Using mass spectrometry to detect buffalo salivary odorant-binding protein and its post-translational modifications

Interplay of hormones and metabolite excretion with fern pattern prove saliva as a potent indicator of male reproductive status in Kangayam breed cattle

Kangayam cattle are one of the drought breeds in India with distinct attributes. Agricultural transformation has led to a decline in many pure-breed indigenous cattle, including the Kangayam breed. Hence, a study on the reproductive physiology of male Kangayam breed cattle is necessary to disentangle problems in the area of livestock improvement. In this study, we investigated the relationship between serum hormones and bio-constituents and ascertained the potential of saliva as an indicator of the reproductive status of Kangayam cattle (Bos indicus). The present study confirms that cholesterol was higher in intact males and lower in prepubertal and castrated males. Testosterone levels were also higher in intact males than in castrated or prepubertal males. Hence, it can be inferred that high cholesterol levels contribute to active derivatization of testosterone in intact males. In contrast, reduced cholesterol availability leads to decreased testosterone synthesis in castrated and prepubertal males. Furthermore, it is reasonable to speculate that testosterone could have influenced salivary fern patterns in intact males, and thus, fern-like crystallization in the saliva was apparent. The unique salivary compounds identified through GC-MS across various reproductive statuses of Kangayam males may advertise their physiological status to conspecifics. In addition, the presence of odorant-binding protein (OBP) in saliva further supports its role in olfactory communication. This study attested to a posssible interlink between gonadal status and serum biochemical profiles. The salivary fern pattern revealed in this study can be used as a predictive tool, and the presence of putative volatiles and OBP adds evidence to the role of saliva in chemical communication.

Comparative Proteome Profiling of Saliva Between Estrus and Non-Estrus Stages by Employing Label-Free Quantitation (LFQ) and Tandem Mass Tag (TMT)-LC-MS/MS Analysis: An Approach for Estrus Biomarker Identification in Bubalus bubalis

Accurate determination of estrus is essentially required for efficient reproduction management of farm animals. Buffalo is a shy breeder and does not manifest overt signs of estrus that make estrus detection difficult resulting in a poor conception rate. Therefore, identifying estrus biomarkers in easily accessible biofluid such as saliva is of utmost interest. In the current study, we generated saliva proteome profiles during proestrus (PE), estrus (E), metestrus (ME), and diestrus (DE) stages of the buffalo estrous cycle using both label-free quantitation (LFQ) and labeled (TMT) quantitation and mass spectrometry analysis. A total of 520 proteins were identified as DEPs in LFQ; among these, 59 and four proteins were upregulated (FC ≥ 1.5) and downregulated (FC ≤ 0.5) during E vs. PE, ME, and DE comparisons, respectively. Similarly, TMT-LC-MS/MS analysis identified 369 DEPs; among these, 74 and 73 proteins were upregulated and downregulated during E vs. PE, ME, and DE stages, respectively. Functional annotations of GO terms showed enrichment of glycolysis, pyruvate metabolism, endopeptidase inhibitor activity, salivary secretion, innate immune response, calcium ion binding, oocyte meiosis, and estrogen signaling. Over-expression of SERPINB1, HSPA1A, VMO1, SDF4, LCN1, OBP, and ENO3 proteins during estrus was further confirmed by Western blotting. This is the first comprehensive report on differential proteome analysis of buffalo saliva between estrus and non-estrus stages. This study generated an important panel of candidate proteins that may be considered buffalo estrus biomarkers which can be applied in the development of a diagnostic kit for estrus detection in buffalo.

Odorant-binding proteins of mammals

Odorant-binding proteins (OBPs) of vertebrates belong to the lipocalin superfamily and perform a dual function: solubilizing and ferrying volatile pheromones to the olfactory receptors, and complexing the same molecules in specialized glands and assisting their release into the environment. Within vertebrates, to date they have been reported only in mammals, apart from two studies on amphibians. Based on the small number of OBPs expressed in each species, on their sites of production outside the olfactory area and their presence in biological fluids known to be pheromone carriers, such as urine, saliva and sexual secretions, we conclude that OBPs of mammals are specifically dedicated to pheromonal communication. This assumption is further supported by the observation that some OBPs present in biological secretions are endowed with their own pheromonal activity, adding renewed interest to these proteins. Another novel piece of evidence is the recent discovery that glycosylation and phosphorylation can modulate the binding activity of these proteins, improving their affinity to pheromones and narrowing their specificity. A comparison with insects and other arthropods shows a completely different scenario. While mammalian OBPs are specifically tuned to pheromones, those of insects, which are completely different in sequence and structure, include carriers for general odorants in addition to those dedicated to pheromones. Additionally, whereas mammals adopted a single family of carrier proteins for chemical communication, insects and other arthropods are endowed with several families of semiochemical-binding proteins. Here, we review the literature on the structural and functional properties of vertebrate OBPs, summarize the most interesting new findings and suggest possible exciting future developments.

The 40-Year Mystery of Insect Odorant-Binding Proteins

The survival of insects depends on their ability to detect molecules present in their environment. Odorant-binding proteins (OBPs) form a family of proteins involved in chemoreception. While OBPs were initially found in olfactory appendages, recently these proteins were discovered in other chemosensory and non-chemosensory organs. OBPs can bind, solubilize and transport hydrophobic stimuli to chemoreceptors across the aqueous sensilla lymph. In addition to this broadly accepted "transporter role", OBPs can also buffer sudden changes in odorant levels and are involved in hygro-reception. The physiological roles of OBPs expressed in other body tissues, such as mouthparts, pheromone glands, reproductive organs, digestive tract and venom glands, remain to be investigated. This review provides an updated panorama on the varied structural aspects, binding properties, tissue expression and functional roles of insect OBPs.

Molecular and functional characterization of buffalo nasal epithelial odorant binding proteins and their structural insights by in silico and biochemical approaches

The olfactory system is capable of detecting and distinguishing thousands of environmental odorants that play a key role in reproduction, social behaviours including pheromones influenced classical events. Membrane secretary odorant binding proteins (OBPs) are soluble lipocalins, localized in the nasal membrane of mammals. They bind and carry odorants within the nasal epithelium to putative olfactory transmembrane receptors (ORs). OBP has not yet been exploited to develop a suitable technique to detect oestrus which is being reported as a difficult task in buffalo. In the present study, using molecular biology and protein engineering approaches, we have cloned six novel OBP isoforms from buffalo nasal epithelium odorant-binding proteins (bnOBPs). Furthermore, 3 D models were developed and molecular-docking, dynamics experiments were performed by in silico approaches. In particular, we found four residues (Phe104, Phe134, Phe69 and Asn118) in OBP1a, which contributed to favourable interactions towards two sex pheromones, specifically oleic acid and p-cresol. We expressed this protein in Escherichia coli from female buffalo urine and validated through fluorescence quenching studies to show similar strong binding affinities of OBP1a to oleic acid and p-cresol. By using structural data, the binding specificity was also verified by site-directed mutagenesis of the four residues followed by in vitro binding assays. Our results enable us to better understand the functions of different nasal epithelium OBP isoforms in buffaloes. They also lead to improved understanding of the interaction between olfactory proteins and odorants to develop highly selective biosensing devices for non-invasive detection of oestrus in buffaloes. Communicated by Ramaswamy H. Sarma.

The MKK-Dependent Phosphorylation of p38α Is Augmented by Arginine Methylation on Arg49/Arg149 during Erythroid Differentiation

The activation of p38 mitogen-activated protein kinases (MAPKs) through a phosphorylation cascade is the canonical mode of regulation. Here, we report a novel activation mechanism for p38α. We show that Arg49 and Arg149 of p38α are methylated by protein arginine methyltransferase 1 (PRMT1). The non-methylation mutations of Lys49/Lys149 abolish the promotive effect of p38α on erythroid differentiation. MAPK kinase 3 (MKK3) is identified as the major p38α upstream kinase and MKK3-mediated activation of the R49/149K mutant p38α is greatly reduced. This is due to a profound reduction in the interaction of p38α and MKK3. PRMT1 can enhance both the methylation level of p38α and its interaction with MKK3. However, the phosphorylation of p38α by MKK3 is not a prerequisite for methylation. MAPK-activated protein kinase 2 (MAPKAPK2) is identified as a p38α downstream effector in the PRMT1-mediated promotion of erythroid differentiation. The interaction of MAPKAPK2 with p38α is also significantly reduced in the R49/149K mutant. Together, this study unveils a novel regulatory mechanism of p38α activation via protein arginine methylation on R49/R149 by PRMT1, which impacts partner interaction and thus promotes erythroid differentiation. This study provides a new insight into the complexity of the regulation of the versatile p38α signaling and suggests new directions in intervening p38α signaling.

Buffalo nasal odorant-binding protein (bunOBP) and its structural evaluation with putative pheromones

Pheromones are odoriferous volatile chemical cues produced by animals for communication among conspecifics so as to regulate their social behaviors. In general, the odor compounds are recognized by receptors in the nasal cavity. Odorant-binding protein (OBP), a lipocalin family protein, mediates the air-borne odor cues to nasal receptors through nasal mucus. The presence of OBP in several mammalian species is well documented but to-date there is no report of a nasal OBP in buffalo. Hence, the present study was undertaken to investigate if OBP is present in buffalo nasal mucus. Uni- and two-dimensional gel electrophoresis of the nasal mucus suggested the presence of OBP, which was confirmed using mass spectrometry. In silico homology model of the OBP was generated and its structural similarity with other mammalian OBPs was assessed. Finally, molecular-docking and -dynamics simulations analysis revealed the efficiency of buffalo nasal OBP (bunOBP) to bind with buffalo pheromones as well as other reported chemical cues. Taken together, the occurrence of nasal OBP in buffalo and its putative role in odor binding are reported for the first time. The potential association of this protein with estrus-specific volatiles could be taken to advantage for non-invasive detection of estrus in buffaloes.

Localization of α 2u-globulin in the acinar cells of preputial gland, and confirmation of its binding with farnesol, a putative pheromone, in field rat (Millardia meltada)

Pheromones, low molecular weight chemical entities that bind to pheromone carrier proteins, are chemical signals that play an important role in the communication system in animals. This has been rather fairly well-studied in the rodents. The preputial gland, a rich source of pheromones in many rodents, contains a low molecular mass protein (18–20 kDa) that acts as one such pheromone carrier. However, the presence of this protein in the notorious rodent pest Millardia meltada has not yet been proven. Therefore, we aimed at identifying this protein, and the pheromones that are bound to it, in this rodent so as to utilize the information in the control of this pest. Twenty volatile compounds were identified in the preputial gland using GC-MS. Total protein of the gland was fractioned by both one and two-dimensional electrophoresis when we identified a low molecular mass protein (19 kDa, pI-4.7). Adopting MALDI-TOF MS and LC-MS analyses, the protein was confirmed as α 2u-globulin. To identify the volatiles bound to this protein, we used column chromatography and GC-MS. We found that farnesol and 6-methyl-1-heptanol are the volatiles that would bind to the protein, which we propose to be putative pheromones. Immunohistochemical analysis confirmed localization of α 2u-globulin in the acinar cells of the preputial gland. Thus, we show that α 2u-globulin, a pheromone-carrier protein, is present in the preputial gland acinar cells of M. meltada and suggest farnesol and 6-methyl-1-heptanol to be the volatiles which would bind to it. The α 2u-globulin together with farnesol and 6-methyl-1-heptanol contribute to pheromonal communication of M. meltada.

Analysis of differentially expressed novel post-translational modifications of plasma apolipoprotein E in Taiwanese females with breast cancer

APOE ε2 or ε4 alleles being used as indicators of breast cancer risk are controversial in Taiwanese females. We provide a concept for relative comparisons of post-translational modifications (PTMs) of plasma apolipoprotein E (ApoE) between normal controls and breast cancer patients to investigate the association of ApoE with breast cancer risk. APOE polymorphisms (ApoE isoforms) were not assessed in this study. The relative modification ratio (%) of 15 targeted and 21 modified peptides were evaluated by 1D SDS-PAGE, in-gel digestion, and label-free nano-LC/MS to compare normal controls with breast cancer patients. Plasma levels of the ApoE protein did not significantly differ between normal controls and breast cancer patients. Eleven sites with novel PTMs were identified from 7 pairs of differentially expressed targeted and modified peptides according to the relative modification ratio including methylation at the E3 (↑1.45-fold), E7 (↑1.45-fold), E11 (↑1.19-fold), E77 (↑2.02-fold), E87 (↑2.02-fold), and Q98 (↑1.62-fold) residues; dimethylation at the Q187 (↑1.44-fold) residue; dihydroxylation at the R92 (↑1.25-fold), K95 (↑1.25-fold), and R103 (↑1.25-fold) residues; and glycosylation at the S129 (↑1.14-fold) residue. The clustered methylation and dihydroxylation of plasma ApoE proteins may play a role in breast cancer.

Effect of high-fat diet on hepatic proteomics of hamsters

A high-fat diet contributes to the etiology of metabolic diseases. As the liver plays a crucial role in metabolism, an insight into the hepatic proteomics will help to illustrate the physiological effect of a high-fat diet. Fourteen nine-week old male Syrian hamsters were maintained on either control (C) or high-fat (HF) diets (0.2% cholesterol +22% fat) for 8 weeks. Hamsters were chosen because they show close similarity to human lipid metabolism. At the end of study, blood and livers were collected for analysis. Liver proteins were fractionated by electrophoresis, digested by trypsin, and then separated by label-free nano-LC/MS/MS. The TurboSequest algorithm was used to identify the peptide sequences against the hamster database in Universal Proteins Resource Knowledgebase (UniProt). The results indicate that 1191 hepatic proteins were identified and 135 of them were expressed differentially in the high-fat group (p < 0.05). Some of these 135 proteins that involve in metabolic diseases were further validated by Western blotting. The animals maintained on the high-fat diet had significantly (p < 0.05) higher serum triglyceride, cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and uric acid. Animals consuming a high-fat diet also had significantly (p < 0.05) more accumulation of triglyceride and cholesterol in livers. Xanthine dehydrogenase (XDH), which plays an important role in uric acid synthesis, was up-regulated by the high-fat diet (p < 0.05). The α-subunit of hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (HADHA), which catalyzes the second and third reactions of β-oxidation, was down-regulated by the high-fat diet (p < 0.05). Aconitate hydratase 2 (ACO2), which catalyzes the conversion of citrate to isocitrate in TCA cycle, was down-regulated in animals of the high-fat group (p < 0.05). Inflammatory markers annexin A3 (ANXA3) and annexin A5 (ANXA5) were up-regulated by the high-fat diet (p < 0.05). Moreover, enzymes involved in the urea cycle were suppressed by high-fat diet, including carbamoyl phosphate synthase 1 (CPS1), ornithine transcarbamoylase (OTC), argininosuccinate synthase (ASS), argininosuccinate lyase (ASL), and arginase 1 (ARG 1). Post-translational modifications (PTM) of ANXA3, ANXA5, and XDH were also analyzed. A set of differentially expressed proteins were identified as molecular markers for elucidating the pathological mechanism of high-fat diet.

Does salivary protein(s) act an ovulation indicator for women? A hypothesis

Ovulation is an important physiological process in human, and its effect may reflect in body fluids via secretion of biomolecules such as proteins, amino acids, antioxidants, antimicrobial peptides and so on. Recently, the non-invasive sampling approaches are used to diagnose disease status and access health condition of human. Saliva comprises various proteins which are secreted through salivary glands. The proteins present in the saliva may vary in their expression according to the hormonal level and physiological nature of the body which are said to be hormone receptors, stress proteins and antimicrobial peptides. Therefore, it is postulated that saliva can be used in the detection of ovulation time in human using specific protein(s) expression and which can be considered as a best non-invasive method. The identification of these proteins by adopting LC-MS/MS followed by Western blot analysis are possible to identify a promising biomarker for ovulation detection in human.

Critical roles of mitochondria in brain activities of torpid Myotis ricketti bats revealed by a proteomic approach

Bats are the only mammals that fly and hibernate. Little is known about their overall metabolism in the brain during hibernation. In this study, brain proteins of torpid and active Myotis ricketti bats were fractionated and compared using a proteomic approach. Results showed that 21% (23 proteins) of identified proteins with significant expression changes were associated with amino acid metabolism and proteostasis. The expression levels of proteins involved in energy metabolism (15 proteins), cytoskeletal structure (18 proteins), and stress response (13 proteins) were also significantly altered in torpid bats. Over 30% (34 proteins) of differentially expressed proteins were associated with mitochondrial functions. Various post-translational modifications (PTMs) on PDHB, DLD, and ARG1 were detected, suggesting that bats use PTMs to regulate protein functions during torpor. Antioxidation and stress responses in torpid bats were similar to those of hibernated squirrels, suggesting a common strategy adopted by small hibernators against brain dysfunction. Since many amino acids that metabolize in mitochondria modulate neuronal transmissions, results of this study reveal pivotal roles of mitochondria in neural communication, metabolic regulation, and brain cell survival during bat hibernation. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

BIOLOGICAL SIGNIFICANCE

This study reveals the mechanisms used by bats to regulate brain activities during torpor. These mechanisms include post-translational modifications and differential expression of proteins involved in mitochondrial electron transport, anaerobic glycolysis, TCA cycle efflux, cytoskeletal plasticity, amino acid metabolism, vesicle structure, antioxidation defense, stress response, and proteostasis. Our study provides insights in metabolic regulation of flying mammals during torpor and common strategies used by small hibernators in response to hibernation. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Consumption of purple sweet potato affects post-translational modification of plasma proteins in hamsters

A high level of intake of vegetables is strongly associated with the prevention of chronic diseases. Because post-translational modifications (PTMs) have been shown to be the important biomarkers of the change in physiological functions, this study aimed to explore the changes in PTMs of plasma proteins when purple sweet potato (PSP), a root vegetable, was incorporated into the daily diet. Male Syrian hamsters were maintained on a rice diet (50% rice) or PSP diet (25% rice and 25% PSP) for 12 weeks. Plasma proteins were fractionated by electrophoresis, digested by trypsin, and then separated by nano-liquid chromatography and tandem mass spectrometry. The TurboSequest algorithm was used to identify peptide sequence against the hamster database in Universal Proteins Resource Knowledgebase, and in-house PTM finder programs were used for identification and quantification of PTMs. The results indicated that 95 plasma proteins were identified and 28 PTM sites on 26 of these 95 proteins were affected by consumption of PSP (p < 0.05). Methylation accounted for the largest percentage of affected modifications (35.71%). This study also showed that incorporation of purple sweet potato into the diet significantly lowered blood and liver lipids (p < 0.05). The results of this study provide a basis for prospective studies evaluating the effects of dietary intervention on modifications of proteins.

Comparative proteomics, network analysis and post-translational modification identification reveal differential profiles of plasma Con A-bound glycoprotein biomarkers in gastric cancer

In the study, we used Con A affinity chromatography, 1-D gel electrophoresis, and nano-LC-MS/MS to screen biomarker candidates in plasma samples obtained from 30 patients with gastric cancer and 30 healthy volunteers. First, we pooled plasma samples matched by age and sex. We identified 17 differentially expressed Con A-bound glycoproteins, including 10 upregulated proteins and 7 downregulated proteins; these differences were significant (Student's t-test, p-value<0.05). Furthermore, 2 of the upregulated proteins displayed expression levels that were increased by 2-fold or more in gastric cancer samples when compared with normal control samples. These proteins included leucine-rich alpha-2-glycoprotein (LRG1) and inter-alpha-trypsin inhibitor heavy chain H3 (ITIH3), and the expression levels were validated by Western blot analysis. Pathway and network analysis of the differentially expressed proteins by Ingenuity Pathway Analysis revealed vital canonical pathways involving acute phase response signaling, the complement system, LXR/RXR activation, hematopoiesis from pluripotent stem cells, and primary immunodeficiency signaling. Our results suggest that Con A-bound LRG1 and ITIH3 may not be practically applicable as a robust biomarker for the early detection of gastric cancer. Additionally, three novel PTMs in ITIH3 were identified and include hexose-N-acetyl-hexosamine at asparagine-(41), trimethylation at aspartic acid-(290), and flavin adenine dinucleotide at histidine-(335).

BIOLOGICAL SIGNIFICANCE

Our study was to describe a combinatorial approach of Con A affinity chromatography, 1-D SDS-PAGE, and nano-LC/MS/MS that provides a label-free, comparative glycoproteomic quantification strategy for the investigation of glycoprotein profiles in plasma from gastric cancer patients versus healthy volunteers and to identify glycoprotein biomarkers for the early clinical detection of gastric cancer. Three novel PTMs, HexHexNAc, trimethylation and FAD, in Con A-bound ITIH3 were identified and built in molecular modeling. The aspartic acid-(290) trimethylation site was located in a metal ion-dependent adhesion site (MIDAS motif; (290)-DXSXS…T…D-(313)) that may influence important function for binding protein ligands.