title: On the absorbance changes in the photocycle of the photoactive yellow protein: a quantum-chemical analysis.
abstract: Spectral changes in the photocycle of the photoactive yellow protein (PYP) are investigated by using ab initio multiconfigurational second-order perturbation theory at the available structures experimentally determined. Using the dark ground-state crystal structure [Genick, U. K., Soltis, S. M., Kuhn, P., Canestrelli, I. L. & Getzoff, E. D. (1998) Nature (London) 392, 206-209], the pipi* transition to the lowest excited state is related to the typical blue-light absorption observed at 446 nm. The different nature of the second excited state (npi*) is consistent with the alternative route detected at 395-nm excitation. The results suggest the low-temperature photoproduct PYP(HL) as the most plausible candidate for the assignment of the cryogenically trapped early intermediate (Genick et al.). We cannot establish, however, a successful correspondence between the theoretical spectrum for the nanosecond time-resolved x-ray structure [Perman, B., Srajer, V., Ren, Z., Teng, T., Pradervand, C., et al. (1998) Science 279, 1946-1950] and any of the spectroscopic photoproducts known up to date. It is fully confirmed that the colorless light-activated intermediate recorded by millisecond time-resolved crystallography [Genick, U. K., Borgstahl, G. E. O., Ng, K., Ren, Z., Pradervand, C., et al. (1997) Science 275, 1471-1475] is protonated, nicely matching the spectroscopic features of the photoproduct PYP(M). The overall contribution demonstrates that a combined analysis of high-level theoretical results and experimental data can be of great value to perform assignments of detected intermediates in a photocycle.
authors: Departamento de Quimica Fisica, Universitat de València, Dr. Moliner 50, Burjassot, E-46100 Valencia, Spain. Vicent.Molina@uv.es
authors: V
authors: V
authors: Molina
authors: M
authors: M
authors: Merchán
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D008958:Models, Molecular; D020283:Photoreceptors, Microbial; D011789:Quantum Theory
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria