Senior Honors Projects, 2010-current

Date of Award

Spring 2014

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Jonathan D. Monroe

Nathan Wright

Christopher Berndsen

Abstract

Plant whole genome sequences started to be available in 1998, and these resources made it possible to identify complete gene families. One of these gene families in Arabidopsis thaliana is called the -amylase gene family, which comprises nine members (BAM1-9). -amylases play an important role in nighttime starch degradation in chloroplasts producing maltose, which is exported to the cytosol for further metabolism. One of the non-catalytic, plastidic BAMs, - amylase9 (BAM9), is conserved in flowering plants, suggesting that it plays an important role in plastid function. Arabidopsis plants lacking BAM9 appear to accumulate starch, so we suspect that BAM9 may function to regulate starch metabolism under certain conditions. Amino acid sequence alignments revealed three loops surrounding the active site of BAM9 that are not conserved compared with active BAMs, suggesting that BAM9 may not bind to starch. Starch binding assays supported this hypothesis. The alignments also showed that the active site residues of BAM9 were not all identical to those in the active BAMs suggesting that some other molecule may bind to BAM9 in the active site. Residues in the deeper half of the active site were conserved among the BAM9 orthologs suggesting that these proteins might bind a small carbohydrate, such as maltose. However, experiments with isothermal titration calorimetry showed BAM9 has a low affinity for maltose.

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