A cascade of 24 histatins (histatin 3 fragments) in human saliva. Suggestions for a pre-secretory sequential cleavage pathway

Micro-heterogeneity of human saliva Peptide P-C characterized by high-resolution top-down Fourier-transform mass spectrometry

Top-down proteomics characterizes protein primary structures with unprejudiced descriptions of expressed and processed gene products. Gene sequence polymorphisms, protein post-translational modifications, and gene sequence errors can all be identified using top-down proteomics. Saliva offers advantages for proteomic research because of availability and the noninvasiveness of collection and, for these reasons, is being used to search for disease biomarkers. The description of natural protein variants, and intra- and inter-individual polymorphisms, is necessary for a complete description of any proteome, and essential for the discovery of disease biomarkers. Here, we report a striking example of natural protein variants with the discovery by top-down proteomics of two new variants of Peptide P-C. Intact mass measurements, and collisionally activated-, infrared multiphoton-, and electron capture-dissociation, were used for characterization of the form predicted from the gene sequence with an average mass 4371 Da, a form postulated to result from a single nucleotide polymorphism of mass 4372 Da, and another form of mass 4370 Da postulated to arise from a novel protein sequence polymorphism. While the biological significance of such subtle variations in protein structure remains unclear, their importance cannot be assigned without their characterization, as is reported here for one of the major salivary proteins.

Evidence of intact histatins in the in vivo acquired enamel pellicle

Understanding the composition and function of the acquired enamel pellicle (AEP) has been a major goal in oral biology. The aim of this study was to test the hypothesis that intact histatins are part of the in vivo AEP and that histatins after adsorption to HA have effects on in vitro enamel demineralization. This is the first study demonstrating the presence of intact histatins in vivo in the AEP. The in vitro experiments show that all naturally occurring histatins in the AEP have the potential to provide some level of protection against acid injury.

Potential therapeutic application of host defense peptides

Host defense peptides (HDPs) are relatively small, mostly cationic, amphipathic, and of variable length, sequence, and structure. The majority of these peptides exhibit broad-spectrum antimicrobial activity and often activity against viruses and some cancer cell lines. In addition, HDPs also provide a range of immunomodulatory activities related to innate immunity defense, inflammation, and wound healing. The development of these multi-faceted molecules and their bioactivities into clinically important therapeutics is being pursued using a number of different approaches. Here we review the role of HDPs in nature and application of this role to the development of novel therapeutics.

Proteomic analysis of saliva: 2D gel electrophoresis, LC-MS/MS, and Western blotting

Saliva harbors a wide spectrum of proteins that may reflect the health/disease status in the human body. Profiling of the proteins in saliva from a disease population can potentially yield valuable clinical parameters to be used for diagnosis and prognosis of the disease. Advances in proteomic technologies have enabled comprehensive profiling of protein expression in cells, tissue, and body fluids. When applied to readily accessible saliva samples from disease patients for biomarker study, such a global approach allows attaining the most discriminatory protein biomarkers that can best predict the disease status. In this chapter, we describe the protocols for proteomic analysis of saliva using 2D gel electrophoresis, Western blotting, and LC-MS/MS.

Peptide-based Antifungal Therapies against Emerging Infections

Acquired drug resistance to mycotic infections is rapidly emerging as a major medical problem. Opportunistic fungal infections create therapeutic challenges, particularly in high risk immunocompromised patients with AIDS, cancer, and those undergoing transplantation. Higher mortality and/or morbidity rates due to invasive mycosis have been increasing over the last 20 years, and in light of growing resistance to commonly used antibiotics, novel antifungal drugs and approaches are required. Currently there is considerable interest in antifungal peptides that are ubiquitous in plant and animal kingdoms. These small cationic peptides may have specific targets or may be multifunctional in their mechanism of action. On the basis of recent advances in protein engineering and solid phase syntheses, the utility and potential of selected peptides as efficient antifungal drugs with acceptable toxicity profiles are being realized. This review will discuss recent advances in peptide therapy for opportunistic fungal infections.

Activity-based mass spectrometric characterization of proteases and inhibitors in human saliva

Proteases present in oral fluid effectively modulate the structure and function of some salivary proteins and have been implicated in tissue destruction in oral disease. To identify the proteases operating in the oral environment, proteins in pooled whole saliva supernatant were separated by anion-exchange chromatography and individual fractions were analyzed for proteolytic activity by zymography using salivary histatins as the enzyme substrates. Protein bands displaying proteolytic activity were particularly prominent in the 50-75 kDa region. Individual bands were excised, in-gel trypsinized and subjected to LC/ESI-MS/MS. The data obtained were searched against human, oral microbial and protease databases. A total of 13 proteases were identified all of which were of mammalian origin. Proteases detected in multiple fractions with cleavage specificities toward arginine and lysine residues, were lactotransferrin, kallikrein-1, and human airway trypsin-like protease. Unexpectedly, ten protease inhibitors were co-identified suggesting they were associated with the proteases in the same fractions. The inhibitors found most frequently were alpha-2-macroglobulin-like protein 1, alpha-1-antitrypsin, and leukocyte elastase inhibitor. Regulation of oral fluid proteolysis is highly important given that an inbalance in such activities has been correlated to a variety of pathological conditions including oral cancer.

Kinetics of histatin proteolysis in whole saliva and the effect on bioactive domains with metal-binding, antifungal, and wound-healing properties

The present study was undertaken to investigate the rate and mode of degradation of individual histatin proteins in whole saliva to establish the impact on its functional domains. Pure synthetic histatins 1, 3, and 5 were incubated with whole saliva supernatant as the enzyme source, and peptides in the resultant digests were separated by reverse-phase-HPLC and structurally characterized by electrospray ionization-tandem mass spectrometry. The overall V(max)/K(m) ratios, a measure of proteolytic efficiency, were on the order of histatin-5 > histatin-3 > histatin-1. Mathematical models predict that histatins 1, 3, and 5 levels in whole saliva stabilize at 5.1, 1.9, and 1.2 microM, representing 59, 27, and 11% of glandular histatins 1, 3, and 5 levels, respectively. Monitoring of the appearance and disappearance of histatin fragments yielded the identification of the first targeted enzymatic cleavage sites as K(13) and K(17) in histatin 1, R(22), Y(24), and R(25) in histatin 3, and Y(10), K(11), R(12), K(13), H(15), E(16), K(17), and H(18) in histatin 5. The data indicate that metal-binding, antifungal, and wound-healing domains are largely unaffected by the primary cleavage events in whole saliva, suggesting a sustained functional activity of these proteins in the proteolytic environment of the oral cavity.

α-Defensin Levels in Whole Saliva of Totally Edentulous Subjects

Salivary levels of α-defensins 1–4 and histatins 1, 3 and 5 were determined in 11 totally edentulous patients, 11 younger healthy adults with normal gingival mucosa (Control group I) and 8 subjects, age-matched with edentulous patients, having a minimum of 25 teeth (Control group II). Whole saliva was treated with trifluoroacetic acid and the acidic soluble fraction analyzed by High Performance Liquid Chromatography-Mass Spectrometry. The area of the extracted ion current peaks was used for peptide quantification. Levels of α-defensinsl-4, but not of histatins, were significantly lower in totally edentulous patients with respect to both Control group I and Control group II. The two control groups did not show significant differences. The reduced level of oral α-defensins, which are mainly of crevicular origin, is most likely due to the absence of the gingival sulcus in the edentulous subjects. The near absence of α-defensins might be in part responsible for the higher vulnerability of the oral cavity to oral pathogen infections observed in totally edentulous patients.

Facts and artifacts in proteomics of body fluids. What proteomics of saliva is telling us?

This review briefly depicts several salient points of the current status of knowledge on salivary peptidoma. It outlines the intrinsic difficulties in its characterization connected to different factors of variability, such as: i) the high genetic polymorphisms, complicated by individual insertions/deletions and alternative splicing; ii) complex post-translational maturations comprehending different proteolytic cleavages, glycosylation, phosphorylation and sulfation processes; iii) physiological variations and different contributions to the whole. Moreover, several technological and analytical problems and pitfalls that had to be surmounted during our studies focussed on the extensive qualitative and quantitative characterization of salivary peptidoma and mainly based on LC-MS analyses of intact naturally occurring peptides are here described. The hope is that the information provided might be helpful to other groups engaged on the analysis of saliva or other body fluids for clinical applications.

Carbachol-induced in vitro secretion of certain human submandibular proteins investigated by mass-spectrometry

OBJECTIVE

To investigate protein content of saliva produced in vitro by samples of human submandibular gland following stimulation with the muscarinic agent carbachol.

DESIGN

Tissue samples, obtained at surgery from seven patients and showing normal morphological appearance, were tested for 30 min: in absence of carbachol and atropine; in presence of carbachol (10 microM); in presence of carbachol (10 microM) and atropine (20 microM); or in presence of just atropine (20 microM). Medium was analysed by high-performance liquid chromatography-mass-spectrometry. Neither before nor during surgery were the patients exposed to drug treatments that were likely to influence the in vitro secretion.

RESULTS

Proline-rich proteins (PRP)-1 and -3, peptide PC and PB, statherin, cystatins SN, S1 and S2 were invariably found in control gland tissue medium. Mean concentrations of these proteins/peptides in the medium were non-proportionally elevated following carbachol exposure to the gland tissues. Difference between basal release and carbachol-induced secretion achieved statistical significance as to all the proteins/peptides under study but for statherin. Atropine alone or atropine plus carbachol caused no significant changes compared to the basal release of proteins/peptides.

CONCLUSIONS

In vitro studies on salivary glands make it possible to study protein secretion from individual glands and thus, to reveal the contribution of the various types of gland to protein/peptide content of whole saliva. The disproportional responses to carbachol may imply that the proteins/peptides are not confined to the same cells or to the same intracellular locations and are therefore not secreted as packages at parasympathetic cholinergic activity.

Identification of Lys-Pro-Gln as a novel cleavage site specificity of saliva-associated proteases

The nonsterile environment of the oral cavity facilitates substantial proteolytic processing, not only of resident salivary proteins but also of dietary proteins. To gain insight into whole saliva enzymatic processes, the in vivo generated peptides in this oral fluid were subjected to nano-flow liquid chromatography electrospray ionization tandem mass spectrometry. The 182 peptides identified were predominantly derived from acidic and basic proline-rich proteins, statherin, and histatins. The proteolytic cleavages in the basic proline-rich proteins occurred preferentially after a Gln residue with predominant specificity for the tripeptide Xaa-Pro-Gln, where Xaa in the P(3) position was mostly represented by Lys. Using the synthetic substrates Lys-Pro-Gln-pNA and Gly-Gly-Gln-pNA, the overall K(m) values were determined to be 97 +/- 7.7 and 611 +/- 28 microm, respectively, confirming glutamine endoprotease activity in whole saliva and the influence of the amino acids in positions P(2) and P(3) on protease recognition. The pH optimum of Lys-Pro-Gln-pNA hydrolysis was 7.0, and the activity was most effectively inhibited by antipain and 4-(2-aminoethyl) benzenesulfonyl fluoride, was metal ion-dependent, and not inhibited by cysteine protease inhibitors. A systematic evaluation of enzyme activities in various exocrine and nonexocrine contributors to whole saliva revealed that the glutamine endoprotease is derived from dental plaque and likely microbial in origin. The P(1) site being occupied by a Gln residue is a nonarchetype with respect to known proteases and indicates the presence of novel glutamine-specific endoprotease(s) in oral fluid.

Saliva as research material: Biochemical, physicochemical and practical aspects

Whole saliva is a complex mixture of proteins and other molecules which originate from several sources. The biochemical and physicochemical properties of saliva contribute to the numerous functions of saliva in, e.g., speech, maintaining oral and general health, and food processing. Interest in saliva has increased in the last few years for its potential to diagnose viral, bacterial and systemic diseases. The use of saliva as research material may pose particular problems due to its inherent variability and instability. This review describes practical aspects of salivary as research material with emphasis on protein biochemistry and physical chemistry.

The P-113 fragment of histatin 5 requires a specific peptide sequence for intracellular translocation in Candida albicans, which is independent of cell wall binding

The activity of histatin 5 (Hst 5) against Candida albicans is initiated through cell wall binding, followed by translocation and intracellular targeting. The C. albicans cell wall protein Ssa2 is involved in the transport of Hst 5 into cells as part of cell killing. P-113 (a 12-amino-acid candidacidal active fragment of Hst 5) and P-113Q2.10 (which is inactivated by a glutamine substitution of the Lys residues at positions 2 and 10) were compared for their levels of cell wall binding and intracellular translocation in Candida wild-type (wt) and ssa2Delta strains. Both P-113 and P-113Q2.10 bound to the walls of C. albicans wt and ssa2Delta cells, although the quantity of P-113Q2.10 in cell wall extracts was higher than that of P-113 in both strains. Increasing the extracellular NaCl concentration to 100 mM completely inhibited the cell wall association of both peptides, suggesting that these interactions are primarily ionic. The accumulation of P-113 in the cytosol of wt cells reached maximal levels within 15 min (0.26 microg/10(7) cells), while ssa2Delta mutant cells had maximal cytosolic levels of less than 0.2 microg/10(7) cells even after 30 min of incubation. Furthermore, P-113 but not P-113Q2.10 showed specific binding with a peptide array of C. albicans Ssa2p. P-113Q2.10 was not transported into the cytosol of either C. albicans wt or ssa2Delta cells, despite the high levels of cell wall binding, showing that the two cationic lysine residues at positions 2 and 10 in the P-113 peptide are important for transport into the cytosol and that binding and transport are independent functional events.

Gastrointestinal fluids proteomics

Seventy million people suffer from diseases of the gastrointestinal tract annually in US, translating to US$85.5 billion in direct healthcare costs. The debilitating effects of these gastrointestinal (GI) diseases can be circumvented with good biomarkers for early detection of these disorders, which will greatly increase the success of curative treatments. GI fluids represent a potential reservoir of biomarkers for early diagnosis of various GI and systemic diseases since these fluids are the most proximal fluid bathing diseased cells. They are anticipated to have proteomes that closely reflect the ensemble of proteins secreted from the respective GI tissues. Most importantly, the disease markers present in GI fluids should be present in higher concentrations than in sera, thus offering greater sensitivity in their detection. However, proteome analysis of GI fluids can be complex mainly due to the dynamic range of protein content and the numerous PTMs of proteins in each specialized GI compartment. This review attempts to discuss the physiology of the various GI fluids, the special technical considerations required for proteome analysis of each fluid, as well as to summarize the current state of knowledge of biomarker discoveries and clinical utility of GI fluids such as salivary, gastric, pancreatic, and biliary secretions.

Pro-oxidant activity of histatin 5 related Cu(II)-model peptide probed by mass spectrometry

Histatin 5 is a cationic salivary peptide with strong candidacidal and bactericidal activity at physiological concentration. In this paper we demonstrate by optical spectroscopy and ESI-IT-MS experiments that a synthetic peptide related to the N-terminus of histatin 5 specifically binds copper ions in vitro and that the complex metal-peptide generates reactive oxygen species at physiological concentration of ascorbate, leading to significant auto-oxidation of the peptide within short reaction time. The oxidative activity of this peptide is associated to the presence of a specific metal binding site present at its N-terminus. The motif is constituted by the amino acid sequence NH(2)-Asp-Ser-His, representing a copper and nickel amino terminal binding site, known as "ATCUN motif". The results of the study suggest that the production of reactive oxygen species can be an intrinsic property of histatin 5 connected to its ability to bind metals.

Tyrosine Polysulfation of Human Salivary Histatin 1. A Post-Translational Modification Specific of the Submandibular Gland

Histatin 1 (His-1) derivatives showing serial mass increases of 80.0 +/- 0.1 Da were detected in human saliva by HPLC-ESI-MS. The same derivatives were also found in granules of submandibular glands and secretions of submandibular/sublingual glands, but not in granules and secretions of parotid glands. Only one phosphate group was present in His-1 and its derivatives, since treatment with alkaline phosphatase provided an 80.0 Da mass decrease. His-1 derivatives were almost completely transformed into His-1 by treatment with 1 M HCl at 100 degrees C, suggesting the presence of O-sulfotyrosine, which is more labile than phospho-Tyr to acidic hydrolysis. CE-MS analysis of pronase extensive digestion of derivatives confirmed the presence of sulfotyrosine. Derivatives were digested by trypsin, proteinase K, and protease V-8 and analyzed by different MS strategies. The results allowed locating sulfation on the last four tyrosines (Tyr 27, 30, 34, and 36). This study is the first report of the gland-specific sulfation of a salivary phosphopeptide in vivo.

Human saliva proteome analysis

Human saliva contains proteins that can be informative for disease detection and surveillance of oral health. Comprehensive analysis and identification of the proteomic content in human whole and ductal saliva is a necessary first step toward the discovery of saliva protein markers for human disease detection. The article will review the recent advances in human saliva proteome analysis, including the efforts of the UCLA saliva proteome consortium funded by the National Institute of Dental and Craniofacial Research (NIDCR). We aim to summarize the proteomics technologies currently used for global analysis of saliva proteins and to elaborate on the application of saliva proteomics to discovery of disease biomarkers, in particular for oral cancer and Sjögren's syndrome, and discuss some of the critical challenges and perspectives for this emerging field. The impact of human saliva proteome analysis in the search for clinically relevant disease biomarkers will be realized through advances made using proteomics technologies.

Salivary protein/peptide profiling with SELDI-TOF-MS

In this study, large-scale profiling of salivary proteins and peptides ranging from 2 to 100 kDa was demonstrated using surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS). Results show that chip surface type and sample type critically affect the amount and composition of detected salivary proteins. Delayed processing time resulted in both increase and decrease of peak numbers consistent with proteolysis. SELDI-TOF-MS profiles also changed, depending on storage temperature, although sample processing by centrifugation and numbers of freeze-thaw cycles had a minimal impact. In conclusion, SELDI-TOF-MS offers a simple, rapid, high-throughput technique for profiling low-mass (<10 kDa) saliva proteins/peptides. We wish to use this technique to gain insight into the human saliva proteome composition and its changes over time in response to food consumption.

Assessing the effects of diurnal variation on the composition of human parotid saliva: quantitative analysis of native peptides using iTRAQ reagents

Changes in salivary composition correlate with disease susceptibility, disease state, or both. However, use of saliva for diagnostic purposes is complicated by the gland-specific effects of circadian rhythm or diurnal variation. We recently characterized a suite of peptides in the < or =10-kDa fraction of human parotid saliva that included many novel species. In this study, we used novel iTRAQ labeling chemistry to investigate possible diurnal effects on peptide generation. We collected samples produced by gustatory stimulation as the ductal secretions at four time points under conditions that minimized proteolysis, pooled them according to collection time, and isolated the LMW fractions. Samples collected at each collection time were derivatized with a different isobaric iTRAQ reagent. The labeled samples were combined, separated by reversed-phase HPLC, co-spotted with matrix on MALDI targets, and analyzed by MALDI TOF/TOF mass spectrometry. With this approach, we achieved relative quantification of the parotid peptides at four time points. In several cases, abundance during the day changed dramatically. iTRAQ tagging improved the efficiency of MS/MS fragmentation, which in turn allowed the identification of several novel peptides. Our results demonstrated both the utility of this method and the importance of diurnal effects on the composition of the human parotid saliva peptidome.

Proteomic Analysis of Salivary Acidic Proline-Rich Proteins in Human Preterm and At-Term Newborns

A 1 year follow-up investigation of salivary acidic proline-rich proteins (aPRPs) in preterm and at-term newborns using HPLC-ESI-IT-MS showed that (i) this class of proteins is constitutive rather than inducible, as it is still found in the oral cavity of preterm newborns from 180 days of postconception age (PCA); (ii) the expression of PRH-2 locus anticipates that of PRH-1, since Db isoforms are expressed some months after the PRP-1 and PRP-2 isoforms. The evaluation of the relative abundances of the different aPRPs isoforms and derivatives (differently phosphorylated and cleaved) as a function of PCA showed that (iii) the proteolytic enzymes generating truncated isoforms are also constitutive because they are fully active since 180 days of PCA; (iv) the kinase involved in aPRP phosphorylation is not fully mature in preterm newborns, but its activity increases with PCA, synchronizing with that of at-term newborns and reaching the adult levels at about 500-600 days of PCA, in concomitance with the beginning of deciduous dentition.

SELDI-TOF-MS of saliva: Methodology and pre-treatment effects

Interest in saliva as a diagnostic fluid for monitoring general health and for early diagnosis of disease has increased in the last few years. In particular, efforts have focused on the generation of protein maps of saliva using advanced proteomics technology. Surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) is a novel high throughput and extremely sensitive proteomic approach that allows protein expression profiling of large sets of complex biological specimens. In this study, large scale profiling of salivary proteins and peptides, ranging from 2 to 100kDa was demonstrated using SELDI-TOF-MS. Various methodological aspects and pre-analytical variables were analysed with respect to their effects on saliva SELDI-TOF-MS profiling. Results show that chip surface type and sample type (unstimulated versus stimulated) critically affect the amount and composition of detected salivary proteins. Factors that influenced normal saliva protein profiling were matrix composition, sample dilution and binding buffer properties. Delayed processing time experiments show certain new peptides evolving 3h post-saliva donation, and quantitative analyses indicate relative intensity of other proteins and peptides changing with time. The addition of protease inhibitors partly counteracted the destabilization of certain protein/peptide mass spectra over time suggesting that some proteins in saliva are subject to digestion by intrinsic salivary proteases. SELDI-TOF-MS profiles also changed by varying storage time and storage temperature whereas centrifugation speed and freeze-thaw cycles had minimal impact. In conclusion, SELDI-TOF-MS offers a high throughput platform for saliva protein and peptide profiling, however, (pre-)analytical conditions must be taken into account for valid interpretation of the acquired data.

Analysis of the human saliva proteome

Interest in the characterization of the salivary proteome has increased in the last few years. This review discusses the different techniques and methodologies applied to the separation and identification of salivary proteins. Nowadays, proteomic techniques are the state of the art for the analysis of biologic materials and saliva is no exception. 2D electrophoresis and tryptic digest analysis by mass spectrometry are the typical methodology, but new approaches using 2D liquid chromatography/mass spectrometry methods have already been introduced for saliva analysis. Due to their important physiologic role in the oral cavity, low-molecular-weight proteins and peptides are also included in this article and the methodologies discussed.

Peptidomic analysis of human acquired enamel pellicle

Human acquired enamel pellicle is the result of a selective interaction of salivary proteins and peptides with the tooth surface. In the present work, the characterization of the peptides as well as the type of interactions established with the enamel surface was performed. Peptides from in vivo bovine enamel implants in the human oral cavity were sequentially extracted using guanidine and trifluoroacetic acid solutions and the fractions obtained were analysed by LC-MS and LC-MS/MS. Based on the LC-MS data, six phosphorylated peptides were identified in an intact form, strongly adsorbed to the enamel surface. Data from the LC-MS/MS analyses allowed us to identified 30 fragment peptides non-covalently bonded to enamel [basic proline-rich proteins, histatins (1 and 3) and acidic proline-rich protein classes]. The tandem mass spectrometry experiments showed the existence of a pattern of amide bond cleavage for the different identified peptide classes suggesting a selective proteolytic activity. For histatins, a predominance of cleavage at Arg, Lys and His residues was observed, while for basic proline-rich proteins, cleavage at Arg and Pro residues prevailed. In the case of acidic proline-rich proteins, a clearly predominance of cleavage of the Gln-Gly amide bond was evident.

Human body fluid proteome analysis

The focus of this article is to review the recent advances in proteome analysis of human body fluids, including plasma/serum, urine, cerebrospinal fluid, saliva, bronchoalveolar lavage fluid, synovial fluid, nipple aspirate fluid, tear fluid, and amniotic fluid, as well as its applications to human disease biomarker discovery. We aim to summarize the proteomics technologies currently used for global identification and quantification of body fluid proteins, and elaborate the putative biomarkers discovered for a variety of human diseases through human body fluid proteome (HBFP) analysis. Some critical concerns and perspectives in this emerging field are also discussed. With the advances made in proteomics technologies, the impact of HBFP analysis in the search for clinically relevant disease biomarkers would be realized in the future.

Detection in human saliva of different statherin and P-B fragments and derivatives

Statherin is a multifunctional polypeptide specific of human saliva involved in oral calcium homeostasis, phosphate buffering and formation of protein networks. Salivary P-B peptide is usually included into the basic proline-rich protein family but it shows some similarities with statherin and its specific biological role is still undefined. In this study, various fragments and derivatives of statherin and P-B peptide were consistently detected by RP-HPLC ESI-IT MS in 23 samples of human saliva. They were: statherin mono- and non-phosphorylated, statherin Des-Phe(43) (statherin SV1), statherin Des-Thr(42),Phe(43), statherin Des-Asp(1), statherin Des(6-15) (statherin SV2), statherin Des(1-9), statherin Des(1-10), statherin Des(1-13) and P-B Des(1-5). Statherin SV3 (statherin Des(6-15), Phe(43)) was detected only in one sample. Identity of the fragments was confirmed either by MS/MS experiments or by enzymatic digestion or by Edman sequencing. Detection of the fragments suggests that statherin and P-B peptide are submitted to post-translational proteolytic cleavages that are common to other classes of salivary proteins.

Oral fluid proteolytic effects on histatin 5 structure and function

Histatins are human salivary antifungal proteins that are prone to extensive enzymatic degradation upon their release into the oral cavity. Histatin proteolysis, leading to the disappearance of the intact protein can be expected to have functional consequences. Histatin 5, comprising 24 residues, is the smallest of the major salivary histatins and the most active in terms of its antifungal properties. The rate and mode of histatin 5 degradation were determined by incubating the protein in whole saliva supernatant for various time intervals. Fragmentation products were collected by reversed-phase high performance liquid chromatography (RP-HPLC), characterised structurally by matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and functionally in a fungal growth inhibition assay. Of the 19 fragments identified, 16 were derived from single proteolytic cleavage events in histatin 5. A remarkable finding was the inter-subject consistency in the histatin 5 degradation pattern. Added histatin 5 disappeared from whole saliva supernatant at an average rate of 105+/-22 microg/ml/h, which in part could explain the virtual absence of histatin 5 in whole saliva. Despite the rapid proteolysis of histatin 5, the early degradation mixture was as active in antifungal assays as intact histatin 5. These data demonstrate that the oral-fluid mediated proteolysis of histatin 5 represents an intrinsic biological property of whole saliva. The data also reveal that the early proteolysis phase of histatin 5 does not abolish the antifungal properties associated with this protein.

Distinct antifungal mechanisms: beta-defensins require Candida albicans Ssa1 protein, while Trk1p mediates activity of cysteine-free cationic peptides

Salivary histatin 5 (Hst 5) kills the fungal pathogen Candida albicans via a multistep process which includes binding to Ssa1/2 proteins on the cell surface and requires the TRK1 potassium transporter. Hst 5-induced membrane permeability to propidium iodide (PI) was nearly abolished in strain CaTK1 (TRK1/trk1), suggesting that Hst 5-induced influx of PI is via Trk1p. To explore the functional role of Trk1p in the mechanism of other antifungal peptides, we evaluated candidacidal activity and PI uptake in wild-type strain CaTK2 (TRK1/TRK1) and strain CaTK1 following treatment with lactoferricin 11 (LFcn 11), bactenecin 16 (BN 16), and virion-associated protein VPR 12. Strain CaTK1 was resistant to killing with these peptides (VPR 12 > LFcn 11 > BN 16), showing the requirement of Trk1p for fungicidal activity. In contrast, human neutrophil defensin 1 (HNP-1), human beta-defensin 2 (hBD-2), and hBD-3 effects on viability of and membrane permeability to PI were not different between mutant and wild-type strains, clearly showing that their candidacidal mechanism does not involve Trk1p as a functional effector. To test whether defensins require binding to Candida surface Ssa1/2 proteins for their activity, we measured the killing effectiveness in SSA1/2 mutant strains. Both hBD-2 and hBD-3, but not HNP-1, exhibited reduced killing of ssa1Delta and ssa2Delta strains compared to the wild type, showing that Ssa1 and Ssa2 proteins are required for their fungicidal activity. These results demonstrate that (i) Trk1p mediates candidacidal activities of cysteine-free peptides, but not of defensins, and (ii) hBD-2 and hBD-3, but not HNP-1, require Ssa1/2p for antifungal activity.

Human antimicrobial peptides: defensins, cathelicidins and histatins

Antimicrobial peptides, which have been isolated from many bacteria, fungi, plants, invertebrates and vertebrates, are an important component of the natural defenses of most living organisms. The isolated peptides are very heterogeneous in length, sequence and structure, but most of them are small, cationic and amphipathic. These peptides exhibit broad-spectrum activity against Gram-positive and Gram-negative bacteria, yeasts, fungi and enveloped viruses. A wide variety of human proteins and peptides also have antimicrobial activity and play important roles in innate immunity. In this review we discuss three important groups of human antimicrobial peptides. The defensins are cationic non-glycosylated peptides containing six cysteine residues that form three intramolecular disulfide bridges, resulting in a triple-stranded beta-sheet structure. In humans, two classes of defensins can be found: alpha-defensins and beta-defensins. The defensin-related HE2 isoforms will also be discussed. The second group is the family of histatins, which are small, cationic, histidine-rich peptides present in human saliva. Histatins adopt a random coil conformation in aqueous solvents and form alpha-helices in non-aqueous solvents. The third group comprises only one antimicrobial peptide, the cathelicidin LL-37. This peptide is derived proteolytically from the C-terminal end of the human CAP18 protein. Just like the histatins, it adopts a largely random coil conformation in a hydrophilic environment, and forms an alpha-helical structure in a hydrophobic environment.

Toward defining the human parotid gland salivary proteome and peptidome: identification and characterization using 2D SDS-PAGE, ultrafiltration, HPLC, and mass spectrometry

Saliva plays many biological roles, from lubrication and digestion to regulating bacterial and leukocyte adhesion. To understand the functions of individual components and families of molecules, it is important to identify as many salivary proteins as possible. Toward this goal, we used a proteomic approach as the first step in a global analysis of this important body fluid. We collected parotid saliva as the ductal secretion from three human donors and separated the protein components by two-dimensional SDS-polyacrylamide gel electrophoresis (2D SDS-PAGE). Proteins in gel spots were identified by peptide mass fingerprinting, and the results were confirmed by tandem mass spectrometry of selected peptides. Complementing this approach we used ultrafiltration to prepare a low-molecular-weight fraction of parotid saliva, which was analyzed directly or after reversed phase high-performance liquid chromatography separation by using mass spectrometric approaches. MS analyses of 2D SDS-PAGE spots revealed known components of saliva, including cystatins, histatins, lysozyme, and isoforms and/or fragments of alpha-amylase, albumin, and proline-rich proteins. We also discovered novel proteins, such as several isoforms of Zn-alpha-2-glycoprotein and secretory actin-binding protein. MS analyses of the ultrafiltrate showed that the low-molecular-weight fraction of parotid saliva was peptide-rich, with novel fragments of proline-rich proteins and histatins in abundance. Experiments using Candida albicans as the test organism showed that at least one of the novel peptides had antifungal activity. Our results show that saliva is a rich source of proteins and peptides that are potential diagnostic and therapeutic targets.

Different isoforms and post-translational modifications of human salivary acidic proline-rich proteins

The human salivary acidic proline-rich proteins (aPRPs) complex was investigated by different chromatographic and mass spectrometric approaches and the main aPRPs, namely PRP-1, PRP-2 and PIF-s (15,515 amu), Db-s (17,632 amu) and Pa (15,462 amu) proteins, were detected. All these isoforms are phosphorylated at Ser-8 and Ser-22 and have a pyroglutamic moiety at the N-terminus. Apart from Pa, all the other aPRPs undergo a proteolytic cleavage at Arg-106 residue (Arg-127 in Db-s protein), that generates the small PC peptide (4371 amu) and PRP-3, PRP-4, PIF-f (11,162 amu) and Db-f (13,280 amu) proteins, all of which were detected. With regard to the Pa protein, the main form detected was the dimeric derivative (Pa 2-mer, 30,922 amu) originated by a disulfide bond involving Cys-103 residue. Besides these known isoforms, several previously undetected aPRP derivatives were found (in minor amounts): (i) the triphosphorylated derivatives of PRP-1/PRP-2/PIF-s and Db-s, showing the additional phosphate group at Ser-17; (ii) the mono-phosphorylated forms at either Ser-22 or Ser-8 of PRP-1/PRP-2/PIF-s, PRP-3/PRP-4/PIF-f, Db-s and Db-f; (iii) a nonphosphorylated form of PRP-3/PRP-4/PIF-f; (iv) the triphosphorylated and diphosphorylated forms of Pa 2-mer. Moreover, minor quantities of PRP-3/PRP-4/PIF-f lacking the C-terminal Arg (11,006 amu), and of Pa 2-mer lacking the C-terminal Gln (30,793 amu) were found. By this approach the different phenotypes of PRH1 locus in 59 different subjects were characterized.