TY  - JOUR
A1  - Li, Jing
A1  - Francisco, Perigio
A1  - Zhou, Wenxu
A1  - Edner, Christoph
A1  - Steup, Martin
A1  - Ritte, Gerhard
A1  - Bond, Charles S.
A1  - Smith, Steven M.
T1  - Catalytically-inactive beta-amylase BAM4 required for starch breakdown in Arabidopsis leaves is a starch- binding-protein
N2  - Of the four chloroplast beta-amylase (BAM) proteins identified in Arabidopsis, BAM3 and BAM4 were previously shown to play the major roles in leaf starch breakdown, although BAM4 apparently lacks key active site residues and beta- amylase activity. Here we tested multiple BAM4 proteins with different N-terminal sequences with a range of glucan substrates and assay methods, but detected no alpha-1,4-glucan hydrolase activity. BAM4 did not affect BAM1, BAM2 or BAM3 activity even when added in 10-fold excess, nor the BAM3-catalysed release of maltose from isolated starch granules in the presence of glucan water dikinase. However, BAM4 binds to amylopectin and to amylose-Sepharose whereas BAM2 has very low beta-amylase activity and poor glucan binding. The low activity of BAM2 may be explained by poor glucan binding but absence of BAM4 activity is not. These results suggest that BAM4 facilitates starch breakdown by a mechanism involving direct interaction with starch or other alpha-1,4-glucan.
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/00039861
U6  - https://doi.org/10.1016/j.abb.2009.07.024
SN  - 0003-9861
ER  -