6j26

Publication Abstract from PubMed

Branched-chain polyamine synthase (BpsA) catalyzes sequential aminopropyl transfer from the donor, decarboxylated S-adenosylmethionine (dcSAM), to the acceptor, linear-chain polyamine, resulting in the production of a quaternary-branched polyamine via tertiary branched polyamine intermediates. Here, we analyzed the catalytic properties and X-ray crystal structure of Tth-BpsA from Thermus thermophilus and compared them with those of Tk-BpsA from Thermococcus kodakarensis, which revealed differences in acceptor substrate specificity and C-terminal structure between these two enzymes. To investigate the role of the C-terminal flexible region in acceptor recognition, a region (QDEEATTY) in Tth-BpsA was replaced with that in Tk-BpsA (YDDEESSTT) to create chimeric Tth-BpsA C9, which showed a severe reduction in catalytic efficiency toward N(4) -aminopropylnorspermidine, but not toward N(4) -aminopropylspermidine, mimicking Tk-BpsA substrate specificity. Tth-BpsA C9 Tyr(346) and Thr(354) contributed to discrimination between tertiary branched-chain polyamine substrates, suggesting that the C-terminal region of BpsA recognizes acceptor substrates. Liquid chromatography-tandem mass spectrometry analysis on a Tk-BpsA reaction mixture with dcSAM revealed two aminopropyl groups bound to two of five aspartate/glutamate residues (Glu(339) , Asp(342) , Asp(343) , Glu(344) , and Glu(345) ) in the C-terminal flexible region. Mutating each of these five amino acid residues to asparagine/glutamine resulted in a slight decrease in activity. The quadruple mutant D342N/D343N/E344Q/E345Q exhibited a severe reduction in catalytic efficiency, suggesting that these aspartate/glutamate residues function to receive aminopropyl chains. In addition, the X-ray crystal structure of the Tk-BpsA ternary complex bound to N(4) -bis(aminopropyl)spermidine revealed that Asp(126) and Glu(259) interacted with the aminopropyl moiety in N(4) -aminopropylspermidine.

The C-terminal flexible region of branched-chain polyamine synthase facilitates substrate specificity and catalysis.,Hidese R, Toyoda M, Yoshino KI, Fukuda W, Wihardja GA, Kimura S, Fujita J, Niitsu M, Oshima T, Imanaka T, Mizohata E, Fujiwara S FEBS J. 2019 Jun 4. doi: 10.1111/febs.14949. PMID:31162806^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.