Exploration of the a-set for Kemp elimination activity. Following our previous success with this approach, we used the FuncLib webserver to computationally search the sequence space corresponding to the three hotspot positions of the a-set. The residues at the hotspot positions in the background V4 variant are A280, A283 and R284. FuncLib identified only a limited available sequence space as being available at those positions (Table and Supplementary Data Table ):