title: Hydrogen bonding in a model bacteriochlorophyll-binding site drives assembly of light harvesting complex.
abstract: In this study, the contribution of intramembrane hydrogen bonding at the interface between polypeptide and cofactor is explored in the native lipid environment by use of model bacteriochlorophyll proteins. In the peripheral antenna complex, LH2, large portions of the transmembrane helices, which make up the dimeric bacteriochlorophyll-binding site, are replaced by simplified, alternating alanine-leucine stretches. Replacement of either one of the two helices with the helices containing the model sequence at a time results in the assembly of complexes with nearly native light harvesting properties. In contrast, replacement of both helices results in the loss of antenna complexes from the membrane. The assembly of such doubly modified complexes is restored by a single intramembrane serine residue at position -4 relative to the liganding histidine of the alpha-subunit. In situ analysis of the spectral properties in a series of site-directed mutants reveals a critical dependence of the model complex assembly on the side chain of the residue at this position in the helix. A hydrogen bond between the hydroxy group of the serine and the 13(1) keto group of one of the central bacteriochlorophylls of the complexes is identified by Raman spectroscopy in the model antenna complex containing one of the alanine-leucine helices. The additional OH group of the serine residue, which participates in hydrogen bonding, increases the thermal stability of the model complexes in the native membrane. Intramembrane hydrogen bonding is thus shown to be a key factor for the binding of bacteriochlorophyll and assembly of this model cofactor-polypeptide site.
authors.affiliation: Department Biologie I der Universität München, Botanik, 80638 München, Germany.
authors.forename: Lee G
authors.initials: LG
authors.lastname: Kwa
authors.forename: Adela
authors.initials: A
authors.lastname: García-Martín
authors.forename: Attila P
authors.initials: AP
authors.lastname: Végh
authors.forename: Brigitte
authors.initials: B
authors.lastname: Strohmann
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
authors.forename: Paula
authors.initials: P
authors.lastname: Braun
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D001429:Bacteriochlorophylls / Q000737:chemistry*; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D018014:Gene Transfer Techniques; D006639:Histidine / Q000737:chemistry; D006860:Hydrogen Bonding; D007930:Leucine / Q000737:chemistry; D008024:Ligands; D045342:Light-Harvesting Protein Complexes; D050356:Lipid Metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013696:Temperature
chemical_list: D001429:Bacteriochlorophylls; D008024:Ligands; D045342:Light-Harvesting Protein Complexes; D010455:Peptides; D006639:Histidine; D007930:Leucine; D000409:Alanine