title: Molecular evolution by change of function. Alkaloid-specific homospermidine synthase retained all properties of deoxyhypusine synthase except binding the eIF5A precursor protein.
abstract: Deoxyhypusine synthase participates in the post-translational activation of the eukaryotic initiation factor 5A (eIF5A). The enzyme transfers the aminobutyl moiety of spermidine to a specific lysine residue in the eIF5A precursor protein, i.e. eIF5A(lys). Homospermidine synthase catalyzes an analogous reaction but uses putrescine instead of eIF5A(lys) as substrate yielding the rare polyamine homospermidine as product. Homospermidine is an essential precursor in the biosynthesis of pyrrolizidine alkaloids, an important class of plant defense compounds against herbivores. Sequence comparisons of the two enzymes indicate an evolutionary origin of homospermidine synthase from ubiquitous deoxyhypusine synthase. The two recombinant enzymes from Senecio vernalis were purified, and their properties were compared. Protein-protein binding and kinetic substrate competition studies confirmed that homospermidine synthase, in comparison to deoxyhypusine synthase, lost the ability to bind the eIF5A(lys) to its surface. The two enzymes show the same unique substrate specificities, catalyze the aminobutylation of putrescine with the same specific activities, and exhibit almost identical Michaelis kinetics. In conclusion, homospermidine synthase behaves like a deoxyhypusine synthase that lost its major function (aminobutylation of eIF5A precursor protein) but retained unaltered its side activity (aminobutylation of putrescine). It is suggested as having evolved from deoxyhypusine synthase by gene duplication and being recruited for a new function.
authors.affiliation: Institut für Pharmazeutische Biologie, Technische Universität Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
authors.forename: Dietrich
authors.initials: D
authors.lastname: Ober
authors.forename: Reiner
authors.initials: R
authors.lastname: Harms
authors.forename: Ludger
authors.initials: L
authors.lastname: Witte
authors.forename: Thomas
authors.initials: T
authors.lastname: Hartmann
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D008401:Gas Chromatography-Mass Spectrometry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000378:metabolism*; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism; D011700:Putrescine / Q000494:pharmacology; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013095:Spermidine / Q000378:metabolism; D013379:Substrate Specificity; D000097574:Eukaryotic Translation Initiation Factor 5A
chemical_list: D019883:Alkyl and Aryl Transferases; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010448:Peptide Initiation Factors; D011498:Protein Precursors; D011700:Putrescine; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D013095:Spermidine; D000097574:Eukaryotic Translation Initiation Factor 5A; C063507:deoxyhypusine synthase; C028376:homospermidine synthetase