Finding a new vaccine in the ricin protein fold.
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 RTA1-198) for presentation of a specific protective epitope (RTA loop 95-110). An optimized protein based upon our modeling design (RTA1-33/44-198) 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, RTA1-198 or RTA1-33/44-198 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.
Olson
Mark A
MA
United States Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA.
Carra
John H
JH
Roxas-Duncan
Virginia
V
Wannemacher
Robert W
RW
Smith
Leonard A
LA
Millard
Charles B
CB
D002942:Circular Dichroism; D008027:Light; D017510:Protein Folding; D012276:Ricin / Q000276:immunology*; D012542:Scattering, Radiation; D014612:Vaccines / Q000276:immunology*
D014612:Vaccines; D012276:Ricin