Department of Physiology of Microorganisms, Faculty of Biology and Biotechnology, Ruhr-University Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany.
J Biol Chem. 2010 Nov 26;285(48):37561-9. doi: 10.1074/jbc.M110.172619. Epub 2010 Sep 28.
In contrast to the majority of cyanobacteria, the unicellular marine cyanobacterium Prochlorococcus marinus MED4 uses an intrinsic divinyl-chlorophyll-dependent light-harvesting system for photosynthesis. Despite the absence of phycobilisomes, this high-light adapted strain possesses β-phycoerythrin (CpeB), an S-type lyase (CpeS), and enzymes for the biosynthesis of phycoerythrobilin (PEB) and phycocyanobilin. Of all linear tetrapyrroles synthesized by Prochlorococcus including their 3Z- and 3E-isomers, CpeS binds both isomers of PEB and its biosynthetic precursor 15,16-dihydrobiliverdin (DHBV). However, dimerization of CpeS is independent of bilins, which are tightly bound in a complex at a ratio of 1:1. Although bilin binding by CpeS is fast, transfer to CpeB is rather slow. CpeS is able to attach 3E-PEB and 3Z-PEB to dimeric CpeB but not DHBV. CpeS transfer of 3Z-PEB exclusively yields correctly bound βCys(82)-PEB, whereas βCys(82)-DHBV is a side product of 3E-PEB transfer. Spontaneous 3E- and 3Z-PEB addition to CpeB is faulty, and products are in both cases βCys(82)-DHBV and likely a PEB bound at βCys(82) in a non-native configuration. Our data indicate that CpeS is specific for 3Z-PEB transfer to βCys(82) of phycoerythrin and essential for the correct configuration of the attachment product.
与大多数蓝藻不同，单细胞海洋蓝藻聚球藻 MED4 利用内在的二乙烯基-叶绿素依赖性光捕获系统进行光合作用。尽管没有藻胆体，但这种高光适应株系拥有β-藻红蛋白（CpeB）、一种 S 型裂解酶（CpeS）和藻胆红蛋白（PEB）和藻蓝胆素生物合成所需的酶。在聚球藻合成的所有线性四吡咯中，包括它们的 3Z-和 3E-异构体，CpeS 结合 PEB 的两种异构体及其生物合成前体 15,16-二氢胆红素（DHBV）。然而，CpeS 的二聚化独立于紧密结合在复合物中的 bilins，比例为 1:1。虽然 CpeS 与 bilins 的结合速度很快，但向 CpeB 的转移速度较慢。CpeS 能够将 3E-PEB 和 3Z-PEB 连接到二聚体 CpeB 上，但不能连接 DHBV。CpeS 将 3Z-PEB 转移到 CpeB 上，只会生成正确结合的 βCys(82)-PEB，而 3E-PEB 转移的产物是 βCys(82)-DHBV。3E-和 3Z-PEB 自发添加到 CpeB 上是错误的，在这两种情况下，产物都是 βCys(82)-DHBV，并且可能是在非天然构型中结合在 βCys(82)上的 PEB。我们的数据表明，CpeS 特异性地将 3Z-PEB 转移到藻红蛋白的 βCys(82)上，对于附着产物的正确构型是必不可少的。
