Postranslational Modification of Phycobiliproteins from the Cryptophyte Guillardia theta

点击翻译按钮获取中文摘要

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.