According to a newly published study, researchers have identified new potential lines of defense against Shiga and ricin toxins and have also shed new light on glycosylation. The research was led by toxin expert Min Dong, Ph.D. at the Boston Children’s Hospital and published in PLOS Biology.
Shiga toxin is a widespread source of food poisoning produced by Shigella dysenteriae and some E. coli strains and ricin is a plant toxin used as a bioterrorism agent. Both cause damage by disrupting cells’ ability to make proteins and require specific receptors to enter the cell. For Shiga toxin, a type of glycolipid called Gb3 acts as that receptor, while a variety of glycans is used for ricins. Beyond this, little was previously known about the two toxins.
The researchers sought to uncover more information by performing CRISPR/Cas9–mediated genome-wide loss-of-function screens to see if deleting any particular gene prevented the toxins from entering.
This had previously been challenging as the receptor for Shiga toxins is not present in mot cell types. Finally, the team landed upon a bladder cancer cell line that happened to have a high level of Gb3, making it highly sensitive to Shiga toxins. The second screen was performed in HeLa cell lines to look for ricin toxicity cell factors.
After performing the screens, the team identified two factors that both toxin classes required to penetrate cells—the transmembrane proteins TMEM165 and TM9SF2, which are both found in the cell’s Golgi apparatus.
While TMEM165 and TM9SF2 are too general to serve as safe targets to block, a third protein called LATMP4a offers a more direct promise. LATMP4a is required for cells to make Shiga toxin. Mass spectrometry analysis of glycolipids and their precursors showed that LAPTM4A knockout cells lack Gb3 biosynthesis, indicating they could be a good target for blocking toxicity.
Not only does this study reveal information that could help in blocking these toxins, but reveals important information on how glycosylation works.