More recently, a genetically encoded FRET-based Pb2+
sensor, Met-lead 1.59, was developed for cellular detection
(Table 10).211c Met-lead 1.59 consists of an ECFP with the last
11 amino acids deleted (ECFPΔC11) and cp173Venus FRET
pair connected by a Pb2+ binding domain derived from the
bacterial metalloregulatory protein PbrR. Live-cell imaging of
HEK293 cells transfected with Met-lead 1.59 and exposed to
high concentrations (10−50 μM) of Pb2+ showed that this
sensor was able to detect cellular increase after a delay time of a
few hours.211c The development of new and more sensitive
genetically encoded FRET sensors is a promising direction for
the cellular detection of Pb2