Post-Translational Modifications in Secreted Peptide Hormones in Plants

More than a dozen secreted peptides are now recognized as important hormones that coordinate and specify cellular functions in plants. Recent evidence has shown that secreted peptide hormones often undergo post-translational modification and proteolytic processing, which are critical for their function. Such ‘small post-translationally modified peptide hormones’ constitute one of the largest groups of peptide hormones in plants. This short review highlights recent progress in research on post-translationally modified peptide hormones, with particular emphasis on their structural characteristics and modification mechanisms

An atlas of O-linked glycosylation on peptide hormones reveals diverse biological roles

Peptide hormones and neuropeptides encompass a large class of bioactive peptides that regulate physiological processes like anxiety, blood glucose, appetite, inflammation and blood pressure. Here, we execute a focused discovery strategy to provide an extensive map of O-glycans on peptide hormones. We find that almost one third of the 279 classified peptide hormones carry O-glycans. Many of the identified O-glycosites are conserved and are predicted to serve roles in proprotein processing, receptor interaction, biodistribution and biostability. We demonstrate that O-glycans positioned within the receptor binding motifs of members of the neuropeptide Y and glucagon families modulate receptor activation properties and substantially extend peptide half-lives. Our study highlights the importance of O-glycosylation in the biology of peptide hormones, and our map of O-glycosites in this large class of biomolecules serves as a discovery platform for an important class of molecules with potential opportunities for drug designs. O-glycosylation is an abundant post-translational modification but its relevance for bioactive peptides is unclear. Here, the authors detect O-glycans on almost one third of the classified peptide hormones and show that O-glycosylation can modulate peptide half-lives and receptor activation properties.This work was supported by the Novo Nordisk Foundation, the Lundbeck Foundation, Danish National Research Foundation Grant DNRF107

Regulation of Peptide Hormones.

C-Terminal amidated peptide hormones regulate numerous physiological process and are associated with many pathological conditions. Their C-terminal amidation is exclusively catalysed by the enzyme peptidylglycine alpha-amidating monooxygenase (PAM), which has two subunits: peptidylglycine alpha-hydroxylating monooxygenase (PHM; EC 1.14.17.3) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL; EC 4.3.2.5). In the present study, the substrate specificity and inhibition of the PAM sourced from DMS53 human small cell lung cancer cells were investigated. A peptide consensus sequence N-Ac-Gly-(S)-Pro-Gln-(S)-Arg-(S)-Phe-Gly-COOH was constructed from the human amidated peptide hormone database, and a library of peptide substrates was designed by varying the amino acids located at the penultimate and antepenultimate positions from the C-terminus. These peptides were synthesised by solid phase peptide synthesis and studied in a competitive PHM binding assay. The results indicated that human glycine-extended hormone precursors having -Arg-Phe-Gly-COOH are likely to bind to PHM effectively in living bodies with IC50 values around twenty micro molar and those having -Asp-Phe-Gly-COOH and -Ala-Phe-Gly-COOH are likely to bind with IC50 values around seventy micro molar. The results also show that antepenultimate amino acids affect binding to PHM but to a lesser degree than the effect of penultimate amino acids. In a prodrug study, the anti-cancer drug Bexarotene was synthetically extended with a glycine to obtain a derivative that was expected to be cleaved by PAM and then deliver a cytotoxic drug. However, the derivative compound showed poor binding to PHM at the millimolar level, but had a similar cytotoxic activity against DMS53 cells to its parent agent. Unlike Bexarotene, a previous study showed that the glycine derivative of Temozolomide (another anti-cancer drug) has strong binding to PHM at micromolar concentration, but somehow does not convert to Temozolomide by PAM. One possible reason is that the glycine derivative possessing an imidazole moiety could inhibit PHM by metal chelation. To investigate this, a structurally-similar molecule N-Ac-(S)-His-Gly-COOH was tested and found to be processed by PAM and not undergo copper coordination. This implies that the glycine derivative of Temozolomide is unlikely to chelate the copper of the PHM active site. To investigate PHM and PAL activity simultaneously, a new PAM assay with a direct, rapid and sensitive HPLC-MS system was established. With this new assay the PAL inhibitor N-Ac-Phe-pyruvate and analogues were evaluated in terms of PAM inhibition through isolated enzyme competitive assays. This demonstrated that N-Ac-Phe-pyruvate is a PAL inhibitor at the nanomolar level against the medium PAM from DMS53 cells and deprotonation of its enol form results in a decrease of PAL inhibition. By using the established HPLC-MS detection system, the intermediate of the C-terminal amidation of calcitonin-Gly (CTG), alpha-hydroxyglycine-extended calcitonin (HO-CTG), was detected in the culture medium of DMS53 cells. This is the first time HO-CTG produced by cells has been detected. With and without a PAL inhibitor, the concentration of the HO-CTG in the medium sample was found to be more than two orders of magnitude lower than those of the corresponding substrate and amidated product, suggesting the PAL catalysis is much faster than PHM catalysis, and PHM catalysis is the rate-limiting step of amidation of calcitonin in human cells

Defying the Stereotype: Non-Canonical Roles of the Peptide Hormones Guanylin and Uroguanylin

The peptide hormones uroguanylin and guanylin have been traditionally thought to be mediators of fluid–ion homeostasis in the vertebrate intestine. They serve as ligands for receptor guanylyl cyclase C (GC-C), and both receptor and ligands are expressed predominantly in the intestine. Ligand binding to GC-C results in increased cyclic GMP production in the cell which governs downstream signaling. In the last decade, a significant amount of research has unraveled novel functions for this class of peptide hormones, in addition to their action as intestinal secretagogues. An additional receptor for uroguanylin, receptor guanylyl cyclase D, has also been identified. Thus, unconventional roles of these peptides in regulating renal filtration, olfaction, reproduction, and cell proliferation have begun to be elucidated in detail. These varied effects suggest that these peptide hormones act in an autocrine, paracrine as well as endocrine manner to regulate diverse cellular processes

The Association of Peptide Hormones with Glycemia, Dyslipidemia, and Obesity in Lebanese Individuals

Peptide-hormones, including pancreatic peptide-YY(PYY), glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK), insulin, and leptin function as satiety signals, while ghrelin promotes hunger. These hormones are also involved in glucose homeostasis and body-weight regulation. The aim of this cross-sectional analysis was to examine the association of these peptide-hormones with obesity-markers, insulin-resistance, and dyslipidemia (total-cholesterol (TC), low-density-lipoprotein-cholesterol (LDL-C), high-density-lipoprotein-cholesterol (HDL-C), triglyceride (TG)). Sixteen-obese (OB) adults and 21 normal-weight (NW) age-and gender-matched counterparts were recruited. OB-participants showed significantly higher levels of leptin, insulin, Homeostatic-Model Assessment of Insulin Resistance (HOMA-IR), and TG. NW participants had significantly higher levels of ghrelin. GLP-1 was positively correlated with insulin, HOMA-IR, and obesity-markers except percent body fat. Leptin was positively correlated with all markers (except glucose and dyslipidemia). PYY was positively correlated with BMI, insulin and HOMA-IR. Ghrelin was inversely correlated with all of the markers except glucose, TC, and LDL-C. In the regression analysis model, leptin was positively associated with obesity markers and insulin resistance. Our results indicate a significant difference in peptide hormones among OB and NW Lebanese individuals. Since there is controversial evidence regarding body-weight and peptide-hormones in the literature, this study highlights a step forward towards finding ethnic based strategies to treat obesity and its consequences

Transcriptomic Analysis of the Kuruma PrawnMarsupenaeus japonicusReveals Possible Peripheral Regulation of the Ovary

Crustacean reproduction has been hypothesized to be under complex endocrinological regulation by peptide hormones. To further improve our understanding of the mechanisms underlying this complex regulation, knowledge is needed regarding the hormones not only of the central nervous system (CNS) such as the X-organ/sinus gland (XOSG), brain, and thoracic ganglia, but also the peripheral gonadal tissues. For example, in vertebrates, some gonadal peptide hormones including activin, inhibin, follistatin, and relaxin are known to be involved in the reproductive physiology. Therefore, it is highly likely that some peptide factors from the ovary are serving as the signals among peripheral tissues and central nervous tissues in crustaceans. In this work, we sought to find gonadal peptide hormones and peptide hormone receptors by analyzing the transcriptome of the ovary of the kuruma prawnMarsupenaeus japonicus. The generated ovarian transcriptome data led to the identification of five possible peptide hormones, including bursicon-alpha and -beta, the crustacean hyperglycemic hormone (CHH)-like peptide, insulin-like peptide (ILP), and neuroparsin-like peptide (NPLP). Dominant gene expressions for the bursicons were observed in the thoracic ganglia and the ovary, in the CNS for the CHH-like peptide, in the heart for NPLP, and in the ovary for ILP. Since the gene expressions of CHH-like peptide and NPLP were affected by a CHH (Penaeus japonicussinus gland peptide-I) from XOSG, we produced recombinant peptides for CHH-like peptide and NPLP usingEscherichia coliexpression system to examine their possible peripheral regulation. As a result, we found that the recombinant NPLP increased vitellogenin gene expression in incubated ovarian tissue fragments. Moreover, contigs encoding putative receptors for insulin-like androgenic gland factor, insulin, neuroparsin, and neuropeptide Y/F, as well as several contigs encoding orphan G-protein coupled receptors and receptor-type guanylyl cyclases were also identified in the ovarian transcriptome. These results suggest that reproductive physiology in crustaceans is regulated by various gonadal peptide hormones, akin to vertebrates

Peptide hormones and lipopeptides: from self-assembly to therapeutic applications

This review describes the properties and activities of lipopeptides and peptide hormones and how the lipidation of peptide hormones could potentially produce therapeutic agents combating some of the most prevalent diseases and conditions. The self-assembly of these types of molecules is outlined, and how this can impact on bioactivity. Peptide hormones specific to the uptake of food and produced in the gastrointestinal tract are discussed in detail. The advantages of lipidated peptide hormones over natural peptide hormones are summarised, in terms of stability and renal clearance, with potential application as therapeutic agent

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4’s role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging