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J. Biol. Chem., Vol. 283, Issue 23, 99921, June 6, 2008

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Fusion Confusion

Polyamines play essential roles in guiding normal growth and development. Within this family the most predominant members are spermidine and spermine, which are formed by the sequential addition of aminopropyl groups onto the precursor molecule putrescine. Currently, the crystal structures for the first three enzymes in this polyamine pathway (up to spermidine synthesis) have been solved. In this Paper of the Week, Hong Wu and colleagues complete the sequence and describe the first x-ray structure for spermine synthase, providing valuable insight into its mechanism of action while also revealing an unexpected fusion of genes. Human spermine synthase is a dimer of two identical subunits, with each subunit composed of three domains: the active site domain, which closely resembles spermidine synthase, a short linker domain, and finally an N-terminal domain that unexpectedly resembles the enzyme (AdoMetDC) that makes the aminopropyl donor groups. The unusual AdoMetDC domain contributes the most significant interactions that lead to dimer formation, and truncation studies show that it also serves as an activator of the catalytic domain. An evolutionary trace of this N-terminal fusion protein suggests that it arose early in eukaryotic development, after the divergence of fungi but before the rise of multicellular organisms.

Structure of spermine synthase monomer, highlighting the resemblance of its two domains to S-adenosylmethionine decarboxylase and spermidine synthase.

FOOTNOTES

See referenced article, J. Biol. Chem. 2008, 283, 16135-16146

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This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content Related Collections Papers Of The Week Social Bookmarking                      What's this?