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Astrid Jung

Publications and source records attributed to Astrid Jung.

6 recordsLinked to original sources
PubMed2006

Crystal structures of the AppA BLUF domain photoreceptor provide insights into blue light-mediated signal transduction.

Proteins containing a sensor of blue light using FAD (BLUF) domain control diverse cellular processes, such as gene expression, nucleotide metabolism and motility, by relaying blue light signals to distinct output units. Despite its crucial and widespread functions, the mechanism of BLUF signal transduction has remained elusive. We determined crystal structures of the dark-adapted state and of a photo-excited, red-shifted photocycle intermediate of the BLUF unit of AppA, a purple bacterial photoreceptor involved in the light-dependent regulation of photosynthesis gene expression. In contrast to a recently published crystal structure of the AppA BLUF domain determined in the presence of detergent molecules, our structural model of the dark state corresponds well to those reported for the BLUF domains of Tll0078 and BlrB. This establishes that a highly conserved methionine (Met106 in AppA) is next to the active site glutamine (Gln63 in AppA), which is of relevance for the latter's orientation in the dark state and for the mechanism of the photoreaction. The comparison of the dark-adapted and photointermediate state structures shows light-induced conformational alterations, which suggest a path for signal propagation. In particular, we observe a significant movement of the Met106 side-chain. Met106 thereby changes its mode of interaction with Gln63, which supports a light-dependent rotation of the latter. In view of other BLUF structures available, our data further suggest that the hydrogen bond between Asn45 and the backbone carbonyl of His105 breaks upon illumination. The ensuing extensive structural rearrangement of beta-strand 5 is predicted to involve a flip of Met106 out of the flavin-binding pocket and Trp104 moving in to fill the void. We propose that the blue light signal is transmitted towards the surface of the BLUF domain via His44, which serves as a reporter of active site changes.

Bacterial Proteins↗
PubMed2005

Structure of a bacterial BLUF photoreceptor: insights into blue light-mediated signal transduction.

Light is an essential environmental factor, and many species have evolved the capability to respond to it. Blue light is perceived through three flavin-containing photoreceptor families: cryptochromes, light-oxygen-voltage, and BLUF (sensor of blue light using flavin adenine dinucleotide, FAD) domain proteins. BLUF domains are present in various proteins from Bacteria and lower Eukarya. They are fully modular and can relay signals to structurally and functionally diverse output units, most of which are implicated in nucleotide metabolism. We present the high resolution crystal structure of the dark resting state of BlrB, a short BLUF domain-containing protein from Rhodobacter sphaeroides. The structure reveals a previously uncharacterized FAD-binding fold. Along with other lines of evidence, it suggests mechanistic aspects for the photocycle that is characterized by a red-shifted absorbance of the flavin. The isoalloxazine ring of FAD binds in a cleft between two helices, whereas the adenine ring points into the solvent. We propose that the adenine ring serves as a hook mediating the interaction with its effector/output domain. The structure suggests a unique photochemical signaling switch in which the absorption of light induces a structural change in the rim surrounding the hook, thereby changing the protein interface between BLUF and the output domain.

Bacterial Proteins↗
PubMed2004

High-temperature solution NMR structure of TmCsp.

Cold shock proteins (Csps) are assumed to play a central role in the regulation of gene expression under cold shock conditions. Acting as single-stranded nucleic acid-binding proteins, they trigger the translation process and are therefore involved in the compensation of the influence of low temperatures (cold shock) upon the cell metabolism. However, it is unknown so far how Csps are switched on and off as a function of temperature. The aim of the present study is the study of possible structural changes responsible for this switching process. (1)H-(15)N HSQC spectra recorded at different temperatures and chemical-shift analysis have indicated subtle conformational changes for the cold-shock protein from the hyperthermophilic bacterium Thermotoga maritima (TmCsp) when the temperature is elevated from 303 K to its physiological temperature (343 K). The three-dimensional structure of TmCsp was determined by nuclear magnetic resonance (NMR) spectroscopy at 343 K to obtain quantitative information concerning these structural changes. By use of residual dipolar couplings, the loss of NOE information at high temperature could be compensated successfully. Most pronounced conformational changes compared with room-temperature conditions are observed for amino acid residues closely neighbored to two characteristic beta-bulges and a well-defined loop region of the protein. Because the residues shown to be responsible for the interaction of TmCsp with single-stranded nucleic acids can almost exclusively be found within these regions, nucleic acid-binding activity might be down-regulated with increasing temperature by the described conformational changes.

Bacterial Proteins↗
PubMed2002

Uncoupling Kapbeta2 substrate dissociation and ran binding.

Karyopherinbeta2 (Kapbeta2) imports a variety of mRNA binding proteins into the nucleus. Release of import substrates in the nucleus involves formation of a high-affinity Kapbeta2-RanGTP complex and concomitant dissociation of import substrates. The crystal structure of the Kapbeta2-RanGppNHp complex shows that Ran binds in the Kapbeta2 N-terminal arch and substrate most likely binds its C-terminal arch. The structure suggested a mechanism for Ran-mediated substrate dissociation where a long internal acidic loop in Kapbeta2 transmits structural information between the GTPase and substrate sites, leading to displacement of substrate by the loop when Ran is bound. To study the molecular mechanism of substrate dissociation, we have cleaved the acidic loop of Kapbeta2 proteolytically (cl-Kapbeta2) and also constructed a mutant of Kapbeta2 with a truncated loop (TL-Kapbeta2). Both modified Kapbeta2s are unable to undergo Ran-mediated substrate dissociation. We have also mapped the boundaries of the Kapbeta2 binding site of substrate mRNA binding protein A1 using a widely applicable method employing NMR spectroscopy. This has allowed design of reagents to quantitate the affinities of the Kapbeta2 proteins for Ran and substrate. cl-Kapbeta2, TL-Kapbeta2, and native Kapbeta2 have comparable affinities for both RanGppNHp and import substrates, indicating that perturbation of the loop has not altered the strength of binary Kapbeta2-Ran or Kapbeta2-substrate interactions. The TL-Kapbeta2 mutant also binds RanGppNHp and substrate simultaneously to form a ternary complex, indicating that in addition to the loss of coupling between Ran binding and substrate dissociation, the two ligand sites on Kapbeta2 are spatially distinct. The uncoupling of Ran binding and substrate dissociation in the TL-Kapbeta2 mutant is further evident in significant loss of Ran-mediated nuclear uptake of fluorescent substrate in digitonin-permeabilized HeLa cells. These results support our previously proposed GTPase-mediated Kapbeta2-substrate dissociation mechanism where the acidic loop of Kapbeta2 physically couples distinct Ran and substrate binding sites.

Active Transport, Cell Nucleus↗
PubMed2002

Automated assignment of NOESY NMR spectra using a knowledge based method (KNOWNOE).

Automated assignment of NOESY spectra is a prerequisite for automated structure determination of biological macromolecules. With the program KNOWNOE we present a novel, knowledge based approach to this problem. KNOWNOE is devised to work directly with the experimental spectra without interference of an expert. Besides making use of routines already implemented in AUREMOL, it contains as a central part a knowledge driven Bayesian algorithm for solving ambiguities in the NOE assignments. These ambiguities mainly arise from chemical shift degeneration which allows multiple assignments of cross peaks. Using a set of 326 protein NMR structures, statistical tables in the form of atom-pairwise volume probability distributions (VPDs) were derived. VPDs for all assignment possibilities relevant to the assignments of interproton NOEs were calculated. With these data for a given cross peak with N possible assignments Ai (i = 1,...,N) the conditional probabilities P(Ai, a/V0) can be calculated that the assignment Ai determines essentially all (a-times) of the cross peak volume V0. An assignment Ak with a probability P(Ak, a/V0) higher than 0.8 is transiently considered as unambiguously assigned. With a list of unambiguously assigned peaks a set of structures is calculated. These structures are used as input for a next cycle of iteration where a distance threshold Dmax is dynamically reduced. The program KNOWNOE was tested on NOESY spectra of a medium size protein, the cold shock protein (TmCsp) from Thermotoga maritima. The results show that a high quality structure of this protein can be obtained by automated assignment of NOESY spectra which is at least as good as the structure obtained from manual data evaluation.

Algorithms↗