Date of Award




Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Biomedical Sciences

Content Description

1 online resource (xvi, 199 pages) : color illustrations

Dissertation/Thesis Chair

Nicholas Mantis

Committee Members

Kathleen McDonough, Janice Pata, Peter Tessier, Richard Cole, Joe Mazurkiewicz


AB toxins, Bispecific Antibodies, Intracellular Trafficking, Neutralizing Mechanisms, Ricin Toxin, Ricin, Bispecific antibodies, Antibody-toxin conjugates, Neutralization (Chemistry), Toxicity testing

Subject Categories

Immunology of Infectious Disease


Engineering anti-toxin antibodies (Ab) is of public health interest for biodefense counter measurements. Ricin toxin is one example of a major biothreat agent that has currently no antidote. Ricin is a glycoprotein from the castor bean plant, Ricinus communis, and belongs to the medically important A-B toxin family that also includes Shiga, anthrax and cholera toxins. Ricin’s enzymatic subunit (RTA) is an RNA N-glycosidase that inhibits protein synthesis by irreversibly depurinating the 28S rRNA of the eukaryotic 60S ribosomal subunit. RTB is a galactose-/N-acetylgalactosamine-specific lectin that has two important functions. First, RTB promotes binding and endocytosis of ricin into mammalian cells. Second, following endocytosis, RTB mediates the retrograde transport of RTA from the plasma membrane to the trans-Golgi network and endoplasmic reticulum, where RTA is then retro-translocated into the cytoplasm. It was previously reported that one anti-ricin heterodimer VHH JJX12, had potent toxin-neutralizing activity in vitro and was also capable of protecting mice from ricin even at low Ab:toxin ratios. JJX12 is composed of two camelid derived heavy-chain only domains physically linked via short peptide where one monomer (RTB-B7) recognizes RTB and the second monomer (RTA-D10) recognizes RTA. In an effort to engineer therapeutics against ricin, the objective of this dissertation was to understand the mechanism by which VHH JJX12 neutralizes the toxin.