Postranslational Modification of Phycobiliproteins from the Cryptophyte Guillardia theta

海洋蓝藻原绿球藻是热带和亚热带海洋中最丰富的浮游植物之一。与其他蓝藻不同的是，原绿球藻具有Chla/b结合天线，只有藻红蛋白（PE）形式的藻胆异构体残余物。此外，所有原绿球藻基因组都携带一套完整的酶，用于合成藻胆素、藻红蛋白（phycoythrbilin， PEB）和藻蓝胆素。原绿球藻宿主细胞需要PebA和PebB两种酶来进行PEB的生物合成，感染它们的噬藻体携带一种双功能酶PebS，它结合了两种宿主酶的活性。在这个建议的范围内，我们试图了解宿主和噬藻酶之间的机制和结构差异。在提案的第二部分，我们将研究藻胆素随后如何转移并附着到载脂蛋白上。因此，几种假定的藻胆蛋白裂解酶将被研究其结合和转移胆囊蛋白到载脂蛋白的特定保守半胱氨酸残基的能力。作为长期目标，我们有兴趣了解PE在海洋原绿球藻中的功能。

The marine cyanobacterium Prochlorococcus marinus is one of the most abundant phytoplankton in tropical and subtropical oceans. Unlike other cyanobacteria, Prochlorococcus sp. possesses an Chla/b-binding antenna and only remnants of the phycobilisomes in the form of a phycoerythrin (PE). In addition, all Prochlorococcus genomes carry a full set of enzyme necessary to synthesize the phycobilins phycoerythrobilin (PEB) and phycocyanobilin. While Prochlorococcus host cells require two enzymes PebA and PebB for PEB biosynthesis, a cyanophage that infects them carries a bifunctional enzyme PebS which combines both host enzyme acitivities. Within the scope of this proposal we seek to understand the mechanistic and structural differences between the host and cyanophage enzymes. In the second part of the proposal we will investigate how the phycobilins are subsequently transferred and attached to the apo-phycobiliprotein. Therefore, several putative phycobiliprotein lyases will be investigated with repect to their ability to bind and transfer bilin to specific conserved cysteine residues of the apo-protein. As a long term goal we are interested to understand the function of PE in Prochlorococcus marinus.