4tq2

Publication Abstract from PubMed

Phycobiliproteins are employed by cyanobacteria, red algae, glaucophytes and cryptophytes for light-harvesting and consist of apo-proteins covalently associated with open-chain tetrapyrrole chromophores. While the majority of organisms assemble the individual phycobiliproteins into larger aggregates called phycobilisomes, members of the cryptophytes use a single phycobiliprotein which is localized in the thylakoid lumen. The cryptophyte Guillardia theta uses phycoerythrin PE545 utilizing the unusual chromophore 15,16-dihydrobiliverdin (DHBV) in addition to phycoerythrobilin (PEB). Both, the biosynthesis and the attachment of chromophores to the apo-phycobiliprotein have not yet been investigated for cryptophytes. In the present study we identified and characterized enzymes involved in PEB biosynthesis. In addition, we present the first in depth biochemical characterization of a eukaryotic phycobiliprotein lyase (GtCPES). Plastid encoded HO (GtHo) was shown to convert heme into biliverdin IXalpha providing the substrate for a putative nucleus encoded DHBV:ferredoxin oxidoreductase (GtPEBA). A PEB:ferredoxin oxidoreductase (GtPEBB) was found to convert DHBV to PEB, which is the substrate for the phycobiliprotein lyase GtCPES. The X-ray structure of GtCPES was solved at 2.0 A revealing a 10 stranded beta-barrel with a modified lipocalin-fold. GtCPES is an S-type lyase specific for binding of phycobilins with reduced C15-C16 double bonds (DHBV, PEB). Site directed mutagenesis identified residues Glu-136 and Arg-146 being involved in phycobilin binding. Based on the crystal structure, a model for the interaction of GtCPES with the apo-phycobiliprotein CpeB is proposed and discussed.

Insights into the Biosynthesis and Assembly of Cryptophycean Phycobiliproteins.,Overkamp KE, Gasper R, Kock K, Herrmann C, Hofmann E, Frankenberg-Dinkel N J Biol Chem. 2014 Aug 5. pii: jbc.M114.591131. PMID:25096577^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.