Postranslational Modification of Phycobiliproteins from the Cryptophyte Guillardia theta

海洋蓝藻Prochlorococcus marinus是热带和亚热带海洋中最丰富的浮游植物之一。与其他蓝细菌不同，原绿球藻具有Chla/b结合天线，只有藻胆体的残余物以藻红蛋白（PE）的形式存在。此外，所有原绿球藻基因组携带一整套合成藻胆素藻红胆素（PEB）和藻蓝胆素所必需的酶。虽然原绿球藻宿主细胞需要两种酶PebA和PebB用于PEB生物合成，但感染它们的噬藻体携带结合两种宿主酶活性的双功能酶PebS。在这个建议的范围内，我们试图了解宿主和噬藻体酶之间的机制和结构差异。在第二部分的建议，我们将调查如何藻胆素随后转移和附着到脱辅基藻胆蛋白。因此，几个假定的藻胆蛋白裂解酶将被调查与respect他们的能力，结合和转移胆色素的特定保守的半胱氨酸残基的脱辅基蛋白。作为一个长期的目标，我们有兴趣了解PE在原绿球藻中的功能。

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.