Unlike most enzymes that are exquisitely efficient in targeting favored motifs, they found that AID was extremely inefficient. AID initiated chemical reactions in favored motifs only about 3 percent of the time. By mutating the motifs so haphazardly, the researchers suggest that AID produces antibody diversity.
The study also sheds light on a little-studied group of enzymes. Enzymes such as AID that scan single-stranded DNA have been studied far less extensively than enzymes that scan double-stranded DNA.
"This is the first really clear picture of what AID is doing during the scanning process," Goodman said.
To identify and describe AID's complex process during scanning, the team used a genetic assay to measure the distribution of AID-induced mutations on individual DNA molecules and then analyzed the mutational data computationally using a random walk model, developed for the study by USC Dornsife researcher Peter Calabrese. By combining the genetic and computational analyses, they were able to calculate the distribution of mutations that occurred with a remarkable fit to their experimental data. The fit entailed matching theory to experiment for the patterns of closely spaced mutations and separately for the distances between mutated and non-mutated target motifs.
|Contact: Michelle Salzman|
University of Southern California