K. Forchhammer - Academia.edu (original) (raw)

Papers by K. Forchhammer

The first step in photosynthesis is an extremely efficient energy transfer mechanism, which is di... more The first step in photosynthesis is an extremely efficient energy transfer mechanism, which is difficult to be explained by classical short-range energy migration (“hopping”) and led to the debate to which extent quantum coherence is involved in the energy transfer between the photosynthetic pigments. Embedding living cyanobacteria between the mirrors of an optical microresonator and using low intensity white light irradiation we observe vacuum Rabi splitting in the transmission and fluorescence spectra as a result of strong light matter coupling of the chlorophyll and the resonator modes. The Rabi-splitting scales with the number of chlorophyll a pigments involved in coherent coupling indicating forming a polaritonic state which is delocalized over the entire cyanobacterial thylakoid system, down to the single photon level. Our data provide evidence that a delocalized polaritonic state is the basis of the extremely high energy transfer efficiency under natural conditions.

Biosynthese und Einbau von Selenocystein in Proteine von Escherichia coli Eine biochemische Analyse

Available from TIB Hannover: DW 5621 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technisch... more Available from TIB Hannover: DW 5621 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Supplementary Material for: Bacterial Predation on Cyanobacteria

Predatory bacteria gained interest in the last 20 years. Nevertheless, only a few species are wel... more Predatory bacteria gained interest in the last 20 years. Nevertheless, only a few species are well characterized. The endobiotic predator Bdellovibrio bacteriovorus invades its prey to consume it from the inside, whereas Myxococcus xanthus hunts as a whole group to overcome its prey. Both species were described to prey on cyanobacteria as well. This minireview summarizes the findings of the last 20 years of predatory bacteria of cyanobacteria and is supplemented by new findings from a screening experiment for bacterial predators of the model organism Anabaena variabilis PCC 7937. Known predatory bacteria of cyanobacteria belong to the phyla Proteobacteria, Bacteroidetes, and Firmicutes and follow different hunting strategies. The underlying mechanisms are in most cases not known in much detail. Isolates from the screening experiment were clustered after predation behaviour and analyzed with respect to their size. The effect of...

Purification and biochemical characterization of SELB, a translation factor involved in selenoprotein synthesis

The Journal of biological chemistry, 1990

The product of the selB gene from Escherichia coli is required for co-translational insertion of ... more The product of the selB gene from Escherichia coli is required for co-translational insertion of selenocysteine into protein. To make the SELB protein accessible to biochemical analysis, the protein was purified from cells that overexpressed the selB gene from a phage T7 promoter plasmid. It was calculated that the overproduced SELB protein was purified 20-fold. The N-terminal amino acid sequence of the purified protein was determined, and it confirmed that the initiation codon of selB mRNA translation overlaps the stop codon of the preceding selA gene by 4 bases. Structural similarity between SELB and elongation factors was demonstrated by limited proteolysis of SELB by trypsin. The cleavage sites within SELB were identified by N-terminal sequencing of the two proteolytic products. The position in the SELB protein of the major cleavage site was homologous to a tryptic cleavage site which is characteristic for elongation factors. Immunological analysis showed that the levels of SELB...

Frontiers in Cellular and Infection Microbiology, 2017

Filamentous cyanobacteria have developed a strategy to perform incompatible processes in one fila... more Filamentous cyanobacteria have developed a strategy to perform incompatible processes in one filament by differentiating specialized cell types, N 2-fixing heterocysts and CO 2-fixing, photosynthetic, vegetative cells. These bacteria can be considered true multicellular organisms with cells exchanging metabolites and signaling molecules via septal junctions, involving the SepJ and FraCD proteins. Previously, it was shown that the cell wall lytic N-acetylmuramyl-L-alanine amidase, AmiC2, is essential for cell-cell communication in Nostoc punctiforme. This enzyme perforates the septal peptidoglycan creating an array of nanopores, which may be the framework for septal junction complexes. In Anabaena sp. PCC 7120, two homologs of AmiC2, encoded by amiC1 and amiC2, were identified and investigated in two different studies. Here, we compare the function of both AmiC proteins by characterizing different Anabaena amiC mutants, which was not possible in N. punctiforme, because there the amiC1 gene could not be inactivated. This study shows the different impact of each protein on nanopore array formation, the process of cell-cell communication, septal protein localization, and heterocyst differentiation. Inactivation of either amidase resulted in significant reduction in nanopore count and in the rate of fluorescent tracer exchange between neighboring cells measured by FRAP analysis. In an amiC1 amiC2 double mutant, filament morphology was affected and heterocyst differentiation was abolished. Furthermore, the inactivation of amiC1 influenced SepJ localization and prevented the filament-fragmentation phenotype that is characteristic of sepJ or fraC fraD mutants. Our findings suggest that both amidases are to some extent redundant in their function, and describe a functional relationship of AmiC1 and septal proteins SepJ and FraCD.

Journal of Bacteriology, 1996

The coexistence of two different PII, proteins in Azospirillum brasilense was established by comp... more The coexistence of two different PII, proteins in Azospirillum brasilense was established by comparing proteins synthesized by the wild-type strain and two null mutants of the characterized glnB gene (encoding PII) adjacent to glnA. Strains were grown under conditions of nitrogen limitation or nitrogen excess. The proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or isoelectric focusing gel electrophoresis and revealed either by [32P]phosphate or [3H]uracil labeling or by cross-reaction with an anti-A. brasilense PII-antiserum. After SDS-PAGE, a single band of 12.5 kDa revealed by the antiserum in all conditions tested was resolved by isoelectric focusing electrophoresis into two bands in the wild-type strain, one of which was absent in the glnB null mutant strains. The second PII protein, named Pz, was uridylylated under conditions of nitrogen limitation. The amino acid sequence deduced from the nucleotide sequence of the corresponding s...

The Molecular Basis of Bacterial Metabolism, 1990

Nitrogen regulatory protein PII from Chlamydomonas reinhardtii in unliganded state

Surface plasmon resonance monitoring of the binding of transcription factors CRP and NtcA from Sy... more Surface plasmon resonance monitoring of the binding of transcription factors CRP and NtcA from Synechocystis sp. PCC6803 to promoter fragments of glnA, glnN (NtcA regulon) and cccS (CRP regulon), revealed exclusive CRP binding to cccS, whereas NtcA was bound to all three promoters with different affinities, which were strongly increased by the NtcA activator 2oxoglutarate. Effective NtcA affinity for 2-oxoglutarate varied with the promoter. High-affinity

Structure of wildtype PII from S. elongatus at medium resolution

Molecular Microbiology, 1997

The phosphorylation state of the putative signal transduction protein P II from the cyanobacteriu... more The phosphorylation state of the putative signal transduction protein P II from the cyanobacterium Synechococcus sp. strain PCC 7942 depends on the cellular state of nitrogen and carbon assimilation. In this study, dephosphorylation of phosphor ylated P II protein (P II-P) was investigated both in vivo and in vitro. The in vivo studies implied that P II-P dephosphorylation is regulated by inhibitor y metabolites involved in the glutamine synthetase-glutamate synthase pathway of ammonium assimilation. An in vitro assay for P II-P dephosphorylation was established that revealed a Mg 2þ-dependent P II-P phosphatase activity. P II-P phosphatase and P II kinase activities could be separated biochemically. A partially purified P II-P phosphatase preparation also catalysed the dephosphorylation of phosphoserine/phosphothreonine residues on other proteins in a Mg 2þ-dependent manner. However, only dephosphorylation of P II-P was regulated by synergistic inhibition by ATP and 2-oxoglutarate. As the same metabolites stimulate the P II kinase activity, it appears that the phosphorylation state of P II is determined by ATP and 2-oxoglutarate-dependent reciprocal reactivity of P II towards its phosphatase and kinase.

Microbiology, 2010

InSynechococcus elongatussp. PCC 7942, PipX forms complexes with PII, a protein found in all thre... more InSynechococcus elongatussp. PCC 7942, PipX forms complexes with PII, a protein found in all three domains of life as an integrator of signals of the nitrogen and carbon balance, and with the cyanobacterial nitrogen regulator NtcA. We recently showed that previous inactivation ofpipXfacilitates subsequent inactivation of theglnBgene. Here, we show that the three spontaneouspipXpoint mutationspipX-92delT,pipX160C>TandpipX194T>A,initially found in differentglnBstrains, are indeed suppressor mutations. When these mutations were reconstructed in the wild-type background, theglnBgene could be efficiently inactivated. Furthermore, the point mutations have different effects on PipX levels, coactivation of NtcA-dependent genes and protein–protein interactions. Further support for anin vivorole of PipX–PIIcomplexes is provided by interaction analysis with thein vivo-generated PIIT-loop+7protein, a PIIderivative unable to interact with its regulatory targetN-acetyl-l-glutamate kinase, b...

Acta Crystallographica Section D Biological Crystallography, 2012

Journal of Molecular Biology, 2010

II signal transduction proteins are highly conserved in bacteria, archaea and plants and have key... more II signal transduction proteins are highly conserved in bacteria, archaea and plants and have key functions in coordination of central metabolism by integrating signals from the carbon, nitrogen and energy status of the cell. In the cyanobacterium Synechococcus elongatus PCC 7942, P II binds ATP and 2oxoglutarate (2-OG) in a synergistic manner, with the ATP binding sites also accepting ADP. Depending on its effector molecule binding status, P II (from this cyanobacterium and other oxygenic phototrophs) complexes and regulates the arginine-controlled enzyme of the cyclic ornithine pathway, N-acetyl-L-glutamate kinase (NAGK), to control arginine biosynthesis. To gain deeper insights into the process of P II binding to NAGK, we searched for P II variants with altered binding characteristics and found P II variants I86N and I86T to be able to bind to an NAGK variant (R233A) that was previously shown to be unable to bind wild-type P II protein. Analysis of interactions between these P II variants and wild-type NAGK as well as with the NAGK R233A variant suggested that the P II I86N variant was a superactive NAGK binder. To reveal the structural basis of this property, we solved the crystal structure of the P II I86N variant at atomic resolution. The large T-loop, which prevails in most receptor interactions of P II proteins, is present in a tightly bended conformation that mimics the T-loop of S. elongatus P II after having latched onto NAGK. Moreover, both P II I86 variants display a specific defect in 2-OG binding, implying a role of residue I86 in 2-OG binding. We propose a two-step model for the mechanism of P II-NAGK complex formation: in an initiating step, a contact between R233 of NAGK and E85 of P II initiates the bending of the extended T-loop of P II , followed by a second step, where a bended T-loop deeply inserts into the NAGK clefts to form the tight complex.

Journal of Bacteriology, 2012

Filamentous cyanobacteria of the order Nostocales display typical properties of multicellular org... more Filamentous cyanobacteria of the order Nostocales display typical properties of multicellular organisms. In response to nitrogen starvation, some vegetative cells differentiate into heterocysts, where fixation of N 2 takes place. Heterocysts provide a micro-oxic compartment to protect nitrogenase from the oxygen produced by the vegetative cells. Differentiation involves fundamental remodeling of the Gram-negative cell wall by deposition of a thick envelope and by formation of a neck-like structure at the contact site to the vegetative cells. Cell wall-hydrolyzing enzymes, like cell wall amidases, are involved in peptidoglycan maturation and turnover in unicellular bacteria. Recently, we showed that mutation of the amidase homologue amiC2 gene in Nostoc punctiforme ATCC 29133 distorts filament morphology and function. Here, we present the functional characterization of two amiC paralogues from Anabaena sp. strain PCC 7120. The amiC1 ( alr0092 ) mutant was not able to differentiate he...

Purification and biochemical characterization of SELB, a translation factor involved in selenoprotein synthesis

Journal of Biological Chemistry

PII-like protein CutA from Nostoc sp. PCC7120 in complex with MES

PII-like protein CutA from Nostoc sp. PCC 7120 in apo form

Carbon regulatory PII-like protein SbtB from Synechocystis sp. 6803 in complex with cyclic AMP (cAMP)

Carbon regulatory PII-like protein SbtB from Synechocystis sp. 6803 in Apo state, hexagonal crystal form

Biosynthese und Einbau von Selenocystein in Proteine von Escherichia coli Eine biochemische Analyse

Supplementary Material for: Bacterial Predation on Cyanobacteria

Purification and biochemical characterization of SELB, a translation factor involved in selenoprotein synthesis

The Journal of biological chemistry, 1990

Frontiers in Cellular and Infection Microbiology, 2017

Journal of Bacteriology, 1996

The Molecular Basis of Bacterial Metabolism, 1990

Nitrogen regulatory protein PII from Chlamydomonas reinhardtii in unliganded state

Structure of wildtype PII from S. elongatus at medium resolution

Molecular Microbiology, 1997

Microbiology, 2010

Acta Crystallographica Section D Biological Crystallography, 2012

Journal of Molecular Biology, 2010

Journal of Bacteriology, 2012

Purification and biochemical characterization of SELB, a translation factor involved in selenoprotein synthesis

Journal of Biological Chemistry

PII-like protein CutA from Nostoc sp. PCC7120 in complex with MES

PII-like protein CutA from Nostoc sp. PCC 7120 in apo form

Carbon regulatory PII-like protein SbtB from Synechocystis sp. 6803 in complex with cyclic AMP (cAMP)

Carbon regulatory PII-like protein SbtB from Synechocystis sp. 6803 in Apo state, hexagonal crystal form