Information Technology Reference
In-Depth Information
Cell-to-Chip Communication
Cell-to-chip communication may be accomplished through the use of reporter
genes, electrochemical means, or through the recording of action potentials.
Reporter gene expression produces a signal that readily couples to the chip. To
be useful in the devices considered here, the reporter gene product or activity
must be readily detected by the chip and fused to the appropriate engineered
information pathway(s) of the cell. Furthermore, while a discrete output (e.g.,
expressed or not expressed) would have some uses, an output that is contin-
uously variable with expression level allows more flexibility in design. Here
we focus on the use of reporter genes in cell-to-chip communication. Com-
prehensive reviews of reporter gene applications may be found elsewhere [25,
74, 122].
There are seven unique reporter protein candidates for cell-to-chip com-
munication: (1) chloramphenicol acetyltransferase (CAT), (2)
-galactosidase,
(3) aequorin, (4) firefly luciferase, (5) green fluorescent protein (GFP), (6) uro-
porphyrinogen III methyltransferase (UMT), and (7) bacterial luciferase (Lux).
CAT,
β
-galactosidase, aequorin, and firefly luciferase require the addition of
an exogenous substrate, which is a significant complication for cell-to-chip
communication as it is considered here. This leaves GFP, UMT, and Lux as
the most viable means of cell-to-chip communication. Each of these is briefly
described below.
β
Lux
Bioluminescent organisms include species of bacteria, algae, dinoflagellates,
fungi, jellyfish, clams, fish, insects, shrimp, and squid. Luminescent bacte-
ria are classified into three genera: (1)
Xenorhabdus
, (2)
Photobacterium
, and
(3)
Vibrio
[73]. The relative ease of transferring cDNA coding for Lux proteins
into prokaryotic and eukaryotic organisms has resulted in their common use
as reporter genes. Bacterial luciferase catalyzes the oxidation of FMNH
2
and
a long-chain fatty aldehyde to FMN and the corresponding fatty acid in the
presence of molecular oxygen (Figure 5.4). This reaction produces blue-green
light with a maximum intensity at 490 nm and quantum efficiency between 0.05
and 0.15 [72]. Fatty aldehydes of chains ranging from 7 to 16 carbons long may
serve as substrates for the reaction [72].
The
structural subunits of bacterial luciferase are encoded by the
luxA
and
luxB
genes, and, with the use of an exogenous substrate, the expression
of these two genes results in bioluminescence. However, three additional genes
in the
lux
operon, C, D, and E, code for proteins required for synthesis and recy-
cling of the fatty aldehyde [11, 120]. Thus, the expression of all five
lux
genes
results in bioluminescence without the addition of an exogenous substrate, and
for the systems considered here, the entire
luxCDABE
cassette is required.
α
and
β
