Manifestation of hawkinsinuria in a patient compound heterozygous for hawkinsinuria and tyrosinemia III

CovET: A covariation-evolutionary trace method that identifies protein structure-function modules

Measuring the relative effect that any two sequence positions have on each other may improve protein design or help better interpret coding variants. Current approaches use statistics and machine learning but rarely consider phylogenetic divergences which, as shown by Evolutionary Trace studies, provide insight into the functional impact of sequence perturbations. Here, we reframe covariation analyses in the Evolutionary Trace framework to measure the relative tolerance to perturbation of each residue pair during evolution. This approach (CovET) systematically accounts for phylogenetic divergences: at each divergence event, we penalize covariation patterns that belie evolutionary coupling. We find that while CovET approximates the performance of existing methods to predict individual structural contacts, it performs significantly better at finding structural clusters of coupled residues and ligand binding sites. For example, CovET found more functionally critical residues when we examined the RNA recognition motif and WW domains. It correlates better with large-scale epistasis screen data. In the dopamine D2 receptor, top CovET residue pairs recovered accurately the allosteric activation pathway characterized for Class A G protein-coupled receptors. These data suggest that CovET ranks highest the sequence position pairs that play critical functional roles through epistatic and allosteric interactions in evolutionarily relevant structure-function motifs. CovET complements current methods and may shed light on fundamental molecular mechanisms of protein structure and function.

Insights into 4-hydroxyphenylpyruvate dioxygenase-inhibitor interactions from comparative structural biology

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a key role in tyrosine metabolism and has been identified as a promising target for herbicide and drug discovery. The structures of HPPD complexed with different types of inhibitors have been determined previously. We summarize the structures of HPPD complexed with structurally diverse molecules, including inhibitors, natural products, substrates, and catalytic intermediates; from these structures, the detailed inhibitory mechanisms of different inhibitors were analyzed and compared, and the key structural factors determining the slow-binding behavior of inhibitors were identified. Further, we propose four subpockets that accommodate different inhibitor substructures. We believe that these analyses will facilitate in-depth understanding of the enzymatic reaction mechanism and enable the design of new inhibitors with higher potency and selectivity.

Discovery of Subnanomolar Inhibitors of 4-Hydroxyphenylpyruvate Dioxygenase via Structure-Based Rational Design

High-potency 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are usually featured by time-dependent inhibition. However, the molecular mechanism underlying time-dependent inhibition by HPPD inhibitors has not been fully elucidated. Here, based on the determination of the HPPD binding mode of natural products, the π-π sandwich stacking interaction was found to be a critical element determining time-dependent inhibition. This result implied that, for the time-dependent inhibitors, strengthening the π-π sandwich stacking interaction might improve their inhibitory efficacy. Consequently, modification with one methyl group on the bicyclic ring of quinazolindione inhibitors was achieved, thereby strengthening the stacking interaction and significantly improving the inhibitory efficacy. Further introduction of bulkier hydrophobic substituents with higher flexibility resulted in a series of HPPD inhibitors with outstanding subnanomolar potency. Exploration of the time-dependent inhibition mechanism and molecular design based on the exploration results are very successful cases of structure-based rational design and provide a guiding reference for future development of HPPD inhibitors.

Biallelic variants in HPDL, encoding 4-hydroxyphenylpyruvate dioxygenase-like protein, lead to an infantile neurodegenerative condition

PURPOSE

Dioxygenases are oxidoreductase enzymes with roles in metabolic pathways necessary for aerobic life. 4-hydroxyphenylpyruvate dioxygenase-like protein (HPDL), encoded by HPDL, is an orphan paralogue of 4-hydroxyphenylpyruvate dioxygenase (HPD), an iron-dependent dioxygenase involved in tyrosine catabolism. The function and association of HPDL with human diseases remain unknown.

METHODS

We applied exome sequencing in a cohort of over 10,000 individuals with neurodevelopmental diseases. Effects of HPDL loss were investigated in vitro and in vivo, and through mass spectrometry analysis. Evolutionary analysis was performed to investigate the potential functional separation of HPDL from HPD.

RESULTS

We identified biallelic variants in HPDL in eight families displaying recessive inheritance. Knockout mice closely phenocopied humans and showed evidence of apoptosis in multiple cellular lineages within the cerebral cortex. HPDL is a single-exonic gene that likely arose from a retrotransposition event at the base of the tetrapod lineage, and unlike HPD, HPDL is mitochondria-localized. Metabolic profiling of HPDL mutant cells and mice showed no evidence of altered tyrosine metabolites, but rather notable accumulations in other metabolic pathways.

CONCLUSION

The mitochondrial localization, along with its disrupted metabolic profile, suggests HPDL loss in humans links to a unique neurometabolic mitochondrial infantile neurodegenerative condition.

Hawkinsinuria clinical practice guidelines: a Mexican case report and literature review

Hawkinsinuria is an autosomal dominant disorder of tyrosine metabolism. Mutations in the 4-hydroxyphenylpyruvate dioxygenase gene ( HPD) result in an altered HPD enzyme, causing hawkinsin and tyrosine accumulation. Persistent metabolic acidosis and failure to thrive are common features in patients with hawkinsinuria. We present the first known Latin American patient diagnosed with hawkinsinuria, and the tenth reported patient in the literature. We aim to establish clinical practice guidelines for patients with hawkinsinuria. The patient’s plasma tyrosine level was 21.5 mg/dL, which is several times higher than the reference value. Mutation analysis indicated heterozygosity for V212M and A33T variants in HPD. In the case of altered tyrosine levels found during newborn screening, we propose exclusive breastmilk feeding supplemented with ascorbic acid. Amino acid quantification is useful for monitoring treatment response. If tyrosinemia persists, protein intake must be decreased via a low-tyrosine diet. Molecular studies can be used to confirm a patient’s disease etiology. Further reports are required to elucidate new pathogenic and phenotypic variations to enable the development of an appropriate therapeutic approach.

4-hydroxyphenylpyruvate dioxygenase promotes lung cancer growth via pentose phosphate pathway (PPP) flux mediated by LKB1-AMPK/HDAC10/G6PD axis

4-hydroxyphenylpyruvate dioxygenase (HPD) is an important modifier of tyrosine metabolism. However, the precise contribution of HPD to cancer metabolism and tumorigenesis remains unclear. In this study, we found that HPD was highly expressed in lung cancer and its higher expression correlated with poor prognosis in lung cancer patients. Suppressed HPD expression was sufficient to decrease oxidative pentose phosphate pathway (PPP) flux, leading to reduced RNA biosynthesis and enhanced reactive oxygen species (ROS) level, attenuated cancer cell proliferation, and tumor growth. Mechanistically, HPD not only promotes tyrosine catabolism leading to increased acetyl-CoA levels, the source of histone acetylation, but also stimulates histone deacetylase 10 (HDAC10) translocation from the nucleus into the cytoplasm mediated by tumor suppressor liver kinase B1 (LKB1)–AMP-activated protein kinase (AMPK) signaling. Both controlled histone acetylation modification, which enhanced transcription of the important PPP enzyme Glucose-6-Phosphate Dehydrogenase (G6PD). Thus, this study reveals HPD as a novel regulator of LKB1–AMPK signaling-mediated HDAC10 nuclear location, which contributes to G6PD expression in promoting tumor growth, which is a promising target for lung cancer treatment.

4-Hydroxyphenylpyruvate Dioxygenase Inhibitors: From Chemical Biology to Agrochemicals

The development of new herbicides is receiving considerable attention to control weed biotypes resistant to current herbicides. Consequently, new enzymes are always desired as targets for herbicide discovery. 4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is an enzyme engaged in photosynthetic activity and catalyzes the transformation of 4-hydroxyphenylpyruvic acid (HPPA) into homogentisic acid (HGA). HPPD inhibitors constitute a promising area of discovery and development of innovative herbicides with some advantages, including excellent crop selectivity, low application rates, and broad-spectrum weed control. HPPD inhibitors have been investigated for agrochemical interests, and some of them have already been commercialized as herbicides. In this review, we mainly focus on the chemical biology of HPPD, discovery of new potential inhibitors, and strategies for engineering transgenic crops resistant to current HPPD-inhibiting herbicides. The conclusion raises some relevant gaps for future research directions.

Expanding the phenotype of hawkinsinuria: new insights from response to N-acetyl-L-cysteine

Hawkinsinuria is a rare disorder of tyrosine metabolism that can manifest with metabolic acidosis and growth arrest around the time of weaning off breast milk, typically followed by spontaneous resolution of symptoms around 1 year of age. The urinary metabolites hawkinsin, quinolacetic acid, and pyroglutamic acid can aid in identifying this condition, although their relationship to the clinical manifestations is not known. Herein we describe clinical and laboratory findings in two fraternal twins with hawkinsinuria who presented with failure to thrive and metabolic acidosis. Close clinical follow-up and laboratory testing revealed previously unrecognized hypoglycemia, hypophosphatemia, combined hyperlipidemia, and anemia, along with the characteristic urinary metabolites, including massive pyroglutamic aciduria. Treatment with N-acetyl-L-cysteine (NAC) restored normal growth and normalized or improved most biochemical parameters. The dramatic response to NAC therapy supports the idea that glutathione depletion plays a key role in the pathogenesis of hawkinsinuria.

Hawkinsinuria in two unrelated Greek newborns: identification of a novel variant, biochemical findings and treatment

BACKGROUND

Hawkinsinuria is a rare inborn error of tyrosine metabolism.

OBJECTIVES

To study novel hawkinsinuria cases by monitoring their biochemical profile and conducting a mutation analysis.

SUBJECTS AND METHODS

Among 92,519 newborns that underwent expanded newborn screening, two unrelated cases with high tyrosine blood levels were further investigated by chromatographic techniques and via genetic testing for 4-hydroxyphenylpyruvate dioxygenase (HPD) gene.

RESULTS

Elevated levels were monitored for blood/plasma tyrosine and for the specific diagnostic markers in urine. The two newborns were put on a special low tyrosine diet. Till completion of the 1st year of their life, liver function tests and brain MRI were normal. The mutation A33T was identified in both cases, while one neonate carried an additional novel mutation of HPD gene (V212M).

CONCLUSIONS

Two mutations of HPD gene, A33T, which are associated with hawkinsinuria and a novel one (V212M) were detected for the 1st time in Greek newborns.

4-Hydroxyphenylpyruvate Dioxygenase and Hydroxymandelate Synthase: 2-Oxo Acid-Dependent Oxygenases of Importance to Agriculture and Medicine

Despite a separate evolutionary lineage, 4-hydroxyphenylpyruvate dioxygenase (HPPD) and hydroxymandelate synthase (HMS) are appropriately grouped with the 2-oxo acid-dependent oxygenase (2OADO) family of enzymes. HPPD and HMS accomplish highly similar overall chemistry to that observed in the majority of 2OADOs but require only two substrates rather than three. 2OADOs typically use the 2-oxo acid of 2-oxoglutarate (2OG) as a source of electrons to reduce and activate dioxygen in order to oxidize a third specific substrate. HPPD and HMS use instead the pyruvate substituent of 4-hydroxyphenylpyruvate to activate dioxygen and then proceed to also hydroxylate this substrate, each yielding a distinctly different aromatic product. HPPD catalyses the second and committed step of tyrosine catabolism, a pathway common to nearly all aerobes. Plants require the HPPD reaction to biosynthesize plastoquinones and therefore HPPD inhibitors can have potent herbicidal activity. The ubiquity of the HPPD reaction, however, has meant that HPPD-specific molecules developed as herbicides have other uses in different forms of life. In humans herbicidal HPPD inhibitors can be used therapeutically to alleviate specific inborn defects and also to retard the progress of certain bacterial and fungal infections. This review is intended as a concise overview of the contextual and catalytic chemistries of HPPD and HMS.

4-Hydroxyphenylpyruvate dioxygenase and hydroxymandelate synthase: exemplars of the α-keto acid dependent oxygenases

4-Hydroxyphenylpyruvate dioxygenase (HPPD) and hydroxymandelate synthase (HMS) are outliers within the α-keto acid dependent oxygenase (αKAO) family. HPPD and HMS catalyze the chemistry of the majority of enzymes within the αKAO family but are clearly mechanistically convergent, having a grossly different structural topology. Some of the unique characteristics of HPPD and HMS have elucidated select parts of the catalytic cycle that are obscured in other family members. Moreover, the inhibitory chemistry of HPPD is a phenomenon with ever-expanding relevance across all kingdoms of life. This review is a synopsis of the literature pertaining to HPPD and HMS. It is not intended as an exhaustive compilation of all observations made for these enzymes but rather a condensed narrative that connects those studies that have advanced the understanding of the chemistry of both enzymes.