Abstract Starch phosphorylation is a general phenomenon existing naturally in the plant kingdom. The reaction of phosphorylation catalyzed by the glucan-water dikinase （GWD） is a necessary process during the degradation of the transitory starch in plant. In this review, we summarized the progress made on GWD from the view of its structure, biological functions and its interactions with other enzymes involved in starch metabolism. We also discussed its potential application in starch processing industries to provide environment-friendly methods for starch modification through genetic engineering. Potato GWD gene （StGWD） encodes a protein of 1 461 amino acid residues with a calculated molecular mass of about 160 ku for the entire coding sequence. From the N-terminal to C-terminal of the mature StGWD protein, there is a chloroplast transit peptide domain, two carbohydrate-binding modules, a phosphohistidine domain and nucleotide binding domain in turn. GWD marks sections for glucan hydrolysis via C6 phosphorylation to initiate granule surface hydration, while phosphoglucan water dikinase （PWD）, an isoform of GWD then recognizes these partially solubilized sections and catalyzes C3 phosphorylation of nascent glucans to induce steric strain that breaks the helical structure and prevents recrystallization. The starch in leaves will encounter an excess accumulation if the expression of the GWD is inhibited or decreased. And the overexpression of the enzyme may increase the phosphate content of the natural starch. In vivo, many enzymes related to starch metabolism can interact with the GWD, but the mechanisms of their real interaction are not clear yet. The growth will be profoundly inhibited if plants are encountered with environmental stress. We hypothesize that higher phosphorylated starch may be accumulated if farmers can make good use of the adversary conditions. However, further research and experimental data are needed to support this hypothesis.
Sun Xiao, Bao Jinsong*. Biological function and application of glucan-water dikinase: a review. Journal of Zhejiang University (Agriculture and Life Sciences), 2014, 40(6): 591-597.
