Proteins that belong to the HAT family are essential for life because they transport amino acids across the cell membrane. Although the members of this family are virtually identical, some carry certain amino acids and others not. This specialization determines their involvement in specific functions, such as cell growth or neuronal functions, and therefore in related diseases such as cancer or neurodegenerative diseases such as Alzheimer’s disease. What gives this specificity and this diversity of functions? This is one of the questions asked by researchers from the Spanish National Cancer Research Center (CNIO) and the Biomedicine Research Institute (IRB Barcelona), who led the study, and whose answer was published this week in the journal Proceedings of the National Academy of Sciences (PNAS).

Using the latest high-resolution structural technologies such as electron cryomicroscopy, combined with computer modeling and mutant design of these proteins, researchers were able to observe the structure of one of the members of this protein family in detail. atomic. and decipher its function. The results of the study show how only a few residues – located in defined regions – of this family of proteins select the specific amino acids to which they will bind and are therefore responsible for the protein’s participation in specific physiological functions.

Armed with this information, researchers are now faced with the challenge of finding new therapies and diagnostic tools for diseases involving the HAT transporter protein family, with particular interest in conditions that pose serious health concerns, such as cancer and neurodegenerative disorders such as Alzheimer’s disease.

Understand how to disrupt their function

Amino acids, the building blocks of life, enter and leave cells, allowing them to grow, divide and develop their functions. This movement inside and outside the cell occurs through gates integrated into the cell membrane that are formed by proteins of the HAT family, among others.

Although HAT proteins are virtually identical in structure, some carry certain amino acids and others not, thus conferring specific functions on each member of the family, such as participation in cell growth; a role in diseases such as cancer; neuronal functions; and the transport of toxic substances and involvement in addiction to substances such as cocaine.

To understand this specificity of function, scientists set out to study the 3D structure of this important family of proteins. “Classical techniques used to determine the structure of proteins, such as those using X-rays, have had limited success with proteins integrated into biological membranes, and so many questions have remained unanswered,” said Oscar Llorca, manager. macromolecular complexes. in DNA Damage Response Group at CNIO, director of the structural biology program of this center and co-author of the work.

The combination of structural resolution by cryomicroscopy with molecular dynamics calculations and functional studies provides an experimental platform with great potential that allows us to unravel the function of amino acid transporters. In this case, we applied this technology to identify the molecular mechanisms that cause these proteins to transport some amino acids but not others. “

Manuel Palacín, head of the Amino acids and disease carriers laboratory at IRB Barcelona, ​​professor at the University of Barcelona and head of unit at CIBERER

New drugs against cancer and Alzheimer’s disease

Thanks to electronic cryomicroscopy, a field in which Llorca is an international expert, the virtualization of the molecular structure of proteins has taken a giant step towards what is today called the golden age of 3D structures. This new technology, which won the Nobel Prize for Chemistry in 2017, has not only been used to observe biological processes like never before, but it is also helping to accelerate the development of new compounds and drugs of interest to treat cancer and d ‘other human diseases.

In this work, using electron cryomicroscopy, the researchers were able to visualize the structure of a member of the HAT family at atomic resolution and determine the pocket where these proteins bind to amino acids, as well as the details of the mechanism by which this recognition occurs.

Atomic details reveal that only a few residues of these proteins determine which amino acids they bind to and therefore their specific functions. In addition, the study demonstrates how substitutions of certain residues by others at these positions in different family members are responsible for modifying the specificity of recognition and transport of some amino acids and not others.

The results of this research will now make it possible to direct efforts towards compounds that could act on specific regions of these proteins, and to manage the disorders in which they participate, such as cancer and neurodegenerative diseases such as Alzheimer’s disease.

Led by IRB Barcelona and CNIO, the study was carried out in collaboration with groups led by Víctor Guallar, at the Barcelona Supercomputing Center (BSC) and Lucía Díaz, at the biotech Nostrum Biodiscovery.

The study was made possible thanks to funding from the Foundation “la Caixa”, which, through its research program Caixa, promotes the best initiatives to fight against diseases that have the greatest impact in the world, such as diseases cardiovascular, neurological, infectious and oncological.

The study also received funding from the Ministry of Science and Innovation, the Instituto de Salud Carlos III, the Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), the European Regional Development Fund and the government of Catalonia.