Fachbereich Biologie, Abteilung für Mikrobiologie, Technische Universität Kaiserslautern, Germany.
Cyanobakterielle Membranprotein Komplexe, Fakultät für Biologie und Biotechnologie, Ruhr-Universität Bochum, Germany.
FEBS J. 2020 Jan;287(2):284-294. doi: 10.1111/febs.15003. Epub 2019 Jul 26.
Substrate channeling is a widespread mechanism in metabolic pathways to avoid decomposition of unstable intermediates, competing reactions, and to accelerate catalytic turnover. During the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXα to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently converted by phycoerythrobilin:ferredoxin oxidoreductase to the final product phycoerythrobilin. Although substrate channeling has been postulated already a decade ago, detailed experimental evidence was missing. Using a new on-column assay employing immobilized enzyme in combination with UV-Vis and fluorescence spectroscopy revealed that both enzymes transiently interact and that transfer of the intermediate is facilitated by a significantly higher binding affinity of DHBV toward phycoerythrobilin:ferredoxin oxidoreductase. Concluding from the presented data, the intermediate DHBV is transferred via proximity channeling.
底物通道化是代谢途径中广泛存在的一种机制，可避免不稳定中间体的分解、竞争反应，并加速催化周转。在蓝藻中藻胆素的生物合成过程中，两种依赖铁氧还蛋白的胆红素还原酶参与将开链四吡咯胆红素 IXα还原为粉红色色素藻红胆素。第一个反应由 15,16-二氢胆红素：铁氧还蛋白氧化还原酶催化，并产生不稳定的中间产物 15,16-二氢胆红素（DHBV）。该中间产物随后由藻红胆素：铁氧还蛋白氧化还原酶转化为最终产物藻红胆素。尽管十多年前已经提出了底物通道化的假设，但缺乏详细的实验证据。使用新的柱上测定法，结合使用固定化酶和 UV-Vis 和荧光光谱学，揭示了两种酶瞬时相互作用，并且中间产物的转移是通过 DHBV 与藻红胆素：铁氧还蛋白氧化还原酶之间显著更高的结合亲和力来促进的。根据所提供的数据推断，中间产物 DHBV 通过临近通道化进行转移。
