New x-ray analysis methodology reveals structure of disordered protein

By Kate Bass, B.Sc.Oct 13 2017

Scientists at The University of Notre Dame have shown that disordered proteins have a structure very close to what would be expected for a truly random structure using a novel X-ray scattering (SAXS) analysis methodology.

Credit: molekuul_be/Shutterstock.com

Every cell in the human body contains protein and it accounts for almost one fifth of a healthy lean adult. It is an essential component for building and repairing tissue. Protein is also essential for the normal functioning of the body as it is used to produce hemoglobin, enzymes, hormones, antibodies and some neurotransmitters.

Proteins are long chains of amino acids that typically fold into precise three-dimensional structures that enable them to interact with specific target molecules. The study of the structure and function of proteins at a molecular level has thus been crucial to helping us understand how the body works and to develop treatments to restore normal function when disease causes things to go wrong.

In addition to the classic proteins that form pre-determined rigid structures, there are also intrinsically disordered proteins (IDPs). These proteins do not have a regular configuration; instead they remain as floppy chains. About a third of proteins fall intro this category.

It was known that the lack of regular structure in IDPs is essential for them to function correctly. However, existing techniques had made it difficult for their exact structures to be determined. It was not known if there was any order to their structure or how they perform their specific functions.

Patricia Clark, a biophysicist at Notre Dame University, explained:

We have excellent methods available for determining the structures of proteins that fold into one rigid structure, but a significant fraction of all proteins are too flexible to be studied using these methods. Even worse, results from two of the most commonly used methods to study IDPs disagree with each other".

In order to help resolve this, scientists at the University of Notre Dame have developed a new x-ray scattering analysis methodology that can show the structure of the more flexible intrinsically disordered proteins. The technique analyzes a broader range of the x-ray scattering pattern than previous SAXS methods. The patterns obtained are then fitted to different degrees of disorder generated by computer simulations.

This new method of protein analysis showed most IDPs are even more disordered than was previously thought. Indeed, it now appears that the floppy structures of IDPs are actually very close to what would be expected for a truly random structure. It is thought that such a random structure may be important to help prevent IDPs from interacting with other proteins accidentally. Incorrect interactions between proteins are known to play a role in a range of diseases, including cancer.

It is hoped that this new discovery will allow these interactions to be studies in more detail and facilitate the development of new strategies to prevent diseases caused by inappropriate protein interactions and protein folding errors.

Patricia Clark said "While this work is a fundamental, basic research demonstration of protein behavior, the implications are really broad".