Comportamiento cuántico en algas
Les pongo una interesante investigación sobre algas que presentan coherencia cuántica en su proceso de fotosíntesis, de hecho la mayoría de los criptofitos presenta un comportamiento cuántico en su proceso de recolección de luz, pero en este caso encontraron una clase de criptofitos, donde lo pueden desconectar por una mutación genética, que altera la forma de la proteina que recolecta la luz, asumen que este proceso tiene el fin de mejorar la eficiencia de la fotosíntesis, permitiendo al alga sobrevivir en condiciones de muy poca luz, de hecho este fenómeno también se encontró en una bacteria de sulfuro verde, les voy a poner un estracto del estudio:
Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins
There is intense interest in determining whether coherent quantum processes play a nontrivial role in biology. This interest was sparked by the discovery of long-lived oscillations in 2D electronic spectra of photosynthetic proteins, including the phycobiliproteins (PBPs) from cryptophyte algae. Using X-ray crystallography, we show that cryptophyte PBPs adopt one of two quaternary structures, open or closed. The key feature of the closed form is the juxtaposition of two central chromophores resulting in excitonic coupling. The switch between forms is ascribed to the insertion of a single amino acid in the open-form proteins. Thus, PBP quaternary structure controls excitonic coupling and the mechanism of light harvesting. Comparing organisms with these two distinct proteins will reveal the role of quantum coherence in photosynthesis.
Observation of coherent oscillations in the 2D electronic spectra (2D ES) of photosynthetic proteins has led researchers to ask whether nontrivial quantum phenomena are biologically significant. Coherent oscillations have been reported for the soluble light-harvesting phycobiliprotein (PBP) antenna isolated from cryptophyte algae. To probe the link between spectral properties and protein structure, we determined crystal structures of three PBP light-harvesting complexes isolated from different species. Each PBP is a dimer of αβ subunits in which the structure of the αβ monomer is conserved. However, we discovered two dramatically distinct quaternary conformations, one of which is specific to the genus Hemiselmis. Because of steric effects emerging from the insertion of a single amino acid, the two αβ monomers are rotated by ∼73° to an "open" configuration in contrast to the "closed" configuration of other cryptophyte PBPs. This structural change is significant for the light-harvesting function because it disrupts the strong excitonic coupling between two central chromophores in the closed form. The 2D ES show marked cross-peak oscillations assigned to electronic and vibrational coherences in the closed-form PC645. However, such features appear to be reduced, or perhaps absent, in the open structures. Thus cryptophytes have evolved a structural switch controlled by an amino acid insertion to modulate excitonic interactions and therefore the mechanisms used for light harvesting.
La ventaja de la superposición que hace, le permite probar cual es el mejor camino simultaneamente, antes de viajar por la ruta mas eficiente, finalmente les cito como hicieron la parte que mas me interesa...
Quantum Chemical Calculations. The initial conformations of the phycobilins were extracted from the Protein Data Bank file with the covalently bound cysteine residue. The cysteine residues were capped with an acetyl and N-methyl amino group. Each of the tetrapyrrole nitrogens was protonated (resulting in a +1 charge), and the two solvent-exposed carbocyclic acid chains were deprotonated (resulting in a −2 charge) with an overall molecular charge of −1 on all phycobilins. The molecular charge also is consistent with polarizable continuum pK a calculations implemented using the universal solvation model designated for solvation model density (39). Hydrogen atoms were added and optimized using b3lyp/cc-pvtz, followedby a bond-length optimization with dihedral angles restrained using the Gaussian 09 software package (Gaussian, Inc.). The phycobilin transition density from the S 0 to the S 1 state was obtained from a configuration interaction singles (CIS)/cc-pvtz calculation, again using the Gaussian 09 software package. Transition density cubes were inspected visually to ensure the proper excited state was probed. The gas-phase couplings were computed from the transition densities using the methodology outlined by Krueger et al. (40). No scaling of the couplings was used to correct for the overall overestimation of the transition dipole moments by the CIS because they were overestimated by only ∼9% compared with the experimental value of 2.34 eÅ (41).
Miguel Angel Vargas Cruz
2017-06-27 11:35:39 Post #2189