The structures of native celluloses, and the origin of their variability

Abstract

The structures of native celluloses have traditionally been presented in terms of two-domain models consisting of crystalline and non-crystalline fractions. Such models have been of little help in advancing understanding of enzyme-substrate interactions. In this report we first address issues that complicate characterization of the structure of native celluloses particularly with respect to information that may be relevant to understanding susceptibility to enzyme action. Key among these is the fact that crystallographic models define structure primarily at the level of the unit cell while susceptibility to the action of enzymes appears to be influenced more by aggregation at the next higher level of structure, that of the elementary fibrils. Recent developments in structural characterization, based primarily on the use of spectroscopic methods, have revealed that native celluloses are species specific composites of two forms of cellulose, Ia and Ib.They appear to possess the same secondary structure but distinctly different tertiary structures. Their aggregation appears to reflect an inherent tendency of the cellulose molecules to self assemble into fibrils at a hierarchy of levels. This is most clearly revealed through observations of the biogenesis of cellulose in model systems incorporating cultures of Acetobacter xylinum. Since the induction of enzyme systems seems to be sensitive to subtle differences in tertiary structure, advances in characterizing the variability of structure at these levels will be central to future explorations of the dynamics of enzyme-substrate interactions.

Citation

Atalla, R. H. 1999. The structures of native celluloses, and the origin of their variability. [Proceedings of the MIE Bioforum 98 : genetics, biochemistry and ecology of cellulose degradation, 1999 September 07-11, Suzuka, Japan. Tokyo, Japan : UNI Publishers Co., LTD, 1999?].:[13] p. : ill.