Biomaterial Database

Single amino acid substitutions in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus. Structural and spectral effects. 1991

M Babst, and H Albrecht, and I Wegmann, and R Brunisholz, and H Zuber

Institut für Molekularbiologie und Biophysik, Eidgenössische Technische Hochschule Zürich, Switzerland.

To obtain information on the structural and functional role of highly conserved amino acid residues in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus, site-directed mutagenesis was performed. 18 mutants with single amino acid substitutions at nine different positions in the B870 antenna polypeptides were prepared in a B800-850-lacking strain. The characterization of the resulting phenotypes was based on a quantification of the core-complex elements (reaction center, light-harvesting polypeptides, bacteriochlorophyll a and carotenoid) and the core-complex spectral characteristics (absorption maximum, absorption coefficient and fluorescence intensity). These data generally showed that strong structural effects were caused by the amino acid substitutions. Thus, the three tryptophan exchanges at the position alpha 8 resulted in either the absence of a core complex (alpha Trp8----Leu), the absence of the core antenna (alpha Trp8----Ala) or a reduction in the carotenoid content (alpha Trp8----Tyr). Likewise, the mutants alpha Pro13Gly (i.e. alpha Pro13----Gly), beta Gly10Val and alpha Phe23Ala demonstrated an abnormal protein/pigment ratio in the core antenna, while a drastically reduced antenna size resulted from the amino acid exchange beta Arg45Asp. In contrast to the structural effects, the absorption maxima and the fluorescence intensities of the mutant antennae differed only slightly from the wild type. The strongest blue shift of the bacteriochlorophyll a (8-11 nm) was induced by substitutions of the Trp at position alpha 43 (alpha Trp43----Ala, Leu or Tyr). Contrary to the other spectral effects, the absorption coefficient of bacteriochlorophyll a was strongly influenced by the amino acid substitutions and varied by 1.6-times less (beta Arg45Asp) and 1.3-times greater (alpha Phe25Ala) than normal. The antenna-free mutant, alpha Trp8Ala, yielded a high rate of B800-850 revertants during phototrophic growth, indicating a direct energy transfer from the B800-850 antenna to the reaction center in these strains. Although conditions for growth were generally observed to influence phenotypic expression, the structural as well as spectral effects were demonstrated to differ to the greatest extent between chemotrophically grown and phototrophically grown cells.

UI	MeSH Term	Description	Entries
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D010957	Plasmids	Extrachromosomal, usually CIRCULAR DNA molecules that are self-replicating and transferable from one organism to another. They are found in a variety of bacterial, archaeal, fungal, algal, and plant species. They are used in GENETIC ENGINEERING as CLONING VECTORS.	Episomes,Episome,Plasmid
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D002462	Cell Membrane	The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.	Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D000596	Amino Acids	Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.	Amino Acid,Acid, Amino,Acids, Amino
D001483	Base Sequence	The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.	DNA Sequence,Nucleotide Sequence,RNA Sequence,DNA Sequences,Base Sequences,Nucleotide Sequences,RNA Sequences,Sequence, Base,Sequence, DNA,Sequence, Nucleotide,Sequence, RNA,Sequences, Base,Sequences, DNA,Sequences, Nucleotide,Sequences, RNA
D013057	Spectrum Analysis	The measurement of the amplitude of the components of a complex waveform throughout the frequency range of the waveform. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Spectroscopy,Analysis, Spectrum,Spectrometry
D016297	Mutagenesis, Site-Directed	Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.	Mutagenesis, Oligonucleotide-Directed,Mutagenesis, Site-Specific,Oligonucleotide-Directed Mutagenesis,Site-Directed Mutagenesis,Site-Specific Mutagenesis,Mutageneses, Oligonucleotide-Directed,Mutageneses, Site-Directed,Mutageneses, Site-Specific,Mutagenesis, Oligonucleotide Directed,Mutagenesis, Site Directed,Mutagenesis, Site Specific,Oligonucleotide Directed Mutagenesis,Oligonucleotide-Directed Mutageneses,Site Directed Mutagenesis,Site Specific Mutagenesis,Site-Directed Mutageneses,Site-Specific Mutageneses
D016354	Rhodobacter capsulatus	Non-pathogenic ovoid to rod-shaped bacteria that are widely distributed and found in fresh water as well as marine and hypersaline habitats.	Rhodopseudomonas capsulatus,Rhodopseudomonas capsulata