Solid-State Nanopore Sensors for Nucleic Acid Analysis - Nanopores: Sensing and Fundamental Biological Interactions - page 5

membranes of cell organelles; and viruses, which dump their genomes into cells via
pores that insert into the cell membrane [ 22 ]. An example of a biological nanopore
that is frequently used in-vitro is the a-hemolysin channel.

1.2.1 -Hemolysin

a

a - hemolysin is a naturally occurring biological protein complex extracted from the

bacterium Staphylococcus aureus that when inserted into a lipid bilayer membrane,
forms a ~1.5 nm diameter pore allowing the passage of ions and ssDNA. In vivo,
bacterium Staphylococcus aureus secretes alpha-hemolysin monomers that bind to
the outer membrane of host cells. These monomers self assemble into seven subunit
oligomers to form a water-filled transmembrane channel that facilitates the uncon-
trolled permeation of water, ions, and small organic molecules in and out of the host
cell. The resulting discharge of vital molecules from the host cell, osmotic swelling
and a loss in ionic gradient can result in irreversible cell damage and eventually
death of the host cell (apoptosis). Apoptosis induced by - hemolysin insertion in

various cell types including rabbit erythrocytes, human erythrocytes, monocytes,
and lymphocytes has been reported [ 4 , 40 ].
In-vitro studies of DNA transport through biological pores have traditionally
focused on

a

- hemolysin as the transmembrane channel of choice. The structure of
the heptameric

a

a - hemolysin pore embedded in a lipid bilayer is shown in Fig. 1.2a .

Fig. 1.2 Single nucleotide detection using a mutant a-hemolysin nanopore [ 18 ], reprinted with
permission. (a) Mutant a-hemolysin protein channel modified with a cyclodextrin adapter embed-
ded in a lipid bilayer (b) Characteristic current recordings from a modified a-hemolysin channel,

showing different blockade levels for each base (c) Current blockade histogram confirms single
base discrimination ability of modified a-hemolysin pore