Resonance‐Enhanced CARS Spectroscopy of Biliproteins: a Comparison Between Phycoerythrocyanin and Phycocyanin of Mastigocladus laminosus

Abstract

Abstract— Resonance‐enhanced coherent anti‐Stokes Raman (CARS) spectra are reported for trimers of phycoerthrocyanin (PEC) dissolved in H2O and D2O. The CARS spectra are significantly different when recorded with pump wavelength either at 585 nm or 630 nm. By comparison of the 630 nm spectra with those of phycocyanin one can conclude that there is a change in the relative location of the lowest excited states of the β84 and β155 chromophores. Upon additional illumination with 514.5 nm laser light, only the spectra recorded with 585 nm pump wavelength change. This is in accordance with earlier observations that the phycoviolobilin chromophore of the a‐subunit exhibits photochromic behavior. The changes in the CARS spectra provide evidence that it is the methine bridge between rings C and D that undergoes the geometrical changes. Furthermore, it is suggested that there are different types of photoinduced rearrangements operative and that the isomeric distribution is different in H2O and D2O.

Protein-Matrix Solvation Dynamics in the α Subunit of C-Phycocyanin

“…The THB line shape at all probe delays is well described by the assumption that the dipole strengths for the PB and SE transitions are equivalent, so the structure of the excited-state phycocyanobilin chromophore cannot be much different than that of the ground state at any point during the dynamic Stokes shift. Note that a structurally similar bile pigment is also found in phytochrome, where it exhibits excited-state photochemistry, , and comparable photochemistry is ascribed to the phycoviolobilin chromophore in R -phycoerythrocyanin . Although the β155 phycocyanobilin chromophore in the β subunit of C -phycocyanin is thought to exhibit photochromism under certain conditions, no photochemistry has been observed in the α84 or β84 chromophores.…”

“…Note that a structurally similar bile pigment is also found in phytochrome, where it exhibits excitedstate photochemistry, 50,51 and comparable photochemistry is ascribed to the phycoviolobilin chromophore in R-phycoerythrocyanin. 52 Although the β155 phycocyanobilin chromophore in the β subunit of C-phycocyanin is thought to exhibit photochromism under certain conditions, 53 no photochemistry has been observed in the R84 or β84 chromophores.…”

Structural analysis at 2.2 Å of orthorhombic crystals presents the asymmetry of the allophycocyanin–linker complex, AP⋅L C 7.8 , from phycobilisomes of Mastigocladus laminosus

“…In addition to the general coordination and stabilization effect, the influence of the linker is expressed by the bathochromic absorbance shift to 653 nm and the decreased shoulder near 620 nm of AP⅐L C 7.8 . Resonance coherent anti-Stokes raman scattering (CARS) spectroscopy demonstrated the effect of the aggregation states (monomer and trimer) on the geometry of the chromophores of both subunits and in addition, geometrical variations of chromophores depending on the linker association (47). The results of the present study prove that the bathochromic shifts are exclusively caused by the charged and polar contacts of the linker with the ␤-chromophore of monomer 1 as well as the conformational change of the ␤-chromophore of monomer 2.…”

Raman Spectroscopy

“…Picosecond time-resolved resonance CARS has been used in studies of the bacteriorhodopsin and bathorhodopsin photocycles (580,581). Resonance CARS has also been applied to aggregation and linker studies in biliproteins (582).…”