Proceedings of the National Academy of Sciences of the United States of America

About the PNAS Member Editor
Name Doi, Roy H.
Location University of California, Davis
Primary Field Animal, Nutritional and Applied Microbial Sciences
 Election Citation
Doi is a leading biotechnologist who developed Bacillus subtilis as host for recombinant DNA production. In recent research, Doi has investigated the cellulosome, a large enzyme complex that can digest plant cell walls and may enable genetically engineered microorganisms to use cellulose as an industrial power source.
 Research Interests
As a microbiologist and biochemist, I have been studying the degradation of plant cell walls by using an anerobic microorganism, Clostridium cellulovorans, which produces a large extracellular enzyme complex called the cellulosome. We have studied the structure, function, regulation and assembly of the cellulosome. The cellulosome is comprised of two major components, a non-enzymatic scaffolding protein, and a number of cellulases and hemicellulases that are capable of degrading plant cell walls to sugars. There is a large gene cluster of cellulosomal subunits, but most of the cellulosomal genes are scattered around the genome. We have found that the cellulosome population is heterogeneous in terms of enzymatic subunit composition and that the variety of cellulosomes gives the organism the potential for degrading various types of plant cell walls. An analysis of the scaffolding protein revealed that it contained a cellulose binding domain, nine enzyme binding sites or cohesins, and four hydrophilic domains that are involved in binding the cellulosome to the substrate and also to the surface of the host cell. We are currently studying the synergy between the various cellulosomal enzymes and between the cellulosome and non-cellulosomal enzymes that are also produced by this organism. Synergy occurs between the cellulosomal cellulases, between the cellulosomal cellulases and hemicellulases, and between the cellulosome and non-cellulosomal enzymes. The results suggest that there is a sequential action of these enzymes against the various components of the plant cell wall which results in their synergistic activity. In other studies we are interested in converting microorganisms that ordinarily do not degrade cellulose into cellulose utilizers, since cellulosic biomass would be a less expensive substrate for industrial microorganisms.

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