2026-04-13T04:51:09Zhttps://recercat.cat/oai/request

oai:recercat.cat:2445/1417992025-12-05T14:11:43Zcom_2072_1057col_2072_478815col_2072_478917col_2072_478924

00925njm 22002777a 4500 dc Corbella Morató, Marina author Toa, Zi. S. D. author Scholes, Gregory D. author Luque Garriga, F. Xavier author Curutchet Barat, Carles E. author 2019-10-07T10:06:27Z 2019-10-07T10:06:27Z 2018-07-30 2019-10-07T10:06:28Z The light-harvesting mechanisms of cryptophyte antenna complexes have attracted considerable attention due to their ability to exhibit maximal photosynthetic activity under very low-light conditions and to display several colors, as well as the observation of vibronic coherent features in their two-dimensional electronic spectra. However, detailed investigations on the interplay between the protein environment and their light-harvesting properties are hampered by the uncertainty related to the protonation state of the underlying bilin pigments. Here we study the protonation preferences of four types of bilin pigments including 15,16-dihydrobiliverdin (DBV), phycoerythrobilin (PEB), phycocyanobilin (PCB) and mesobiliverdin (MBV), which are found in phycoerythrin PE545 and phycocyanin PC577, PC612, PC630 and PC645 complexes. We apply quantum chemical calculations coupled to continuum solvation calculations to predict the intrinsic acidity of bilins in aqueous solution, and then combine molecular dynamics simulations with empirical pKa estimates to investigate the impact of the local protein environment on the acidity of the pigments. We also report measurements of the absorption spectra of the five complexes in a wide range of pH in order to validate our simulations and investigate possible changes in the light harvesting properties of the complexes in the range of physiological pH found in the lumen (pH ∼ 5-7). The results suggest a pKa > 7 for DBV and MBV pigments in the α polypeptide chains of PE545 and PC630/PC645 complexes, which are not coordinated to a negatively charged amino acid. For the other PEB, DBV and PCB pigments, which interact with a Glu or Asp side chain, higher pKa values (pKa > 8) are estimated. Overall, the results support a preferential population of the fully protonated state for bilins in cryptophyte complexes under physiological conditions regardless of the specific type of pigment and local protein environment. Fluorescència Pigments (Biologia) Química quàntica Química física Fluorescence Pigments (Biology) Quantum chemistry Physical and theoretical chemistry Determination of the protonation preferences of bilin pigments in cryptophyte antenna complexes