Side chain decoration of Anthocyanins; Mechanisms and Effects On functionality

Kallam, Kalyani (2012) Side chain decoration of Anthocyanins; Mechanisms and Effects On functionality. Doctoral thesis, University of East Anglia.

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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.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Users 2259 not found.
Date Deposited: 14 May 2013 10:59
Last Modified: 14 May 2013 10:59


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