pH‐dependent structural conformations of B‐phycoerythrin from Porphyridium cruentum

Abstract

B-phycoerythrin from the red alga Porphyridium cruentum was crystallized using the technique of capillary counter-diffusion. Crystals belonging to the space group R3 with almost identical unit cell constants and diffracting to 1.85 and 1.70 Å were obtained at pH values of 5 and 8, respectively. The most important difference between structures is the presence of the residue His88a in two different conformations at pH 8. This residue is placed next to the chromophore phycoerythrobilin PEB82a and the new conformation results in the relocation of the hydrogen-bond network and hydration around PEB82a, which probably contributes to the observed pH dependence of the optical spectrum associated with this chromophore.Comparison with the structures of B-phycoerythrin from other red algae shows differences in the conformation of the A-ring of the chromophore PEB139a. This conformational difference in B-phycoerythrin from P. cruentum enables the formation of several hydrogen bonds that connect PEB139a with the chromophore PEB158b at the (ab) 3 hexamer association interface. The possible influence of these structural differences on the optical spectrum and the ability of the protein to perform energy transfer are discussed, with the two pH-dependent conformations of His88a and PEB82a being proposed as representing critical structural features that are correlated with the pH dependence of the optical spectrum and transient optical states during energy transfer. DatabaseStructural data have been deposited in the Protein Data Bank under accession numbers 3V58 and 3V57. Structured digital abstract• B-phycoerythrin beta and B-phycoerythrin alpha bind by x-ray crystallography (View interaction)Abbreviations PDB, Protein Data Bank; PEB, phycoerythrobilin; PUB, phycourobilin.

Structural Properties of Phycoerythrin from DulsePalmaria palmata

“…Phycoerythrobilins were linked covalently with each of aCys82, aCys139, bCys82 and bCys158, whereas a phycourobilin was linked doubly to bCys50 and bCys61. The presence of chromophores at these sites is highly conserved among PEs of which structures have been reported (Lundell et al 1984;Chang et al 1996;Ritter et al 1999;Contreras-Martel et al 2001;Camara-Artigas et al 2012). Taken these observations together, we concluded that dulse PE has structural characteristics common to other PEs.…”

“…; Camara‐Artigas et al . ). Taken these observations together, we concluded that dulse PE has structural characteristics common to other PEs.…”

Connecting color with assembly in the fluorescent B‐phycoerythrin protein complex

“…2A, Table 1). This value is in the middle between the value reported from size exclusion chromatography (272 AE 5 kDa) [12] and the widely accepted molecular weight for B-PE of~240 kDa [10,24], thus we attribute these peaks to the intact B-PE protein complex. Peaks were also observed at the lower m/z region corresponding to a protein complexes of 39 304 Da and 117 955 Da and at higher m/z corresponding to a complex of 528 kDa in size.…”

“…In contrast, the γ subunit is predicted to contain four bilin subunits; two PEB and two phycourobilins (PUB) . Physiologically, B‐PE is thought to reside as a large macromolecular complex composed of two [(αβ) 2 ] 3 hexamers and a single γ polypeptide . The specific inter‐ and intramolecular interactions present within the complex are crucial for B‐PE's role in light transmission.…”

Color Stability of Phycoerythrin Crude Extract (PECE) from Rhodomonas Salina Toward Physicochemical Factors

“…According to González-Ramírez et al (2014), changes in the state of protonation on amino acid residues have a large effect on changes in spectral properties of PB. Spectroscopic changes due to low pH may be the result of differences in the state of protonation in the propionate group in the structure of PEB or in the aspartate residues that bind to the group (Camara-Artigas et al, 2012).…”