The C‐terminal flexible region of branched‐chain polyamine synthase facilitates substrate specificity and catalysis. (21st June 2019)

• Record Type: Journal Article
• Authors: Hidese, Ryota; Toyoda, Masataka; Yoshino, Ken‐ichi; Fukuda, Wakao; Wihardja, Gita Adhirani; Kimura, Seigo; Fujita, Junso; Niitsu, Masaru; Oshima, Tairo; Imanaka, Tadayuki; Mizohata, Eiichi; Fujiwara, Shinsuke
• Is Part Of: FEBS journal. Volume 286:Number 19(2019)
• Page Start: 3926
• Page End: 3940
• Publication Date: 2019-06-21
• Subjects: branched‐chain polyamine -- crystal structure -- enzyme mechanism -- thermophile; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pathology, Molecular -- Periodicals; 572
• DOI: 10.1111/febs.14949
• Languages: English
• ISSNs: 1742-464X

Abstract

Abstract : 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. Abstract : Branched‐chain polyamine synthase (BpsA) catalyzes aminopropyl transfer from decarboxylated S ‐adenosylmethionine to linear‐chain polyamines, resulting in the production of branched‐chain polyamines, which contribute to microbial survival at high temperatures. Here, we show that the C‐terminal flexible region of BpsA recognizes the tertiary branched‐chain polyamine substrates and also functions to receive aminopropyl chains as carrier, supporting the proposed ping‐pong Bi–Bi mechanism.