New Process for the
Rapid and Selective Detection of
Lead
Lead is a toxic heavy metal that can be very
dangerous to humans and the environment. Lead
poisoning is one of the most common diseases
caused by environmental pollution. For rapid
diagnosis and on-the-spot environmental analysis,
a simple, handy, and reliable lead detection
system is a desirable complement to conventional,
instrumentally complex laboratory methods.
Researchers from the University of Chicago and the Brookhaven National Laboratory
in New York have now presented a preliminary
process for such a quick test for lead; they have
developed a fluorescent probe that very
selectively responds to lead.
Not all living things react negatively to heavy
metals; some organisms, such as bacteria, have
developed resistance. Of these bacteria, Ralstonia
metallidurans is the only type known that has a
lead-specific resistance mechanism. This is
switched on whenever the bacterium finds itself in
a lead-rich environment. The bacterium must thus
have a means of detecting the lead ions. This task
is performed by a "scout" protein, called PbrR,
that "keeps a lookout" for lead ions. PbrR docks
to the bacterial DNA at a location that acts as an
"on/off switch" for the lead- resistance gene. If
lead ions get into the cell, they bind to the
"scout", which then changes its form such that it
pulls the two strands of the DNA apart somewhat,
switching the gene "on".
This system is similar to that used by the
research team headed by Chuan He. However, instead
of using PbrR, they chose PbrR691, a previously
functionally uncharacterized and closely related
protein that can easily be produced in larger
quantities by genetic methods. As they hoped, this
protein also recognizes lead ions. It was also
necessary to slightly alter the bacterial DNA;
within the "switch" region, the researchers
replaced an adenine group with a fluorescent
analogue. Bound tight in the DNA double helix, it
does not fluoresce under normal, lead-free
circumstances. However, if a lead ion binds to
PbrR691, the two strands are locally pulled apart,
which causes the fluorescent component to protrude
from the double helix and begin to glow. The
intensity of the fluorescence indicates the lead
concentration of the sample. The probe is
approximately 1000-fold more selective towards
lead than other metal ions.
"Our lead probe is a starting point for the
development of a simple, lead-specific analysis
process," says He. "In addition, we are
investigating why PbrR691 binds lead ions so
selectively. This insight could help in the design
of a lead-binding antidote for lead poisoning."
http://www.angewandte.org/
Posted 6th April 2005
