PEDS Advance Access originally published online on June 8, 2004
Protein Engineering Design and Selection 2004 17(4):391-397; doi:10.1093/protein/gzh043
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Finding a new vaccine in the ricin protein fold
United States Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA
1 To whom correspondence should be addressed. E-mail: charles.b.millard{at}us.army.mil
Previous attempts to produce a vaccine for ricin toxin have been hampered by safety concerns arising from residual toxicity and the undesirable aggregation or precipitation caused by exposure of hydrophobic surfaces on the ricin A-chain (RTA) in the absence of its natural B-chain partner. We undertook a structure-based solution to this problem by reversing evolutionary selection on the ribosome inactivating protein fold of RTA to arrive at a non-functional, compacted single-domain scaffold (sequence RTA1198) for presentation of a specific protective epitope (RTA loop 95110). An optimized protein based upon our modeling design (RTA133/44198) showed greater resistance to thermal denaturation, less precipitation under physiological conditions and a reduction in toxic activity of at least three orders of magnitude compared with RTA. Most importantly, RTA1198 or RTA133/44198 protected 100% of vaccinated animals against supra-lethal challenge with aerosolized ricin. We conclude that comparative protein analysis and engineering yielded a superior vaccine by exploiting a component of the toxin that is inherently more stable than is the parent RTA molecule.
Received May 3, 2004; accepted May 10, 2004.
Edited by Amnon Horovitz
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