Chromophore composition of the phycobiliprotein Cr-PC577 from the cryptophyte Hemiselmis pacifica
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The cryptophyte phycocyanin Cr-PC577 from Hemiselmis pacifica is a close relative of Cr-PC612 found in Hemiselmis virescens and Hemiselmis tepida. The two biliproteins differ in that Cr-PC577 lacks the major peak at around 612 nm in the absorption spectrum. Cr-PC577 was thus purified and characterized with respect to its bilin chromophore composition. Like other cryptophyte phycobiliproteins, Cr-PC577 is an (αβ)(α′β) heterodimer with phycocyanobilin (PCB) bound to the α-subunits. While one chromophore of the β-subunit is also PCB, mass spectrometry identified an additional chromophore with a mass of 585 Da at position β-Cys-158. This mass can be attributed to either a dihydrobiliverdin (DHBV), mesobiliverdin (MBV), or bilin584 chromophore. The doubly linked bilin at position β-Cys-50 and β-Cys-61 could not be identified unequivocally but shares spectral features with DHBV. We found that Cr-PC577 possesses a novel chromophore composition with at least two different chromophores bound to the β-subunit. Overall, our data contribute to a better understanding of cryptophyte phycobiliproteins and furthermore raise the question on the biosynthetic pathway of cryptophyte chromophores.
KeywordsCryptophyte Cr-PC577 Hemiselmis pacifica Dihydrobiliverdin Mesobiliverdin Phycobiliprotein Phycocyanin Phycocyanobilin
Basic Local Alignment Search Tool
Provasoli-Guillard Culture Collection for the Culture of Marine Phytoplankton (now NCMA, National Center for Marine Algae and Microbiota East Boothbay Maine, USA)
Ferredoxin-dependent bilin reductase
High performance liquid chromatography
Sodium dodecylsulfate polyacrylamide gel electrophoresis
KEO was supported by a PhD scholarship from the Studienstiftung des Deutschen Volkes e.V. whose support is kindly acknowledged. JEB acknowledges financial support for the Synapt G2-S mass spectrometer by the state of North Rhine Westphalia (Forschungsgroßgeräte der Länder) and NFD was supported by the German Research Foundation (DFG). KHE wishes to thank Prof. Michael Melkonian for access to lab and culturing facilities. We would like to thank Dr. Dirk Heinz and colleagues, Helmholtz Centre for Infection Research, Braunschweig, Germany for their help with N-terminal sequencing. Thanks are also due to Dr. Jessica Jordan for initial help with the project.
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