Novel Chemical Tools to Study Ion Channel Biology (Advances in Experimental Medicine and Biology)

128 L. Leisle et al.

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a

b

Fig. 3 Evolving substrate specificity of aminoacyl-tRNA synthetases (aa-RSs) for ncAAs. a In
prokaryotic expression systems, a two-step evolution procedure for aa-RSs is well established.
After choosing an aa-RS/tRNA pair orthogonal to the host, a library containing randomized resi-
dues in the amino acid binding site of the enzyme is constructed. This population of aa-RS variants
( grey and red spheres) is subjected together with its cognate tRNA ( black cross) to a round of
positive selection and screened for activity with either canonical ( grey circle) or non-canonical