The tryptophan hydroxylase 2 (TPH2) enzyme catalyzes the first step of serotonin biosynthesis. Serotonin is known for its role in several homeostatic systems related to sleep, mood, and food intake. As the reaction catalyzed by TPH2 is the rate-limiting step of serotonin biosynthesis, mutations in TPH2 have been associated with several psychiatric disorders (PD). This work undertakes an in silico analysis of the effects of genetic mutations in the human TPH2 protein. Ten algorithms were used to predict the functional and stability effects of the TPH2 mutations. ConSurf was used to estimate the evolutionary conservation of TPH2 amino acids. GROMACS was used to perform molecular dynamics (MD) simulations of TPH2 WT and P260S, R303W, and R441H, which had already been associated with the development of PD. Forty-six TPH2 variants were compiled from the literature. Among the analyzed variants, those occurring at the catalytic domain were shown to be more damaging to protein structure and function. The ConSurf analysis indicated that the mutations affecting the catalytic domain were also more conserved throughout evolution. The variants S364K and S383F were predicted to be deleterious by all the functional algorithms used and occurred at conserved positions, suggesting that they might be deleterious. The MD analyses indicate that the mutations P206S, R303W, and R441H affect TPH2 flexibility and essential mobility at the catalytic and oligomerization domains. The variants P206S, R303W, and R441H also exhibited alterations in dimer binding affinity and stability throughout the simulations. Thus, these mutations may impair TPH2 functional interactions and, consequently, its function, leading to the development of PD. Furthermore, we developed a database, SNPMOL (http://www.snpmol.org/), containing the results presented in this paper. Understanding the effects of TPH2 mutations on protein structure and function may lead to improvements in existing treatments for PD and facilitate the design of further experiments.

Psychiatric disorders are syndromes characterized by cognitive disturbance and behavioral dysfunction, which affect over 800 million people worldwide. It is considered a major public health problem responsible for severe distress with significant impairment in social and working relationships. In the United States and Canada, psychiatric disorders are considered the main cause of disability in young individuals, in addition to being a key factor underlying suicide. Missense mutations in tryptophan hydroxylase 2 enzyme (TPH2) are associated with the development of psychiatric disorders. TPH2 catalyzes the first step of serotonin biosynthesis, a neurotransmitter that plays a central role in the regulation of emotional behavior and cognition. These mutations lead to TPH2 dysfunction with impaired enzymatic activity, which ultimately results in abnormally low levels of serotonin in the brain. Despite the importance of missense mutations in TPH2 to the development of psychiatric disorders, most of them have not yet been characterized, so their effects are still unknown. In this study, we characterized the impact of missense mutations in TPH2 using prediction algorithms and evolutionary conservation analysis. We also used a penalty system to prioritize the most likely harmful mutations of TPH2 by combining the predictive analyses, evolutionary conservation, literature review, and alterations in physicochemical properties upon amino acid substitution. Three hundred and eighty-four missense mutations of TPH2 were compiled from the literature and databases. Our predictive analysis pointed to a high rate of deleterious and destabilizing predictions for the TPH2 mutations. These mutations mainly affect conserved and, possibly, functionally important residues. Among the uncharacterized mutations of TPH2, variants V295E, R441C T311P, Y281C, R441S, S383F, P308S, Y281H, and E363G received the highest penalties, thus, being the most likely deleterious and, consequently, important targets for future investigation. Our findings may guide the design of clinical and laboratory experiments, optimizing time and resources.

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