Li Bin, Liang Jue, Phillips Margaret A, Michael Anthony J
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, U.S.A.
Biochem J. 2024 Sep 18;481(18):1241-1253. doi: 10.1042/BCJ20240411.
The only known pathway for biosynthesis of the polyamine norspermidine starts from aspartate β-semialdehyde to form the diamine 1,3-diaminopropane, which is then converted to norspermidine via a carboxynorspermidine intermediate. This pathway is found primarily in the Vibrionales order of the γ-Proteobacteria. However, norspermidine is also found in other species of bacteria and archaea, and in diverse single-celled eukaryotes, chlorophyte algae and plants that do not encode the known norspermidine biosynthetic pathway. We reasoned that products of polyamine catabolism could be an alternative route to norspermidine production. 1,3-diaminopropane is formed from terminal catabolism of spermine and spermidine, and norspermidine can be formed from catabolism of thermospermine. We found that the single-celled chlorophyte alga Chlamydomonas reinhardtii thermospermine synthase (CrACL5) did not aminopropylate exogenously-derived 1,3-diaminopropane efficiently when expressed in Escherichia coli. In contrast, it completely converted all E. coli native spermidine to thermospermine. Co-expression in E. coli of the polyamine oxidase 5 from lycophyte plant Selaginella lepidophylla (SelPAO5), together with the CrACL5 thermospermine synthase, converted almost all thermospermine to norspermidine. Although CrACL5 was efficient at aminopropylating norspermidine to form tetraamine norspermine, SelPAO5 oxidizes norspermine back to norspermidine, with the balance of flux being inclined fully to norspermine oxidation. The steady-state polyamine content of E. coli co-expressing thermospermine synthase CrACL5 and polyamine oxidase SelPAO5 was an almost total replacement of spermidine by norspermidine. We have recapitulated a potential hybrid biosynthetic-catabolic pathway for norspermidine production in E. coli, which could explain norspermidine accumulation in species that do not encode the known aspartate β-semialdehyde-dependent pathway.
多胺亚精胺生物合成的唯一已知途径是从天冬氨酸β-半醛开始形成二胺1,3-二氨基丙烷，然后通过羧基亚精胺中间体将其转化为亚精胺。该途径主要存在于γ-变形菌纲的弧菌目中。然而，亚精胺也存在于其他细菌和古菌物种以及多种单细胞真核生物、绿藻和植物中，这些生物并不编码已知的亚精胺生物合成途径。我们推测多胺分解代谢的产物可能是亚精胺产生的另一条途径。1,3-二氨基丙烷由精胺和亚精胺的末端分解代谢形成，亚精胺可由热精胺的分解代谢形成。我们发现，单细胞绿藻莱茵衣藻的热精胺合酶（CrACL5）在大肠杆菌中表达时，不能有效地将外源来源的1,3-二氨基丙烷氨丙基化。相反，它将所有大肠杆菌天然亚精胺完全转化为热精胺。石松植物卷柏的多胺氧化酶5（SelPAO5）与CrACL5热精胺合酶在大肠杆菌中共表达，几乎将所有热精胺转化为亚精胺。尽管CrACL5能有效地将亚精胺氨丙基化形成四胺亚精胺，但SelPAO5会将亚精胺氧化回亚精胺，通量平衡完全倾向于亚精胺氧化。共表达热精胺合酶CrACL5和多胺氧化酶SelPAO5的大肠杆菌的稳态多胺含量几乎完全是亚精胺取代了亚精胺。我们在大肠杆菌中重现了一条潜在的亚精胺产生的杂交生物合成-分解代谢途径，这可以解释在不编码已知的天冬氨酸β-半醛依赖性途径的物种中亚精胺的积累。
