Mechanistic peptidomics: factors that dictate specificity in the formation of endogenous peptides in human milk

MDPAO1 peptide from human milk enhances brown adipose tissue thermogenesis and mitigates obesity

The regulatory effect of breastfeeding on offspring metabolism has garnered significant attention as an effective strategy in combating childhood obesity. However, the underlying mechanism remains largely unknown. Through integrated analysis of multiple human milk peptide databases and functional screening, MDPAO1 (milk-derived peptide associated with obesity 1) was identified as having potential activity in promoting the expression of thermogenic genes. In lactating mice, intervention with MDPAO1 enhanced the thermogenic phenotype of brown adipose tissue (BAT) and overall metabolic activity. Moreover, MDPAO1 intervention led to reduced body weight gain, increased brown fat mass, and improved glucose tolerance and insulin sensitivity in a mouse model of high-fat diet (HFD)-induced obesity. RNA-seq analysis of BAT post-MDPAO1 intervention revealed close association with mitochondrial oxidative respiratory chain and mitophagy. Subsequent in vitro experiments conducted on primary brown adipocytes confirmed that MDPAO1 inhibited mitophagy, increased mitochondrial mass, and elevated levels of mitochondrial respiratory chain complexes. In conclusion, this study underscores the potential of MDPAO1, a peptide enriched in breast milk, in activating the thermogenic phenotype of brown adipose tissue and mitigating obesity, thus offering novel insights into the mechanisms underlying breastfeeding's role in preventing childhood obesity.

Optimizing workflow efficiency for analyzing low molecular weight endogenous peptides in colostrum

Bovine milk and colostrum play pivotal roles in the nutritional support of both human and bovine infants. Colostrum, the initial milk secretion, is crucial for neonatal growth, providing essential nutrients, growth factors, immunity, and defense mechanisms through a diverse array of bioactive compounds, including bioactive proteins and peptides. Peptidomics, leveraging the potential health benefits of peptides derived from food and body fluids, has become prominent in contemporary research. Endogenous peptides (EPs) have gained notable scientific and commercial interest due to their potential biofunctional significance in areas such as immune health, antimicrobial, anti-inflammatory, antihypertensive, and antioxidative studies. In this investigation, we aimed to extract and analyze low molecular weight EPs from colostrum using four distinct peptide extraction methods, previously employed for EPs extraction from other bodily fluids. The efficiency of these methods was systematically compared and analysed to identify the most effective extraction technique for maximizing the identification of low molecular weight EPs from colostrum. This study represents a pioneering effort as no prior research has systematically compared different extraction methods for low molecular weight EPs from colostrum. Given the unique physical and chemical composition of colostrum compared to milk and other body fluids, a comprehensive analysis of EPs extraction methods was deemed essential. In the present study, we successfully extracted over 3200 EPs from colostrum using trichloroacetic acid (TCA) and a molecular weight cut off (MWCO) extraction method. The findings of this study revealed the extraction of EPs from colostrum, demonstrating potential inherent bioactivities as predicted by in silico tools.

Peptidome profiling of human, bovine, and donkey colostrum through label-free quantitative analysis reveals proteolysis of milk proteins

Proteins and peptides play vital roles in different biological processes in vivo. As a dynamic hydrolysis system, milk is rich in proteins and proteases and provides a constant supply of endogenous bioactive peptides to newborn mammals. Previous studies have primarily focused on researching bioactive peptides by adding exogenous enzymes to milk samples. However, such an approach overlooks the significance of endogenous peptides and parent proteins that naturally exist in milk. Herein, we analyzed and compared parent proteins and their releasing peptides in human colostrum (HC), bovine colostrum (BC), and donkey colostrum (DC). The predominant proteins and hydrolyzed peptides in the three types of milk were identified. Among them, peptides were found to possess common bioactivities, including ACE inhibitory, antioxidant, antibacterial and immunomodulatory properties in HC, BC, and DC. Furthermore, the biological functions of these parent proteins were clarified using bioinformatics. These insights offer a novel perspective on natural bioactive peptides and the potential utilization of specific parent proteins and peptides to develop infant formulae derived from diverse milk sources.

Revealing the diversity of endogenous peptides and parent proteins in human colostrum and mature milk through peptidomics analysis

Endogenous peptides and their parent proteins are important nutritional components with diverse biological functions. The objective of this study was to analyze and compare endogenous peptides and parent proteins found in human colostrum (HC) and human mature milk (HM) using a 4D label-free technique. In total, 5162 and 940 endogenous peptides derived from 258 parent proteins were identified in human milk by database (DB) search and de novo, respectively. Among these peptides, 2446 differentially expressed endogenous peptides with various bioactivities were identified. The Gene Ontology analysis unveiled the cellular components, biological processes, and molecular functions associated with these parent proteins. Metabolic pathway analysis suggested that neutrophil extracellular trap formation had the greatest significance with 24 parent proteins. These findings will offer a fresh perspective on the development of infant formula powder, highlighting the potential for incorporating these changes to enhance its nutritional composition and benefits.

Proteomic Analysis of Arachis hypogaea Seeds from Different Maturity Classes

Physiological maturity impacts seed quality through various mechanisms including vigor, desiccation tolerance, dormancy induction, synthesis of raw materials (including seed storage proteins), and the reorganization of metabolisms. Peanut seed development can be classified into seven classes with four incremental stages per class. Based on the mesocarp color, the final three stages are commonly referred to as "orange", "brown", and "black". In 2017, freshly harvested pods from one genotype of runner market-type peanuts grown under conventional practices were obtained from the University of Georgia research facility. The pods were removed from the plant material and 'pod blasted' to reveal the mesocarp. After separation, the remainder of the pod outer layer was removed, and the seeds were segregated for proteomic analysis. The raw peanuts were analyzed by bottom-up LC-MS/MS proteomics, which was conducted by the Proteomics Resource Center at the Rockefeller University, to identify the significant protein composition differences in each maturity class. The proteomic data revealed differentially expressed proteins as a function of maturity class with multiple functions including plant defense, metabolism, cell signaling, nutrient accumulation, and packaging. Understanding the processes needed for seed maturation will enable peanut scientists to evaluate the traits needed for robust germination, hardiness of the seed in response to disease, and nutrient quality.

Network analysis of the proteome and peptidome sheds light on human milk as a biological system

Proteins and peptides found in human milk have bioactive potential to benefit the newborn and support healthy development. Research has been carried out on the health benefits of proteins and peptides, but many questions still need to be answered about the nature of these components, how they are formed, and how they end up in the milk. This study explored and elucidated the complexity of the human milk proteome and peptidome. Proteins and peptides were analyzed with non-targeted nanoLC-Orbitrap-MS/MS in a selection of 297 milk samples from the CHILD Cohort Study. Protein and peptide abundances were determined, and a network was inferred using Gaussian graphical modeling (GGM), allowing an investigation of direct associations. This study showed that signatures of (1) specific mechanisms of transport of different groups of proteins, (2) proteolytic degradation by proteases and aminopeptidases, and (3) coagulation and complement activation are present in human milk. These results show the value of an integrated approach in evaluating large-scale omics data sets and provide valuable information for studies that aim to associate protein or peptide profiles from biofluids such as milk with specific physiological characteristics.

Human proinsulin production in the milk of transgenic cattle

BACKGROUND

The worldwide growing demand for human insulin for treating diabetes could be supplied by transgenic animals producing insulin in their milk.

METHODS AND RESULTS

Pseudo-lentivirus containing the bovine β-casein promoter and human insulin sequences was used to produce modified adult fibroblasts, and the cells were used for nuclear transfer. Transgenic embryos were transferred to recipient cows, and one pregnancy was produced. Recombinant protein in milk was evaluated using western blotting and mass spectrometry. One transgenic cow was generated, and in milk analysis, two bands were observed in western blotting with a molecular mass corresponding to the proinsulin and insulin. The mass spectrometry analysis showed the presence of human insulin more than proinsulin in the milk, and it identified proteases in the transgenic milk that could convert proinsulin into insulin and insulin-degrading enzyme that could degrade the recombinant protein.

CONCLUSION

The methodologies used for generating the transgenic cow allowed the detection of the production of recombinant protein in the milk at low relative expression compared to milk proteins, using mass spectrometry, which was efficient for detecting recombinant protein with low expression in milk. Milk proteases could act on protein processing converting recombinant protein to functional protein. On the other hand, some milk proteases could act in degrading the recombinant protein.

Human colostrum in vitro protein digestion: peptidomics by liquid chromatography-Orbitrap-high-resolution MS and prospection for bioactive peptides via bioinformatics

Breast milk is known to contain bioactive peptides that are released during digestion, being a major source of bioactive peptides to the new-born, some of which act against invading pathogens. However, the formation of bioactive peptides during digestion of human colostrum remains largely uninvestigated. This study aimed to investigate the formation of peptides during simulated digestion of human colostrum from adult women and to prospect antimicrobial peptides. For this purpose, we used high-resolution MS to monitor the release of peptides during in vitro digestion. Bioinformatics was used for the prospection of antimicrobial activity of peptides. During simulated digestion (oral, gastric and duodenal phases), 2318 peptide sequences derived from 112 precursor proteins were identified. At the end of simulated digestion, casein-derived peptide sequences were the most frequently observed. Among precursors, some proteins were seen for the first time in this study. The resulting peptides were rich in proline, glutamine, valine and leucine residues, providing characteristic traits of antimicrobial peptides. From bioinformatics analysis, seven peptides showed potentially high antimicrobial activity towards bacteria, viruses and fungi, from which the latter was the most prominent predicted activity. Antimicrobial peptides released during digestion may provide a defence platform with controlled release for the new-born.

Fingerprinting of Proteases, Protease Inhibitors and Indigenous Peptides in Human Milk

The presence of proteases and their resulting level of activity on human milk (HM) proteins may aid in the generation of indigenous peptides as part of a pre-digestion process, of which some have potential bioactivity for the infant. The present study investigated the relative abundance of indigenous peptides and their cleavage products in relation to the abundance of observed proteases and protease inhibitors. The proteomes and peptidomes in twelve HM samples, representing six donors at lactation months 1 and 3, were profiled. In the proteome, 39 proteases and 29 protease inhibitors were identified in 2/3 of the samples. Cathepsin D was found to be present in higher abundance in the proteome compared with plasmin, while peptides originating from plasmin cleavage were more abundant than peptides from cathepsin D cleavage. As both proteases are present as a system of pro- and active- forms, their activation indexes were calculated. Plasmin was more active in lactation month 3 than month 1, which correlated with the total relative abundance of the cleavage product ascribed to plasmin. By searching the identified indigenous peptides in the milk bioactive peptide database, 283 peptides were ascribed to 10 groups of bioactivities. Antimicrobial peptides were significantly more abundant in month 1 than month 3; this group comprised 103 peptides, originating from the β-CN C-terminal region.

Identification of Potential Bioactive Peptides in Sheep Milk Kefir through Peptidomic Analysis at Different Fermentation Times

Sheep farming is an important socioeconomic activity in most Mediterranean countries, particularly Spain, where it contributes added value to rural areas. Sheep milk is used in Spain mainly for making cheese, but it can be used also for making other dairy products, such as the lactic-alcoholic fermentation product known as kefir. Dairy products have health benefits because, among other reasons, they contain molecules with biological activity. In this work, we performed a proteomics strategy to identify the peptidome, i.e., the set of peptides contained in sheep milk kefir fermented for four different periods of time, aiming to understand changes in the pattern of digestion of milk proteins, as well as to identify potential bioactive peptides. In total, we identified 1942 peptides coming from 11 different proteins, and found that the unique peptides differed qualitatively among samples and their numbers increased along the fermentation time. These changes were supported by the increase in ethanol, lactic acid, and D-galactose concentrations, as well as proteolytic activity, as the fermentation progressed. By searching in databases, we found that 78 of the identified peptides, all belonging to caseins, had potential biological activity. Of these, 62 were not previously found in any milk kefir from other animal species. This is the first peptidomic study of sheep milk kefir comprising time-course comparison.

Ahrné L, Cardoso DR. UV-C light promotes the reductive cleavage of disulfide bonds in β-Lactoglobulin and improves in vitro gastric digestion

β-Lactoglobulin (β-Lg) is the main protein in whey and is known for its allergenicity and resistance to the digestion of pepsin and trypsin. The UV-C photoinduced cleavage of disulfide bonds in β-Lactoglobulin, as promoted by excitation of tryptophan residues (Trp), is shown to induce changes in the protein's secondary structure, significantly reducing the protein's resistance to pepsin digestion. The UV-C light-induced changes in the protein secondary structure are marked by an increase in the contribution of β-sheet and α-helix structures with a concomitantly smaller contribution of the β-turn structural motif. The photoinduced cleavage of disulfide bonds in β-Lg has an apparent quantum yield of ф = 0.0015 ± 0.0003 and was shown by transient absorption laser flash photolysis to arise by two different pathways: a) the reduction of the disulfide bond Cys₆₆Cys₁₆₀ occurs by direct electron transfer from the triplet-excited ³Trp to the disulfide bond due to the existence of a CysCys/Trp triad (Cys₆₆Cys₁₆₀/Trp₆₁) and b) the reduction of the buried Cys₁₀₆Cys₁₁₉ disulfide bond involves a reaction with a solvated electron originated by the photoejection of electrons from the triplet-excited ³Trp decay. The in vitro gastric digestion index for UV-C-treated β-Lg is revealed to have increased significantly by 36 ± 4 % and 9 ± 2 % under simulated elderly and young adult digestive conditions, respectively. When compared to the native protein, the peptide mass fingerprint profile of digested UV-C-treated β-Lg shows a higher content and variety of peptides, including the production of some exclusive bioactive peptides such as PMHIRL and EKFDKALKALPMH.

Ecologies, synergies, and biological systems shaping human milk composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 2

Human milk is universally recognized as the preferred food for infants during the first 6 mo of life because it provides not only essential and conditionally essential nutrients in necessary amounts but also other biologically active components that are instrumental in protecting, communicating important information to support, and promoting optimal development and growth in infants. Despite decades of research, however, the multifaceted impacts of human milk consumption on infant health are far from understood on a biological or physiological basis. Reasons for this lack of comprehensive knowledge of human milk functions are numerous, including the fact that milk components tend to be studied in isolation, although there is reason to believe that they interact. In addition, milk composition can vary greatly within an individual as well as within and among populations. The objective of this working group within the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to provide an overview of human milk composition, factors impacting its variation, and how its components may function to coordinately nourish, protect, and communicate complex information to the recipient infant. Moreover, we discuss the ways whereby milk components might interact such that the benefits of an intact milk matrix are greater than the sum of its parts. We then apply several examples to illustrate how milk is better thought of as a biological system rather than a more simplistic "mixture" of independent components to synergistically support optimal infant health.

Influence of maternal body mass index on human milk composition and associations to infant metabolism and gut colonisation: MAINHEALTH - a study protocol for an observational birth cohort

INTRODUCTION

Human milk provides all macronutrients for growth, bioactive compounds, micro-organisms and immunological components, which potentially interacts with and primes infant growth and, development, immune responses and the gut microbiota of the new-born. Infants with an overweight mother are more likely to become overweight later in life and overweight has been related to the gut microbiome. Therefore, it is important to investigate the mother-milk-infant triad as a biological system and if the maternal weight status influences the human milk composition, infant metabolism and gut microbiome.

METHODS AND ANALYSIS

This study aims to include 200 mother-infant dyads stratified into one of three body mass index (BMI) categories based on mother's prepregnancy BMI. Multiomics analyses include metabolomics, proteomics, glycomics and microbiomics methods, aiming to characterise human milk from the mothers and further relate the composition to infant gut microbiota and its metabolic impact in the infant. Infant gut microbiota is analysed using 16S sequencing of faeces samples. Nuclear magnetic resonance and mass spectrometry are used for the remaining omics analysis. We investigate whether maternal pre-pregnancy BMI results in a distinct human milk composition that potentially affects the initial priming of the infant's gut environment and metabolism early in life.

ETHICS AND DISSEMINATION

The Central Denmark Region Committees on Health Research Ethics has approved the protocol (J-nr. 1-10-72-296-18). All participants have before inclusion signed informed consent and deputy informed consent in accordance with the Declaration of Helsinki II. Results will be disseminated to health professionals including paediatricians, research community, nutritional policymakers, industry and finally the public. The scientific community will be informed via peer-reviewed publications and presentations at scientific conferences, the industry will be invited for meetings, and the public will be informed via reports in science magazines and the general press. Data cleared for personal data, will be deposited at public data repositories.

TRIAL REGISTRATION NUMBER

Danish regional committee of the Central Jutland Region, journal number: 1-10-72-296-18, version 6.Danish Data Protection Agency, journal number: 2016-051-000001, 1304.

CLINICALTRIALS

gov, identifier: NCT05111990.

Proteomics Characterization of Food-Derived Bioactive Peptides with Anti-Allergic and Anti-Inflammatory Properties

Bioactive peptides are found in foods and dietary supplements and are responsible for health benefits with applications in human and animal medicine. The health benefits include antihypertensive, antimicrobial, antithrombotic, immunomodulatory, opioid, antioxidant, anti-allergic and anti-inflammatory functions. Bioactive peptides can be obtained by microbial action, mainly by the gastrointestinal microbiota from proteins present in food, originating from either vegetable or animal matter or by the action of different gastrointestinal proteases. Proteomics can play an important role in the identification of bioactive peptides. High-resolution mass spectrometry is the principal technique used to detect and identify different types of analytes present in complex mixtures, even when available at low concentrations. Moreover, proteomics may provide the characterization of epitopes to develop new food allergy vaccines and the use of immunomodulating peptides to induce oral tolerance toward offending food allergens or even to prevent allergic sensitization. In addition, food-derived bioactive peptides have been investigated for their anti-inflammatory properties to provide safer alternatives to nonsteroidal anti-inflammatory drugs (NSAIDs). All these bioactive peptides can be a potential source of novel drugs and ingredients in food and pharmaceuticals. The following review is focused on food-derived bioactive peptides with antiallergic and anti-inflammatory properties and summarizes the new insights into the use of proteomics for their identification and quantification.

HLAB: learning the BiLSTM features from the ProtBert-encoded proteins for the class I HLA-peptide binding prediction

Human Leukocyte Antigen (HLA) is a type of molecule residing on the surfaces of most human cells and exerts an essential role in the immune system responding to the invasive items. The T cell antigen receptors may recognize the HLA-peptide complexes on the surfaces of cancer cells and destroy these cancer cells through toxic T lymphocytes. The computational determination of HLA-binding peptides will facilitate the rapid development of cancer immunotherapies. This study hypothesized that the natural language processing-encoded peptide features may be further enriched by another deep neural network. The hypothesis was tested with the Bi-directional Long Short-Term Memory-extracted features from the pretrained Protein Bidirectional Encoder Representations from Transformers-encoded features of the class I HLA (HLA-I)-binding peptides. The experimental data showed that our proposed HLAB feature engineering algorithm outperformed the existing ones in detecting the HLA-I-binding peptides. The extensive evaluation data show that the proposed HLAB algorithm outperforms all the seven existing studies on predicting the peptides binding to the HLA-A^*01:01 allele in AUC and achieves the best average AUC values on the six out of the seven k-mers (k=8,9,...,14, respectively represent the prediction task of a polypeptide consisting of k amino acids) except for the 9-mer prediction tasks. The source code and the fine-tuned feature extraction models are available at http://www.healthinformaticslab.org/supp/resources.php.

Exploring Human Milk Dynamics: Interindividual Variation in Milk Proteome, Peptidome, and Metabolome

Human milk is a dynamic biofluid, and its detailed composition receives increasing attention. While most studies focus on changes over time or differences between maternal characteristics, interindividual variation receives little attention. Nevertheless, a comprehensive insight into this can help interpret human milk studies and help human milk banks provide targeted milk for recipients. This study aimed to map interindividual variation in the human milk proteome, peptidome, and metabolome and to investigate possible explanations for this variation. A set of 286 milk samples was collected from 29 mothers in the third month postpartum. Samples were pooled per mother, and proteins, peptides, and metabolites were analyzed. A substantial coefficient of variation (>100%) was observed for 4.6% and 36.2% of the proteins and peptides, respectively. In addition, using weighted correlation network analysis (WGCNA), 5 protein and 11 peptide clusters were obtained, showing distinct characteristics. With this, several associations were found between the different data sets and with specific sample characteristics. This study provides insight into the dynamics of human milk protein, peptide, and metabolite composition. In addition, it will support future studies that evaluate the effect size of a parameter of interest by enabling a comparison with natural variability.

Combining in silico and in vitro approaches to identify endogenous hypoglycemic peptides from human milk

Potential endogenous hypoglycemic peptides derived from breast milk were screened by in silico approaches against intestinal glucose absorption- and metabolism-related membrane proteins (i.e., SGLT1, ATPase, and GPR40), and their inhibitory...

CLIP-170S is a microtubule +TIP variant that confers resistance to taxanes by impairing drug-target engagement

Taxanes are widely used cancer chemotherapeutics. However, intrinsic resistance limits their efficacy without any actionable resistance mechanism. We have discovered a microtubule (MT) plus-end-binding CLIP-170 protein variant, hereafter CLIP-170S, which we found enriched in taxane-resistant cell lines and patient samples. CLIP-170S lacks the first Cap-Gly motif, forms longer comets, and impairs taxane access to its MT luminal binding site. CLIP-170S knockdown reversed taxane resistance in cells and xenografts, whereas its re-expression led to resistance, suggesting causation. Using a computational approach in conjunction with the connectivity map, we unexpectedly discovered that Imatinib was predicted to reverse CLIP-170S-mediated taxane resistance. Indeed, Imatinib treatment selectively depleted CLIP-170S, thus completely reversing taxane resistance. Other RTK inhibitors also depleted CLIP-170S, suggesting a class effect. Herein, we identify CLIP-170S as a clinically prevalent variant that confers taxane resistance, whereas the discovery of Imatinib as a CLIP-170S inhibitor provides novel therapeutic opportunities for future trials.

Three Distinct Proteases Are Responsible for Overall Cell Surface Proteolysis in Streptococcus thermophilus

The lactic acid bacterium Streptococcus thermophilus was believed to display only two distinct proteases at the cell surface, namely, the cell envelope protease PrtS and the housekeeping protease HtrA. Using peptidomics, we demonstrate here the existence of an additional active cell surface protease, which shares significant homology with the SepM protease of Streptococcus mutans. Although all three proteases-PrtS, HtrA, and SepM-are involved in the turnover of surface proteins, they demonstrate distinct substrate specificities. In particular, SepM cleaves proteins involved in cell wall metabolism and cell elongation, and its inactivation has consequences for cell morphology. When all three proteases are inactivated, the residual cell-surface proteolysis of S. thermophilus is approximately 5% of that of the wild-type strain. IMPORTANCE Streptococcus thermophilus is a lactic acid bacterium used widely as a starter in the dairy industry. Due to its "generally recognized as safe" status and its weak cell surface proteolytic activity, it is also considered a potential bacterial vector for heterologous protein production. Our identification of a new cell surface protease made it possible to construct a mutant strain with a 95% reduction in surface proteolysis, which could be useful in numerous biotechnological applications.

Monitoring Human Milk β-Casein Phosphorylation and O-Glycosylation Over Lactation Reveals Distinct Differences between the Proteome and Endogenous Peptidome

Human milk is a vital biofluid containing a myriad of molecular components to ensure an infant's best start at a healthy life. One key component of human milk is β-casein, a protein which is not only a structural constituent of casein micelles but also a source of bioactive, often antimicrobial, peptides contributing to milk's endogenous peptidome. Importantly, post-translational modifications (PTMs) like phosphorylation and glycosylation typically affect the function of proteins and peptides; however, here our understanding of β-casein is critically limited. To uncover the scope of proteoforms and endogenous peptidoforms we utilized mass spectrometry (LC-MS/MS) to achieve in-depth longitudinal profiling of β-casein from human milk, studying two donors across 16 weeks of lactation. We not only observed changes in β-casein's known protein and endogenous peptide phosphorylation, but also in previously unexplored O-glycosylation. This newly discovered PTM of β-casein may be important as it resides on known β-casein-derived antimicrobial peptide sequences.

Bringing New Methods to the Seed Proteomics Platform: Challenges and Perspectives

For centuries, crop plants have represented the basis of the daily human diet. Among them, cereals and legumes, accumulating oils, proteins, and carbohydrates in their seeds, distinctly dominate modern agriculture, thus play an essential role in food industry and fuel production. Therefore, seeds of crop plants are intensively studied by food chemists, biologists, biochemists, and nutritional physiologists. Accordingly, seed development and germination as well as age- and stress-related alterations in seed vigor, longevity, nutritional value, and safety can be addressed by a broad panel of analytical, biochemical, and physiological methods. Currently, functional genomics is one of the most powerful tools, giving direct access to characteristic metabolic changes accompanying plant development, senescence, and response to biotic or abiotic stress. Among individual post-genomic methodological platforms, proteomics represents one of the most effective ones, giving access to cellular metabolism at the level of proteins. During the recent decades, multiple methodological advances were introduced in different branches of life science, although only some of them were established in seed proteomics so far. Therefore, here we discuss main methodological approaches already employed in seed proteomics, as well as those still waiting for implementation in this field of plant research, with a special emphasis on sample preparation, data acquisition, processing, and post-processing. Thereby, the overall goal of this review is to bring new methodologies emerging in different areas of proteomics research (clinical, food, ecological, microbial, and plant proteomics) to the broad society of seed biologists.

Proteolysis and Process-Induced Modifications in Synbiotic Yogurt Investigated by Peptidomics and Phosphopeptidomics

Probiotic and synbiotic yogurt preparations were manufactured at the semi-industrial pilot scale with Lactobacillus acidophilus and Bifidobacteria strains without inulin or fortified with 1 and 3% (w/w) inulin. The pathway of casein breakdown was determined in probiotic, synbiotic, conventional yogurt, and nonstarted milk base using HPLC-ESI-MS/MS-based peptidomics and phosphopeptidomics; in the latter case, casein phosphorylated peptides (CPPs) were previously enriched by hydroxyapatite chromatography. Compared with traditional yogurt, casein proteolysis increased in probiotic and even more in synbiotic yogurt with 1% inulin. Fortification with 3% inulin greatly modified the proteolytic pattern, indicating a characteristic contribution of probiotics to proteolysis. The enhanced proteolysis in synbiotic yogurt exposed the neo-formed peptides to progressively increase enzymatic or chemical modifications, such as dephosphorylation of CPPs, methionine oxidation, and formation of N-terminal pyroglutamic acids. These modifications might constitute molecular signature descriptors of metabolic processes mediated by complex bacterial communities, with technological, nutritional, and sensorial significance.

Differences in human milk peptide release along the gastrointestinal tract between preterm and term infants

BACKGROUND & AIMS

Preterm infants are born with a gastrointestinal tract insufficiently developed to digesting large quantities of human milk proteins. Peptides released from the digestion of human milk proteins have been identified with bioactivities that may be beneficial to the developing infant. However, it is unknown how prematurity affects total and bioactive peptide release along the gastrointestinal tract. The aim of this study was to compare milk peptide release from milk to stomach to stool between preterm and term infants.

METHODS

Milk, gastric, and stool samples were collected from preterm infants as early collection (days 8 and 9 of life) and late collection (days 21 and 22 of life), and from term infants as early collection. Milk peptides were extracted from the samples and identified using Orbitrap mass spectrometry. Peptide abundance and count were compared across digestion and between the three infant groups at each stage of digestion.

RESULTS

Total milk peptide count and abundance increased from milk to stomach then decreased in stool. Total peptide release was similar among the three infant groups for milk and stool samples. In the stomach, preterm early collection had significantly higher peptide abundance and count than the other two groups. Patterns for peptide release from individual milk proteins were distinct from total peptide release both across digestion and among the infant groups. When analyzing single peptides, term early collection gastric samples had significantly higher peptide abundance than preterm early collection for a known antimicrobial peptide, QELLLNPTHQIYPVTQPLAPVHNPISV.

CONCLUSIONS

Preterm and term infants digest milk proteins differently along their gastrointestinal tracts. While preterm infants released more total peptides in the stomach, term infants released specific bioactive peptides at higher abundance. We identified a region at the C-terminus of β-casein that is conserved from milk through stool and from which are released known and potential antimicrobial peptides.

The anti-ageing effects of a natural peptide discovered by artificial intelligence

OBJECTIVE

As skin ages, impaired extracellular matrix (ECM) protein synthesis and increased action of degradative enzymes manifest as atrophy, wrinkling and laxity. There is mounting evidence for the functional role of exogenous peptides across many areas, including in offsetting the effects of cutaneous ageing. Here, using an artificial intelligence (AI) approach, we identified peptide RTE62G (pep_RTE62G), a naturally occurring, unmodified peptide with ECM stimulatory properties. The AI-predicted anti-ageing properties of pep_RTE62G were then validated through in vitro, ex vivo and proof of concept clinical testing.

METHODS

A deep learning approach was applied to unlock pep_RTE62G from a plant source, Pisum sativum (pea). Cell culture assays of human dermal fibroblasts (HDFs) and keratinocytes (HaCaTs) were subsequently used to evaluate the in vitro effect of pep_RTE62G. Distinct activities such as cell proliferation and ECM protein production properties were determined by ELISA assays. Cell migration was assessed using a wound healing assay, while ECM protein synthesis and gene expression were analysed, respectively, by immunofluorescence microscopy and PCR. Immunohistochemistry of human skin explants was employed to further investigate the induction of ECM proteins by pep_RTE62G ex vivo. Finally, the clinical effect of pep_RTE626 was evaluated in a proof of concept 28-day pilot study.

RESULTS

In vitro testing confirmed that pep_RTE62G is an effective multi-functional anti-ageing ingredient. In HaCaTs, pep_RTE62G treatment significantly increases both cellular proliferation and migration. Similarly, in HDFs, pep_RTE62G consistently induced the neosynthesis of ECM protein elastin and collagen, effects that are upheld in human skin explants. Lastly, in our proof of concept clinical study, application of pep_RTE626 over 28 days demonstrated anti-wrinkle and collagen stimulatory potential.

CONCLUSION

pep_RTE62G represents a natural, unmodified peptide with AI-predicted and experimentally validated anti-ageing properties. Our results affirm the utility of AI in the discovery of novel, functional topical ingredients.

Bioactive peptides derived from human milk proteins: an update

PURPOSE OF REVIEW

Human milk contains a variety of bioactive proteins, and some of the bioactivities are exerted only after proteins are digested in the gastrointestinal tract. This review aims to overview recent studies on bioactive peptides in human milk and gastric digesta of breast-fed infants.

RECENT FINDINGS

Milk protein-derived peptides are endogenously present in human milk, and some of them have been reported to be bioactive peptides, such as a homologue of caseinophosphopeptide, an antimicrobial peptide, and an immunomodulatory peptide. A larger number of peptides are identified in gastric aspirates from breast-fed infants, and bioactive peptides such as angiotensin I-converting enzyme-inhibitory peptides, an antioxidative peptide, opioid agonist peptides are only found in the digesta of human milk but not in human milk per se. Casein is the greatest source of released bioactive peptides.

SUMMARY

Technological advances have considerably increased our capability to identify and characterize peptides derived from human milk proteins. However, their physiological significance and the roles of these bioactive peptides in growth and development of breast-fed infants have not yet been sufficiently elucidated, and further in-vivo experiments and clinical trials are warranted.

Gene-Specific Control of tRNA Expression by RNA Polymerase II

Increasing evidence suggests that tRNA levels are dynamically and specifically regulated in response to internal and external cues to modulate the cellular translational program. However, the molecular players and the mechanisms regulating the gene-specific expression of tRNAs are still unknown. Using an inducible auxin-degron system to rapidly deplete RPB1 (the largest subunit of RNA Pol II) in living cells, we identified Pol II as a direct gene-specific regulator of tRNA transcription. Our data suggest that Pol II transcription robustly interferes with Pol III function at specific tRNA genes. This activity was further found to be essential for MAF1-mediated repression of a large set of tRNA genes during serum starvation, indicating that repression of tRNA genes by Pol II is dynamically regulated. Hence, Pol II plays a direct and central role in the gene-specific regulation of tRNA expression.

Peptidomic Analysis of Urine from Youths with Early Type 1 Diabetes Reveals Novel Bioactivity of Uromodulin Peptides In Vitro

Chronic hyperglycemia is known to disrupt the proteolytic milieu, initiating compensatory and maladaptive pathways in the diabetic kidney. Such changes in intrarenal proteolysis are captured by the urinary peptidome. To elucidate the early kidney response to chronic hyperglycemia, we conducted a peptidomic investigation into urines from otherwise healthy youths with type 1 diabetes and their non-diabetic peers using unbiased and targeted mass spectrometry-based techniques. This cross-sectional study included two separate cohorts for the discovery (n = 30) and internal validation (n = 30) of differential peptide excretion. Peptide bioactivity was predicted using PeptideRanker and subsequently verified in vitro Proteasix and the Nephroseq database were used to identify putative proteases responsible for peptide generation and examine their expression in diabetic nephropathy. A total of 6550 urinary peptides were identified in the discovery analysis. We further examined the subset of 162 peptides, which were quantified across all thirty samples. Of the 15 differentially excreted peptides (p < 0.05), seven derived from a C-terminal region (589SGSVIDQSRVLNLGPITRK607) of uromodulin, a kidney-specific protein. Increased excretion of five uromodulin peptides was replicated in the validation cohort using parallel reaction monitoring (p < 0.05). One of the validated peptides (SGSVIDQSRVLNLGPI) activated NFκB and AP-1 signaling, stimulated cytokine release, and enhanced neutrophil migration in vitro. In silico analyses highlighted several potential proteases such as hepsin, meprin A, and cathepsin B to be responsible for generating these peptides. In summary, we identified a urinary signature of uromodulin peptides associated with early type 1 diabetes before clinical manifestations of kidney disease and discovered novel bioactivity of uromodulin peptides in vitro Our present findings lay the groundwork for future studies to validate peptide excretion in larger and broader populations, to investigate the role of bioactive uromodulin peptides in high glucose conditions, and to examine proteases that cleave uromodulin.

Alternate RNA Structures

RNA molecules fold into complex three-dimensional structures that sample alternate conformations ranging from minor differences in tertiary structure dynamics to major differences in secondary structure. This allows them to form entirely different substructures with each population potentially giving rise to a distinct biological outcome. The substructures can be partitioned along an existing energy landscape given a particular static cellular cue or can be shifted in response to dynamic cues such as ligand binding. We review a few key examples of RNA molecules that sample alternate conformations and how these are capitalized on for control of critical regulatory functions.

Peptidomic analysis reveals multiple protection of human breast milk on infants during different stages

It has been shown that human breast milk (HBM) is an important nutrient for the growth and development of newborns. Currently, peptide drugs provide promising regimes in neonatal disease treatment, especially peptides from HBM that exhibit multiple functions within cells. To explore the potential biological function peptides among the colostrum, transition and mature milk from mother of extremely low birth weight children (the samples were collected from Women's Hospital of Nanjing Medical University from December 2016 to February 2017). A total of 3,182 nonredundant peptides were identified and compared among colostrum, transitional and mature milk using liquid chromatography/mass spectrometry technology, and the numbers and fragments of peptides were various. The isoelectric point and molecular weight analysis of the differentially expressed peptides basically accord with the range of mass spectrometry identification (<3 kDa). Gene Ontology analysis and Pathway analysis, restriction sites analysis, as well as bioinformatics analysis showed that these differentially expressed peptides enriched a variety of biological processes. We identified several putative peptides that might have bioactive effects in diseases and development of newborns, which will inform further functional investigations. Our preliminary research provided a better understanding of the function of peptides during the newborn periods. Furthermore, it laid a foundation for discovering new peptide drugs in neonatal disease treatment.

The Functional Power of the Human Milk Proteome

Human milk is the most complete and ideal form of nutrition for the developing infant. The composition of human milk consistently changes throughout lactation to meet the changing functional needs of the infant. The human milk proteome is an essential milk component consisting of proteins, including enzymes/proteases, glycoproteins, and endogenous peptides. These compounds may contribute to the healthy development in a synergistic way by affecting growth, maturation of the immune system, from innate to adaptive immunity, and the gut. A comprehensive overview of the human milk proteome, covering all of its components, is lacking, even though numerous analyses of human milk proteins have been reported. Such data could substantially aid in our understanding of the functionality of each constituent of the proteome. This review will highlight each of the aforementioned components of human milk and emphasize the functionality of the proteome throughout lactation, including nutrient delivery and enhanced bioavailability of nutrients for growth, cognitive development, immune defense, and gut maturation.

Proteomic analysis of goat milk kefir: Profiling the fermentation-time dependent protein digestion and identification of potential peptides with biological activity

Kefir is a fermented dairy product, associated to health benefits because of being a probiotic and due to the presence of molecules with biological activity. In this work, we have profiled the peptide composition of goat milk kefir at three different fermentation times using a peptidomics approach, in order to study changes in peptide concentrations and patterns of protein digestion throughout the fermentation time. We identified 2328 unique peptides corresponding to 22 protein annotations, with a maximum of peptides found after 24 h fermentation. We established different digestion patterns according to the nature of the proteins, and quantified the changes in the peptides appearing in all the fermentation times. We also identified 11 peptides that matched exactly to sequences with biological activity in databases, almost all of them belonging to caseins. This is the most comprehensive proteomic analysis of goat milk kefir to date.

Toward an efficient workflow for the analysis of the human milk peptidome

There is a growing interest for investigating endogenous peptides from human biofluids which may provide yet unknown functional benefits or provide an early indication of disease states as potential biomarkers. A major technical bottleneck in the investigation of endogenous peptides from body fluids, e.g., serum, urine, saliva, and milk, is that each of these fluids seems to require unique workflows for peptide extraction and analysis. Thus, protocols optimized for serum cannot be directly translated to milk. One biofluid that is readily available, but which has not been extensively explored, is human milk, whose analysis could contribute to our understanding of the immune development of the newborn infant. Due to the occurrence of highly abundant lipids, proteins, and saccharides, milk peptidomics requires dedicated sample preparation steps. The aim of this study was to develop a time and cost-efficient workflow for the analysis of the human milk peptidome, for which we compared peptide extraction methodologies and peptide fragmentation methods. A method using strong acid protein precipitation and analysis by collision-induced dissociation fragmentation was found to be superior to all other test methods, allowing us qualitative and quantitative detection of about 4000 endogenous human milk peptides in a total analysis time of just 18 h.

Release of functional peptides from mother's milk and fortifier proteins in the premature infant stomach

Digestion of milk proteins in the premature infant stomach releases functional peptides; however, which peptides are present has not been reported. Premature infants are often fed a combination of human milk and bovine milk fortifiers, but the variety of functional peptides released from both human and bovine milk proteins remains uncharacterized. This study applied peptidomics to investigate the peptides released in gastric digestion of mother’s milk proteins and supplemental bovine milk proteins in premature infants. Peptides were assessed for homology against a database of known functional peptides—Milk Bioactive Peptide Database. The peptidomic data were analyzed to interpret which proteases most likely released them from the parent protein. We identified 5,264 unique peptides from bovine and human milk proteins within human milk, fortifier or infant gastric samples. Plasmin was predicted to be the most active protease in milk, while pepsin or cathepsin D were predicted to be most active in the stomach. Alignment of the peptide distribution showed a different digestion pattern between human and bovine proteins. The number of peptides with high homology to known functional peptides (antimicrobial, angiotensin-converting enzyme-inhibitory, antioxidant, immunomodulatory, etc.) increased from milk to the premature infant stomach and was greater from bovine milk proteins than human milk proteins. The differential release of bioactive peptides from human and bovine milk proteins may impact overall health outcomes in premature infants.

Antimicrobial Resistance: Its Surveillance, Impact, and Alternative Management Strategies in Dairy Animals

Antimicrobial resistance (AMR), one among the most common priority areas identified by both national and international agencies, is mushrooming as a silent pandemic. The advancement in public health care through introduction of antibiotics against infectious agents is now being threatened by global development of multidrug-resistant strains. These strains are product of both continuous evolution and un-checked antimicrobial usage (AMU). Though antibiotic application in livestock has largely contributed toward health and productivity, it has also played significant role in evolution of resistant strains. Although, a significant emphasis has been given to AMR in humans, trends in animals, on other hand, are not much emphasized. Dairy farming involves surplus use of antibiotics as prophylactic and growth promoting agents. This non-therapeutic application of antibiotics, their dosage, and withdrawal period needs to be re-evaluated and rationally defined. A dairy animal also poses a serious risk of transmission of resistant strains to humans and environment. Outlining the scope of the problem is necessary for formulating and monitoring an active response to AMR. Effective and commendably connected surveillance programs at multidisciplinary level can contribute to better understand and minimize the emergence of resistance. Besides, it requires a renewed emphasis on investments into research for finding alternate, safe, cost effective, and innovative strategies, parallel to discovery of new antibiotics. Nevertheless, numerous direct or indirect novel approaches based on host-microbial interaction and molecular mechanisms of pathogens are also being developed and corroborated by researchers to combat the threat of resistance. This review places a concerted effort to club the current outline of AMU and AMR in dairy animals; ongoing global surveillance and monitoring programs; its impact at animal human interface; and strategies for combating resistance with an extensive overview on possible alternates to current day antibiotics that could be implemented in livestock sector.

Origins, Technological Development, and Applications of Peptidomics

Peptidomics is the comprehensive characterization of peptides from biological sources mainly by HPLC and mass spectrometry. Mass spectrometry allows the detection of a multitude of single peptides in complex mixtures. The term first appeared in full papers in the year 2001, after over 100 years of peptide research with a main focus on one or a few specific peptides. Within the last 15 years, this new field has grown to over 1200 publications. Mass spectrometry techniques, in combination with other analytical methods, were developed for the fast and comprehensive analysis of peptides in proteomics and specifically adjusted to implement peptidomics technologies. Although peptidomics is closely linked to proteomics, there are fundamental differences with conventional bottom-up proteomics. The development of peptidomics is described, including the most important implementations for its technological basis. Different strategies are covered which are applied to several important applications, such as neuropeptidomics and discovery of bioactive peptides or biomarkers. This overview includes links to all other chapters in the book as well as recent developments of separation, mass spectrometric, and data processing technologies. Additionally, some new applications in food and plant peptidomics as well as immunopeptidomics are introduced.

Milk Peptidomics to Identify Functional Peptides and for Quality Control of Dairy Products

Human milk and dairy products are important parts of human nutrition. In addition to supplying nutrients, milk proteins contain fragments-peptides-with important biological functions that are released during processing or digestion. Besides their potential functional relevance, peptides released during processing can be used as markers of ripening stage or product deterioration. Hence, identification and quantification of peptides in milk can be used to assay potential health benefits or product quality. This chapter describes how to extract, identify, and analyze peptides within breast milk, dairy products, and dairy digestive samples. We describe how to analyze extracted peptides with liquid chromatography-mass spectrometry, to use software to identify peptides based on database searching, and to extract peak areas for relative quantification of each peptide. We describe methods for data analysis, including predicting which enzymes are responsible for protein cleavage, identifying the site specificity of protein breakdown, mapping identified peptides to known bioactive peptides, and applying models to predict novel functional peptides.

Investigation into the antimicrobial action and mechanism of a novel endogenous peptide β-casein 197 from human milk

A novel endogenous peptide cleaved from 197–213 AA of β-casein, named β-casein 197, was identified by tandem mass spectrometry. β-casein 197 constituted a significant proportion of the peptide content in preterm milk. This study investigated the antibacterial effects and mechanisms against common pathogenic bacteria. Six bacterial strains were selected for this study: Escherichia coli, Staphylococcus aureus, Yersinia enterocolitica, Listeria monocytogenes, Klebsiella pneumonia and Bacillus subtilis. After synthesis, serial twofold dilutions of β-casein 197 were added to select for sensitive bacteria. The disk diffusion method and analysis of bacterial staining were used to identify antibacterial effect, while DNA-binding, scanning electron microscopy and transmission electron microscopy were used to explore antimicrobial mechanisms. Disk diffusion showed that E. coli, S. aureus and Y. enterocolitica were sensitive to the β-casein 197. In addition, live/dead fluorescent staining also confirmed antibacterial effects. Scanning electron and transmission electron microscopy revealed affected extracellular and intracellular structure for three species of bacteria, while a DNA-binding assay showed that the antimicrobial activity did not occur through DNA binding. This study suggests that β-casein 197 has antimicrobial activity against common pathogenic bacteria in newborns with infection. The peptide induced membrane permeabilization but did not bind to genomic DNA. Based on our findings, β-casein 197 has potential clinical value for preventing infections of premature infants.

Milk Proteins Are Predigested Within the Human Mammary Gland

Previous work demonstrates that proteases present in human milk release hundreds of peptides derived from milk proteins. However, the question of whether human milk protein digestion begins within the mammary gland remains incompletely answered. The primary objective of this study was to determine whether proteolytic degradation of human milk proteins into peptides begins within the mammary gland. The secondary objectives were to determine which milk proteases participate in the proteolysis and to predict which released peptides have bioactivity. Lactating mothers (n = 4) expressed their milk directly into a mixture of antiproteases on ice followed by immediate freezing of the milk to limit post-expression protease activity. Samples were analyzed for their peptide profiles via mass spectrometry and database searching. Peptidomics-based protease prediction and bioactivity prediction were each performed with several different approaches. The findings demonstrate that human milk contains more than 1,100 unique peptides derived from milk protein hydrolysis within the mammary gland. These peptides derived from 42 milk proteins and included 306 potential bioactive peptides. Based on the peptidomics data, plasmin was predicted to be the milk protease most active in the hydrolysis of human milk proteins within the mammary gland. Milk proteases actively cleave milk proteins within the mammary gland, initiating the release of functional peptides. Thus, the directly breastfed infant receives partially pre-digested proteins and numerous bioactive peptides.

Peptides Released from Foremilk and Hindmilk Proteins by Breast Milk Proteases Are Highly Similar

Human milk contains active proteases that initiate hydrolysis of milk proteins within the mammary gland. Milk expressed at the beginning of feeding is known as foremilk and that at the end of feeding is known as hindmilk. As hindmilk contains higher fat, vitamins A and E, and higher calories than foremilk, feeding only hindmilk initially and reserving foremilk for later are practiced in some neonatal intensive care units. This study investigated the difference in peptide profiles, predicted milk protease activities, and bioactive peptides between foremilk and hindmilk. Bioactive peptides are short fragments of proteins that influence biological processes. Four mothers pumped 10 mL of their foremilk and 10 mL of their hindmilk into iced containers prepared with antiproteases and the samples were immediately frozen. The peptide profile of each sample was analyzed by liquid chromatography nano-electrospray ionization Orbitrap Fusion tandem mass spectrometry. Peptide abundance (sum of ion intensities) and count (number of unique peptide sequences) in each milk sample were determined from this analysis. The specific enzymes that participated in peptide release were predicted based on the amino acids positioned at each cleavage site. Peptide bioactivity was predicted based on homology to a known functional peptide database and two bioactivity prediction algorithms. Hindmilk contained a higher count of peptides than foremilk. The higher number of unique peptide sequences in hindmilk was related to hydrolysis of β-casein, osteopontin, α_s1-casein and mucin-1 via plasmin and elastase cleavage, and possible aminopeptidase and carboxypeptidase activities. Though hindmilk contained a greater number of peptides than foremilk, the overall peptide abundance did not differ and most of the total peptide abundance derived from peptide sequences that were present in both milk types. The presence of higher numbers of predicted bioactive peptides in the hindmilk could indicate that the practice of providing hindmilk rather than foremilk to premature infants could positively impact health outcomes; however, as there are few differences in overall peptide abundance, the overall effect is likely limited.

The Peptidome Comes of Age: Mass Spectrometry-Based Characterization of the Circulating Cancer Peptidome

Peptides play a seminal role in most physiological processes acting as neurotransmitters, hormones, antibiotics, and immune regulation. In the context of tumor biology, it is hypothesized that endogenous peptides, hormones, cytokines, growth factors, and aberrant degradation of select protein networks (e.g., enzymatic activities, protein shedding, and extracellular matrix remodeling) are fundamental in mediating cancer progression. Analysis of peptides in biological fluids by mass spectrometry holds promise of providing sensitive and specific diagnostic and prognostic information for cancer and other diseases. The identification of circulating peptides in the context of disease constitutes a hitherto source of new clinical biomarkers. The field of peptidomics can be defined as the identification and comprehensive analysis of physiological and pathological peptides. Like proteomics, peptidomics has been advanced by the development of new separation strategies, analytical detection methods such as mass spectrometry, and bioinformatic technologies. Unlike proteomics, peptidomics is targeted toward identifying endogenous protein and peptide fragments, defining proteolytic enzyme substrate specificity, as well as protease cleavage recognition (degradome). Peptidomics employs "top-down proteomics" strategies where mass spectrometry is applied at the proteoform level to analyze intact proteins and large endogenous peptide fragments. With recent advances in prefractionation workflows for separating peptides, mass spectrometry instrumentation, and informatics, peptidomics is an important field that promises to impact on translational medicine. This review covers the current advances in peptidomics, including top-down and imaging mass spectrometry, comprehensive quantitative peptidome analyses (developments in reproducibility and coverage), peptide prefractionation and enrichment workflows, peptidomic data analyses, and informatic tools. The application of peptidomics in cancer biomarker discovery will be discussed.

Gender proteomics II. Which proteins in sexual organs

In continuity with the review dealing with differences by gender in non-sexual organs [1], this review collects data on the proteomes of the sexual organs as involved in human reproduction, under both physiological and pathological conditions. It also collects data on the tissue structures and biological fluids typical of pregnancy, such as placenta and amniotic fluid, as well as what may be tested on preimplantation embryos during medically assisted reproduction. The review includes as well mention to all fluids and secretions connected with sex organs and/or reproduction, including sperm and milk, to exemplify two distinctive items in male and female physiology.

SIGNIFICANCE

The causes of infertility are only incompletely understood; the same holds for the causes, and even the early markers, of the most frequent complications of pregnancy. To these established medical challenges, present day practice adds new issues connected with medically assisted reproduction. Omics approaches, including proteomics, are building the database for basic knowledge to possibly translate into clinical testing and eventually into medical routine in this critical branch of health care.

Analysis of Milk from Mothers Who Delivered Prematurely Reveals Few Changes in Proteases and Protease Inhibitors across Gestational Age at Birth and Infant Postnatal Age

Background: Peptidomics research has demonstrated that protease activity is higher in breast milk from preterm-delivering mothers than from term-delivering mothers. However, to our knowledge, the effect of the degree of prematurity and postnatal age on proteases and protease inhibitors in human milk remains unknown.Objective: We aimed to determine the change of proteases and protease inhibitors in milk from mothers who delivered prematurely across gestational age (GA) and postnatal age.Methods: Milk samples were collected from 18 mothers aged 26-40 y who delivered preterm infants and who lacked mastitis. For analysis, samples were separated into 2 groups: 9 from early GA (EGA) (24-26 wk GA)-delivering mothers and 9 from late GA (LGA) (27-32 wk GA)-delivering mothers. Within the 9 samples in each group, the collection time ranged from postnatal days 2 to 47. The activity and predicted activity of proteases in preterm milk were determined with the use of fluorometric and spectrophotometric assays and peptidomics, respectively. Protease and protease inhibitor concentrations were determined with the use of ELISA. Linear mixed models were applied to compare enzymes across GA and postnatal age.Results: Carboxypeptidase B2, kallikrein, plasmin, elastase, thrombin, and cytosol aminopeptidase were present and active in the milk of preterm-delivering mothers. Most milk protease and antiprotease concentrations did not change with GA or postnatal age. However, the concentration and activity of kallikrein, the most abundant and active protease in preterm milk, increased by 25.4 ng · mL-1 · d-1 and 0.454 μg · mL-1 · d-1 postnatally, respectively, in EGA milk samples while remaining stable in LGA milk samples.Conclusions: This research demonstrates that proteases are active in human milk and begin to degrade milk protein within the mammary gland before consumption by infants. Proteases and protease inhibitors in milk from mothers of premature infants mostly did not vary substantially across GA and postnatal age.

Milk bioactive peptide database: A comprehensive database of milk protein-derived bioactive peptides and novel visualization

During processing and digestion, milk proteins are disassembled into peptides with an array of biological functions, including antimicrobial, angiotensin-converting enzyme inhibition, antioxidant, opioid, and immunomodulation. These functions are summarized in numerous reviews, yet information on which peptides have which functions remains scattered across hundreds of research articles. We systematically searched the literature for all instances of bioactive peptides derived from milk proteins from any mammalian source. The data were compiled into a comprehensive database, which can be used to search for specific functions, peptides, or proteins (http://mbpdb.nws.oregonstate.edu). To review this large dataset, the bioactive peptides reported in the literature were visually mapped on the parent protein sequences, providing information on sites with highest abundance of bioactive peptides.

Enzymes in Human Milk

Milk proteins are a complex and diverse source of biological activities. Beyond their function, intact milk proteins also act as carriers of encrypted functional sequences that, when released as peptides, exert biological functions, including antimicrobial and immunomodulatory activity, which could contribute to the infant's competitive success. Research has now revealed that the release of these functional peptides begins within the mammary gland itself. A complex array of proteases produced in mother's milk has been shown to be active in the milk, releasing these peptides. Moreover, our recent research demonstrates that these milk proteases continue to digest milk proteins within the infant's stomach, possibly even to a larger extent than the infant's own proteases. As the neonate has relatively low digestive capacity, the activity of milk proteases in the infant may provide important assistance to digesting milk proteins. The coordinated release of these encrypted sequences is accomplished by selective proteolytic action provided by an array of native milk proteases and infant-produced enzymes. The task for scientists is now to discover the selective advantages of this protein-protease-based peptide release system.