Protein-Protein Interactions During Starch Biosynthesis

Abstract

Starch biosynthesis requires the ordered assembly of glucose units into amylose and amylopectin from ADPglucose. Whilst amylose has a relatively simple linear structure, the synthesis of amylopectin requires the formation of regular, repeating clusters of glucan chains. These clusters have a 9 nm periodicity and comprise a crystalline, alpha helical region and an amorphous branched region, a unit which is repeated many times over to give rise to blocklets of amylopectin. Although the individual enzymes of starch biosynthesis have been studied extensively, our knowledge of the mechanisms which give rise to this highly ordered structure is limited. There is an increasing body of literature which has demonstrated that several reactions are regulated post-translationally, including via redox modulation, protein-protein interactions and protein phosphorylation. This chapter summarises our current knowledge of these mechanisms and offers a model of how they serve to coordinate the biosynthesis of amylopectin in particular.

Production of very‐high‐amylose cassava by post‐transcriptional silencing of branching enzyme genes

“…These indicate divergent function of BE isoforms in different plant species. Further investigation is required to decipher the enzymatic process of cassava BE1 protein and its interactions with other starch biosynthetic enzymes (Tetlow et al 2015). Nevertheless, similar reduction in biomass for both BE1i and BE2i plants indicated that BE1 and BE2 are equally important for cassava growth and development.…”

Barley Starch: Composition, Structure, Properties, and Modifications

“…A number of recent reports cover the impact of genetic mutation and biosynthetic enzymes on starch properties. The roles of diverse starch biosynthetic enzymes have been well reviewed previously and are not covered in this review (Nakamura ; Tetlow and others ). Readers, especially those who are new to the starch research field, are strongly encouraged to refer to these previous publications to gain the necessary background knowledge.…”

Starch Biosynthesis in the Developing Endosperms of Grasses and Cereals

“…Evidence suggests that some granule-associated proteins become entrapped in the granule through association in heteromeric protein complexes, the formation of which is controlled by protein phosphorylation [289,315,316]. All SBE isoforms in cereal endosperms are found in protein complexes in association with other starch biosynthetic enzymes, e.g., SSs, and many of the protein complexes identified contain SBEs (for recent reviews on protein complexes associated with starch biosynthesis see [228,317]. The precise function of the various protein complexes identified in amyloplasts remains unclear.…”

“…Mutations of SSII in dicot storage tissues, such as pea (Pisum sativum L.) and potato (Solanum tuberosum L.), produce similar starch phenotypes as their counterparts in monocots (see [141]), suggesting that functional specificity of some SS isoforms was established prior to the divergence of the monocots and dicots. Both SSI and SSII are also localized within the starch granules [202,221,225], and have been shown to interact with other enzymes of starch biosynthesis, notably the SBEII class in cereal endosperm, as well as SSIII [226][227][228]. Loss of SSIIa in cereal endosperms, e.g., in wheat, barley, or the sugary2 mutant of maize leads to the loss of other proteins from the starch granule [229][230][231], and studies by Liu et al [231] showed that SSIIa was a central component of a protein complex with SSI and SBEIIb, and is involved in mediating the movement of all the components of this protein complex into the starch granule.…”