Takahashi Yoshihiro, Ono Kaede, Akamine Yuuta, Asano Takuya, Ezaki Masatoshi, Mouri Itsupei
Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kyushu Sangyo University, 2-3-1 Matsukadai Higashi-ku, Fukuoka, 813-8503, Japan.
J Plant Res. 2018 Mar;131(2):341-348. doi: 10.1007/s10265-017-0989-2. Epub 2017 Oct 24.
To understand the polyamine (PA) catabolic pathways in Brachypodium distachyon, we focused on the flavin-containing polyamine oxidase enzymes (PAO), and characterized them at the molecular and biochemical levels. Five PAO isoforms were identified from database searches, and we named them BdPAO1 to BdPAO5. By gene expression analysis using above-ground tissues such as leaf, stem and inflorescence, it was revealed that BdPAO2 is the most abundant PAO gene in normal growth conditions, followed by BdPAO3 and BdPAO4. BdPAO1 and BdPAO5 were expressed at very low levels. All Arabidopsis thaliana and rice orthologs belonging to the same clade as BdPAO2, BdPAO3 and BdPAO4 have conserved peroxisome-targeting signal sequences at their C-termini. Amino acid sequences of BdPAO2 and BdPAO4 also showed such a sequence, but BdPAO3 did not. We selected the gene with the highest expression level (BdPAO2) and the peroxisome-targeting signal lacking PAO (BdPAO3) for biochemical analysis of substrate specificity and catabolic pathways. BdPAO2 catalyzed conversion of spermine (Spm) or thermospermine to spermidine (Spd), and Spd to putrescine, but its most-favored substrate was Spd. In contrast, BdPAO3 favored Spm as substrate and catalyzed conversion of tetraamines to Spd. These results indicated that the major PAOs in B. distachyon have back-conversion activity.
为了解短柄草中多胺（PA）的分解代谢途径，我们聚焦于含黄素的多胺氧化酶（PAO），并在分子和生化水平上对其进行了表征。通过数据库搜索鉴定出了5种PAO亚型，我们将它们命名为BdPAO1至BdPAO5。通过对叶、茎和花序等地上组织进行基因表达分析，结果显示在正常生长条件下，BdPAO2是最丰富的PAO基因，其次是BdPAO3和BdPAO4。BdPAO1和BdPAO5的表达水平非常低。与BdPAO2、BdPAO3和BdPAO4属于同一进化枝的所有拟南芥和水稻直系同源物在其C端都有保守的过氧化物酶体靶向信号序列。BdPAO2和BdPAO4的氨基酸序列也显示出这样的序列，但BdPAO3没有。我们选择了表达水平最高的基因（BdPAO2）和缺乏过氧化物酶体靶向信号的PAO（BdPAO3）进行底物特异性和分解代谢途径的生化分析。BdPAO2催化精胺（Spm）或热精胺转化为亚精胺（Spd），以及Spd转化为腐胺，但它最偏好的底物是Spd。相比之下，BdPAO3偏好Spm作为底物，并催化四胺转化为Spd。这些结果表明，短柄草中的主要PAO具有逆向转化活性。
