Rhamnosyl transferase

Figure 6.1 Major branch pathways of flavonoid biosynthesis in Arabidopsis. Branch pathways, enzymes, and end products present in other plants but not Arabidopsis are shown in light gray. Abbreviations cinnamate-4-hydroxylase (C4H), chalcone isomerase (CHI), chalcone synthase (CHS), 4-coumarate CoA-ligase (4CL), dihydroflavonol 4-reductase (DFR), flavanone 3-hydroxylase (F3H), flavonoid 3 or 3 5 hydroxylase (F3 H, F3 5 H), leucoanthocyanidin dioxygenase (LDOX), leucoanthocyanidin reductase (LCR), O-methyltransferase (OMT), phenylalanine ammonia-lyase (PAL), rhamnosyl transferase (RT), and UDP flavonoid glucosyl transferase (UFGT).

The UGT78D1 gene of. f/rrz/frzwrz encodes a specific UDP-rhamnose flavonol-3-0-rhamnosyl-transferase with activity only on kaempferol and quercetin, out of various flavonoids tested. 

Figure 6-2. Biosynthesis of maysin proposed by McMullen et al. (2004) based on the analysis of flavones in the silks of maize salmon silk mutants, a. flavone 3 hydroxylase (encoded by the maize Prl gene), b. flavone synthase, c. C-glucosyltransferase, d. putative rhamnosyl transferase (encoded by the Salmon silk2 gene), e. the step(s) controlled by the Salmon silkl gene.

Fig. 1. Simplified diagram of the phenylpropanoid and flavonoid biosynthetic pathways. Enzymes that catalyze the reactions are placed on the left-hand side, and transcription factors on the right-hand side of the arrows. Both transcription factors for which their control over the enzymatic steps has been genetically proven, as well as transcription factors that have been shown to interact with promoters of the structural genes, are shown. PAL Phenylalanine ammonia lyase C4H cinnamate 4-hydroxylase 4CL 4-coumaroyl-coenzyme A ligase CHS chalcone synthase CHI chalcone-flavanone isomerase F3H flavanone 3(3-hydroxylase DFR dihydroflavonol 4-reductase AS anthocyanin synthase UFGT UDP glucose-flavonol glucosyl transferase RT anthocyanin rhamnosyl transferase...

Several glycosyltransferase genes in the gene clusters of S. enterica 0-antigen (serogroup B, C2, El) biosynthesis have been reported. In theses studies mannosyl- and rhamnosyl transferase genes were identified and characterized [142]. Mannosyl transferases and rhamnosyl transferases form two separate families, but there was no relation between them nor were any conserved motifs. 

Dihydroflavonol 4-reductase (DFR) converted dihydroflavonols (3-OH-flava-nones, 32) to leucoanthocyanidins (flavan-3,4-diols, 37). The leucoanthocyanidins (flavan-3,4-diols, 37) were converted by leucoanthocyanidin dioxygenase (LDOX) to 3-hydroxy-anthocyanidins (38). Finally, 3-hydroxy-antho-cyanidins (38) were converted by three enzymes of O-methyltransferase (OMT), UDPG-flavonoid glucosyl transferase (UFGT) and rhamnosyl transferase (UFGT) to anthocyanins (39) (Fig. 8) [23,24],... 

Yonekura-Sakakibara, K. et al. (2007) Identification of a flavonol 7-0-rhamnosyl-transferase gene determining flavonoid pattern... 

Frydman, A. et al. (2004) Citrus fruit bitter flavors isolation and functional characterization of the gene Cml, 2RhaT encoding a 1,2 rhamnosyl-transferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus. Plant J. 40, 88-100... 

Kamsteeg, J., Van Brederode, J., Hommels, C.H. and Van Nigtevecht, G. (1980) Identification, properties and genetic control of hydroxycinnamoy 1-coenzyme A antho-cyanidin 3-rhamnosyl (1 6) glucoside, 4 -hydroxycinnamoyl transferase isolated from petals of Silene dioica. Biochem. Physiol. Pfanzen, 175, 403-11. 

Each enzyme is specific for the sugar transferred, its nucleotide precursor, the residue to which it is transferred and the bond formed. All are effectively irreversible transfers and all the enzymes are membrane-bound. The rhamnosyl and mannosyl transferases can be solubilised with non-ionic... 

Sometimes, however, the distribution of B in A is neither regular nor random. An example is the occurrence of rhamnosyl residues in the a 1,4 galacturonan chains of pectinic acids. In this instance rhamnose and galact-uronic acid are too unlike each other to make it at all probable that a single transferase can add them both and it is very hard to see how the rhamnosyl insertion could take place other than by the action of specific transferases, which are in some way externally triggered. 

Hi) The Synthesis of the Short Branches of Pectins, There is no metabolic information as to the mechanisms by which these chains are formed, but the minimum necessary number of glycosyl transferases can be reasonably predicted. If structures of the types so far discovered (see above) were all to be constructed in the same pectinic acid, a minimum of six transferases would be required. Some pectins are simpler than this, but most are likely to be more complex. If the chains also occur on rhamnosyl residues, at least one more... 

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