Studies of Thermobifida fusca plant cell wall degrading enzymes.

Abstract

I have been studying the Thermobifida fusca cellulose degrading proteins for the past 25 years. In this period, we have purified and characterized the six extracellular cellulases and an intracellular beta- glucosidase used by T. fusca for cellulose degradation, cloned and sequenced the structural genes encoding these enzymes, and helped to determine the 3-dimensional structures of two of the cellulase catalytic domains. This research determined the mechanism of a novel class of cellulase, family 9 processive endoglucanases, and helped to show that there were two types of exocellulases, ones that attacked the non-reducing ends of cellulose and ones that attacked the reducing ends. It also led to the sequencing of the T. fusca genome by the DOE Joint Genome Institute. We have studied the mechanisms that regulate T. fusca cellulases and have shown that cellobiose is the inducer and that cellulase synthesis is repressed by any good carbon source. A regulatory protein (CelR) that functions in the induction control has been purified, characterized, and its structural gene cloned and expressed in E. coli. I have also carried out research on two rumen bacteria, Prevotella ruminicola and Fibrobacter succinogenes, in collaboration with Professor James Russell, helping to arrange for the genomes of these two organisms to be sequenced by TIGR, funded by a USDA grant to the North American Consortium for Genomics of Fibrolytic Ruminal Biology.