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How Can We Master Energy and Information on the Nanoscale to Create
New Technologies with Capabilities Rivaling Those of Living Things?
Progress on Grand Challenge
CLSF researchers have made large
strides in understanding the
machinery underlying cellulose
synthesis and also a novel way to
connect cellulose microfibrils in plant
cell walls. See attached highlights.
New Horizons for Grand Challenge
Has the focus/scope of the Grand
Challenge evolved?
It is still a good Grand Challenge.
Remaining Challenge
Refreshed Grand Challenge?
To harness these discoveries by moving
into the realm of synthetic biology and
in-vitro reconstitution of synthesizing
complex, to engineer new forms of
cellulose in a science-based manner.
• Is a new statement of the Grand
Challenge needed?
• Should the Grand Challenge be
retired?
How about ‘rival or exceed those of
living organisms’
Submitted by: Daniel Cosgrove
Affiliation: Penn State University
In-vitro Reconstitution of Bacterial Cellulose Biosynthesis
Scientific Achievement
Significance and Impact
The multi-subunit bacterial cellulose
synthase was purified and functionally
reconstituted in vitro, producing high
molecular weight cellulose.
This is the first example of cellulose biosynthesis from
purified components. It reveals the essential subunits
required for function and enables a detailed
biochemical analysis of the many reactions required
for cellulose synthesis and membrane translocation.
Research Details
– BcsA is the catalytically active subunit of the
cellulose synthase complex but requires BcsB for
function.
– BcsA synthesizes a cellulose polymer 200 to 300
glucose units in length from UDP-activated glucose.
– Cellulose synthesis occurs at a reaction rate of at
least 90 glucose units per second.
– BcsA is highly specific for UDP-glucose as substrate.
– Only the membrane associated region of BcsB is
crucial to maintain catalytic activity of BcsA.
Omadjela, O., Narahari, Strumillo, J., A., Melida, H., Mazur, O., Bulone,
V. & Zimmer, J., BcsA and BcsB form the catalytically active core of
bacterial cellulose synthase sufficient for cellulose synthesis,
PNAS 2013, 110, 17856-61
2
All-atom model of plant cellulose synthase
Scientific Achievement
Predicted a three dimensional structure of the large cytosolic (catalytic) region of a plant
cellulose synthase using computational methods
Significance and Impact
Our model can be used to explain numerous
structure-activity relationships within plant cellulose
synthases and may be useful for the selection and
subsequent testing of appropriate mutants in order
to optimize cellulose and biomass properties.
Research Details
– Demonstrated that a large (506 amino acid) protein
structure can now be now successfully predicted
using computational methods
– Predicted a conserved mechanism for cellulose
catalytic mechanism across Kingdoms
– Showed that regions unique to plant CESAs, the CSR
and P-CR, fold into distinct subdomains within the
cytosolic region, supporting the potential importance
of these regions for CESA assembly into plant CSCs.
L. Sethaphong, C. H. Haigler, J. D. Kubicki, J. Zimmer, D. Bonetta, S. DeBolt, Y. G. Yingling, "Tertiary model of a plant cellulose synthase", PNAS (2013) 110:7512-7
3
A Revised Architecture for Plant Primary Cell Walls
Tethered network model
Revised model
Scientific Achievement
Showed that structurally important xyloglucan is not
accessible to enzymes that can break it down
(xyloglucanases) but instead is intertwined with cellulose in
a protected form or compartment
Significance and Impact
Suggests new ways to loosen cell walls for faster plant
growth and for more efficient conversion of plant biomass
to biofuels. Also explains why approaches based solely on
xyloglucan digestion do not work.
Research Details
Xyloglucans (black lines) were thought to tether
cellulose microfibrils (red lines) in 1o cell walls (top
panel). New results indicate a different arrangement,
with the load-bearing xyloglucans hidden in tight
junctions that bind microfibrils together .
Y.B. Park, D.J. Cosgrove
Plant Physiology 2012, 158, 1933-1943
Work was performed at Penn State University
– Measured cell wall biomechanical responses to enzymes that
specifically hydrolyze xyloglucan, cellulose, or both.
– Xyloglucanases and cellulases, alone or added together, were
ineffective for cell wall loosening
– Only single enzymes with dual specificities (capable of cutting
both xyloglucan and cellulose) were effective in cell wall
loosening
– Results suggest the common depiction of xyloglucan acting as a
tether between cellulose microfibrils is inaccurate