Protein vaccine fully protects mice from lethal aerosol challenge with r...( rty of RTA increase protein stability...)

In the August online issue of Protein Engineering, Design and Selection, Olson and his team--John H. Carra, Virginia Roxas-Duncan, Robert W. Wannemacher, Leonard A. Smith, and Charles B. Millard--describe using a combination of molecular modeling and protein engineering to design the new vaccine. The team started with an extensive computer-aided analysis of the toxin structure, using a three-dimensional model provided by colleagues at the University of Texas, Austin.

"We compared ricin with other proteins of the same family," Olson explained. "We tried to figure out where the protein molecules are diverging within the family--to see what changes were made by nature so we could make the changes we needed to make."

To improve upon its stability--in effect, to make it go against its natural tendencies--Olson and his team had to change the structure of the RTA molecule. Once they had developed the necessary genetic sequences, they handed them off to Smith and others at USAMRIID for protein engineering.

"We went straight from the computer to molecular biology," explained Smith. "We had to clone and purify the proteins, and test them in animals for toxicity and protection."

RTA 1-33/44-198, the most promising vaccine candidate, was tested in three groups of ten mice each. One group received the purified protein alone; a second group received the protein plus an adjuvant called Alhydrogel; and a third group served as the control, receiving an injection of saline solution instead of the vaccine.

Purified RTA 1-33/44-198 protected 10 out of 10 mice from a whole-body aerosol challenge with lethal doses of ricin. The survival rate was the same with or without the adjuvant. All 10 animals in the unvaccinated control group died.

"Molecular modeling and protein engineering represent a sig
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Contact: Caree Vander Linden
Caree.Vander-Linden@amedd.army.mil
301-619-2285
US Army Medical Research Institute of Infectious Diseases
4-Aug-2004