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

B.E.J. van Rossum, D.B. Steengaard, G.J. Boender, K. Schaffner, A.R. Holzwarth, H.J.M. de Groot

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    122 Citations (Scopus)

    Abstract

    Heteronuclear 2-D and 3-D magic-angle spinning NMR dipolar correlation spectroscopy was applied to determine solid-state 1H shifts for aggregated bacteriochlorophyll c (BChl c) in uniformly 13C-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 21-H3, 32-H3, and 31-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 17-171 bond. The analogy between aggregation shifts for BChl c in the chlorosome and for self-assembled chlorophyll a/H2O is explored, and a bilayer model for the tubular supra-structure of sheets of BChl c is proposed, from a homology modeling approach.
    Original languageEnglish
    Pages (from-to)1587-1595
    JournalBiochemistry
    Volume40
    DOIs
    Publication statusPublished - 2001

    Keywords

    • energy-transfer processes
    • bacteriochlorophyll-c
    • chloroflexus-aurantiacus
    • photosynthetic bacteria
    • cross-polarization
    • rotating solids
    • sulfur bacteria
    • spectral forms
    • spinning nmr
    • c-13 nmr

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