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The C‐terminal flexible region of branched‐chain polyamine synthase facilitates substrate specificity and catalysis
Author(s) -
Hidese Ryota,
Toyoda Masataka,
Yoshino Kenichi,
Fukuda Wakao,
Wihardja Gita Adhirani,
Kimura Seigo,
Fujita Junso,
Niitsu Masaru,
Oshima Tairo,
Imanaka Tadayuki,
Mizohata Eiichi,
Fujiwara Shinsuke
Publication year - 2019
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.14949
Subject(s) - polyamine , chemistry , catalysis , substrate (aquarium) , glutamine , stereochemistry , thermus thermophilus , biochemistry , amino acid , biology , escherichia coli , ecology , gene
Branched‐chain polyamine synthase (BpsA) catalyzes sequential aminopropyl transfer from the donor, decarboxylated S ‐adenosylmethionine (dc SAM ), 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 dc SAM 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.