Computational determination of the pigment binding motif  in the chlorosome protein a of green sulfur bacteria.
We present a molecular-scale model of Bacteriochlorophyll a (BChl a) binding to the chlorosome protein A (CsmA) of Chlorobaculum tepidum, and the aggregated pigment–protein dimer, as determined from protein–ligand docking and quantum chemistry calculations. Our calculations provide strong evidence that the BChl a molecule is coordinated to the His25 residue of CsmA, with the magnesium center of the bacteriochlorin ring situated\3 A° from the imidazole nitrogen atom of the histidine sidechain, and the phytyl tail aligned along the nonpolar residues of the a-helix of CsmA. We also confirm that the Qy band in the absorption spectra of BChl a experiences a large (?16 to ?43 nm) redshift when aggregated with another BChl a molecule in the CsmA dimer, compared to the BChl a in solvent; this redshift has been previously established by experimental researchers. We propose that our model of the BChl a–CsmA binding motif, where the dimer contains parallel aligned N-terminal regions, serves as the smallest repeating unit in a larger model of the para-crystalline chlorosome baseplate protein.
Sándor Á
SÁ
Kovács
William P
WP
Bricker
Dariusz M
DM
Niedzwiedzki
Peter F
PF
Colletti
Cynthia S
CS
Lo
D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D025541:Bacteriochlorophyll A / Q000737:chemistry / Q000378:metabolism*; D041883:Chlorobium / Q000737:chemistry* / Q000378:metabolism; D003198:Computer Simulation; D003460:Crystallization; D008961:Models, Structural; D015388:Organelles / Q000378:metabolism; D010788:Photosynthesis; D010860:Pigments, Biological / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization
D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; C404706:CsmA protein, Chlorobium tepidum; D010860:Pigments, Biological