Crystallization and 2.2 Å resolution structure of R-phycoerythrin fromGracilaria chilensis: a case of perfect hemihedral twinning

Abstract

R-phycoerythrin, a light-harvesting component from the red algae Gracilaria chilensis, was crystallized by vapour diffusion using ammonium sulfate as precipitant agent. Red crystals grew after one week at 293 K and diffracted to 2.70 A resolution. Three serial macroseeding assays were necessary to grow a second larger crystal to dimensions of 0.68 x 0.16 x 0.16 mm. This crystal diffracted to 2.24 A resolution using synchrotron radiation at beamline BM14 of the European Synchrotron Radiation Facility (ESRF) at Grenoble, France and was used for structure determination. Data were collected at 100 K to a completeness of 98.6%. The crystal was trigonal, space group R3, with unit-cell parameters a = b = 187.3, c = 59.1 A, alpha = beta = 90, gamma = 120 degrees. Data treatment using the CCP4 suite of programs indicated that the crystal was twinned ((I(2))/(I)(2) = 1.41). Molecular replacement was performed with AMoRe using the R-phycoerythrin from Polysiphonia urceolata [Chang et al. (1996), J. Mol. Biol. 249, 424-440] as a search model. In order to overcome the twinning problem, SHELX97 was used for the crystallographic refinement. The twin fraction was 0.48, indicating a nearly perfect hemihedrally twinned crystal. The final R(work) and R(free) factors are 0.16 and 0.25, respectively. All the residues and chromophores of the alpha- and beta-chains are well defined in the electron-density maps. Some residues belonging to the gamma-linker are also recognizable.

The structure at 2 Å resolution of Phycocyanin from Gracilaria chilensis and the energy transfer network in a PC–PC complex

“…Aspartic acids (D α 13 , D β 13 , D β 39 ) interact with A and D rings of the respective chromophore. The involvement of Aspartic acids maintaining the curvature of phycobilins has been reported in all the phycobiliproteins [7,44] and it may be a relevant feature for the biological activity. The docking procedure performed by ZDOCK [29] involved a rigid body interaction of two hexamers of phycocyanin (PC).…”

“…The three dimensional structure of phycoerythrin from this algae was reported in 2001 [7]. The structure of the next component of the rods, phycocyanin, is now presented in this paper.…”

“…The phycobilisome of Gracilaria chilensis contains three phycobiliproteins: Phycoerythrin (PE), phycocyanin (PC) and allophycocyanin (APC) [6,7]. The absorption and emission spectra of these proteins overlap, which allows a non-radiative, direct and efficient transfer of the excitation energy among them (PEλ This transfer is channeled along an energy gradient from the rods to the core and finally transferred to chlorophyll a in the thylakoid membrane [1,3].…”

In silico model of an antenna of a phycobilisome and energy transfer rates determination by theoretical Förster approach

“…The hexamers present a ring-like shape that allows them to pile up to form the rod. The three-dimensional structures of PE (PDB code: 1eyx) 4 and PC (PDB code: 2vb8) 5 from this algae have been determined previously in our group, and the structure of both proteins is shown in Figure 1(B,C), respectively. Table I 3,6 shows their chromophore composition and the main spectroscopic absorption and emission wavelengths.…”

Antitumor function and mechanism of phycoerythrin from Porphyra haitanensis

“…The PE hexamers can pile up to form rods which allow the pigment molecules to play an important role in light absorption, storage and transmission. The PE purifi ed from Porphyra haitanensis belongs to R type PE (R-PE), with characteristic absorption peak of 498 nm from its linked PUB which allows it to play a photosensitive role (1)(2)(3)(4).…”