Disease relevance of DHA

• Microbial metabolites isolated in screening programs for their ability to activate transcription of the tipA promoter (ptipA) in Streptomyces lividans define a class of cyclic thiopeptide antibiotics having dehydroalanine side chains ("tails") [1].
• Substitution of pyridoxal 5'-phosphate in the O-acetylserine sulfhydrylase from Salmonella typhimurium by cofactor analogs provides a test of the mechanism proposed for formation of the alpha-aminoacrylate intermediate [2].
• Presence and quantity of dehydroalanine in histidine ammonia-lyase from Pseudomonas putida [3].
• The reactions of the indole analogues indoline and aniline with the Escherichia coli tryptophan synthase alpha-aminoacrylate Schiff base intermediate have been characterized by UV-visible and 1H NMR absorption spectroscopy and compared with the interactions of indole and the potent inhibitor benzimidazole [4].
• Nisin is a small gene-encoded antimicrobial protein produced by Lactococcus lactis that contains unusual dehydroalanine and dehydrobutyrine residues [5].

High impact information on DHA

• Three post-translational modifications (i.e. oxidation of Met and Trp, conversion of Ser to dehydroalanine, and formylation of His) were observed in alphaA-crystallin fragment, and the first two modifications could cross-link proteins [6].
• Finally, in the presence of homocysteine the alpha-aminoacrylate-enzyme absorption band readily disappears with the concomitant formation of the absorption band of the internal aldimine, indicating that cystathionine beta-synthase crystals catalyze both beta-elimination and beta-replacement reactions [7].
• Histidase and phenylalanine ammonia-lyase are the only two enzymes that have been postulated to require the modified amino acid, dehydroalanine, for enzyme activity [8].
• Replacement by site-directed mutagenesis of the Ser-5 codon in nisZ by a Thr codon, led to a mutant with a dehydrobutyrine instead of a dehydroalanine residue at position 5, as shown by NMR [9].
• The formation of dehydroalanine in thyroglobulin is the result of the side chain elimination of an iodophenyl group during the thyroid hormone formation from two iodotyrosyl residues [10].

Chemical compound and disease context of DHA

• In the absence of other substrates, L-Ser reacts rapidly with the tryptophan synthase alpha 2 beta 2 bienzyme from Salmonella typhimurium at pH 7.8 and 25 degrees C to give an equilibrating mixture of species dominated by comparable amounts of the L-Ser external aldimine Schiff base, E(Aex1), and the alpha-aminoacrylate Schiff base, E(A-A) [11].
• Ancovenin, an inhibitor of angiotensin I converting enzyme isolated from the culture broth of a Streptomyces species, is a dialysable peptide composed of sixteen amino acid residues containing unusual amino acids such as threo-beta-methyllanthionine, meso-lanthionine, and dehydroalanine [12].

Biological context of DHA

• As an initial step to determining the precursor of dehydroalanine in histidase, we have isolated a functional cDNA clone for histidase from a rat liver cDNA library using an affinity-purified antiserum [13].
• We conclude that serine-143 is the most probable precursor of the active-site dehydroalanine [14].
• Elimination of phenol then has been proposed to give an alpha-aminoacrylate Schiff base, which releases iminopyruvate that ultimately undergoes hydrolysis to yield ammonium pyruvate [15].
• Our findings are discussed in the light of a model in which specific protein conformations are associated with the external aldimine and the alpha-aminoacrylate Schiff bases, the latter being stabilized by temperature, protons, and alpha-subunit ligands [16].
• Efficient 14-step syntheses of (-)-fumiquinazolines C (7) and E (3) and a 15-step synthesis of (-)-fumiquinazoline H (8) using FmocNHCH(CH2SePh)CO2H as a dehydroalanine precursor that spontaneously eliminated benzeneselenol without oxidation under the cyclization conditions are also reported [17].

Anatomical context of DHA

• We developed a new assay method for dehydroalanine residues in thyroglobulin, which had been proposed to be the 'lost side chains' during thyroid hormonogenesis [18].
• The target compounds were designed as mimetics of the dehydroalanine side chain of the macrocyclic antibiotic thiostrepton that acts on the bacterial ribosome [19].
• One of those compounds, the AD-5 (N-(paramethoxyphenylacetyl) dehydroalanine) has been examined for its ability to decrease the amount of reactive oxygen species which appeared when liver microsomes (isolated from rats pretreated with phenobarbital) are incubated in the presence of Nitrofurantoin (NF) [20].

Associations of DHA with other chemical compounds

• Formation of dehydroalanine residues during thyroid hormone synthesis in thyroglobulin [21].
• Letter: alpha-aminoacrylate schiff base in nonenzymatic pyridoxal catalysis [22].
• The active-site serine of thrombin was modified to dehydroalanine by promoting the beta-elimination of phenylmethylsulfonic acid from phenylmethylsulfonyl fluoride-inactivated thrombin under conditions in which the enzyme is unfolded [23].
• The alpha-aminoacrylate intermediate can be formed from l-cysteine and l-serine with the S272A,D mutant enzymes, but not with the wild-type enzyme, and taken together with the increased K(d) for the serine external Schiff base is consistent with a change in cofactor orientation in the active site [24].
• Data suggest an asymmetric transition state for alpha-proton abstraction by the active site lysine and the elimination of the acetyl group of O-acetyl-L-serine (OAS) to form the alpha-aminoacrylate intermediate [25].

Gene context of DHA

• Moreover, at minimum levels of iodination, when thyroglobulin contains the lowest number of hormone molecules, dehydroalanine is mostly found in the 15,900-Da peptide [10].
• The reaction occurs via a ping-pong kinetic mechanism in which alpha-aminoacrylate in Schiff base with the active site PLP is an intermediate [Cook, P. F., Hara, S., Nalabolu, S. R., and Schnackerz, K. D. (1992) Biochemistry 31, 2298-2303] [26].
• Furthermore, the alpha-aminoacrylate Schiff base intermediate, E(A-A), formed between L-Ser and enzyme-bound PLP has an unusual spectrum with lambda(max) = 350 nm and a shoulder extending to greater than 500 nm [27].
• A chemoselective strategy for oligosaccharide-peptide ligation is described in which alpha-thio analogues of mucin-related glycoconjugates can be readily accessed through site-selective conjugate addition of complex oligosaccharide thiolates to dehydroalanine-containing peptides [28].
• Use of a dehydroalanine-containing peptide as an efficient inhibitor of tripeptidyl peptidase II [29].

Analytical, diagnostic and therapeutic context of DHA

• It was named sublancin 168, and its behavior during Edman sequence analysis and its NMR spectrum suggested that sublancin is a dehydroalanine-containing lantibiotic [30].
• Colorimetry of dehydroalanine residues preserved as 'lost side chains' in thyroglobulin [18].
• The presence of dehydroalanine was confirmed by hydrogenation and subsequent amino acid analysis with combined gas liquid chromatography/mass spectrometry [31].
• Both ammonia-lyases have a catalytically important electrophilic group, which was believed to be dehydroalanine for 30 years but has now been revealed by X-ray crystallography and UV spectroscopy to be a highly electrophilic 5-methylene-3,5-dihydroimidazol-4-one (MIO) group [32].

References