A refined model of the chlorosomal antennae of the green bacterium Chlorobium tepidum from proton chemical shift constraints obtained with high-field 2-D and 3-D MAS NMR dipolar correlation spectroscopy.
Heteronuclear 2-D and 3-D magic-angle spinning NMR dipolar correlation spectroscopy was applied to determine solid-state (1)H shifts for aggregated bacteriochlorophyll c (BChl c) in uniformly (13)C-enriched light harvesting chlorosomes of the green photosynthetic bacterium Chlorobium tepidum. A complete assignment of 29 different observable resonances of the 61 protons of the aggregated BChl c in the intact chlorosomes is obtained. Aggregation shifts relative to monomeric BChl c in solution are detected for protons attached to rings I, II, and III/V and to their side chains. The 2(1)-H(3), 3(2)-H(3), and 3(1)-H resonances are shifted upfield by -2.2, -1, and -3.3 ppm, respectively, relative to monomeric BChl c in solution. Although the resonances are inhomogeneously broadened and reveal considerable global structural heterogeneity, the 5-CH and the 7-Me responses are doubled, which provides evidence for the existence of at least two relatively well-defined structurally different arrangements. Ab initio quantum chemical modeling studies were performed to refine a model for the self-assembled BChl c with two different types of BChl stacks. The BChl in the stacks can adopt either anti- or syn-configuration of the coordinative bond, where anti and syn designate the relative orientation of the Mg-OH bond relative to the direction of the 17-17(1) bond. The analogy between aggregation shifts for BChl c in the chlorosome and for self-assembled chlorophyll a/H(2)O is explored, and a bilayer model for the tubular supra-structure of sheets of BChl c is proposed, from a homology modeling approach.
van Rossum
B J
BJ
Leiden Institute of Chemistry, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Steensgaard
D B
DB
Mulder
F M
FM
Boender
G J
GJ
Schaffner
K
K
Holzwarth
A R
AR
deGroot
H J
HJ
D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls; D002247:Carbon Isotopes; D019414:Chlorobi / Q000737:chemistry*; D003198:Computer Simulation; D045342:Light-Harvesting Protein Complexes; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D015388:Organelles / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry; D011522:Protons; D012996:Solutions
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002247:Carbon Isotopes; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D012996:Solutions; C002084:bacteriochlorophyll c