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Title: Side chain decoration of anthocyanins : mechanisms and effects on functionality
Author: Kallam, Kalyani
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2012
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Anthocyanins are plant pigments offering a range of colours to fruits and flowers. Many properties of anthocyanins are influenced by the degree and type of side chain modifications. Though much is known about the biosynthesis of anthocyanins and the enzymes involved in side-chain decoration, there is limited understanding of the structural features of anthocyanin acyltransferases that determine their substrate preference. Anthocyanin acyltransferases belong to the BAHD family of enzymes and are involved in acylation. Through mutagenesis I showed that an arginine positioned close to motif-1 in aliphatic anthocyanin acyltransferase determines the enzyme’s specificity for malonyl transfer. Modification of arginine to phenylalanine in Ch3MAT, led to gain of acetylation property. This study thus suggests that CoA interacting residues are conserved in aliphatic acyltansferases. A phenylalanine in a similar position, close to motif 1 in aromatic anthocyanin acyltransferases is crucial for the specificity for aromatic-CoA of aromatic acyltransferases. To understand the influence of different side-chain modifications on the formation of anthocyanic vacuolar inclusions (AVIs), I showed that coumaroylation of anthocyanins leads to AVI formation when high levels of anthocyanins are accumulating. Malonylation does not lead to the formation of AVIs, suggesting that the ability of aromatic moieties to form intra-molecular stacks can cause formation of AVIs. Neither the presence of flavonols nor light or high amounts of anthocyanins can lead to the formation of AVIs. Therefore, the type of decoration mainly aromatic acylation of anthocyanins is responsible for AVI formation. From understanding the molecular mechanisms of acyltransferases for side chain decoration to their activity, anthocyanins can be engineered by anthocyanin acyltransferases in plants for novel functionalities. I showed that coumaroylation of anthocyanins promotes copigmentation more effectively than 5-glucosylation. 5- glucosylation, together with coumaroylation, offered stability to anthocyanins, both invitro and in-vivo. I also showed that flavonols copigment better than phenolics with anthocyanins, a property which could be useful for developing natural food colours. Thus, my study provided an in-depth investigation from molecular mechanisms to final applications of side chain decoration of anthocyanins.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available