Theory of the optical spectra of the bacteriochlorophyll a antenna protein trimer from Prosthecochloris aestuarii

Abstract

A reasonable theoretical fit to the experimental low-temperature absorption and CD spectra of the BChl a-protein from Prosthecochloris aestuarii has been obtained for the unaggregated protein trimer based on standard assumptions regarding QY transition moment directions. The fits depend to some extent upon varying the site wavelengths of the individual BChls not just in one subunit but in the entire trimer, a procedure not tried before. Features in both spectra, but especially in CD, at wavelengths longer than ≈810 nm are very strongly influenced by the intersubunit interactions of BChls 7 (in the Fenna-Matthews numbering). Unlike earlier theoretical models, which also gave reasonable fits but were based on unorthodox or incorrect assumptions, this exciton model gives every indication of being refineable by improved choices of site wavelengths and exciton-transition lineshapes. Calculated exciton-transition wavelengths and line widths are compared with values deduced from recent laser hole-burning experiments (Johnson and Small 1991). As in the case of the absorption and CD spectra, agreement is best for the long-wavelength half of the QY region.

Antenna Complexes from Green Photosynthetic Bacteria

“…The FMO protein has been studied intensely by spectroscopic (Philipson and Sauer, 1972;Johnson and Small, 1991;Savikhin and Struve, 1994;Savikhin eta!., 1994bSavikhin eta!., , 1997Savikhin eta!., ,1998van Mourik eta!., 1994;Reddy et al, 1995;Freiberg et al, 1997;Louwc et a!., l997a, 1998;Vulto eta!., 1997Vulto eta!., , 1998aFranken et al, 1998;Ratsep et al, 1998Ratsep et al, , 1999Matsuzaki etal., 2000;Wendling eta!., 2000) and theoretical methods (Pearlstein, 1992;Gi.ilen, 1996;Lou we et al, 1997b;Vulto et al, 1998bVulto et al, , 1999Renger and May, 1998;Iseri and Giilen, 1999;Owen and Hoff, 2001). In pioneering early theoretical work, Pearlstein and coworkers (Pearlstein and Hemcngcr, 1978;Whitten et al, 1980;Pearlstein, 1992;Lu and Pearlstein, 1993) estimated the strength ofthe exciton coupling among the pigments both within a protein monomer and between monomers in the trimeric complex and proposed that the lowest energy pigment is pigment #7 in the Fenna and Matthews numbering system.…”

“…In pioneering early theoretical work, Pearlstein and coworkers (Pearlstein and Hemcngcr, 1978;Whitten et al, 1980;Pearlstein, 1992;Lu and Pearlstein, 1993) estimated the strength ofthe exciton coupling among the pigments both within a protein monomer and between monomers in the trimeric complex and proposed that the lowest energy pigment is pigment #7 in the Fenna and Matthews numbering system. Attempts to simulate the absorption and CD spectra of the FMO complex were only partially successful.…”

Crystal structure of the bacteriochlorophyll a protein from Chlorobium tepidum 1 1Edited by R. Huber

“…For the BChl a protein from P. aestuarii , the lowest energy state corresponding to the low temperature absorption band centered at 825 nm has been modeled as arising from an excitation energy trap primarily localized on BChl 7. BChl 7 is also special because it is in the center of the seven BChl a molecules in a subunit and the pigment with the largest intersubunit interactions within the trimer (Olson et al, 1976;Pearlstein & Hemenger, 1978;Gudowska-Nowak et al, 1990;Johnson & Small, 1991;Pearlstein, 1987Pearlstein, , 1992Lu & Pearlstein, 1993;van Mourik et al, 1994). However, based on the simultaneous simulation of the 4K absorption, linear dichroism and singlet-triplet absorption difference spectra, the lowest energy state has been assigned as localized primarily on the BChl 6 (Gu È len, 1996).…”

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

“…In the simplest case, only two point charges may be used to represent the transition dipole moment for a given transition, thus giving rise to the so-called extended-dipole approximation. [245,246] In contrast to the Fçrster approximation, which uses point dipoles, the spatial extent of the transition density can be modeled by the positions at which the point charges are placed. Methods based on transition monopoles derive partial charges ("transition charges") for all atoms, which should represent the full transition energy.…”