Peptidylglycine α-amidating monooxygenase as a therapeutic target or biomarker for human diseases

Peptidylglycine alpha-amidating monooxygenase is important in mice for beta-cell cilia formation and insulin secretion but promotes diabetes risk through beta-cell independent mechanisms

OBJECTIVES

Carriers of PAM (peptidylglycine alpha-amidating monooxygenase) coding variant alleles have reduced insulinogenic index, higher risk of developing type 2 diabetes (T2D), and islets from heterozygous carriers of the PAM p.Asp563Gly variant display reduced insulin secretion. Exactly how global PAM deficiency contributes to hyperglycemia remains unclear. PAM is the only enzyme capable of converting glycine-extended peptide hormones into amidated products. Like neuropeptide Y (NPY), α-melanocyte stimulating hormone (αMSH), and glucagon-like peptide 1 (GLP-1), islet amyloid polypeptide (IAPP), a beta cell peptide that forms islet amyloid in type 2 diabetes, is a PAM substrate. We hypothesized that Pam deficiency limited to beta cells would lead to reduced insulin secretion, prevent the production of amidated IAPP, and reveal the extent to which loss of Pam in β-cells could accelerate the onset of hyperglycemia in mice.

METHODS

PAM activity was assessed in human islets from donors based on their PAM genotype. We generated beta cell-specific Pam knockout (Ins1Cre/+, Pamfl/fl; βPamKO) mice and performed islet culture, histological, and metabolic assays to evaluate the physiological roles of Pam in beta cells. We analyzed human IAPP (hIAPP) amyloid fibril forming kinetics using synthetic amidated and non-amidated hIAPP peptides, and generated hIAPP knock-in beta cell-specific Pam knockout (hIAPPw/w βPamKO) mice to determine the impact of hIAPP amidation on islet amyloid burden, islet graft survival, and glucose tolerance.

RESULTS

PAM enzyme activity was significantly reduced in islets from donors with the PAM p. Asp563Gly T2D-risk allele. Islets from βPamKO mice had impaired second-phase glucose- and KCl-induced insulin secretion. Beta cells from βPamKO mice had larger dense-core granules and fewer and shorter cilia. Interestingly, non-amidated hIAPP was less fibrillogenic in vitro, and high glucose-treated hIAPPw/w βPamKO islets had reduced amyloid burden. Despite these changes in beta cell function, βPamKO mice were not more susceptible to diet-induced hyperglycemia. In vitro beta cell death and in vivo islet graft survival remained comparable between hIAPPw/w βPamKO and hIAPPw/w islets. Surprisingly, aged hIAPPw/w βPamKO mice had improved insulin secretion and glucose tolerance.

CONCLUSIONS

Eliminating Pam expression only in beta cells leads to morphological changes in insulin granules, reduced insulin secretion, reduced hIAPP amyloid burden and altered ciliogenesis. However, in mice beta-cell Pam deficiency has no impact on the development of diet- or hIAPP-induced hyperglycemia. Our data are consistent with current studies revealing ancient, highly conserved roles for peptidergic signaling in the coordination of the diverse signals needed to regulate fundamental processes such as glucose homeostasis.

The binuclear copper state of peptidylglycine monooxygenase visualized through a selenium-substituted peptidyl-homocysteine complex

Bioactive peptides generally require post-translational processing to convert them to their fully active forms. Peptidylglycine monooxygenase (PHM) is a copper-dependent enzyme that catalyzes C-alpha hydroxylation of a glycine-extended pro-peptide, a critical post-translational step in peptide amidation. A canonical mechanism based on experimental and theoretical considerations proposes that molecular oxygen reacts at the mononuclear CuM-center to form a reactive Cu(II)-superoxo intermediate capable of H-atom abstraction from the peptidyl substrate, followed by long range ET from the CuH center positioned 11 Å away across a solvent-filled cleft. However, recent data has challenged this mechanism, suggesting instead that an "open-to-closed" conformational transition brings the copper centers closer to facilitate reaction at a binuclear copper site. Here we present direct observations of an enzyme-bound binuclear copper species, which was enabled by the use of an Ala-Ala-Phe-homoselenocysteine (hSeCys) species. EXAFS, UV/vis, and EPR studies are used to show that this reagent reacts with the oxidized enzyme to form a novel mixed valence entity which is subtly different from that observed previously for the S-peptidyl complex (K. W. Rush, K. A. S. Eastman, E. F. Welch, V. Bandarian and N. J. Blackburn, J. Am. Chem. Soc., 2024, 146, 5074-5080). In the ascorbate-reduced Cu(I) state of PHM, EXAFS measurements at both the Se and Cu absorption edges provide a unique signature of a bridging mode of binding, with Se-Cu site occupancy (1.8) measured from the Se-EXAFS simulating to twice that of the Cu-Se site occupancy (0.85) measured at the Cu edge. The ability of the hSeCys entity to induce a binuclear state is further emphasized by the XAS of the selenomethionyl peptide complex, where no such bridging chemistry is observed. The properties of the binuclear PHM derivative are of interest due to their unique chemical signatures, as well as providing the basis for a completely new mechanistic paradigm for PHM and its monooxygenase congeners.

The pharmacology of vitamin C

Ascorbic acid, the reduced form of vitamin C, is a ubiquitous small carbohydrate. Despite decades of focused research, new metabolic functions of this universal electron donor are still being discovered and add to the complexity of our view of vitamin C in human health. Although praised as an unsurpassed water-soluble antioxidant in plasma and cells, the most interesting functions of vitamin C seem to be its roles as specific electron donor in numerous biological reactions ranging from the well-known hydroxylation of proline to cofactor for the epigenetic master regulators ten-eleven translocation enzymes and Jumonji domain-containing histone-lysine demethylases. Some of these functions may have important implications for disease prevention and treatment and have spiked renewed interest in, eg, vitamin C's potential in cancer therapy. Moreover, some fundamental pharmacokinetic properties of vitamin C remain to be established including if other mechanisms than passive diffusion governs the efflux of ascorbate anions from the cell. Taken together, there still seems to be much to learn about the pharmacology of vitamin C and its role in health and disease. This review explores new avenues of vitamin C and integrates our present knowledge of its pharmacology. SIGNIFICANCE STATEMENT: Vitamin C is involved in multiple biological reactions of which most are essential to human health. Hundreds of millions of people are considered deficient in vitamin C according to accepted guidelines, but little is known about the long-term consequences. Although the complexity of vitamin C's physiology and pharmacology has been widely disregarded in clinical studies for decades, it seems clear that a deeper understanding of particularly its pharmacology holds the key to unravel and possibly exploit the potential of vitamin C in disease prevention and therapy.

Enhancing Stability and Bioavailability of Peptidylglycine Alpha-Amidating Monooxygenase in Circulation for Clinical Use

Peptidylglycine alpha-amidating monooxygenase (PAM) is the only enzyme known to catalyze C-terminal amidation, a final post-translational modification step essential for the biological activity of over 70 bioactive peptides, including adrenomedullin (ADM), calcitonin gene-related peptide (CGRP), amylin, neuropeptide Y (NPY), and others. Bioactive (amidated) peptide hormones play crucial roles in various physiological processes and have been extensively explored as therapeutic compounds in clinical and preclinical research. However, their therapeutic viability is limited due to their short half-life and, in most cases, the need for prolonged infusion to maintain effective concentrations. PAM itself has also been considered as a therapeutic compound aiming to increase the level of amidated peptide hormones; however, similarly to peptide hormones, PAM's rapid degradation limits its utility. Here, we present a strategy to enhance PAM stability and bioavailability through PEGylation, significantly extending the enzyme's half-life in circulation assessed in healthy rats. Furthermore, single subcutaneous (s.c.), intramuscular (i.m.), or intraperitoneal (i.p.) administration of PEGylated PAM resulted in a sustained increase in circulating amidating activity, with peak activity observed at 12-24 h post-bolus administration. Notably, amidating activity remained significantly elevated above baseline levels for up to seven days post-administration, with no observable adverse effects. These findings highlight PEGylated PAM's potential as a viable therapeutic compound.

Comorbid Diabetes Is Associated With Dyspnea Severity and Cardiometabolic Biomarkers in Black Adults With Heart Failure

BACKGROUND

Comorbidities such as Type 2 diabetes mellitus significantly and adversely influence heart failure outcomes, especially in Black adult populations. Likewise, heart failure has a negative effect on diabetes and cardiometabolic outcomes. Dyspnea, a common symptom of heart failure, often correlates with disease severity and prognosis. However, the relationship between comorbid diabetes, dyspnea severity, and cardiometabolic biomarkers in Black adults with heart failure remains understudied.

OBJECTIVES

The purpose of this pilot study was to examine differences in the distressing heart failure symptom of dyspnea and in cardiometabolic and inflammatory biomarkers in Black adults living with heart failure with and without diabetes.

METHODS

Black adults with heart failure were enrolled in this cross-sectional pilot study. Cardiometabolic and inflammatory biomarkers were measured via multiplex immunoassay. Univariate general liner models were used to identify group differences between persons with heart failure with comorbid diabetes and those without, controlling for age, sex, and comorbid burden.

RESULTS

Participants were mostly female with a mean age of 55 years and mean left ventricular ejection fraction of 33%. Participants with diabetes exhibited higher dyspnea scores compared to those without diabetes, indicating greater symptom burden. Moreover, individuals with comorbid diabetes demonstrated higher levels of cardiometabolic and inflammatory markers.

DISCUSSION

Comorbid diabetes was associated with higher dyspnea severity and adverse cardiometabolic profiles in Black adults with heart failure. These findings underscore the importance of targeted interventions addressing diabetes management and cardiometabolic risk factors to improve symptom control and outcomes in this high-risk population. Further research is warranted to elucidate the underlying mechanisms and develop tailored therapeutic strategies for managing comorbidities in persons with heart failure, particularly in minoritized communities.

Mammalian copper homeostasis: physiological roles and molecular mechanisms

In the past decade, evidence for the numerous roles of copper (Cu) in mammalian physiology has grown exponentially. The discoveries of Cu involvement in cell signaling, autophagy, cell motility, differentiation, and regulated cell death (cuproptosis) have markedly extended the list of already known functions of Cu, such as a cofactor of essential metabolic enzymes, a protein structural component, and a regulator of protein trafficking. Novel and unexpected functions of Cu transporting proteins and enzymes have been identified, and new disorders of Cu homeostasis have been described. Significant progress has been made in the mechanistic studies of two classic disorders of Cu metabolism, Menkes disease and Wilson's disease, which paved the way for novel approaches to their treatment. The discovery of cuproptosis and the role of Cu in cell metastatic growth have markedly increased interest in targeting Cu homeostatic pathways to treat cancer. In this review, we summarize the established concepts in the field of mammalian Cu physiology and discuss how new discoveries of the past decade expand and modify these concepts. The roles of Cu in brain metabolism and in cell functional speciation and a recently discovered regulated cell death have attracted significant attention and are highlighted in this review.

Exploring Copper's role in stroke: progress and treatment approaches

Copper is an important mineral, and moderate copper is required to maintain physiological processes in nervous system including cerebral ischemia/reperfusion (I/R) injury. Over the past few decades, copper induced cell death, named cuprotosis, has attracted increasing attention. Several lines of evidence have confirmed cuprotosis exerts pivotal role in diverse of pathological processes, such as cancer, neurodegenerative diseases, and I/R injury. Therefore, an in-depth understanding of the interaction mechanism between copper-mediated cell death and I/R injury may reveal the significant alterations about cellular copper-mediated homeostasis in physiological and pathophysiological conditions, as well as therapeutic strategies deciphering copper-induced cell death in cerebral I/R injury.

Identification of potential drug targets for insomnia by Mendelian randomization analysis based on plasma proteomics

Introduction

Insomnia, a common clinical disorder, significantly impacts the physical and mental well-being of patients. Currently, available hypnotic medications are unsatisfactory due to adverse reactions and dependency, necessitating the identification of new drug targets for the treatment of insomnia.

Methods

In this study, we utilized 734 plasma proteins as genetic instruments obtained from genome-wide association studies to conduct a Mendelian randomization analysis, with insomnia as the outcome variable, to identify potential drug targets for insomnia. Additionally, we validated our results externally using other datasets. Sensitivity analyses entailed reverse Mendelian randomization analysis, Bayesian co-localization analysis, and phenotype scanning. Furthermore, we constructed a protein-protein interaction network to elucidate potential correlations between the identified proteins and existing targets.

Results

Mendelian randomization analysis indicated that elevated levels of TGFBI (OR = 1.01; 95% CI, 1.01-1.02) and PAM ((OR = 1.01; 95% CI, 1.01-1.02) in plasma are associated with an increased risk of insomnia, with external validation supporting these findings. Moreover, there was no evidence of reverse causality for these two proteins. Co-localization analysis confirmed that PAM (coloc.abf-PPH4 = 0.823) shared the same variant with insomnia, further substantiating its potential role as a therapeutic target. There are interactive relationships between the potential proteins and existing targets of insomnia.

Conclusion

Overall, our findings suggested that elevated plasma levels of TGFBI and PAM are connected with an increased risk of insomnia and might be promising therapeutic targets, particularly PAM. However, further exploration is necessary to fully understand the underlying mechanisms involved.

Efficient production of peptidylglycine α-hydroxylating monooxygenase in yeast for protein C-terminal functionalization

Peptidylglycine α-hydroxylating monooxygenase (PHM) is pivotal for C-terminal amidation of bioactive peptides in animals, offering substantial potential for customized protein synthesis. However, efficient PHM production has been hindered by the complexity of animal cell culture and the absence of glycosylation in bacterial hosts. Here, we demonstrate the recombinant expression of Caenorhabditis elegans PHM in the yeast Pichia pastoris, achieving a remarkable space-time yield of 28.8 U/L/day. This breakthrough surpasses prior PHM production rates and eliminates the need for specialized cultivation equipment or complex transfection steps. Mass spectrometry revealed N-glycosylation at residue N182 of recombinant CePHM, which impacts the enzyme's activity as indicated by biochemical experiments. To showcase the utility of CePHM, we performed C-terminal amidation on ubiquitin at a substrate loading of 30 g/L, a concentration meeting the requirements for pharmaceutical peptide production. Overall, this work establishes an efficient PHM production method, promising advancements in scalable manufacturing of C-terminally modified bioactive peptides and probe proteins.

Capturing the Binuclear Copper State of Peptidylglycine Monooxygenase Using a Peptidyl-Homocysteine Lure

Peptidylglycine monooxygenase is a copper-dependent enzyme that catalyzes C-alpha hydroxylation of glycine extended pro-peptides, a critical post-translational step in peptide hormone processing. The canonical mechanism posits that dioxygen binds at the mononuclear M-center to generate a Cu(II)-superoxo species capable of H atom abstraction from the peptidyl substrate, followed by long-range electron tunneling from the CuH center. Recent crystallographic and biochemical data have challenged this mechanism, suggesting instead that an "open-to-closed" transition brings the copper centers closer, allowing reactivity within a binuclear intermediate. Here we present the first direct observation of an enzyme-bound binuclear copper species, captured by the use of an Ala-Ala-Phe-hCys inhibitor complex. This molecule reacts with the fully reduced enzyme to form a thiolate-bridged binuclear species characterized by EXAFS of the WT and its M314H variant and with the oxidized enzyme to form a novel mixed valence entity characterized by UV/vis and EPR. Mechanistic implications are discussed.

Immunoassay-based quantification of full-length peptidylglycine alpha-amidating monooxygenase in human plasma

A one-step sandwich chemiluminescence immunometric assay (LIA) was developed for the quantification of bifunctional peptidylglycine-α-amidating monooxygenase (PAM) in human plasma (PAM-LIA). PAM is responsible for the activation of more than half of known peptide hormones through C-terminal α-amidation. The assay employed antibodies targeting specific catalytic PAM-subunits, peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL), to ensure detection of full-length PAM. The PAM-LIA assay was calibrated with a human recombinant PAM enzyme and achieved a detection limit of 189 pg/mL and a quantification limit of 250 pg/mL. The assay demonstrated good inter-assay (6.7%) and intra-assay (2.2%) variabilities. It exhibited linearity when accessed by gradual dilution or random mixing of plasma samples. The accuracy of the PAM-LIA was determined to be 94.7% through spiking recovery experiments, and the signal recovery after substance interference was 94-96%. The analyte showed 96% stability after six freeze-thaw cycles. The assay showed strong correlation with matched EDTA and serum samples, as well as matched EDTA and Li-Heparin samples. Additionally, a high correlation was observed between α-amidating activity and PAM-LIA. Finally, the PAM-LIA assay was successfully applied to a sub-cohort of a Swedish population-based study, comprising 4850 individuals, confirming its suitability for routine high throughput screening.

New structures reveal flexible dynamics between the subdomains of peptidylglycine monooxygenase. Implications for an open to closed mechanism

Peptidylglycine monooxygenase (PHM) is essential for the biosynthesis of many neuroendocrine peptides via a copper-dependent hydroxylation of a glycine-extended pro-peptide. The "canonical" mechanism requires the transfer of two electrons from one mononuclear copper (CuH, H-site) to a second mononuclear copper (CuM, M-site) which is the site of oxygen binding and catalysis. In most crystal structures the copper centers are separated by 11 Å of disordered solvent, but recent work has established that a PHM variant H108A forms a closed conformer in the presence of citrate with a reduced Cu-Cu site separation of ~4 Å. Here we report three new PHM structures where the H and M sites are separated by a longer distance of ~14 Å. Variation in Cu-Cu distance is the result of a rotation of the M subdomain about a hinge point centered on the pro199 -leu200 -ile201 triad which forms the linker between subdomains. The energetic cost of domain dynamics is likely small enough to allow free rotation of the subdomains relative to each other, adding credence to recent suggestions that an open-to-closed transition to form a binuclear oxygen binding intermediate is an essential element of catalysis. This inference would explain many experimental observations that are inconsistent with the current canonical mechanism including substrate-induced oxygen activation and isotope scrambling during the peroxide shunt.