tryptophan-tryptophylquinone and cysteine-tryptophylquinone

Tryptophan (Trp) holds a unique place in biology for a multitude of reasons. It is the largest of all twenty amino acids in the translational toolbox. Its side chain is indole, which is aromatic with a binuclear ring structure, whereas those of Phe, Tyr, and His are single-ring aromatics. In part due to these elaborate structural features, the biosynthetic pathway of Trp is the most complex and the most energy-consuming among all amino acids. Essential in the animal diet, Trp is also the least abundant amino acid in the cell, and one of the rarest in the proteome. In most eukaryotes, Trp is the only amino acid besides Met, which is coded for by a single codon, namely UGG. Due to the large and hydrophobic π-electron surface area, its aromatic side chain interacts with multiple other side chains in the protein, befitting its strategic locations in the protein structure. Finally, several Trp derivatives, namely tryptophylquinone, oxitriptan, serotonin, melatonin, and tryptophol, have specialized functions. Overall, Trp is a scarce and precious amino acid in the cell, such that nature uses it parsimoniously, for multiple but selective functions. Here, the various aspects of the uniqueness of Trp are presented in molecular terms.

Topics: Animals; Codon; Dipeptides; Humans; Hydrophobic and Hydrophilic Interactions; Indolequinones; Indoles; Kynurenine; Protein Biosynthesis; Protein Interaction Domains and Motifs; Proteins; Serotonin; Structure-Activity Relationship; Thermodynamics; Tryptophan

A protein-derived cofactor is a catalytic or redox-active site in a protein that is formed by post-translational modification of one or more amino acid residues. These post-translational modifications are irreversible and endow the modified amino acid residues with new functional properties. This Perspective focuses on the following advances in this area that have occurred during recent years. The biosynthesis of the tryptophan tryptophylquinone cofactor is catalyzed by a diheme enzyme, MauG. A bis-Fe

Topics: Amino Acids; Coenzymes; Dipeptides; Electron Transport; Heme; Humans; Indolequinones; Lysine; Models, Molecular; Oxidation-Reduction; Oxidoreductases Acting on CH-NH Group Donors; Protein Processing, Post-Translational; Quinones; Tryptophan

Topics: Animals; Coenzymes; Dihydroxyphenylalanine; Dipeptides; Humans; Indolequinones; Lysine; PQQ Cofactor; Quinones; Tryptophan

Topics: Amine Oxidase (Copper-Containing); Amino Acid Sequence; Animals; Catalysis; Codon, Terminator; Coenzymes; Copper; Crystallography, X-Ray; Dihydroxyphenylalanine; Dipeptides; Endonucleases; Humans; Indolequinones; Ions; Molecular Sequence Data; Oxidoreductases Acting on CH-NH Group Donors; RNA-Directed DNA Polymerase; Tryptophan

The electronic effects of the C-4 substituent on the physicochemical properties and reactivity of the 6,7-inodolequinone cofactors (CTQ and TTQ) have extensively been investigated with use of a series of C-4 substituted 6,7-inodolequinone derivatives (1-4). The one-electron reduction potentials of the 6,7-inodolequinone derivatives decrease with increasing the electron donating ability of the C-4 substituent (with the following order of E degrees': 4>1>2>3). The reaction of indolequinones 1-3 with benzylamine proceeds stepwise through the iminoquinone and the product-imine intermediates to give aminophenol as the final product as the case of TTQ model compound 4. The rate constants of each step have been determined by the detailed kinetic analysis, and the kinetic deuterium isotope effects have also been examined to confirm the rate-determining step. The reactivity of CTQ model compound 1 toward the amines is by one order of magnitude lower than that of TTQ model compound 4. The reactivity of indolequinones 2 and 3 is further decreased due to their stronger electron-donating substituents at C-4. A more important difference between CTQ model compound 1 and TTQ model compound 4 is the reactivity of the iminoquinone intermediate: the reaction of the CTQ model compound with amines stops at the iminoquinone formation stage at room temperature, whereas the reaction of the TTQ model compound with amines proceeds up to the aminophenol formation. Thus, the energy barrier for the rearrangement of the iminoquinone to the product-imine is higher in the CTQ model system than in the TTQ model system.

Topics: Alcohol Oxidoreductases; Amines; Aminophenols; Coenzymes; Crystallography, X-Ray; Dipeptides; Electrochemistry; Imines; Indolequinones; Molecular Structure; Quinones; Spectrophotometry, Infrared; Spectrophotometry, Ultraviolet; Structure-Activity Relationship; Tryptophan