Physiology of Microorganisms, Faculty of Biology and Biotechnology, Ruhr-University Bochum, 44780 Bochum, Germany.
Biochem J. 2011 Oct 15;439(2):257-64. doi: 10.1042/BJ20110814.
PEB (phycoerythrobilin) is one of the major open-chain tetrapyrrole molecules found in cyanobacterial light-harvesting phycobiliproteins. In these organisms, two enzymes of the ferredoxin-dependent bilin reductase family work in tandem to reduce BV (biliverdin IXα) to PEB. In contrast, a single cyanophage-encoded enzyme of the same family has been identified to catalyse the identical reaction. Using UV-visible and EPR spectroscopy we investigated the two individual cyanobacterial enzymes PebA [15,16-DHBV (dihydrobiliverdin):ferredoxin oxidoreductase] and PebB (PEB:ferredoxin oxidoreductase) showing that the two subsequent reactions catalysed by the phage enzyme PebS (PEB synthase) are clearly dissected in the cyanobacterial versions. Although a highly conserved aspartate residue is critical for both reductions, a second conserved aspartate residue is only involved in the A-ring reduction of the tetrapyrrole in PebB and PebS. The crystal structure of PebA from Synechococcus sp. WH8020 in complex with its substrate BV at a 1.55 Å (1 Å=0.1 nm) resolution revealed further insight into the understanding of enzyme evolution and function. Based on the structure it becomes obvious that in addition to the importance of certain catalytic residues, the shape of the active site and consequently the binding of the substrate highly determines the catalytic properties.
藻红蛋白（PEB）是蓝藻光捕获藻胆蛋白中发现的主要开链四吡咯分子之一。在这些生物体中，两种铁氧还蛋白依赖性胆红素还原酶家族的酶协同作用将 BV（胆绿素 IXα）还原为 PEB。相比之下，已经鉴定出一种单一的噬菌体编码的相同家族的酶能够催化相同的反应。我们使用紫外可见和 EPR 光谱研究了两种单独的蓝藻酶 PebA [15,16-DHBV（二氢胆绿素）：铁氧还蛋白氧化还原酶]和 PebB（PEB：铁氧还蛋白氧化还原酶），表明噬菌体酶 PebS（PEB 合酶）催化的两个后续反应在蓝藻版本中明显分开。尽管高度保守的天冬氨酸残基对两种还原反应都至关重要，但第二个保守的天冬氨酸残基仅参与 PebB 和 PebS 中天冬氨酸残基的 A 环还原。来自聚球藻 sp. WH8020 的 PebA 与其底物 BV 的复合物的晶体结构在 1.55 Å（1 Å=0.1 nm）分辨率下进一步深入了解了酶进化和功能的理解。基于结构，除了某些催化残基的重要性之外，活性位点的形状以及因此底物的结合高度决定了催化特性。
