Biomedical subjects

Markus Fischer

Publications and source records attributed to Markus Fischer.

At least 37 records · Page 2Linked to original sources

PubMed2005

Biosynthesis of vitamin B2: diastereomeric reaction intermediates of archaeal and non-archaeal riboflavin synthases.

The dismutation of 6,7-dimethyl-8-ribityllumazine catalyzed by riboflavin synthase affords riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. A pentacyclic adduct of two 6,7-dimethyl-8-ribityllumazines has been identified earlier as a catalytically competent reaction intermediate of the Escherichia coli enzyme. Acid quenching of reaction mixtures of riboflavin synthase of Methanococcus jannaschii, a paralog of 6,7-dimethyl-8-ribityllumazine synthase devoid of similarity with riboflavin synthases of eubacteria and eukaryotes, afforded a compound whose optical absorption and NMR spectra resemble that of the pentacyclic E. coli riboflavin synthase intermediate, whereas the circular dichroism spectra of the two compounds have similar envelopes but opposite signs. Each of the compounds could serve as a catalytically competent intermediate for the enzyme by which it was produced, but not vice versa. All available data indicate that the respective pentacyclic intermediates of the M. jannaschii and E. coli enzymes are diastereomers.

Archaea↗

PubMed2005

Biosynthesis of flavocoenzymes.

The biosynthesis of one riboflavin molecule requires one molecule of GTP and two molecules of ribulose 5-phosphate. The imidazole ring of GTP is hydrolytically opened, yielding a 2,5-diaminopyrimidine that is converted to 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione by a sequence of deamination, side chain reduction, and dephosphorylation. Condensation of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione with 3,4-dihydroxy-2-butanone 4-phosphate obtained from ribulose 5-phosphate affords 6,7-dimethyl-8-ribityllumazine. Dismutation of the lumazine derivative yields riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione, which is recycled in the biosynthetic pathway. The enzymes of the riboflavin pathway are potential targets for antibacterial agents.

Amino Acid Sequence↗

PubMed2005

Synthesis and structural characterization of novel neutral hexacoordinate silicon(IV) complexes with SiO2N4 skeletons containing cyanato-N or thiocyanato-N ligands.

A series of novel hexacoordinate silicon(IV) complexes with an SiO2N4 skeleton (compounds (OC-6-12)-3, (OC-6-12)-4, (OC-6-12)-5, (OC-6-12)-6, and (OC-6-2'2)-7) were synthesized, starting from Si(NCO)4 or Si(NCS)4. These compounds contain (i) two bidentate O,N-chelate ligands (or one tetradentate O,N,N,O-chelate ligand) derived from 4-aminopent-3-en-2-ones of the formula type Me-C(NRH)=CH-C(O)-Me (R = organyl) and (ii) two monodentate cyanato-N or thiocyanato-N ligands. Formally, the bidentate singly negatively charged O,N-chelate ligands (tetradentate 2-fold negatively charged O,N,N,O-chelate ligand) behave as ligands of the imino-enolato type. In addition, the adduct trans-8 was synthesized by reaction of Si(NCS)4 with 2 molar equiv of Me-C(Ni-PrH)=CH-C(O)-Me. This hexacoordinate silicon(IV) complex contains (i) four monodentate thiocyanato-N ligands and (ii) two neutral monodentate ligands of the iminio-enolato type. All compounds synthesized were structurally characterized by single-crystal X-ray diffraction and solid-state and solution NMR spectroscopy. To get more information about the stereochemistry of these compounds, the experimental investigations were complemented by computational studies.

Journal Article↗

PubMed2005

How to find soluble proteins: a comprehensive analysis of alpha/beta hydrolases for recombinant expression in E. coli.

BACKGROUND: In screening of libraries derived by expression cloning, expression of active proteins in E. coli can be limited by formation of inclusion bodies. In these cases it would be desirable to enrich gene libraries for coding sequences with soluble gene products in E. coli and thus to improve the efficiency of screening. Previously Wilkinson and Harrison showed that solubility can be predicted from amino acid composition (Biotechnology 1991, 9(5):443-448). We have applied this analysis to members of the alpha/beta hydrolase fold family to predict their solubility in E. coli. alpha/beta hydrolases are a highly diverse family with more than 1800 proteins which have been grouped into homologous families and superfamilies. RESULTS: The predicted solubility in E. coli depends on hydrolase size, phylogenetic origin of the host organism, the homologous family and the superfamily, to which the hydrolase belongs. In general small hydrolases are predicted to be more soluble than large hydrolases, and eukaryotic hydrolases are predicted to be less soluble in E. coli than prokaryotic ones. However, combining phylogenetic origin and size leads to more complex conclusions. Hydrolases from prokaryotic, fungal and metazoan origin are predicted to be most soluble if they are of small, medium and large size, respectively. We observed large variations of predicted solubility between hydrolases from different homologous families and from different taxa. CONCLUSION: A comprehensive analysis of all alpha/beta hydrolase sequences allows more efficient screenings for new soluble alpha/beta hydrolases by the use of libraries which contain more soluble gene products. Screening of hydrolases from families whose members are hard to express as soluble proteins in E. coli should first be done in coding sequences of organisms from phylogenetic groups with the highest average of predicted solubility for proteins of this family. The tools developed here can be used to identify attractive target genes for expression using protein sequences published in databases. This analysis also directs the design of degenerate, family-specific primers to amplify new members from homologous families or superfamilies with a high probability of soluble alpha/beta hydrolases.

Animals↗

PubMed2005

A metastable prerequisite for the growth of lumazine synthase crystals.

Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and small-molecule materials. They have been shown to serve as a prerequisite for the nucleation of crystals and other ordered solid phases. Here, using crystals of the protein lumazine synthase from Bacillus subtilis, which grow by the generation and spreading of layers, we demonstrate that within a range of supersaturations the only mechanism of generation of growth layers involves the association of submicrometer-size droplets of the dense liquid to the crystal surface. The dense liquid is metastable not only with respect to the crystals, but also with respect to the low-concentration solution: dynamic light scattering reveals that the droplets' lifetime is limited to several seconds, after which they decay into the low-concentration solution. The short lifetime does not allow growth to detectable dimensions so that liquid-liquid phase separation is not observed within a range of conditions broader than the one used for crystallization. If during their lifetime the droplets encounter a crystal surface, they lower their free energy not by decay, but by transformation into crystalline matter, ensuring perfect registry with the substrate. These observations illustrate two novel features of phase transformations in solutions: the existence of doubly metastable, short-lifetime dense phases and their crucial role for the growth of an ordered solid phase.

Crystallization↗

PubMed2005

A high-throughput screen utilizing the fluorescence of riboflavin for identification of lumazine synthase inhibitors.

A high-throughput screening method based on the competitive binding of a lumazine synthase inhibitor and riboflavin to the active site of Schizosaccharomyces pombe lumazine synthase was developed. This assay is sensitive, simple, and robust. During assay development, all of the known active inhibitors tested were positively identified. Preliminary high-throughput screening in 384-well format resulted in a Z factor of 0.7. The approach utilizes a thermodynamic assay to bypass the problems associated with the instabilities of both lumazine synthase substrates that complicate the use of a kinetic assay in a high-throughput format, and it removes the time element from the assay, thus simplifying the procedure.

Binding Sites↗

PubMed2005

Crystal structure of lumazine synthase from Mycobacterium tuberculosis as a target for rational drug design: binding mode of a new class of purinetrione inhibitors.

The enzymes involved in the biosynthesis of riboflavin represent attractive targets for the development of drugs against bacterial pathogens, because the inhibitors of these enzymes are not likely to interfere with enzymes of the mammalian metabolism. Lumazine synthase catalyzes the penultimate step in the riboflavin biosynthesis pathway. A number of substituted purinetrione compounds represent a new class of highly specific inhibitors of lumazine synthase from Mycobacterium tuberculosis. To develop potent antibiotics for the treatment of tuberculosis, we have determined the structure of lumazine synthase from M. tuberculosis in complex with two purinetrione inhibitors and have studied binding via isothermal titration calorimetry. The structures were determined by molecular replacement using lumazine synthase from Saccharomyces cerevisiae as a search model and refined at 2 and 2.3 A resolution. The R-factors were 14.7 and 17.4%, respectively, and the R(free) values were 19.3 and 26.3%, respectively. The enzyme was found to be a pentamer consisting of five subunits related by 5-fold local symmetry. The comparison of the active site architecture with the active site of previously determined lumazine synthase structures reveals a largely conserved topology with the exception of residues Gln141 and Glu136, which participate in different charge-charge interactions in the core space of the active site. The impact of structural changes in the active site on the altered binding and catalytic properties of the enzyme is discussed. Isothermal titration calorimetry measurements indicate highly specific binding of the purinetrione inhibitors to the M. tuberculosis enzyme with dissociation constants in micromolar range.

Amino Acid Sequence↗

PubMed2005

A threefold genetic allee effect: population size affects cross-compatibility, inbreeding depression and drift load in the self-incompatible Ranunculus reptans.

A decline in population size can lead to the loss of allelic variation, increased inbreeding, and the accumulation of genetic load through drift. We estimated the fitness consequences of these processes in offspring of controlled within-population crosses from 13 populations of the self-incompatible, clonal plant Ranunculus reptans. We used allozyme allelic richness as a proxy for long-term population size, which was positively correlated with current population size. Crosses between plants of smaller populations were less likely to be compatible. Inbreeding load, assessed as the slope of the relationship between offspring performance and parental kinship coefficients, was not related to population size, suggesting that deleterious mutations had not been purged from small populations. Offspring from smaller populations were on average more inbred, so inbreeding depression in clonal fitness was higher in small populations. We estimated variation in drift load from the mean fitness of outbred offspring and found enhanced drift load affecting female fertility within small populations. We conclude that self-incompatibility systems do not necessarily prevent small populations from suffering from inbreeding depression and drift load and may exacerbate the challenge of finding suitable mates.

Alleles↗

PubMed2005

Crystal structures of oxidized and reduced stellacyanin from horseradish roots.

Umecyanin (UMC) is a type 1 copper-containing protein which originates from horseradish roots and belongs to the stellacyanin subclass of the phytocyanins, a ubiquitous family of plant cupredoxins. The crystal structures of Cu(II) and Cu(I) UMC have been determined at 1.9 and 1.8 A, respectively. The protein has an overall fold similar to those of other phytocyanins. At the active site the cupric ion is coordinated by the N(delta1) atoms of His44 and His90, the S(gamma) of Cys85, and the O(epsilon)(1) of Gln95 in a distorted tetrahedral geometry. Both His ligands are solvent exposed and are surrounded by nonpolar and polar side chains on the protein surface. Thus, UMC does not possess a distinct hydrophobic patch close to the active site in contrast to almost all other cupredoxins. UMC has a large surface acidic patch situated approximately 10-30 A from the active site. The structure of Cu(I) UMC is the first determined for a reduced phytocyanin and demonstrates that the coordination environment of the cuprous ion is more trigonal pyramidal. This subtle change in geometry is primarily due to the Cu-N(delta1)(His44) and Cu-O(epsilon1)(Gln95) bond lengths increasing from 2.0 and 2.3 A in Cu(II) UMC to 2.2 and 2.5 A, respectively, in the reduced form, as a consequence of slight rotations of the His44 and Gln95 side chains. The limited structural changes upon redox interconversion at the active site of this stellacyanin are analogous to those observed in a typical type 1 copper site with an axial Met ligand and along with its surface features suggest a role for UMC in interprotein electron transfer.

Amino Acid Sequence↗

PubMed2005

A chimera encoding the fusion of an acetylcholine-binding protein to an ion channel is stabilized in a state close to the desensitized form of ligand-gated ion channels.

To understand the mechanism of allosteric coupling between the ligand-binding domain and the ion channel of the Cys-loop ligand-gated ion channels (LGICs), we fused the soluble acetylcholine-binding protein (AChBP), which lacks an ion channel, to either the cationic serotonin type-3A ion channel (5HT(3A)) or the anionic glycine ion channel. Both linear chimeras expressed in HEK-293 cells display high affinity for the nicotinic agonist epibatidine (K(D) = 0.2-0.5 nM), but are not targeted to the cell surface. Only after substituting a ring of three loops located at the putative membrane side of the AChBP three-dimensional structure by the homologous residues of 5HT(3A), the resulting chimera AChBP(ring)/5HT(3A) (i) still displayed on intact cells an apparent high affinity for epibatidine, yet with a fourfold decrease (K(D) = 2.1 nM), (ii) displayed a high proportion of low affinity sites (11 +/- 7 microM) for the resting state stabilizing competitive antagonist alpha-bungarotoxin and (iii) was successfully targeted to the cell surface, as seen by immunofluorescence labelling. The AChBP(ring)/5HT(3A) chimera forms a pentameric structure, as revealed by sucrose gradient sedimentation. However, no whole-cell patch-clamp currents were detectable. Interestingly, binding assays with membrane fragments prepared from cells expressing AChBP(ring)/5HT(3A) showed a decrease in the apparent affinity for the agonists nicotine and epibatidine (5-fold), concomitant with an increase in the proportion of high-affinity sites (48 +/- 1 nM) for alpha-bungarotoxin. These results indicate that fusion of AChBP to an ion channel forms a pentameric receptor exposed to the cell surface and able to convert between discrete allosteric states, but stabilized in a high affinity state for epibatidine that likely corresponds to a desensitized form of LGICs. These artificial chimeras might offer a useful system to investigate signal transduction in LGICs.

Acetylcholine↗

PubMed2005

Constraints on the evolution of adaptive phenotypic plasticity in plants.

The high potential fitness benefit of phenotypic plasticity tempts us to expect phenotypic plasticity as a frequent adaptation to environmental heterogeneity. Examples of proven adaptive plasticity in plants, however, are scarce and most plastic responses actually may be 'passive' rather than adaptive. This suggests that frequently requirements for the evolution of adaptive plasticity are not met or that such evolution is impeded by constraints. Here we outline requirements and potential constraints for the evolution of adaptive phenotypic plasticity, identify open questions, and propose new research approaches. Important open questions concern the genetic background of plasticity, genetic variation in plasticity, selection for plasticity in natural habitats, and the nature and occurrence of costs and limits of plasticity. Especially promising tools to address these questions are selection gradient analysis, meta-analysis of studies on genotype-by-environment interactions, QTL analysis, cDNA-microarray scanning and quantitative PCR to quantify gene expression, and two-dimensional gel electrophoresis to quantify protein expression. Studying plasticity along the pathway from gene expression to the phenotype and its relationship with fitness will help us to better understand why adaptive plasticity is not more universal, and to more realistically predict the evolution of plastic responses to environmental change.

Adaptation, Physiological↗

PubMed2005

Pre-steady-state kinetic analysis of riboflavin synthase using a pentacyclic reaction intermediate as substrate.

Riboflavin synthase catalyses a mechanistically complex dismutation affording riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H )-pyrimidinedione from 6,7-dimethyl-8-ribityllumazine. A pentacyclic adduct (compound 2 ) of two substrate molecules was used as substrate for pre-steady-state kinetic analysis. Whereas the wild-type enzyme catalyses the decomposition of compound 2 into a mixture of riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H )-pyrimidinedione, as well as into two equivalents of 6,7-dimethyl-8-ribityllumazine, a H102Q mutant enzyme predominantly catalyses the former reaction. Stopped-flow experiments with this mutant enzyme failed to identify a reaction intermediate between compound 2 and riboflavin. However, the apparent rate constants for the formation of riboflavin as observed by stopped-flow and quenched-flow experiments were significantly different, thus suggesting that the reaction proceeds via a significantly populated intermediate, the absorbance of which is similar to that of compound 2 . An F2A mutant enzyme converts compound 2 predominantly into 6,7-dimethyl-8-ribityllumazine. Stopped-flow experiments using compound 2 as substrate indicated a slight and rapid initial increase in absorbance at 310 nm, followed by a slower decrease. This finding, in conjunction with different apparent rates for the formation of 6,7-dimethyl-8-ribityllumazine, suggests the involvement of a significantly populated intermediate in the transition between compound 2 and 6,7-dimethyl-8-ribityllumazine, the optical spectrum of which is similar to that of compound 1.

Escherichia coli↗

PubMed2005

Evolution of vitamin B2 biosynthesis: riboflavin synthase of Arabidopsis thaliana and its inhibition by riboflavin.

A synthetic gene specifying the catalytic domain of the Arabidopsis thaliana riboflavin synthase was expressed with high efficiency in a recombinant Escherichia coli strain. The recombinant pseudomature protein was shown to convert 6,7-dimethyl-8-ribityllumazine into riboflavin at a rate of 0.027 s-1 at 25 degrees C. The protein sediments at a rate of 3.9 S. Sedimentation equilibrium analysis afforded a molecular mass of 67.5 kDa, indicating a homotrimeric structure, analogous to the riboflavin synthases of Eubacteria and fungi. The protein binds its product riboflavin with relatively high affinity (Kd =1.1 microM). Product inhibition results in a characteristic sigmoidal velocity versus substrate concentration relationship. Characterization of the enzyme/product complex by circular dichroism and UV absorbance spectroscopy revealed a shift of the absorption maxima of riboflavin from 370 and 445 to 399 and 465 nm, respectively. Complete or partial sequences for riboflavin synthase orthologs were analyzed from 11 plant species. In each case for which the complete plant gene sequence was available, the catalytic domain was preceded by a sequence of 1-72 amino acid residues believed to function as plastid targeting signals. Comparison of all available riboflavin synthase sequences indicates that hypothetical gene duplication conducive to the two-domain architecture occurred very early in evolution.

Amino Acid Sequence↗

PubMed2004

Unknown primary tumors: detection with dual-modality PET/CT--initial experience.

PURPOSE: To retrospectively evaluate fused positron emission tomography (PET)/computed tomography (CT) in depicting the primary lesion in cancer of an unknown primary tumor, compared with PET, CT, and PET and CT side-by-side evaluation. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Forty-five patients (26 men and 19 women) with metastatic cervical adenopathy (n = 18) or extracervical metastases (n = 27) of unknown primary tumor were included. The mean age of the patients was 57 years (range, 29-95 years). PET/CT imaging was performed in all patients 1 hour after administration of 350 MBq of fluorodeoxyglucose with a whole-body field of view. Contrast agents were administered orally and intravenously in all patients to ensure diagnostic CT data. PET/CT data sets were evaluated for the primary tumor, and imaging results were compared with those of CT, PET, and PET and CT side-by-side evaluation. Differences in diagnostic performance were assessed by using the McNemar test with Bonferroni correction, which accounts for multiple comparisons. RESULTS: PET/CT depicted the primary tumor in 15 (33%) of 45 patients. In 30 (67%) patients, the primary tumor site remained occult (P > .05). PET and CT side-by-side evaluation depicted 13 (29%) of 45 tumors (P > .05). PET alone revealed the primary tumor in 11 (24%) of 45 patients (P > .05), while CT alone helped in the correct diagnosis in eight (18%) of 45 patients (P > .05). There were no significant differences between the diagnostic accuracies of PET/CT and the other imaging modalities. CONCLUSION: PET/CT was able to depict more primary tumors, though not significantly, than either of the other imaging modalities, but larger patient cohorts are required to finally judge its value for revealing the primary tumor site.

Adult↗

PubMed2004

A brilliant monomeric red fluorescent protein to visualize cytoskeleton dynamics in Dictyostelium.

Red fluorescent proteins (RFPs) combined with GFP are attractive probes for double-fluorescence labeling of proteins in live cells. However, the application of these proteins is restrained by stable oligomer formation and by their weak fluorescence in vivo. Previous attempts to eliminate these problems by mutagenesis of RFP from Discosoma (DsRed) resulted in the monomeric mRFP1 and in the tetrameric RedStar RFP, which is distinguished by its enhanced fluorescence in vivo. Based on these mutations, we have generated an enhanced monomeric RFP, mRFPmars, and report its spectral properties. Together with green fluorescent labels, we used mRFPmars to visualize filamentous actin structures and microtubules in Dictyostelium cells. This enhanced RFP proved to be suitable to monitor the dynamics of cytoskeletal proteins in cell motility, mitosis, and endocytosis using dual-wavelength fluorescence microscopy.

Amino Acid Sequence↗

PubMed2004

Design, synthesis, and evaluation of acyclic C-nucleoside and N-methylated derivatives of the ribitylaminopyrimidine substrate of lumazine synthase as potential enzyme inhibitors and mechanistic probes.

Lumazine synthase and riboflavin synthase catalyze the last two steps in the biosynthesis of riboflavin, a vitamin that is involved in many critical biochemical reactions that are essential for the maintenance of life. To obtain inhibitors and structural probes that could be useful in studying the structures of bound reaction intermediates, the ribitylamino N-H moiety of the lumazine synthase substrate was replaced by CH(2) and N-CH(3) groups. The CH(2) replacement unexpectedly and completely abolished the affinity for lumazine synthase, thus revealing a critical, yet unexplained, role of the ribitylamino N-H moiety in conferring affinity for the enzyme. In contrast, the N-CH(3) replacement resulted in an inhibitor of both lumazine synthase and riboflavin synthase. Replacement of the ribitylamino N-H moiety with epimeric C-F moieties led to inhibition of lumazine synthase and riboflavin synthase when combined with the replacement of the 5-amino group with a nitro substituent.

Enzyme Inhibitors↗

PubMed2004

Evolution of vitamin B2 biosynthesis. A novel class of riboflavin synthase in Archaea.

The open reading frame MJ1184 of Methanococcus jannaschii with similarity to riboflavin synthase of Methanothermobacter thermoautotrophicus was cloned into an expression vector but was poorly expressed in an Escherichia coli host strain. However, a synthetic open reading frame that was optimized for expression in E.coli directed the synthesis of abundant amounts of a protein with an apparent subunit mass of 17.5 kDa. The protein was purified to apparent homogeneity. Hydrodynamic studies indicated a relative mass of 88 kDa suggesting a homopentamer structure. The enzyme was shown to catalyze the formation of riboflavin from 6,7-dimethyl-8-ribityllumazine at a rate of 24 nmol mg(-1) min(-1) at 40 degrees C. Divalent metal ions, preferably manganese or magnesium, are required for maximum activity. In contrast to pentameric archaeal type riboflavin synthases, orthologs from plants, fungi and eubacteria are trimeric proteins characterized by an internal sequence repeat with similar folding patterns. In these organisms the reaction is achieved by binding the two substrate molecules in an antiparallel orientation. With the enzyme of M.jannaschii, 13C NMR spectroscopy with 13C-labeled 6,7-dimethyl-8-ribityllumazine samples as substrates showed that the regiochemistry of the dismutation reaction is the same as observed in eubacteria and eukaryotes, however, in a non-pseudo-c2 symmetric environment. Whereas the riboflavin synthases of M.jannaschii and M.thermoautotrophicus are devoid of similarity with those of eubacteria and eukaryotes, they have significant sequence similarity with 6,7-dimethyl-8-ribityllumazine synthases catalyzing the penultimate step of riboflavin biosynthesis. 6,7-Dimethyl-8-ribityllumazine synthase and the archaeal riboflavin synthase appear to have diverged early in the evolution of Archaea from a common ancestor. Some Archaea have eubacterial type riboflavin synthases which may have been acquired by lateral gene transfer.

Amino Acid Sequence↗

PubMed2004

On the reaction mechanism of adduct formation in LOV domains of the plant blue-light receptor phototropin.

The blue-light sensitive photoreceptor, phototropin, is a flavoprotein which regulates the phototropism response of higher plants. The photoinduced triplet state and the photoreactivity of the flavin-mononucleotide (FMN) cofactor in two LOV domains of Avena sativa, Adiantum capillus-veneris, and Chlamydomonas reinhardtii phototropin have been studied by time-resolved electron paramagnetic resonance (EPR) and UV-vis spectroscopy at low temperatures (T < or = 80 K). Differences in the electronic structure of the FMN as reflected by altered zero-field splitting parameters of the triplet state could be correlated with changes in the amino acid composition of the binding pocket in wild-type LOV1 and LOV2 as well as in mutant LOV domains. Even at cryogenic temperatures, time-resolved EPR experiments indicate photoreactivity of the wild-type LOV domains, which was further characterized by UV-vis spectroscopy. Wild-type LOV1 and LOV2 were found to form an adduct between the FMN cofactor and the functional cysteine with a yield of 22% and 68%, respectively. The absorption maximum of the low-temperature photoproduct of wild-type LOV2 is red-shifted by about 15 nm as compared with the FMN C(4a)-cysteinyl adduct formed at room temperature. In light of these observations, we discuss a radical-pair reaction mechanism for the primary photoreaction in LOV domains.

Adiantum↗