Kosugi Naoki, Araki Takuma, Fujita Junpei, Tanaka Satoru, Fujiwara Taketomo
Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan.
PLoS One. 2017 Dec 28;12(12):e0189913. doi: 10.1371/journal.pone.0189913. eCollection 2017.
Halophilic euryarchaea lack many of the genes necessary for the protoporphyrin-dependent heme biosynthesis pathway previously identified in animals and plants. Bioinformatic analysis suggested the presence of two heme biosynthetic processes, an Fe-coproporphyrinogen III (coproheme) decarboxylase (ChdC) pathway and an alternative heme biosynthesis (Ahb) pathway, in Haloferax volcanii. PitA is specific to the halophilic archaea and has a unique molecular structure in which the ChdC domain is joined to the antibiotics biosynthesis monooxygenase (ABM)-like domain by a histidine-rich linker sequence. The pitA gene deletion variant of H. volcanii showed a phenotype with a significant reduction of aerobic growth. Addition of a protoheme complemented the phenotype, supporting the assumption that PitA participates in the aerobic heme biosynthesis. Deletion of the ahbD gene caused a significant reduction of only anaerobic growth by denitrification or dimethylsulfoxide (DMSO) respiration, and the growth was also complemented by addition of a protoheme. The experimental results suggest that the two heme biosynthesis pathways are utilized selectively under aerobic and anaerobic conditions in H. volcanii. The molecular structure and physiological function of PitA are also discussed on the basis of the limited proteolysis and sequence analysis.
嗜盐广古菌缺乏许多动物和植物中先前鉴定出的原卟啉依赖性血红素生物合成途径所需的基因。生物信息学分析表明，嗜盐栖热菌中存在两种血红素生物合成过程，即铁原卟啉原III（粪卟啉）脱羧酶（ChdC）途径和另一种血红素生物合成（Ahb）途径。PitA是嗜盐古菌特有的，具有独特的分子结构，其中ChdC结构域通过富含组氨酸的连接序列与抗生素生物合成单加氧酶（ABM）样结构域相连。嗜盐栖热菌的pitA基因缺失变体表现出需氧生长显著减少的表型。添加原血红素可补充该表型，支持了PitA参与需氧血红素生物合成的假设。ahbD基因的缺失仅导致通过反硝化或二甲基亚砜（DMSO）呼吸进行的厌氧生长显著减少，添加原血红素也可补充生长。实验结果表明，嗜盐栖热菌在需氧和厌氧条件下选择性地利用这两种血红素生物合成途径。还基于有限的蛋白水解和序列分析讨论了PitA的分子结构和生理功能。
