Dextrans and related glucans produced from sucrose by lactic acid bacteria have been studied for many years and are used in numerous commercial applications and products. Most of these glucans are water-soluble, except for a few notable exceptions from cariogenic Streptococcus spp. and a very small number of Leuconostoc mesenteroides strains. The ability to produce water-insoluble glucans in situ may be of value in encapsulation technology and in the production of biocompatible films and fibers. To that end, we have cloned an insoluble-glucan producing glucansucrase (DSR-I) from the type strain of L. mesenteroides and studied its activity and some of the properties of its insoluble product. Evidence indicates that the product is either a block or graft copolymer of a-1,3-linked and a-1,6-linked D-glucose units. Mutation of a single amino acid residue that is believed to be critical for acceptor sugar orientation (i.e., oligosaccharide or growing glucan chain) leads to enzymes that produce significantly altered proportions of the two linkage types, with correlating changes in the physical properties of the polysaccharide. How a single enzyme produces a polymer with two different structural domains is intriguing. Although we are still in the early stages of our investigation, we will present preliminary results that may provide some clues.

Glucansucrases from lactic acid bacteria which produce water-insoluble polysaccharides from sucrose

244th National Meeting (2012)

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