Proteins are large, complex molecules that are fundamental to life. They perform a huge variety of functions, and every protein is specific to a function.
They are formed by chains of amino acids that are linked by hydrogen bonds. These chains can be as short as one amino acid or as long as thousands of amino acids.
By applying the right amount of heat, you can disrupt all the hydrogen bonds in a protein. What level of structure will be preserved? How much heat must be applied to change the structure of a protein?
Researchers from the University of Cambridge conducted experiments to determine how much heat must be applied to change the structure of a protein and still preserve its function. Their results were published in the journal Cell Structure and Function.
Read on to learn more about this groundbreaking research.
Beta sheet
Beta sheets are a type of protein structure formed by hydrogen bonds between adjacent beta chains. These are called beta chains because each chain consists of a number of amino acids linked by beta-carbons.
To disrupt all hydrogen bonds in a protein would mean to remove all functionality. Beta sheets are part of the structure of proteins, so removing this feature would change the entire protein.
Beta sheets can be either parallel or anti-parallel. Parallel beta sheets have the same orientation for all of the chains, while anti-parallel has opposite orientations.
Disrupting only the hydrogen bonds holding the parallel beta sheets together would still leave the individual chains in place. This would no longer be a parallel beta sheet, but it would still be part of the protein structure.
Whether or not anti-parallel beta sheets remain intact depends on whether or not you disrupt all hydrogen bonds holding the anti-parallel beta sheets together.
Turn
When a protein loses a hydrogen bond, the most common type of structural destruction observed is the loss of an alpha helix.
This is because hydrogen bonds play an important role in the structure of an alpha helix. When you disrupt all hydrogen bonds in a protein, the most stable structure that can be preserved is an alpha helix.
If you were to disrupt all hydrogen bonds in a protein molecule, it would not possess any secondary or tertiary structure. All that would be left is the primary structure of amino acids arranged in a chain. This would result in what is called a peptide – a very simple molecule without any shape or organization.
By learning how to selectively disrupt hydrogen bonds within a specific region of a protein, you can preserve more complex structures like the tertiary structure or quaternary structures.
Helix
When a protein is denatured, its secondary and tertiary structures are lost. This means that the protein loses its ability to coiled and twist in specific ways.
If the helices are disturbed, the protein loses its ability to coil. If all of the helices are preserved, then the protein has retained at least some secondary structure.
Disrupting all of the hydrogen bonds in a protein requires high heat. This makes it difficult to cook a protein without also denaturing it. Heating it quickly will also increase the chance of breaking structural components.
It is possible to denature a protein at any level. A linear chain of amino acids can be broken down into individual amino acids or stuck together as crude proteins. These are both lower levels of structure than secondary and tertiary structures.
Sheet
A Sheet is a flat, continuous two-dimensional surface. A Sheet can be imagined as a piece of paper, or a protein that has lost its bonds but remains intact.
Sheets are considered one of the lowest levels of structural preservation. When you dissolve a protein in water, the protein bonds are broken and the protein molecule unravels into individual amino acids.
These amino acids can then combine with each other to form new proteins, essentially re-shaping what the original protein looked like before it was dissolved.
Sheets can be hard to detect unless you use special equipment to see them. For example, if you pull out all of the amino acids that make up a protein and lay them out in a line, then you have discovered your very own sheet!
However, not all proteins are small and easily detected by the naked eye. Therefore, using equipment like an optical microscope can help detect whether or not the remaining structure is on a sheet level.
Coil
A coil is a structure that consists of a series of loops. Proteins can have coils within their structure, as well as being part of the protein structure itself.
Capsules and transport proteins are examples of where coils are part of the protein structure. These proteins must maintain their shape while transporting something through them.
Coils can be found in many places within the protein and can be both stable and unstable features. Unstable coils can occur during transitions between other structures.
They are able to do this because they have kinks in the chain that break down the regular alignment of amino acids, making them less stable.
By now, you should have a good grasp on the level of structure preservation for each defect type.
Complex structure
The next level of structure to be preserved is the complex structure of the protein. This would be defined by the spatial arrangement of all the atoms and bonds within the protein.
For example, if all hydrogen bonds were disrupted in a protein, but the overall structure of the protein (i.e., its conformation) was preserved, then you would still have a functioning protein.
A conformation is defined as the 3-dimensional arrangement of atoms, groups, and rings that form the backbone structure of a molecule. This includes things like how twisted or coiled the backbone is, where sugar rings are located, and how far apart various groups are from each other.
By only preserving these two levels of structural complexity in a protein, you have created a less complex molecule than before. This makes it easier to analyze and understand its properties.
Amino acid sequence
The next level of structure preservation happens at the amino acid sequence level. Once the hydrogen bonds are disrupted, the next step is to organize the amino acids by their sequence.
Amino acids come in left and right forms, so this step also organizes them by direction. Like with other structures, if all of the amino acids are not organized correctly, then the structure will not be preserved.
Some viruses use this tactic to their advantage- they organize amino acids in a particular sequence that supports their function as a virus. Changing this arrangement would likely prevent formation of a virus.
By organizing the amino acids in order by sequence, this step further compresses the structure of the protein. Compressing the structure of the protein further increases its resistance to denaturing.
Loss of function
Over the past few years, CD-dedicated labs have been exploring ways to use the CD mechanism to disrupt only parts of a protein, rather than the whole thing.
They’ve done this by showing that when you break down a protein with CD, not all of its components are broken down. Some of its components remain intact.
In particular, they’ve found that when they break down a protein with CD, its so-called secondary structure is preserved.
What is secondary structure? It refers to parts of a protein that form either loops or helixes (like a coiled spring). These structures are formed because of how the amino acid chains interact with each other.
By showing that only this level of structure is preserved during breakdown by CD, researchers can now test whether other types of proteins are also protected from breakdown in this way.
