional tomograms are then generated from these projections, which are then analyzed by segmenting the elements of interest, such as entire organelles, macromolecular machines, membrane compartments, and cytoskeletal filaments.
Because of the limitations of cryo-ET, such as that it is limited by how far the electrons can travel into a sample, joint cryo-ET methods are being developed, which scientists consider will open up new applications in the future.
Combining cryo-ET with FIB milling is becoming a popular technique because it allows samples to be targeted and manipulated directly. Future applications will be able to take advantage of the combination of cryo-ET and FIB milling, which will allow for the visualization of important cellular structures, such as chloroplasts, Golgi ultrastructures, proteasomes in intact hippocampal neurons, organelle organization in embryos, translocon-associated protein complex (TRAP) within human fibroblasts, and more.
One particular application that is expected to emerge from the developments in cryo-ET is in the field of bacteria study. There is a great potential to gain insights into the structural cell biology of bacteria using cryo-ET.
This is important because bacteria are used by humans for a variety of purposes. In addition, there are many beneficial uses of these microorganisms that have seen their use being applied in commercial products such as in food and agricultural fertilizer.
Other developments are also opening avenues to developing new applications. One major group of applications will be in the treatment of cancer.
First, scientists are predicting that macromolecule dynamics will become a more important focus rather than visualizing their average structures.
This will allow for a greater understanding of the underlying activities related to the development of the disease. Molecular imaging technologies will likely develop a greater role in clinical oncology, with applications developing in early diagnosis methods, techniques for monitoring treatment response, and in research developing new and more effective therapies for different cancers.
Already, structural biology is demonstrating its potential in facilitating the advancement of the clinical management of cancer.
Finally, there are currently developments underway in the use of free electron lasers in studying macromolecular crystal structures.
Devices are being innovated that produce short pulses of X-rays that are far brighter than the radiation pulses generated by 3rd generation synchrotrons.
Using this method, researchers are collecting diffraction data from crystals whose orders of magnitude smaller than those needed when collecting conventional data.
It is predicted that in the future, this method will be able to collect data from single macromolecules at the level of the single atom.
This level of imaging is vital to furthering our knowledge of the macromolecules that perform the variety of life-essential functions in the body. It is likely that applications will develop out of this technological advancement in the fields of enzyme and hormone studies, which may enable the development of new treatments for a number of diseases.
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- Moore, P. (2017). Structural biology: Past, present, and future. New Biotechnology, 38, pp.29-35. www.sciencedirect.com/science/article/abs/pii/S187167841632324X
- Nitta, R., Imasaki, T., and Nitta, E. (2018). Recent progress in structural biology: lessons from our research history. Microscopy, 67(4), pp.187-195. https://academic.oup.com/jmicro/article/67/4/187/4996565
- Plitzko, J., Schuler, B. and Selenko, P. (2017). Structural Biology outside the box — inside the cell. Current Opinion in Structural Biology, 46, pp.110-121.