4 research outputs found
CpeF is the bilin lyase that ligates the doubly linked phycoerythrobilin on -phycoerythrin in the cyanobacterium Fremyella diplosiphon
Phycoerythrin (PE) is a green light–absorbing protein present in the light-harvesting complex of cyanobacteria and red algae. The spectral characteristics of PE are due to its prosthetic groups, or phycoerythrobilins (PEBs), that are covalently attached to the protein chain by specific bilin lyases. Only two PE lyases have been identified and characterized so far, and the other bilin lyases are unknown. Here, using in silico analyses, markerless deletion, biochemical assays with purified and recombinant proteins, and site-directed mutagenesis, we examined the role of a putative lyase-encoding gene, cpeF, in the cyanobacterium Fremyella diplosiphon. Analyzing the phenotype of the cpeF deletion, we found that cpeF is required for proper PE biogenesis, specifically for ligation of the doubly linked PEB to Cys-48/Cys-59 residues of the CpeB subunit of PE. We also show that in a heterologous host, CpeF can attach PEB to Cys-48/Cys-59 of CpeB, but only in the presence of the chaperone-like protein CpeZ. Additionally, we report that CpeF likely ligates the A ring of PEB to Cys-48 prior to the attachment of the D ring to Cys-59. We conclude that CpeF is the bilin lyase responsible for attachment of the doubly ligated PEB to Cys-48/Cys-59 of CpeB and together with other specific bilin lyases contributes to the post-translational modification and assembly of PE into mature light-harvesting complexes
Structural and Biochemical Characterization of the Bilin Lyase CpcS from Thermosynechococcus elongatus
Cyanobacterial phycobiliproteins
have evolved to capture light
energy over most of the visible spectrum due to their bilin chromophores,
which are linear tetrapyrroles that have been covalently attached
by enzymes called bilin lyases. We report here the crystal structure
of a bilin lyase of the CpcS family from Thermosynechococcus
elongatus (<i>Te</i>CpcS-III). <i>Te</i>CpcS-III is a 10-stranded β barrel with two alpha helices and
belongs to the lipocalin structural family. <i>Te</i>CpcS-III
catalyzes both cognate as well as noncognate bilin attachment to a
variety of phycobiliprotein subunits. <i>Te</i>CpcS-III
ligates phycocyanobilin, phycoerythrobilin, and phytochromobilin to
the alpha and beta subunits of allophycocyanin and to the beta subunit
of phycocyanin at the Cys82-equivalent position in all cases. The
active form of <i>Te</i>CpcS-III is a dimer, which is consistent
with the structure observed in the crystal. With the use of the UnaG
protein and its association with bilirubin as a guide, a model for
the association between the native substrate, phycocyanobilin, and <i>Te</i>CpcS was produced