Structural Analysis of Toxin-Neutralizing, Single-Domain Antibodies that Bridge Ricin's A-B Subunit Interface.Rudolph, M.J., Poon, A.Y., Kavaliauskiene, S., Myrann, A.G., Reynolds-Peterson, C., Davis, S.A., Sandvig, K., Vance, D.J., Mantis, N.J.
(2021) J Mol Biol 433: 167086-167086
- PubMed: 34089718
- DOI: 10.1016/j.jmb.2021.167086
- Primary Citation of Related Structures:
7KBI, 7KBK, 7KC9, 7KD0, 7KD2, 7KDM, 7KDU
- PubMed Abstract:
Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER) ...
Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER). RTA is liberated from RTB in the ER and translocated into the cell cytoplasm, where it functions as a ribosome-inactivating protein. While antibodies against ricin's individual subunits have been reported, we now describe seven alpaca-derived, single-domain antibodies (V H Hs) that span the RTA-RTB interface, including four Tier 1 V H Hs with IC 50 values <1 nM. Crystal structures of each V H H bound to native ricin holotoxin revealed three different binding modes, based on contact with RTA's F-G loop (mode 1), RTB's subdomain 2γ (mode 2) or both (mode 3). V H Hs in modes 2 and 3 were highly effective at blocking ricin attachment to HeLa cells and immobilized asialofetuin, due to framework residues (FR3) that occupied the 2γ Gal/GalNAc-binding pocket and mimic ligand. The four Tier 1 V H Hs also interfered with intracellular functions of RTB, as they neutralized ricin in a post-attachment cytotoxicity assay (e.g., the toxin was bound to cell surfaces before antibody addition) and reduced the efficiency of toxin transport to the TGN. We conclude that the RTA-RTB interface is a target of potent toxin-neutralizing antibodies that interfere with both extracellular and intracellular events in ricin's cytotoxic pathway.
Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA. Electronic address: firstname.lastname@example.org.