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Topic Name: Nanobiotechnology Research Featured in Prominent Journals
Category: Nanobiotechnology
Research persons: Eric Ackerman, Chenghong Lei, Yongsoon Shin, Jun Liu, Jon Magnuson, Glen Fryxell, Linda Lasure, Doug Elliott, Michelle Valenta and K Prasad Saripalli, all PNNL.
Location: Pacific Northwest National Laboratory, NY, United States
Details
A Research Focus article commenting on recently published nanobiotechnology
work at Pacific Northwest National Laboratory (PNNL)
appears in the May 2007 issue of the journal
Trends in Biotechnology.
In their abstract, authors Keith Dunker and Ariel Fernandez state that:
"PNNL scientist
Eric Ackerman
and colleagues showed that an entrapping environment consisting of
functionalized mesoporous silica actually enhances enzyme activity beyond the
test-tube levels of free enzymes in solution. These findings provide an
approach for dissecting the effect of various contributors to enzyme activity
and thereby provide a means for fine-tuning the entrapping matrices to
optimize enzyme performance in a rational way."
This article is in response to a recent spate of journal articles published
by Ackerman's team on their characterization of functionalized mesoporous silica
(FMS) for protein confinement and enzyme immobilization. Their article that was
featured in the November 28 issue of
Nanotechnology
was highlighted on the journal's webpage. A PNNL news release about their work,
"Night of the living enzyme,"
generated a flurry of media interest and appeared in thousands of publications.
In their recently published paper in Nano Letters, they report
that an immobilized enzyme in FMS can still work better in the presence of high
concentrations of urea (a strong denaturant). "Rather than losing all activity
in the highly concentrated denaturant solution, the specific activity of the
enzyme entrapped in FMS remained higher than the highest specific activity of
free enzyme in solution," says lead author Chenghong Lei.
Why it matters: Mesoporous materials have a very high
surface-to-volume ratio, large nanoporosity and ordered, uniform pore structure.
Enzymes and proteins are the nanomachines of cells and are required to sustain
life. These nanomachines synthesize and degrade cellular components and generate
energy. The only ways to use these molecular machines are either inside cells or
by separating them from cells. For many applications, it is not feasible to use
entire cells, especially if the necessary molecular machines are scattered among
many incompatible species.
The barrier to harnessing enzymes and molecular machines outside cells is
that they are fragile and lose their activities once removed from cells. The
results from the work by the PNNL team mean that it may be possible to mimic the
crowded and stabilizing environment of cells by using FMS. This could in turn
lead to environmentally friendly, efficient, chemical reactors based on cellular
molecular machines.
The team found that a dramatic increase of enzyme loading occurred when using
FMS compared to using unfunctionalized mesoporous silica and normal porous
silica. Interestingly, the inactive or less active enzymes in solution become
active, or more active once entrapped in FMS. These results are noteworthy
because the specific activity of immobilized enzymes using conventional methods
is usually far less than that of free enzymes in solution before immobilization.
In the work with urea, the team's results mean that immobilized enzymes in
FMS can work well under harsh conditions that would kill cells or
non-immobilized enzymes. "This can lead to combining solubilizing reagents with
immobilized enzymes to chew up targets that are usually very resistant to
degradation (e.g., lignocellulose waste site environmental contaminants) and
convert them to energy or harmless byproducts. Under the correct reactions
conditions, enzymes can drive reactions in both directions. Instead of an enzyme
helping to convert substance A to B, it can catalyze the reverse reaction from B
to A. Exploiting these reverse reactions would greatly extend the utility of
enzymes, but the required reaction conditions are often harmful to living cells.
Our immobilization approach means that biological molecular machines might be
harnessed, and even optimized through high-throughput expression methods, to
work under reaction-favorable, nonbiological conditions," says Ackerman.
Methods: The general approach the scientists took was to
incubate the enzymes with an appropriate FMS, so it should be applicable to many
enzymes, proteins, and protein complexes, because both pore sizes and functional
groups of FMS are controllable. Unlike traditional approaches to immobilize
enzymes, here it is unnecessary to expose the enzymes to activity-killing
reagents or conditions during the immobilization procedure because all harsh
chemical synthesis conditions involved in immobilization material production
were completed before introduction of the enzyme.
Next steps: The team wants to understand how much farther
the activity and stability of immobilized enzymes can be enhanced by rationally
altering the enzymes and the nanopore sizes and functional groups. They also
hope to expand the repertoire of enzymes and proteins under investigation to
include those that can generate energy from sugars, provide extremely sensitive
and stable sensors, and promote environmental remediation.
Research team: Eric Ackerman, Chenghong Lei, Yongsoon Shin,
Jun Liu, Jon Magnuson, Glen Fryxell, Linda Lasure, Doug Elliott, Michelle
Valenta and K Prasad Saripalli, all PNNL.
Funding: This work was supported by the U.S. Department of
Energy's Office of Biological and Environmental Research and PNNL's Laboratory
Directed Research and Development program.
Reference
Dunker AK and A Fernandez. 2007. "Engineering productive enzyme confinement."
Trends in Biotechnology 25(5):189-190.
doi:10.1016/j.tibtech.2007.03.009.
Lei C, Y Shin, J Liu, and EJ Ackerman. 2007. "Synergetic effects of
nanoporous support and urea on enzyme activity." Nano Letters
7(4):1050-1053.
Lei C, Y Shin, JK Magnuson, GE Fryxell, LL Lasure, DC Elliott, J Liu and EJ
Ackerman. 2006. "Characterization of functionalized nanoporous supports for
protein confinement." Nanotechnology 17(22):5531-5538.
Lei C, MM Valenta, K Prasad Saripalli, and EJ Ackerman. 2007. "Biosensing
paraoxon in simulated environmental samples by immobilized organophosphorus
hydrolase in functionalized mesoporous silica." Journal of Environmental
Quality 36: 233-238. doi:10.2134/jeq2006.0216.
Learn more by scientists in PNNL's
Biological Sciences Division.
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