Structural role of (bacterio)chlorophyll ligated in the energetically unfavorable beta-position.
Chlorophyll is attached to apoprotein in diastereotopically distinct ways, by beta- and alpha-ligation. Both the beta- and alpha-ligated chlorophylls of photosystem I are shown to have ample contacts to apoprotein within their proteinaceous binding sites, in particular, at C-13 of the isocyclic ring. The H-bonding patterns for the C-13(1) oxo groups, however, are clearly distinct for the beta-ligated and alpha-ligated chlorophylls. The beta-ligated chlorophylls frequently employ their C-13(1) oxo in H-bonds to neighboring helices and subunits. In contrast, the C-13(1) oxo of alpha-ligated chlorophylls are significantly less involved in H-bonding interactions, particularly to neighboring helices. Remarkably, in the peripheral antenna, light harvesting complex (LH2) from Rhodobacter sphaeroides, a single mutation in the alpha-subunit, introduced to eliminate H-bonding to the beta-bacteriochlorophyll-B850, which is ligated in the "beta-position," results in significant thermal destabilization of the LH2 in the membrane. In addition, in comparison with wild type LH2, the expression level of the LH2 lacking this H-bond is significantly reduced. These findings show that H-bonding to the C-13(1) keto group ofbeta-ligated (bacterio)-chlorophyll is a key structural motif and significantly contributes to the stability of bacteriochlorophyll proteins in the native membrane. Our analysis of photosystem I and II suggests that this hitherto unrecognized motif involving H-bonding to beta-ligated chlorophylls may be equally critical for the stable assembly of the inner core antenna of these multicomponent chlorophyll proteins.
Garcia-Martin
Adela
A
Department I, Botanik, der Universität München, 80638 Münich, Germany.
Kwa
Lee Gyan
LG
Strohmann
Brigitte
B
Robert
Bruno
B
Holzwarth
Alfred R
AR
Braun
Paula
P
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001429:Bacteriochlorophylls / Q000737:chemistry*; D002734:Chlorophyll / Q000737:chemistry; D002942:Circular Dichroism; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D018014:Gene Transfer Techniques; D006358:Hot Temperature; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009154:Mutation; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry; D016992:Rhodobacter / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013059:Spectrum Analysis, Raman
D001429:Bacteriochlorophylls; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011506:Proteins; D002734:Chlorophyll