Studying These Cell Structures May Help Shed Light on Alzheimer’s & ALS
By LIDA TUNESI
Do you remember learning in high school biology about organelles? They’re tiny structures located inside living cells. Different types of organelles play distinct biological roles. For instance, mitochondria crank out molecules used as the cell’s energy currency, while a cell’s nucleus houses DNA.
Typically, each organelle is individually encased in a membrane within the cell. But recently, scientists discovered that some organelles lack membranes. These organelles form when liquid molecules inside the cell converge into droplets. Researchers think that dysfunction in these membrane-less organelles could be related to neurodegenerative diseases such as Alzheimer’s and ALS. Understanding how these organelles work sheds light on what happens when they stop working, and that knowledge could someday lead to new therapeutics.
A new study examines two components of these droplet organelles called lysine and arginine. The study, co-authored by postdoctoral research associate Rachel Fisher and Professor Shana Elbaum-Garfinkle of the Advanced Science Research Center at The Graduate Center, CUNY, appears in Nature Communications.
Lysine and arginine are amino acids, or protein building blocks. “I wanted to understand how two amino acids that both have a positive charge could have different behaviors and lead to different droplet properties,” Fisher said, explaining that a molecule’s charge is normally thought to be an important factor in how droplets form.
Droplets that are rich in chains of arginine are 100 times more viscous, or thicker, than lysine-rich droplets. And like oil and water, the two don’t mix. Instead, they can form layers encasing each other. Arginine, the researchers also found, is capable of dissolving or replacing lysine chains in droplets.
These droplet organelles play a wide variety of roles in the cell, like regulation of gene expression and processing mRNA. Some last only seconds before falling apart and mixing back into the surrounding liquid, and others can last several days. They are largely made of proteins, as well as DNA, RNA, and other small molecules.
With a good understanding of their properties, researchers could find ways to control droplet formation and action, and find ways to correct it when disease steers things off-course.