Homospermidine synthase

Pyrrolizidine alkaloids Homospermidine synthase Senecio vemalis, Senecio vulgaris... 

Bottcher, F., Adolph, R.-D. and Hartmann, T. 1993. Homospermidine synthase, the first pathway-specific enzyme in pyrrolozidine alkaloid biosynthesis. Phytochemistry, 32 679-689. 

Figure 9.2. Metabolism of pyrrolizidine alkaloids (PAs) in Senecio vernalis. The substrates for alkaloid biosynthesis, putrescine and spermidine, are derived from primary metabolism. Homospermidine, synthesized by homospermidine synthase (HSS), is the first pathway specific intermediate. It is exclusively incorporated into the necine base moiety of senecionine A-oxide, the backbone structure of all PAs found in this Senecio species. During allocation from the roots as site of synthesis to the shoots, it is chemically modified to provide the species specific PA-pattem.

MOLL, S., ANKE, S., KAHMANN, U., HANSCH, R., HARTMANN, T., OBER, D., Cell-specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloid pathway in Senecio vemalis, in comparison with its ancestor, deoxyhypusine synthase. Plant Physiol, 2002,130,47-57. 

OBER, D THOLL, D., MARTIN, W., HARTMANN, T Homospermidine synthase of Rhodopseudomonas viridis Substrate specificity and effects of the heterologously expressed enzyme on polyamine metabolism of Escherichia coli. J. Gen. Appl. Microbiol., 1996,42,411-419. 

THOLL, D., OBER, D MARTIN, W., KELLERMANN, J., HARTMANN, T, Purification, molecular cloning and expression in Escherichia coli of homospermidine synthase from Rhodopseudomonas viridis. Eur. J. Biochem., 1996, 240,373-379. 

OBER, D., HARTMANN, T., Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc. Natl. Acad. Sci. U. S. A., 1999,96, 14777-14782. 

Figure 2.4 Biosynthesis of the pyrrolizidine alkaloid. senecionine-N-oxide. ODC, ornithine decarboxylase ADC, arginine decarboxylase SPDS, spermidine synthase HHS, homospermidine synthase. (See Plate 9 in colour plate section.)...

There are two other examples for the recraitment of genes from primary metabolism. The homospermidine synthase from Senecio vernalis is derived from deoxyh T3usine synthase, an enzyme required for activation of translation factor 5A, and a serine carboxypeptidase-like protein that functions as an acyltransferase in secondary metabolism has been found in Arabidopsis thaliana. 

Scheme 5. Biosynthesis of pyrrolizidine alkaloids. A molecular clone has been isolated for only one biosynthetic enzyme. Abbreviation HSS, homospermidine synthase.

Figure 5.27 The role of homospermidine synthase (HSS) in pyrrolizidine alkaloid biosynthesis and deoxyhypusine synthase (DHS) in the activation of the eukaryotic initiation factor 5A (eIF5A).

Figure 5.28 Evolutionary origin of homospermidine synthase (HSS) by duphcation of the gene encoding deoxyhypnsine synthase (DHS). eIF5A(lys), the eukaryotic initiation factor 5A precursor protein with unmodified lysine residue, is only bound by DHS but not by HSS.

Fig. 2. Biogenetic links between A primary metabolism and B the alkaloid-specific pathway. CAP, N-carbamoylputrescine GABA, 4-aminobutyric acid. Inhibitors DFMA, a-difluorome-thylarginine, HEH, /1-hydroxyethylhydrazine. Enzymes 1, arginine decarboxylase 2, agmatine iminohydrolase 3, JV-carbamoylputrescine amidohydrolase 4, diamine oxidase 5, pyrroline dehydrogenase (NAD+-dependent) 6, spermidine synthase 7, a putrescine-producing poly-amine oxidase (H H-insensitive) 8, homospermidine synthase 9, an HEH-sensitive polyamine oxidase...

The enzyme catalyzing the formation of homospermidine was identified as a homospermidine synthase [26], an enzyme previously described from two bacterial sources [27,28] and seedlings of Lathyrus sativus [29]. None of these species produces PAs. One of the bacterial enzymes [28] has been purified. Bacterial homospermidine synthase was suggested to catalyze the following reaction ... 

Homospermidine synthase (HSS) activity was detected in root cultures of four Senecio and two Eupatorium species. The enzyme was partially purified from root cultures ofE. cannabinuniythe source with the highest specific activity... 

Fig. 3. Reactions catalyzed by bacterial and plant homospermidine synthase...

The relationship between deoxyhypusine synthase and homospermidine synthase becomes also evident by a comparison of their reactions. Deoxyhypusine synthase transfers the aminobutyl moiety of spermidine to the e-amino group of a single specific lysine residue in the elF-5A (Fig. 18). Homospermidine synthase catalyzes exactly the same reaction but uses putrescine instead of the elF-5A as acceptor for the aminobutyl moiety (Fig. 18). AH other mechanistic... 

Fig. 18. Homospermidine synthase (A) and deoxyhypusine synthase (B) catalyze analogous reactions. The two enzymes transfer an aminobutyl moiety from spermidine to a primary amino group of putrescine and a proteinous lysyl residue of a protein, respectively...

Fig. 19. Alignment of homospermidine synthase (HSS) amino acid sequence from Senecio ver-nalis (Sv) in comparison to deoxyhypusine synthase amino acid sequences from six different species. Sv, Senecio vernalis Nt, Nicotiana tabacumi Hs, Homo sapiens Sc, Saccharomyces cerevisiae Nc, Neurospora crassa Mj, Methanococcus jannaschii. Black boxes denote identical amino acid residues in all seven sequences, framed boxes conservative replacement...

Niemiiller D, Reimann A, Ober D (2012) Distinct cell-specific expression of homospermidine synthase involved in pyrrolizidine alkaloid biosynthesis in three species of the Boraginales. Plant Physiol Preview. doi 10.1104/pp. 112.195024... 

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