A reporter system that discriminates EF-hand-sensor motifs from signal-modulators at the single-motif level

► Ca2+ controls TyrA activity in canonical-EF-hand-TyrA fusion proteins. ► Pseudo-EF-hand-TyrA fusion protein shows high TyrA activity levels in excess-Ca2+ conditions. ► An engineered pseudo-EF-hand motif confers Ca2+ control to pseudo-EF-hand-TyrA fusion protein.