New insights into starch metabolism from the analysis of non-enzymatic, starch binding proteins and from heterologous reconstruction of the biosynthetic pathway in yeast

Orateur : Samuel C. ZEEMAN (ETH Zürich, Switzerland)

Starch is a vital plant product for society. Learning more about its metabolism gives us options for crop improvement by altering starch structure, properties and yields. Much progress has been made by studying starch metabolism in crops and in model species such as Chlamydomonas reinhardtii and Arabidopsis thaliana. In the leaves of Arabidopsis, starch is a primary product of photosynthesis, representing a temporary carbohydrate store in the chloroplast that can be remobilized during the night. Functional genomic and biochemical studies in this system have advanced our understanding of the roles of known starch-metabolizing enzymes and facilitated the discovery of new ones. Recently, bioinformatic and proteomic analyses have identified previously unstudied and apparently non-enzymatic starch-binding proteins. Functional analyses reveal that such proteins serve to deliver or target enzymes to the their substrates, such as malto-oligosaccharides or the starch granule surface, thereby contributing to granule initiation and formation. Despite this work, and a wealth of results from other research groups, starch biosynthesis is still not fully understood and has not been recreated in vitro or in a heterologous system. Therefore, we have recently expressed over 100 combinations of Arabidopsis starch biosynthetic enzymes in the heterologous system Saccharomyces cerevisiae in order to try and define which enzyme sets are required for starch production. In my presentation, I will summarize our current understanding of starch structure and its biosynthesis using these and other examples from our lab and from the literature.

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