Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: KEGG:D02011 (FAD)
5,530 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA photolyase is a photoactive flavoprotein that contains three tryptophan residues between the FAD cofactor and the protein surface, the solvent-exposed Trp being located 14.8 A from the flavin. Photoreduction of the neutral radical FADH. form to the catalytically active FADH- form occurs via electron transfer through this chain. The first step in this chain takes 30 ps, the second less than 4 ps. Using a combination of site-directed mutagenesis and femtosecond polarization spectroscopy to discriminate the spectroscopically indistinguishable Trp residues, we show that the third step occurs in less than 30 ps. This implies that the first photoreduction step is rate limiting and that the Trp chain effectively acts as molecular "wire" ensuring rapid and directed long-range charge translocation across the protein. This finding is important for the functioning of the large class of cryptochrome blue-light receptors, where the Trp chain is conserved. In DNA photolyase we make use of the natural photoactivation of the process, but more generally chains of aromatic amino acids may allow very fast long-range electron transfer also in nonphotoactive proteins.
...
PMID:Electron hopping through the 15 A triple tryptophan molecular wire in DNA photolyase occurs within 30 ps. 1885 Jul 8

The crystal structure of the FAD-dependent chondrochloren halogenase CndH has been established at 2.1 A resolution. The enzyme contains the characteristic FAD-binding scaffold of the glutathione reductase superfamily. Except for its C-terminal domain, the chainfold of CndH is virtually identical with those of FAD-dependent aromatic hydroxylases. When compared to the structurally known FAD-dependent halogenases PrnA and RebH, CndH lacks a 45 residue segment near position 100 and deviates in the C-terminal domain. Both variations are near the active center and appear to reflect substrate differences. Whereas PrnA and RebH modify free tryptophan, CndH halogenates the tyrosyl group of a chondrochloren precursor that is most likely bound to a carrier protein. In contrast to PrnA and RebH, which enclose their small substrate completely, CndH has a large non-polar surface patch that may accommodate the putative carrier. Apart from the substrate binding site, the active center of CndH corresponds to those of PrnA and RebH. At the halogenation site, CndH has the characteristic lysine (Lys76) but lacks the required base Glu346 (PrnA). This base may be supplied by a residue of its C-terminal domain or by the carrier. These differences were corroborated by an overall sequence comparison between the known FAD-dependent halogenases, which revealed a split into a PrnA-RebH group and a CndH group. The two functionally established members of the CndH group use carrier-bound substrates, whereas three members of PrnA-RebH group are known to accept a free amino acid. Given the structural and functional distinction, we classify CndH as a new variant B of the FAD-dependent halogenases, adding a new feature to the structurally established variant A enzymes PrnA and RebH.
...
PMID:Structure and action of the myxobacterial chondrochloren halogenase CndH: a new variant of FAD-dependent halogenases. 1900 Jun 96

Mutations in the genes encoding the alpha-subunit and beta-subunit of the mitochondrial electron transfer flavoprotein (ETF) and the electron transfer flavoprotein:ubiquinone oxidoreductase (ETF:QO) cause multiple acyl-CoA dehydrogenation deficiency (MADD), a disorder of fatty acid and amino acid metabolism. Point mutations in ETF, which may compromise folding, and/or activity, are associated with both mild and severe forms of MADD. Here we report the investigation on the conformational and stability properties of the disease-causing variant ETFbeta-D128N, and our findings on the effect of flavinylation in modulating protein conformational stability and activity. A combination of biochemical and biophysical methods including circular dichroism, visible absorption, flavin, and tryptophan fluorescence emission allowed the analysis of structural changes and of the FAD moiety. The ETFbeta-D128N variant retains the overall fold of the wild type, but under stress conditions its flavin becomes less tightly bound. Flavinylation is shown to improve the conformational stability and biological activity of a destabilized D128N variant protein. Moreover, the presence of flavin prevented proteolytic digestion by avoiding protein destabilization. A patient homozygous for the ETFbeta-D128N mutation developed severe disease symptoms in association with a viral infection and fever. In agreement, our results suggest that heat inactivation of the mutant may be more relevant at temperatures above 37 degrees C. To mimic a situation of fever in vitro, the flavinylation status was tested at 39 degrees C. FAD exerts the effect of a pharmacological chaperone, improving ETF conformation, and yielding a more stable and active enzyme. Our results provide a structural and functional framework that could help to elucidate the role that an increased cellular FAD content obtained from riboflavin supplementation may play in the molecular pathogenesis of not only MADD, but genetic disorders of flavoproteins in general.
...
PMID:Role of flavinylation in a mild variant of multiple acyl-CoA dehydrogenation deficiency: a molecular rationale for the effects of riboflavin supplementation. 1908 74

Nanomolar concentrations of cysteine-capped CdTe quantum dots (QDs) quenched the fluorescence of tryptophan moieties in glucose oxidase (GOX), while the fluorescence of the other fluorophore in the enzyme, FAD (Flavin Adenine Dinucleotide), was not affected by the QDs. The quenching followed a linear Stern-Volmer equation and its static nature was confirmed by time-resolved photoluminescence (PL) spectroscopy. The binding of substrate to the GOX resulted in a decrease of the Stern-Volmer quenching constant, which is attributable to a change in tertiary structure of GOX as revealed by circular dichroism (CD) spectroscopy. The quenching constant was further lowered for the free tryptophan. A strong size dependence of quenching pattern was observed and the quenching efficiency increased with increasing average size of the CdTe QDs. For a given size, quenching constants exhibit an increasing trend with a gradual decrease in polarity of the solvent indicating binding between GOX and CdTe QDs. Fourier-transform infra-red (FTIR) spectroscopy has revealed the involvement of the indole ring of tryptophan in binding with CdTe QDs. Interestingly, the quenching pattern also showed a strong dependence on activity of the enzyme. An empirical equation has been derived to correlate the enzyme activity with the quenching constant based on which a novel QD-based fluorimetric method for activity determination could be devised.
...
PMID:Conformation and activity dependent interaction of glucose oxidase with CdTe quantum dots: towards developing a nanoparticle based enzymatic assay. 1925 77

The electronic structure of the two lowest excited electronic states of FAD and FADH(*) in folate-depleted E. coli DNA photolyase (PL(OX) and PL(SQ), respectively) was measured using absorption Stark spectroscopy. The experimental analysis was supported by TDDFT calculations of both the charge redistribution and the difference dipole moments for the transitions of both oxidation states using lumiflavin as a model. The difference dipole moments and polarizabilities for PL(OX) are similar to those obtained in our previous work for flavins in simple solvents and in an FMN-containing flavoprotein. No such comparison can be made for PL(SQ), as we believe this to be the first experimental report of the direction and magnitude of excited-state charge redistribution in any flavosemiquinone. The picture that emerges from these studies is discussed in the context of electron transfer in photolyase, particularly for the semiquinone photoreduction process, which involves nearby tryptophan residues as electron donors. The direction of charge displacement derived from an analysis of the Stark spectra rationalizes the positioning of the critical Trp382 residue relative to the flavin for efficient vectorial electron transfer leading to photoreduction. The ramifications of vectorial charge redistribution are discussed in the context of the wider class of flavoprotein blue light photoreceptors.
...
PMID:Charge redistribution in oxidized and semiquinone E. coli DNA photolyase upon photoexcitation: stark spectroscopy reveals a rationale for the position of Trp382. 1929 45

Cyclohexanone monooxygenase (CHMO) is a flavoprotein that carries out the archetypical Baeyer-Villiger oxidation of a variety of cyclic ketones into lactones. Using NADPH and O(2) as cosubstrates, the enzyme inserts one atom of oxygen into the substrate in a complex catalytic mechanism that involves the formation of a flavin-peroxide and Criegee intermediate. We present here the atomic structures of CHMO from an environmental Rhodococcus strain bound with FAD and NADP(+) in two distinct states, to resolutions of 2.3 and 2.2 A. The two conformations reveal domain shifts around multiple linkers and loop movements, involving conserved arginine 329 and tryptophan 492, which effect a translation of the nicotinamide resulting in a sliding cofactor. Consequently, the cofactor is ideally situated and subsequently repositioned during the catalytic cycle to first reduce the flavin and later stabilize formation of the Criegee intermediate. Concurrent movements of a loop adjacent to the active site demonstrate how this protein can effect large changes in the size and shape of the substrate binding pocket to accommodate a diverse range of substrates. Finally, the previously identified BVMO signature sequence is highlighted for its role in coordinating domain movements. Taken together, these structures provide mechanistic insights into CHMO-catalyzed Baeyer-Villiger oxidation.
...
PMID:Crystal structures of cyclohexanone monooxygenase reveal complex domain movements and a sliding cofactor. 1938 44

Cryptochromes and DNA photolyases are related flavoproteins with flavin adenine dinucleotide as the common cofactor. Whereas photolyases repair DNA lesions caused by UV radiation, cryptochromes generally lack repair activity but act as UV-A/blue light photoreceptors. Two distinct electron transfer (ET) pathways have been identified in DNA photolyases. One pathway uses within its catalytic cycle, light-driven electron transfer from FADH(-)* to the DNA lesion and electron back-transfer to semireduced FADH(o) after photoproduct cleavage. This cyclic ET pathway seems to be unique for the photolyase subfamily. The second ET pathway mediates photoreduction of semireduced or fully oxidized FAD via a triad of aromatic residues that is conserved in photolyases and cryptochromes. The 5,10-methenyltetrahydrofolate (5,10-methenylTHF) antenna cofactor in members of the photolyase family is bleached upon light excitation. This process has been described as photodecomposition of 5,10-methenylTHF. We show that photobleaching of 5,10-methenylTHF in Arabidopsis cry3, a member of the cryptochrome DASH family, with repair activity for cyclobutane pyrimidine dimer lesions in single-stranded DNA and in Escherichia coli photolyase results from reduction of 5,10-methenylTHF to 5,10-methyleneTHF that requires the intact tryptophan triad. Thus, a third ET pathway exists in members of the photolyase family that remained undiscovered so far.
...
PMID:Photoreduction of the folate cofactor in members of the photolyase family. 1953 78

Anthranilate is an important intermediate of tryptophan metabolism. In this study, a hydroxylase system consisting of an FADH(2)-utilizing monooxygenase (GTNG_3160) and an FAD reductase (GTNG_3158), as well as a bifunctional riboflavin kinase/FMN adenylyltransferase (GTNG_3159), encoded in the anthranilate degradation gene cluster in Geobacillus thermodenitrificans NG80-2 were functionally characterized in vitro. GTNG_3159 produces FAD to be reduced by GTNG_3158 and the reduced FAD (FADH(2)) is utilized by GTNG_3160 to convert anthranilate to 3-hydroxyanthranilate (3-HAA), which is further degraded to acetyl-CoA through a meta-cleavage pathway also encoded in the gene cluster. Utilization of this pathway for the degradation of anthranilate and tryptophan by NG80-2 under physiological conditions was confirmed by real-time RT-PCR analysis of representative genes. This is believed to be the first time that the degradation pathway of anthranilate via 3-HAA has been characterized in a bacterium. This pathway is likely to play an important role in the survival of G. thermodenitrificans in the oil reservoir conditions from which strain NG80-2 was isolated.
...
PMID:Characterization of the anthranilate degradation pathway in Geobacillus thermodenitrificans NG80-2. 1994 60

The photoactivation dynamics of two new flavoproteins (OtCPF1 and OtCPF2) of the cryptochrome photolyase family (CPF), belonging to the green alga Ostreococcus tauri , was studied by broadband UV-vis femtosecond absorption spectroscopy. Upon excitation of the protein chromophoric cofactor, flavin adenine dinucleotide in its oxidized form (FAD(ox)), we observed in both cases the ultrafast photoreduction of FAD(ox): in 390 fs for OtCPF1 and 590 fs for OtCPF2. Although such ultrafast electron transfer has already been reported for other flavoproteins and CPF members, the present result is the first demonstration with full spectral characterization of the mechanism. Analysis of the photoproduct spectra allowed identifying tryptophan as the primary electron donor. This residue is found to be oxidized to its protonated radical cation form (WH(*+)), while FAD(ox) is reduced to FAD(*-). Subsequent kinetics were observed in the picosecond and subnanosecond regime, mostly described by a biexponential partial decay of the photoproduct transient signal (9 and 81 ps for OtCPF1, and 13 and 340 ps for OtCPF2), with reduced spectral changes, while a long-lived photoproduct remains in the nanosecond time scale. We interpret these observations within the model proposed by the groups of Brettel and Vos, which describes the photoreduction of FADH(*) within E. coli CPD photolyase (EcCPD) as a sequential electron transfer along a chain of three tryptophan residues, although in that case the rate limiting step was the primary photoreduction in 30 ps. In the present study, excitation of FAD(ox) permitted to reveal the following steps and spectroscopically assign them to the hole-hopping process along the tryptophan chain, accompanied by partial charge recombination at each step. In addition, structural analysis performed by homology modeling allowed us to propose a tentative structure of the relative orientations of FAD and the conserved tryptophan triad. The results of preliminary transient anisotropy measurements performed on OtCPF2 finally showed good compatibility with the oxidation of the distal tryptophan residue (WH(351)) in 340 ps, hence, with the overall Brettel-Vos mechanism.
...
PMID:Spectro-temporal characterization of the photoactivation mechanism of two new oxidized cryptochrome/photolyase photoreceptors. 2022 48

The initial photochemistry of plant cryptochromes has been extensively investigated in recent years. It is hypothesized that cryptochrome photoexcitation involves a Trp-triad-dependent photoreduction. According to this hypothesis, cryptochromes in the resting state contain oxidized FAD; light triggers a sequential electron transfer from three tryptophan residues to reduce FAD to a neutral semiquinone (FADH*); FADH* is the presumed signaling state and it is re-oxidized to complete the photocycle. However, this photoreduction hypothesis is currently under debate. An alternative model argues that the initial photochemistry of cryptochromes involves a photolyase-like cyclic electron shuttle without a bona fide redox reaction mediated by the Trp-triad residues, leading to conformational changes, signal propagation, and physiological responses.
...
PMID:Searching for a photocycle of the cryptochrome photoreceptors. 2094 27


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---