The Three-Dimensional Structure of Protein that Causes Macular Degeneration and Correction of Defects

Stephen Aller, PhD
University of Alabama at Birmingham (Birmingham, AL)

Co-Principal Investigators

Alecia K. Gross, PhD
Year Awarded:
2019
Grant Duration:
July 1, 2019 to June 30, 2021
Disease:
Macular Degeneration
Award Amount:
$200,000
Grant Reference ID:
M2019212
Award Type:
Standard
Award Region:
US Southeastern
Stephen Aller

Cryo-EM of ABCA4 and Correction in Macular Degeneration Defects

Summary

A critical part of our visual process is the recycling of a special molecule called a chromatophore after exposure to light by a molecular pump that allows the cell to regenerate the active form of the chromatophore. Some diseases of the eye result in misfolding and malfunction of the pump, called ABCA4, which can eventually lead to blindness. We propose to determine the three-dimensional structure of the active form of ABCA4, as well as to develop a drug selection process to discover new drugs that can correct folding defects of the ABCA4 pump.  Our work may likely allow new FDA-approved treatements for visual diseases such as macular degeneration.

Details

The goal of this project is to better understand the mechanism of the ABCA4 pump involved in vision, and to correct defects of the pump for treating diseases in macular degeneration (MD). Certain molecules in the visual process need to be regenerated and recycled when they are exposed to light.  ABCA4 works just like a molecular pump and is involved in recycling an important light-sensitive molecule call retinal.  In Aim1, we proposed to determine the structure of the ABCA1 protein in its dimeric state, which very likely represents the active form of the pump.  To date, no complete autonomous pump that utilizes the energy from ATP of any protein family in the human genome has been determined in a dimeric configuration.  In Aim2, we will adapt our drug screening assay previously used for Cystic Fibrosis to identify novel compounds that could be developed into drugs for treating problems in vision related to defecting ABCA1 folding. Each aim is very innovative because no dimeric configuration of ABCA1 has been described, and no yeast-based assay using protein folding readout has been applied to ABCA1 in the visual process.  Our work could allow identification of new drugs to treat MD through the processes of drug screening and cutting-edge rational drug design.

About the Researcher

In his recent address to the Senate Appropriations Committee, NIH Director Francis Collins made cryo-EM of membrane proteins, like ABCA1, a national funding priority and he highlighted my group’s plans and efforts toward this exceptional scientific opportunity. Dr. Aller is a world-renowned expert in the structural biology of molecular pumps that reside at the surface of cells in the membrane that forms the protective boundary for the cell.  During his research efforts at the University of Alabama at Birmingham (UAB), he has been working to understand the atomic structure of these proteins, their molecular dynamics, and the mechanisms by which novel drugs can interact and influence their function.  He has extensive training and experience studying membrane proteins, including NRSA post-doctoral training in x-ray crystallography in which he solved the first structure of any mammalian ATP-Binding Cassette (ABC) transporter, called P-glycoprotein (Pgp), and published in Science. Pgp is perhaps the most dominant drug pump involved in classical multidrug resistance. In independent work at UAB, his group refined the Pgp model using new x-ray data to produce more accurate structure that revealed new amino acid residues involved in drug-binding. He showed these first structures represent high-affinity drug-binding conformations. His group has also published the first atomic model of Pgp in the low-affinity outward-facing conformation to better understand the complete catalytic cycle of the transporter and low-affinity drug interactions. His group also builds new computational tools for training students in cutting-edge structural biology and they have published more than 25 manuscripts. Dr. Aller was awarded a prestigious NIH Director's New Innovator Award to accelerate the high-resolution crystal structure determination of human membrane proteins. Dr. Aller now turns his attention to the study of ABCA4 structure and function by forging an exciting new direction using cryo-EM to achieve the first-ever high-resolution structure of ABCA4. Dr. Aller will also adapt a drug screening assay used for Cystic Fibrosis to find new drugs for treating ABCA1-mediated disease in vision.

Personal Story

Prior to graduate school, Dr. Aller worked as a laboratory technician at Yale University where he worked and studied under some of the greatest structural biologists of our generation (Drs. Paul Sigler, Thomas Steitz and Peter Moore). Dr. Aller was particularly inspired by Dr. Sigler, who briefly served as a mentor and encouraged him to strive for Ph.D. training in structural biology, which was accomplished in the laboratory of Dr. Vinzenz Unger, also at Yale, in cryo-EM. Since that time, Dr. Aller has had expert training in the x-ray crystallography of membrane proteins at The Scripps Research Institute and he continues to work on this challenging class of proteins in his own laboratory at UAB.  Dr. Aller finds problems surrounding membrane protein structure and function both highly challenging and very rewarding to tackle, and the BrightFocus Foundation is one of the few foundations in the U.S. that actively fund high-risk/high-reward membrane protein projects like this one. We anticipate that work accomplished with this funding will allow new drug screens for macular degeneration and other diseases in vision, as well as new structural information that could be used to achieve a new class of drugs.  Dr. Aller and his group are grateful for this BFF funding, and they can’t wait to get to work!

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