A novel strategy of engineering genetically encoded probe for ultrasensitive sensing Hg with unusual planar trigonometric coordination configuration.

At present, few genetically encoded fluorescent probes are currently available for the analysis of toxic heavy metal ions, and most have poor performance that cannot meet the requirements of sensitive and dynamic detection in living cells. In this study, we designed a single fluorescent protein-based probe sfGFP-MerBD, which can specifically response to Hg with high binding affinity and wide dynamic range. More importantly, the developing probe can timely and reversibly monitor changes of Hg concentration in living mammalian cells. The excellent performance of this probe is largely due to the recognition element of the probe, MerBD, which adopts an unusual planar trigonometric coordination configuration with Hg, and the coordination can cause enough conformational change to influence the fluorescence of skeleton protein sfGFP coupled with it. The small peptide MerBD was delicately designed based on the three-dimensional structure of metalloprotein MerR. This novel design strategy solves the challenging problems that there are few natural functional proteins in the process of constructing fluorescent probes for toxic metal ions and some functional proteins cannot be directly used as recognition elements. Based on the new strategy, more genetically encoded fluorescent probes of toxic heavy metal ions can be efficiently constructed and applied in the future.