Humboldt-University Berlin, Life Sciences Faulty, Institute of Biology/Plant Physiology, Philippstraße 13, Building 12, 10115, Berlin, Germany.
Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Molecular Plant Nutrition, OT Gatersleben, Corrensstrasse 3, D-06466, Seeland, Germany.
Plant J. 2018 May;94(3):485-496. doi: 10.1111/tpj.13869. Epub 2018 Mar 22.
Chlorophyll is synthesized from activated glutamate in the tetrapyrrole biosynthesis pathway through at least 20 different enzymatic reactions. Among these, the MgProto monomethylester (MgProtoME) cyclase catalyzes the formation of a fifth isocyclic ring to tetrapyrroles to form protochlorophyllide. The enzyme consists of two proteins. The CHL27 protein is proposed to be the catalytic component, while LCAA/YCF54 likely acts as a scaffolding factor. In comparison to other reactions of chlorophyll biosynthesis, this enzymatic step lacks clear elucidation and it is hardly understood, how electrons are delivered for the NADPH-dependent cyclization reaction. The present study intends to elucidate more precisely the role of LCAA/YCF54. Transgenic Arabidopsis lines with inactivated and overexpressed YCF54 reveal the mutual stability of YCF54 and CHL27. Among the YCF54-interacting proteins, the plastidal ferredoxin-NADPH reductase (FNR) was identified. We showed in N. tabacum and A. thaliana that a deficit of FNR1 or YCF54 caused MgProtoME accumulation, the substrate of the cyclase, and destabilization of the cyclase subunits. It is proposed that FNR serves as a potential donor for electrons required in the cyclase reaction and connects chlorophyll synthesis with photosynthetic activity.
叶绿素是通过四吡咯生物合成途径中的活化谷氨酸合成的，该途径需要至少 20 种不同的酶促反应。其中，MgProto 单甲酯（MgProtoME）环化酶催化五重环化反应，形成原叶绿素。该酶由两种蛋白质组成。CHL27 蛋白被认为是催化成分，而 LCAA/YCF54 可能充当支架因子。与叶绿素生物合成的其他反应相比，该酶促步骤缺乏明确的阐明，并且很难理解 NADPH 依赖性环化反应中电子是如何传递的。本研究旨在更精确地阐明 LCAA/YCF54 的作用。具有失活和过表达 YCF54 的转基因拟南芥品系揭示了 YCF54 和 CHL27 的相互稳定性。在 YCF54 相互作用的蛋白质中，鉴定出质体铁氧还蛋白-NADPH 还原酶（FNR）。我们在 N. tabacum 和 A. thaliana 中表明，FNR1 或 YCF54 的缺陷导致 MgProtoME 积累，即环化酶的底物，以及环化酶亚基的不稳定。据推测，FNR 作为环化酶反应所需电子的潜在供体，并将叶绿素合成与光合作用活性联系起来。
