Spermidine synthase

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spermidine synthase
1iy9.jpg
Spermidine synthase tetramer, Bacillus subtilis
Identifiers
Symbol SRM
Alt. symbols SRML1
Entrez 6723
HUGO 11296
OMIM 182891
RefSeq NM_003132
UniProt P19623
Other data
EC number 2.5.1.16
Locus Chr. 1 p36-p22

Spermidine synthase is an enzyme (EC 2.5.1.16) that catalyzes the transfer of the propylamine group from S-adenosylmethioninamine to putrescine in the biosynthesis of spermidine. The systematic name is S-adenosyl 3-(methylthio)propylamine:putrescine 3-aminopropyltransferase and it belongs to the group of aminopropyl transferases. It does not need any cofactors. Most spermidine synthases exist in solution as dimers.[1]

Specificity[edit]

With exception of the spermidine synthases from Thermotoga maritimum and from Escherichia coli, which accept different kinds of polyamines, all enzymes are highly specific for putrescine.[2] No known spermidine synthase can use S-adenosyl methionine. This is prevented by a conserved aspartatyl residue in the active site, which is thought to repel the carboxyl moiety of S-adenosyl methionine.[3] The putrescine-N-methyl transferase whose substrates are putrescine and S-adenosyl methionine and which is evolutionary related to the spermidine synthases lacks this aspartyl residue.[4] It is even possible to convert the spermidine synthase by some mutations to a functional putrescine-N-methyltransferase.[5]

Mechanism[edit]

It is assumed that the synthesis of spermidine follows the Sn2 mechanism.[6] There is some uncertainty if the reaction occurs via a ping-pong or via a ternary-complex mechanism. Some kinetic data, but not all, suggest a ping-pong mechanism,[7] while the investigation of the stereochemical path of the reaction argues for a ternary-complex mechanism.[8] Prior to the nucleophilic attack of the putrescine onto the S-adenosylmethioninamine the putrescine has to be deprotonated rendering the nitrogen nucleophilic since the putrescine is protonated at physiological pH and is therefore inactive.

Inhibitors[edit]

The spermidine synthase can be inhibited by a wide variety of analogues of putrescine, S-adenosyl methioninamine and transition state analogues as Adodato (for further information see here)

See also[edit]

References[edit]

  1. ^ Ikeguchi Y, Bewley MC, Pegg AE (January 2006). "Aminopropyltransferases: function, structure and genetics". Journal of Biochemistry. 139 (1): 1–9. doi:10.1093/jb/mvj019. PMID 16428313. 
  2. ^ Wu H, Min J, Ikeguchi Y, Zeng H, Dong A, Loppnau P, Pegg AE, Plotnikov AN (July 2007). "Structure and mechanism of spermidine synthases". Biochemistry. 46 (28): 8331–9. doi:10.1021/bi602498k. PMID 17585781. 
  3. ^ Korolev S, Ikeguchi Y, Skarina T, Beasley S, Arrowsmith C, Edwards A, Joachimiak A, Pegg AE, Savchenko A (January 2002). "The crystal structure of spermidine synthase with a multisubstrate adduct inhibitor". Nature Structural Biology. 9 (1): 27–31. doi:10.1038/nsb737. PMC 2792006Freely accessible. PMID 11731804. 
  4. ^ Biastoff S, Brandt W, Dräger B (2009-10-01). "Putrescine N-methyltransferase--the start for alkaloids". Phytochemistry. Evolution of Metabolic Diversity. 70 (15-16): 1708–18. doi:10.1016/j.phytochem.2009.06.012. PMID 19651420. 
  5. ^ Junker A, Fischer J, Sichhart Y, Brandt W, Dräger B (2013-01-01). "Evolution of the key alkaloid enzyme putrescine N-methyltransferase from spermidine synthase". Frontiers in Plant Science. 4: 260. doi:10.3389/fpls.2013.00260. PMC 3725402Freely accessible. PMID 23908659. 
  6. ^ Golding B, Nassereddin lK, Billington D. "The Biosynthesis of Spermidine. Part I : Biosynthesis of Spermidine from L-[3,4-13C2] Methionine and L-[2,3,3-2H3] Methionine". J. Chem. Soc. Perkin Trans. 
  7. ^ Yoon SO, Lee YS, Lee SH, Cho YD (June 2000). "Polyamine synthesis in plants: isolation and characterization of spermidine synthase from soybean (Glycine max) axes". Biochimica et Biophysica Acta. 1475 (1): 17–26. doi:10.1016/s0304-4165(00)00039-8. PMID 10806333. 
  8. ^ Golding B, Nassereddin I. "The Biosynthesis of Spermidine. Part 3: The Stereochemistry of the Formationof the N-CH2, Group in the Biosynthesis of Spermidine". J. Chem. Soc. Perkin Trans.: 2017. doi:10.1039/P19850002017. 

External links[edit]