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

The T-protein is a single-polypeptide bi-functional enzyme composed of a chorismate mutase domain fused to a prephenate dehydrogenase domain (TyrA). We replaced the chorismate mutase domain with canonical or pseudo-Ca²⁺-binding motifs (EF-hand). Canonical-EF-hand-motifs differentiate from pseudo-EF-hand-motifs by experimenting a Ca²⁺-dependent conformational change. The Ca²⁺-free EF-hand-TyrA fusion-proteins showed TyrA activity at the T-protein level. Canonical-EF-hand-TyrA fusions showed a Ca²⁺-dependent loss of TyrA activity, but a pseudo-EF-hand-TyrA fusion showed high TyrA activity level in excess-Ca²⁺ conditions. Because TyrA activity exhibits robust changes in response to Ca²⁺-dependent-EF-hand conformational alterations, TyrA could be a good Ca²⁺-reporter enzyme. A chimeric canonical/pseudo-EF-hand strategy is proposed to confer pseudo-EF-hand motifs with a Ca²⁺-dependent conformational change.