1B-05
Improved Cellulases for Biomass Conversion
Colin Mitchinson
Genencor International Inc.
Phone: (650)846 5853
Fax: (650)845 6510
Genencor International has been working under a DOE subcontract for cellulase cost reduction for biomass conversion to
fermentable sugars. The goal of this
three-year program was to reduce the cost of cellulase
by ten-fold. Reaching this aggressive
target required improvements in both the production, and in the specific performance,
of the cellulase mixture. Cellulolytic
biomass conversion is performed in nature by a
complex mixture of enzymes. Cellobiohydrolases play a key role and all effective cellulase
mixtures contain a large excess of cellobiohydrolases
over endoglucanases, suggesting that it is the exocellulase activity that is limiting. The fundamental dependence of reaction rate
on temperature predicts that large increases in performance, and decreased
enzyme cost, would be achieved if the enzymatic conversion could be operated at
elevated temperatures. However, T. reesei CBHI
is not expected to have sufficient stability to perform at high temperatures.
Therefore the thermal stability of the CBH1 enzyme from T. reesei needs to be improved. This talk discusses
how we have produced CBHI enzymes with altered thermal stability and specific
activity: We will present our natural diversity, site-directed mutagenesis and
protein engineering / directed evolution approaches which have resulted in
greatly stabilised CBHI homologs
and variants.