Summary: A new imaging study reveals how the MFSD2A transporter protein provides a gateway for omega-3 fatty acids to enter the brain.
Source: Columbia University
Spectacular images of a molecule that shuttles omega-3 fatty acids into the brain may open a doorway for delivering neurological therapeutics to the brain.
“We’ve managed to obtain a three-dimensional structure of the transporter protein that provides a gateway for omega-3s to enter the brain. In this structure, we can see how omega-3s bind to the transporter. This information may allow for the design of drugs that mimic omega-3s to hijack this system and get into the brain,” says first author Rosemary J. Cater, PhD, a Simons Society Fellow in the Mancia Lab at Columbia University Vagelos College of Physicians and Surgeons.
The study was published online on June 16 in the journal Nature.
A major challenge in treating neurological diseases is getting drugs across the blood-brain barrier–a layer of tightly packed cells that lines the brain’s blood vessels and zealously blocks toxins, pathogens, and some nutrients from entering the brain. Unfortunately, the layer also blocks many drugs that are otherwise promising candidates to treat neurological disorders.
Essential nutrients like omega-3s require the assistance of dedicated transporter proteins that specifically recognize them and get them across this barrier. “The transporters are like bouncers at a club, only letting molecules with invites or backstage passes in,” Cater says.
The transporter–or bouncer–that lets omega-3s in is called MFSD2A and is the focus of Cater’s research. “Understanding what MFSD2A looks like and how it pulls omega-3s across the blood-brain barrier may provide us with the information we need to design drugs that can trick this bouncer and gain entry passes.”
To visualize MFSD2A, Cater used a technique called single-particle cryo-electron microscopy.
“The beauty of this technique is that we’re able to see the shape of the transporter with details down to a fraction of a billionth of a meter,” says study co-leader Filippo Mancia, PhD, associate professor of physiology & cellular biophysics at Columbia University Vagelos College of Physicians and Surgeons and an expert in the structure and function of membrane proteins.
“This information is critical for understanding how the transporter works at a molecular level.”
For cryo-EM analysis, protein molecules are suspended in a thin layer of ice under an electron microscope. Powerful cameras take millions of pictures of the proteins from countless angles which can then be pieced together to construct a 3D map.
Into this map researchers can build a 3D model of the protein, putting each atom in its place. “It reminds me of solving a jigsaw puzzle,” Mancia explains. This technique has become remarkably powerful in visualizing biological molecules in recent years, thanks in part to Joachim Frank, PhD, professor of biochemistry & molecular biophysics at Columbia University Vagelos College of Physicians and Surgeons, who won the Nobel Prize in 2017 for his role in developing cryo-electron microscopy data analysis algorithms.
“Our structure shows that MFSD2A has a bowl-like shape and that omega-3s bind to a specific side of this bowl,” Cater explains. “The bowl is upside down and faces the inside of the cell, but this is just a single 3D snapshot of the protein, which in real life has to move to transport the omega-3s. To understand exactly how it works, we need either multiple different snapshots or, better yet, a movie of the transporter in motion.”
To understand what these movements might look like, a second co-leader of the study, George Khelashvili, PhD, assistant professor of physiology and biophysics at Weill Cornell Medicine, used the 3D model of the protein as a starting point to run computational simulations that revealed how the transporter moves and adapts its shape to release omega-3s into the brain.
A third co-leader of the study, David Silver, PhD, professor at the Duke-NUS Medical School in Singapore and pioneer in MFSD2A biology, together with his team tested and confirmed hypotheses derived from the structure and the computational simulations on how MFSD2A works to pinpoint specific parts of the protein that are important.
The team also included researchers from the New York Structural Biology Center, the University of Chicago, and the University of Arizona, all using their specific skills to make this project possible.
The team is now investigating how the transporter first recognizes omega-3s from the bloodstream. “But our study has already given us tremendous insight into how MFSD2A delivers omega-3s to the brain, and we are really excited to see where our results lead to,” Cater says.
The study is titled “Structural basis of omega-3 fatty acid transport across the blood-brain barrier.”
Other authors: Geok Lin Chua (Duke-NUS Medical School), Satchal K. Erramilli (University of Chicago), James E. Keener (University of Arizona), Brendon C. Choy (Columbia), Piotr Tokarz (University of Chicago), Cheen Fei Chin (Duke-NUS Medical School), Debra Q.Y. Quek (Duke-NUS Medical School), Brian Kloss (New York Structural Biology Center), Joseph G. Pepe (Columbia), Giacomo Parisi (Columbia), Bernice H. Wong (Duke-NUS Medical School), Oliver B. Clarke (Columbia), Michael T. Marty (University of Arizona), and Anthony A. Kossiakoff (University of Chicago).
Funding: The study was supported by funds from the National Institutes of Health (R35 GM132120, R21 MH125649, R35 GM128624, and R01 GM117372); the National Research Foundation and Ministry of Health, Singapore; the Simons Society of Fellows; the HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational Biomedicine at Weill Cornell Medical College through the 1923 Fund; and the Khoo Postdoctoral Research Fellowship.
David Silver is a scientific founder and advisor of Travecta Therapeutics, which has developed a drug delivery platform that uses MFSD2A transport. All other authors declare no competing interests.
About this omega-3 and neuroscience research news
Source: Columbia University
Contact: Helen Garey – Columbia University
Image: The image is in the public domain
Original Research: Closed access.
“Structural basis of omega-3 fatty acid transport across the blood–brain barrier” by Rosemary J. Cater, Geok Lin Chua, Satchal K. Erramilli, James E. Keener, Brendon C. Choy, Piotr Tokarz, Cheen Fei Chin, Debra Q. Y. Quek, Brian Kloss, Joseph G. Pepe, Giacomo Parisi, Bernice H. Wong, Oliver B. Clarke, Michael T. Marty, Anthony A. Kossiakoff, George Khelashvili, David L. Silver & Filippo Mancia. Nature
Structural basis of omega-3 fatty acid transport across the blood–brain barrier
Docosahexaenoic acid is an omega-3 fatty acid that is essential for neurological development and function, and it is supplied to the brain and eyes predominantly from dietary sources.
This nutrient is transported across the blood–brain and blood–retina barriers in the form of lysophosphatidylcholine by major facilitator superfamily domain containing 2A (MFSD2A) in a Na+-dependent manner.
Here we present the structure of MFSD2A determined using single-particle cryo-electron microscopy, which reveals twelve transmembrane helices that are separated into two pseudosymmetric domains.
The transporter is in an inward-facing conformation and features a large amphipathic cavity that contains the Na+-binding site and a bound lysolipid substrate, which we confirmed using native mass spectrometry.
Together with our functional analyses and molecular dynamics simulations, this structure reveals details of how MFSD2A interacts with substrates and how Na+-dependent conformational changes allow for the release of these substrates into the membrane through a lateral gate.
Our work provides insights into the molecular mechanism by which this atypical major facility superfamily transporter mediates the uptake of lysolipids into the brain, and has the potential to aid in the delivery of neurotherapeutic agents.