Starch phosphorylation: insights and perspectives

Abstract

During starch metabolism, the phosphorylation of glucosyl residues of starch, to be more precise of amylopectin, is a repeatedly observed process. This phosphorylation is mediated by dikinases, the glucan, water dikinase (GWD) and the phosphoglucan, water dikinase (PWD). The starch-related dikinases utilize ATP as dual phosphate donor transferring the terminal γ-phosphate group to water and the β-phosphate group selectively to either C6 position or C3 position of a glucosyl residue within amylopectin. By the collaborative action of both enzymes, the initiation of a transition of α-glucans from highly ordered, water-insoluble state to a less order state is realized and thus the initial process of starch degradation. Consequently, mutants lacking either GWD or PWD reveal a starch excess phenotype as well as growth retardation. In this review, we focus on the increased knowledge collected over the last years related to enzymatic properties, the precise definition of the substrates, the physiological implications, and discuss ongoing questions.

The analysis of the different functions of starch‐phosphorylating enzymes during the development of Arabidopsis thaliana plants discloses an unexpected role for the cytosolic isoform GWD2

“…Because of the strong sex phenotype associated to the GWD1 mutation, gwd1 mutants have been deeply investigated. The role of GWD1 on nocturnal mobilization of transitory starch is well established (for a recent review see Lloyd and Kossmann , Mahlow et al ) and the knowledge acquired from the model plant Arabidopsis has been already transferred to some crops (Carciofi et al , Ral et al , Weise et al , Hirose et al ), in some cases with unexpected results. In wheat, for instance, the endosperm‐specific inhibition of GWD homologs by RNA interference (RNAi) caused the increase in vegetative biomass and grain yield compared with wild‐type plants (Ral et al , Bowerman et al ).…”

“…In comparison to gwd1 , less is known about mutants pwd and gwd2 (Mahlow et al ). This is especially true for gwd2 , presumably because of the lack of sex phenotype associated to leaves of this mutant (Glaring et al ).…”

“…Several studies have been conducted on plants with altered expression of genes involved in starch metabolism (for a recent review see Lloyd and Kossmann , Mahlow et al ). Much attention has been paid to severe phenotypes, as those of starch‐less mutants (e.g.…”

The starch‐binding domain family CBM41—An in silico analysis of evolutionary relationships

“…Remarkably, in a special case, the SBD is inserted within the domain B, which itself represents a long loop in the catalytic (β/α) 8 ‐barrel domain A, characteristic of all members of the α‐amylase family GH13 . The N‐terminal position is thus typical for families CBM21, 34, 41, 45, 48, 53, and 68, while families CBM20, 25, 26, 69, and 74 occur in a C‐terminal position, and the special case of the insertion within domain B involves the family CBM58 …”

“…42 The N-terminal position is thus typical for families CBM21, 34,41,45,48,53, and 68, while families CBM20, 25,26,69, and 74 occur in a C-terminal position, and the special case of the insertion within domain B involves the family CBM58. [6][7][8][9][10][11][12][43][44][45][46][47][48][49][50] SBDs were originally recognized as a module found typically in microbial amylolytic and related enzymes. It is worth mentioning that various SBDs and GBDs have also been identified in other plant and animal enzymes and proteins, such as plant starch synthase III, 28,51-53 glucanwater dikinases, 26,29,31 starch-excess protein-4, 54,55 animal laforin, 56-59 genethonin-1, 60-62 as well as the b-subunit of AMP-activated protein kinase 63,64 and its homologues in plants, 65,66 and even in lytic polysaccharide monooxygenases from fungi.…”