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Different polyamine pathways from bacteria have replaced eukaryotic spermidine biosynthesis in ciliates T etrahymena thermophila and P aramecium tetaurelia
Author(s) -
Li Bin,
Kim Sok Ho,
Zhang Yang,
Hanfrey Colin C.,
Elliott Katherine A.,
Ealick Steven E.,
Michael Anthony J.
Publication year - 2015
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13066
Subject(s) - spermidine , biology , polyamine , biochemistry , tetrahymena , spermine , enzyme
Summary The polyamine spermidine is absolutely required for growth and cell proliferation in eukaryotes, due to its role in post‐translational modification of essential translation elongation factor e IF 5 A , mediated by deoxyhypusine synthase. We have found that free‐living ciliates T etrahymena and P aramecium lost the eukaryotic genes encoding spermidine biosynthesis: S ‐adenosylmethionine decarboxylase ( AdoMetDC ) and spermidine synthase ( S pd S yn). In T etrahymena , they were replaced by a gene encoding a fusion protein of bacterial AdoMetDC and S pd S yn, present as three copies. In P aramecium , a bacterial homospermidine synthase replaced the eukaryotic genes. Individual AdoMetDC – S pd S yn fusion protein paralogues from T etrahymena exhibit undetectable AdoMetDC activity; however, when two paralogous fusion proteins are mixed, AdoMetDC activity is restored and spermidine is synthesized. Structural modelling indicates a functional active site is reconstituted by sharing critical residues from two defective protomers across the heteromer interface. P aramecium was found to accumulate homospermidine, suggesting it replaces spermidine for growth. To test this concept, a budding yeast spermidine auxotrophic strain was found to grow almost normally with homospermidine instead of spermidine. Biosynthesis of spermidine analogue aminopropylcadaverine, but not exogenously provided norspermidine, correlated with some growth. Finally, we found that diverse single‐celled eukaryotic parasites and multicellular metazoan S chistosoma worms have lost the spermidine biosynthetic pathway but retain deoxyhypusine synthase.