title: Finding a new vaccine in the ricin protein fold.
abstract: 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.
authors.affiliation: United States Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, MD 21702-5011, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Olson
authors.forename: John H
authors.initials: JH
authors.lastname: Carra
authors.forename: Virginia
authors.initials: V
authors.lastname: Roxas-Duncan
authors.forename: Robert W
authors.initials: RW
authors.lastname: Wannemacher
authors.forename: Leonard A
authors.initials: LA
authors.lastname: Smith
authors.forename: Charles B
authors.initials: CB
authors.lastname: Millard
mesh_terms: D002942:Circular Dichroism; D008027:Light; D017510:Protein Folding; D012276:Ricin / Q000276:immunology*; D012542:Scattering, Radiation; D014612:Vaccines / Q000276:immunology*
chemical_list: D014612:Vaccines; D012276:Ricin