Abstract
L-Tryptophan is the unique protein amino acid (AA) bearing an indole ring: its biotransformation in living organisms contributes either to keeping this chemical group in cells and tissues or to breaking it, by generating in both cases a variety of bioactive molecules. Investigations on the biology of Trp highlight the pleiotropic effects of its small derivatives on homeostasis processes. In addition to protein turn-over, in humans the pathways of Trp indole derivatives cover the synthesis of the neurotransmitter/hormone serotonin (5-HT), the pineal gland melatonin (MLT), and the trace amine tryptamine. The breakdown of the Trp indole ring defines instead the “kynurenine shunt” which produces cell-response adapters as L-kynurenine, kynurenic and quinolinic acids, or the coenzyme nicotinamide adenine dinucleotide (NAD+). This review aims therefore at tracing a “map” of the main molecular effectors in human tryptophan (Trp) research, starting from the chemistry of this AA, dealing then with its biosphere distribution and nutritional value for humans, also focusing on some proteins responsible for its tissue-dependent uptake and biotransformation. We will thus underscore the role of Trp biochemistry in the pathogenesis of human complex diseases/syndromes primarily involving the gut, neuroimmunoendocrine/stress responses, and the CNS, supporting the use of -Omics approaches in this field.
Highlights
L-Tryptophan (L-Trp) is a large neutral amino acid (LNAA) present in living organisms, precisely one of the 20 L-amino acids (AAs) incorporated in proteins during the process of mRNA translation
Trp formation in plants has been found tightly regulated by several transcriptional factors acting on gene expression of the enzymes of the shikimate pathway and aromatic AAs (AAAs) metabolism, as evidenced in the Brassicaceae Arabidopsis
Genes of Trp biosynthesis would have been lost in plastid-lacking animal eukaryote cells. These considerations lead to reasonably think that AAAs metabolism and production of their bioactive derivatives occupy a central position in the early stages of the evolution of living organisms and trophism lineages
Summary
L-Tryptophan (L-Trp) is a large neutral amino acid (LNAA) present in living organisms, precisely one of the 20 L-amino acids (AAs) incorporated in proteins during the process of mRNA translation. Besides being an intermediate of protein/peptide synthesis and turn-over, Trp is the object of scientific investigations in human biological research since decades because of its transformation, after absorption, into a series of small bioactive, pleiotropic compounds, each capable of influencing a number of cell metabolic pathways and physiological responses. Alterations of L-Trp-deriving compounds can be found associated with a variety of metabolic diseases and syndromes affecting those systems and organs responsible for maintaining the chemical, cellular, and behavioural homeostasis: the gut-liver apparatus and the neuroendocrine and immune systems along with the CNS. Amongst Trp-derived compounds produced in the human body, there is the ancient neurotransmitter serotonin (5-hydroxy-tryptamine, 5-HT), a biogenic amine which is known to regulate, in the human CNS, the main adaptive reactions and responses to environmental changes, such as mood-anxiety, cognition, nociception, impulsivity, aggressiveness, libido, feeding behaviour, and body temperature [2, 3]. We will briefly introduce some Trp research targets under investigation for therapeutic strategies in human pathology as well as the utility of -Omics approaches
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
