Tryptophan variants

The emission maximum of tryptophan in proteins can range fiom 308 mn for a residue buried in a completely apolar enviroiunent (as in the single tryptophan variant of azurin (37)) to 350 nm for a fully solvent-exposed residue (38-40). Due to their apolar character, tryptophan residues are usually either fully or partially buried in the three-dimensional structures of proteins and are expected to have emission maxima from 320 to 340 nm. Unfolding of a protein, and concomitant increase in the solvent exposure of tiyptophan residues will invariably lead to a red-shift in the fluorescence of a tryptophan-containing protein. 

The first objective was the conversion of L-tryptophan into a derivative that could be converted to pyrroloindoline 3, possessing a cis ring fusion and a syn relationship of the carboxyl and hydroxyl groups. This was achieved by the conversions shown in Scheme 1. A critical step was e. Of many variants tried, the use of the trityl group on the NH2 of tryptophan and the t-butyl group on the carboxyl resulted in stereospecific oxidative cyclization to afford 3 of the desired cis-syn stereochemistry in good yield. 

The results of 15N CP MAS NMR studies for lysine, tryptophan and methionine labelled green variant of proteorhodopsin were presented by Shastri et al.80... 

Comings DE et al. Exon and intron variants in the human tryptophan 2,3-dioxy-genase gene potential association with Tourette syndrome, substance abuse and other disorders. Pharmacogenetics 1996 6(4) 307—318. 

Han, L., Nielson, D.A., Rosenthal, N.E., Jefferson, K., Kaye, W., Murphy, D., Altemus, M., Humphries, J., Casssano, G., Rotondo, A., Virkkhunen, M., Linnoila, M., and Goldman, D. (1999) No coding variant of the tryptophan hydroxylase gene detected in seasonal affective disorder, obsessive-compulsive disorder, anorexia nervosa, and alcoholism. Biol Psychiatry 45 615-619. 

Yutani, K., Ogasahara, K., Tsujita, T. and Sugino, Y. (1987) Dependence of conformations stability on hydrophobicity of the amino acid residue in a series of variant proteins substituted at a unique position of tryptophan synthase subunit. Proc. Natl. Acad. Sci. USA, 84, 4441-4444. 

Bacterial De-Novo Synthesis. The basic idea behind this variant is to use the synthetic potential of bacteria to produce the indole precursor (Scheme 3). Although indole (23) does not occur as an intermediate in bacterial metabolism, it appears as an enzyme-linked intermediate in the biocatalytic transformation ofD-glucose (17) to L-tryptophan (22). The crucial biosynthetic step is the conversion of indole-3-glycerine phosphate (21) to L-tryptophan (22) by the enzyme tryptophan synthase. 

The dynamic properties of wild-type /A ll E and several thermostable variants were investigated by monitoring the phosphorescence lifetimes of buried tryptophan residues at room temperature (Gershenson et al.,... 

Finally, it could also be demonstrated that it is possible to improve VP catalytic properties by modifying the amino acid residues around the catalytic tryptophan. In this sense, simultaneous removal of Arg257 and incorporation of a phenylalanine residue, homologous to LiP Phe267 involved in VA binding [80], resulted in a VP variant with VA transient-state kinetic constants comparable to those of LiP [76]. 

Ruiz-Duenas FJ, Pogni R, Morales M et al (2009) Protein radicals in fungal versatile peroxidase catalytic tryptophan radical in both Compound I and Compound II and studies on W164Y, W164H and W164S variants. J Biol Chem 284 7986—7994... 

Blodig W, Smith AT, WA D et al (2001) Crystal structures of pristine and oxidatively processed lignin peroxidase expressed in Escherichia coli and of the W171F variant that eliminates the redox active tryptophan 171. Implications on the reaction mechanism. J Mol Biol 305 851-861... 

The comQXP loci of a set of natural Bacillus isolates have been sequenced and shown to possess a striking polymorphism that determines specific patterns of both activation and inhibition of the quorum sensing response.217 Genetic and biochemical evidence demonstrate that all the ComX variants are isoprenylated by the posttranslational modification of a conserved tryptophan residue and that the modifications on the ComX peptide backbones vary in mass among the various phenotypes. 

Employing an in vitro competition assay (see Section VI,C), denatured BPTI, RNase A, the a subunit of tryptophan synthase, and an unstable mRBP variant were each found to compete with mMBP for SecB binding (Hardy and Randall, 1991). Half-maximal competition occurred at molar ratios (competitor MBP) of about 2.5,4,6, and 25, respectively. A dissociation constant of approximately 5 nM for the SecB-BPTI complex was calculated from the binding curve obtained from stepwise addition of carboxamidomethylated BPTI (R-BPTI) to a solution of SecB (the reaction is monitored by the increase in fluorescence that results when SecB... 

Among the other spectroscopies, either in the direct or reflection mode, fluorescence spectroscopy may be mentioned. A promising variant is Total Internal Reflection Fluorescence spectroscopy (TIRF). The decay rate of an excited fluorescing probe is usually Interpreted in terms of the local fluidity and polarity. The technique has been used to estimate the extent of ordering inside adsorbed surfactant layers, but this is not an absolute method because a fluorescent probe has to be inserted, and such probes themselves affect the local fluidity. More rigorous are fluorescence experiments with molecules that possess such a probe as an intrinsic part of their structure, such as tryptophans in... 

Brown SM, Peet E, Manuck SB, Williamson DE, Dahl RE, Ferrell RE, Hariri AR. A regulatory variant of the human tryptophan 58. hydroxylase-2 gene biases amygdala reactivity. Mol. Psychiatry 2005 10 884-888, 805. 

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