Functional Expression of a Starch Biosynthetic System in Yeast

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Plant starches are the most important calorie source in the human diet and also are renewable resources for a wide variety of industrial applications. The chemical structure of the glucose polymers that make up starch is relatively simple, however, in an architectural sense, these molecules exhibit several hierarchical levels of structural complexity. The biosynthetic mechanisms responsible for producing such a structurally ordered product are largely unknown. These mechanisms are the subject of this research project, which is justified owing to the potential to modify starch production in plants for practical applications, and also for gathering fundamental biological information about the relationship between biosynthetic activity and architectural structure of the product. The enzymes that produce starch have been isolated in recent years, and the genes that code for them have been cloned. A general observation is that for each enzyme in the process, that is, the starch synthases, the starch branching enzymes, and the starch debranching enzymes, multiple forms exist. To try to simplify the system, this research project will use genetic engineering techniques to move the starch biosynthetic enzymes one at a time from their native environment in maize kernels into yeast cells. The technology allows combination of several maize genes in one yeast strain. The structure of the glucose polymers that are formed by these enzymes will then be analyzed. From these data we may be able to discern the specific structural characteristics of starch that are imparted by each enzyme, either alone or in specific combinations with other This knowledge is expected to be useful for future research directed at exploiting starch as a renewable resource.