Some proteins naturally form
nanometer-scale pores that serve as channels for useful biochemical
ions. Through this ionic communication, nanopores enable many
functions in cells, such as allowing nerve cells to communicate
(they are even responsible for twitching the frog leg in Galvani's
famous discovery in the 1700s).
Nanopores can be destructive, too.
When the proteins of bacteria and viruses attach to a cell, their
nanopores can facilitate infection, for example by shooting viral
DNA through them into the cell.
Last week, at the March Meeting of the
American Physical Society in Baltimore,
John J. Kasianowicz (National Institute of Standards and Technology,
firstname.lastname@example.org) showed how single
biological nanopores can be used to detect and characterize
individual molecules of RNA and DNA. He also demonstrated
constructive uses for anthrax-related nanopores in diagnosing
anthrax infections and testing anti-anthrax drugs.
secrete a protein called "protective antigen" that attaches to an
organic membrane such as a cell wall. The protein forms a nanopore
that penetrates the membrane. When another anthrax protein, called
"lethal factor," attaches to the protective antigen nanopore, it
prevents ionic current from flowing through the pore and out of the
By monitoring animal blood samples for changes in
ion current, Kasianowicz and his colleagues at the National Cancer
Institute and the United States Army Medical Research Institute for
Infectious Diseases electronically detected a complex of two anthrax
proteins in less than an hour, as opposed to the existing methods
which can take up to several days. Also, they demonstrated a method
for screening potential therapeutic agents against anthrax toxins
using the anthrax nanopore (see the
NIST Web site
for a picture and more information).
A Brown University group led by Sean Ling (Xinsheng_Ling@brown.edu)
was among those reporting progress in developing a nanopore-based
method for sequencing DNA faster and more cheaply than traditional
In one scenario, the change in ion current
as DNA moves through the nanopore could yield the sequence of bases, or
letters, in the DNA. However, the letters in DNA are so close to
each other (about .4 nm), and the DNA moves so quickly through
the nanopore, that researchers have had to come up with creative
solutions for reading the individual letters. For example, the
Brown group attaches complementary blocks of DNA, about six letters
long, to the DNA sequence of interest, so that the researchers would
read blocks of multiple letters at a time, while slowing down the
passage of the DNA by attaching a magnetic bead to it.
Other researchers are finding value in developing nanopores for
fundamental biology studies. Discussing his group's latest work
with artificial, silicon-based nanopores, Cees Dekker of the Delft
University of Technology in Delft, Holland (email@example.com), showed how lasers
and other manipulations with the artificial pores are enabling new
single-molecule biophysics studies on the properties of
DNA, RNA, and proteins by studying how they pass through the pores.
Artist's rendering of DNA traversing
through a nanopore at
Physics News Graphics
NIST Web site
with another picture and more information