The parotid secretory protein BPIFA2 is a salivary surfactant that affects lipopolysaccharide action.

NEW FINDINGS: What is the central question of this study? The salivary protein BPIFA2 binds lipopolysaccharide, but its physiological function is not known. This study uses a new knockout mouse model to explore the physiological role of BPIFA2 in the oral cavity and systemic physiology. What is the main finding and its importance? BPIFA2 is a crucial surfactant in mouse saliva. In its absence, saliva exhibits the surface tension of water. Depletion of BPIFA2 affects salivary and ingested lipopolysaccharide and leads to systemic sequelae that include increased insulin secretion and metabolomic changes. These results suggest that the lipopolysaccharide-binding activity of BPIFA2 affects the activity of ingested lipopolysaccharide in the intestine and that BPIFA2 depletion causes mild metabolic endotoxaemia. ABSTRACT: Saliva plays important roles in the mastication, swallowing and digestion of food, speech and lubrication of the oral mucosa, antimicrobial and anti-inflammatory activities, and the control of body temperature in grooming animals. The salivary protein BPIFA [BPI fold containing family A member 2; former names: parotid secretory protein (PSP), SPLUN2 and C20orf70] is related to lipid-binding and lipopolysaccharide (LPS)-binding proteins expressed in the mucosa. Indeed, BPIFA2 binds LPS, but the physiological role of BPIFA2 remains to be determined. To address this question, Bpifa2 knockout (Bpifa2tm1(KOMP)Vlcg ) (KO) mice were phenotyped, with emphasis on the saliva and salivary glands. Stimulated whole saliva collected from KO mice was less able to spread on a hydrophobic surface than wild-type saliva, and the surface tension of KO saliva was close to that of water. These data suggest that BPIFA2 is a salivary surfactant that is mainly responsible for the low surface tension of mouse saliva. The reduced surfactant activity of KO saliva did not affect consumption of dry food or grooming, but saliva from KO mice contained less LPS than wild-type saliva. Indeed, mice lacking BPIFA2 responded to ingested LPS with an increased stool frequency, suggesting that BPIFA2 plays a role in the solubilization and activity of ingested LPS. Consistent with these findings, BPIFA2-depleted mice also showed increased insulin secretion and metabolomic changes that were consistent with a mild endotoxaemia. These results support the distal physiological function of a salivary protein and reinforce the connection between oral biology and systemic disease.

Solution and Solid-State Nuclear Magnetic Resonance Structural Investigations of the Antimicrobial Designer Peptide GL13K in Membranes.

The antimicrobial peptide GL13K encompasses 13 amino acid residues and has been designed and optimized from the salivary protein BPIFA2 to exhibit potent bacteriocidal and anti-biofilm activity against Gram-negative and Gram-positive bacteria as well as anti-lipopolysaccharide activity in vitro and in vivo. Here, the peptide was analyzed in a variety of membrane environments by circular dichroism spectroscopy and by high-resolution multidimensional solution nuclear magnetic resonance (NMR) spectroscopy. Whereas in the absence of membranes a random coil conformation predominates, the peptide adopts a helical structure from residue 5 to 11 in the presence of dodecylphosphocholine micelles. In contrast, a predominantly ß-sheet structure was observed in the presence of lipid bilayers carrying negatively charged phospholipids. Whereas 15N solid-state NMR spectra are indicative of a partial alignment of the peptide 15N-1H vector along the membrane surface, 2H and 31P solid-state NMR spectra indicate that in this configuration the peptide exhibits pronounced disordering activities on the phospholipid membrane, which is possibly related to antimicrobial action. GL13K, thus, undergoes a number of conformational transitions, including a random coil state in solution, a helical structure upon dilution at the surface of zwitterionic membranes, and ß-sheet conformations at high peptide:lipid ratios.

Membrane selectivity and biophysical studies of the antimicrobial peptide GL13K.

GL13K is a short (13 amino acid) antimicrobial peptide derived from the parotid secretory protein. GL13K has been found to exhibit anti-inflammatory and antibacterial activities in physiological salt conditions. We investigated the mechanism of interaction of GL13K, with model membranes comprising 1, 2-dioleoylphosphatidylcholine (DOPC) and 1, 2-dioleoylphosphatidylglycerol (DOPG) using various biophysical and imaging techniques. Circular dichroism studies showed that GL13K adopts a ß-sheet structure in the presence of negatively charged DOPG liposomes while it retains its random coil structure with zwitterionic DOPC liposomes. GL13K did not cause any fusion of these liposomes but was able to selectively disrupt the negatively charged membranes of DOPG leading to vesicular leakage. There was no or minimal evidence of GL13K interaction with DOPC liposomes, however an analysis of supported lipid bilayers (SLBs) using atomic force microscopic (AFM) imaging and dual polarization interferometry (DPI) suggested that GL13K can interact with the surface of a DOPC planar bilayer. In the case of DOPG bilayers, AFM and DPI clearly showed membrane thinned regions where a portion of lipid molecules has been removed. These results suggest that the mechanism of GL13K action on bacterial membranes involves localized removal of lipid from the membrane via peptide-induced micellization.

Antimicrobial peptide GL13K is effective in reducing biofilms of Pseudomonas aeruginosa.

Human parotid secretory protein (PSP; BPIF2A) is predicted to be structurally similar to bactericidal/permeability-increasing protein and lipopolysaccharide (LPS)-binding protein. Based on the locations of known antimicrobial peptides in the latter two proteins, potential active peptides in the PSP sequence were identified. One such peptide, GL13NH2 (PSP residues 141 to 153) was shown previously to interfere with LPS binding and agglutinate bacteria without bactericidal activity. By introducing three additional positively charged lysine residues, the peptide was converted to the novel bactericidal cationic peptide GL13K (MIC for Pseudomonas aeruginosa, 8 µg/ml [5.6 µM]). We investigated the antibiofilm activity of GL13K against static, monospecies biofilms of P. aeruginosa PAO1. Two-hour exposure of a 24-h biofilm to 64 µg/ml (44.8 µM) GL13K reduced biofilm bacteria by 10(2), and 100 µg/ml (70 µM) GL13K reduced bacteria by 10(3). Similar results could be achieved on 48-h-old biofilms. Lower concentrations of GL13K (32 µg/ml [22.4 µM]) were successful in reducing biofilm cell numbers in combination with tobramycin. This combination treatment also achieved total eradication of the biofilm in a majority (67.5%) of tested samples. An alanine scan of GL13K revealed the importance of the leucine residue in position six of the peptide sequence, where replacement led to a loss of antibiofilm activity, whereas the impact of replacing charged residues was less pronounced. Bacterial metalloproteases were found to partially inactivate GL13K but not a d amino acid version of the peptide.

Human parotid secretory protein is a lipopolysaccharide-binding protein: identification of an anti-inflammatory peptide domain.

Parotid secretory protein (PSP) (C20orf70) is a salivary protein of unknown function. The protein belongs to the palate, lung, and nasal epithelium clone (PLUNC) family of mucosal secretory proteins that are predicted to be structurally similar to lipid-binding and host-defense proteins including bactericidal/permeability-increasing protein and lipopolysaccharide-binding protein. However, the PLUNC proteins exhibit significant sequence variation and different biological functions have been proposed for different family members. This study tested the functional implications of the proposed similarity of PSP to the acute phase protein lipopolysaccharide-binding protein (LBP). PSP was identified in human saliva and was soluble in 70% ethanol, as shown for other PLUNC proteins. PSP binds lipopolysaccharide and can be eluted by non-ionic detergent, but not by urea or high salt. A synthetic PSP peptide, GL13NH2, which corresponds to a lipopolysaccharide-inhibiting peptide from LBP, inhibited the binding of lipopolysaccharide to both PSP and lipopolysaccharide-binding protein. Peptides from other regions of PSP and the control peptide polymyxin B showed no effect on the binding of PSP to lipopolysaccharide. GL13NH2 also inhibited lipopolysaccharide-stimulated secretion of tumor necrosis factor from macrophages. The other PSP peptides had no effect in this assay. PSP peptides had no or only minor effect on macrophage cell viability. These results indicate that PSP is a lipopolysaccharide-binding protein that is functionally related to LBP, as suggested by their predicted structural similarities.

Text-mining applied to autoimmune disease research: the Sjögren's syndrome knowledge base.

BACKGROUND: Sjögren's syndrome is a tissue-specific autoimmune disease that affects exocrine tissues, especially salivary glands and lacrimal glands. Despite a large body of evidence gathered over the past 60 years, significant gaps still exist in our understanding of Sjögren's syndrome. The goal of this study was to develop a database that collects and organizes gene and protein expression data from the existing literature for comparative analysis with future gene expression and proteomic studies of Sjögren's syndrome. DESCRIPTION: To catalog the existing knowledge in the field, we used text mining to generate the Sjögren's Syndrome Knowledge Base (SSKB) of published gene/protein data, which were extracted from PubMed using text mining of over 7,700 abstracts and listing approximately 500 potential genes/proteins. The raw data were manually evaluated to remove duplicates and false-positives and assign gene names. The data base was manually curated to 477 entries, including 377 potential functional genes, which were used for enrichment and pathway analysis using gene ontology and KEGG pathway analysis. CONCLUSIONS: The Sjögren's syndrome knowledge base ( http://sskb.umn.edu) can form the foundation for an informed search of existing knowledge in the field as new potential therapeutic targets are identified by conventional or high throughput experimental techniques.

The antimicrobial peptide DGL13K is active against drug-resistant gram-negative bacteria and sub-inhibitory concentrations stimulate bacterial growth without causing resistance.

Antimicrobial peptides may be alternatives to traditional antibiotics with reduced bacterial resistance. The antimicrobial peptide GL13K was derived from the salivary protein BPIFA2. This study determined the relative activity of the L-and D-enantiomers of GL13K to wild-type and drug-resistant strains of three gram-negative species and against Pseudomonas aeruginosa biofilms. DGL13K displayed in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing and Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (MICs 16-32 µg/ml), MDR and XDR P. aeruginosa, and XDR Acinetobacter baumannii carrying metallo-beta-lactamases (MICs 8-32 µg/ml). P. aeruginosa showed low inherent resistance to DGL13K and the increased metabolic activity and growth caused by sub-MIC concentrations of GL13K peptides did not result in acquired bacterial resistance. Daily treatment for approximately two weeks did not increase the MIC of DGL13K or cause cross-resistance between LGL13K and DGL13K. These data suggest that DGL13K is a promising antimicrobial peptide candidate for further development.

Dual host-defence functions of SPLUNC2/PSP and synthetic peptides derived from the protein.

PSP (parotid secretory protein)/SPLUNC2 (short palate, lung and nasal epithelium clone 2) is expressed in human salivary glands and saliva. The protein exists as an N-glycosylated and non-glycosylated form and both appear to induce agglutination of bacteria, a major antibacterial function for salivary proteins. Both forms of PSP/SPLUNC2 bind LPS (lipopolysaccharide), suggesting that the protein may also play an anti-inflammatory role. Based on the predicted structure of PSP/SPLUNC2 and the location of known antibacterial and anti-inflammatory peptides in BPI (bactericidal/permeability-increasing protein) and LBP (LPS-binding protein), we designed GL13NH2 and GL13K, synthetic peptides that capture these proposed functions of PSP/SPLUNC2. GL13NH3 agglutinates bacteria, leading to increased clearance by macrophages and reduced spread of infection in a plant model. GL13K kills bacteria with a minimal inhibitory concentration of 5-10 µg/ml, kills bacteria in biofilm and retains activity in 150 mM NaCl and 50% saliva. Both peptides block endotoxin action, but only GL13K appears to bind endotoxin. The peptides do not cause haemolysis, haemagglutination in serum, inhibit mammalian cell proliferation or induce an inflammatory response in macrophages. These results suggest that the GL13NH2 and the modified peptide GL13K capture the biological activity of PSP/SPLUNC2 and can serve as lead compounds for the development of novel antimicrobial and anti-inflammatory peptides.

Antimicrobial peptides and periodontal disease.

AIMS: The goal of this review is to identify the antimicrobial proteins in the oral fluids, saliva and gingival crevicular fluid and identify functional families and candidates for antibacterial treatment. RESULTS: Periodontal biofilms initiate a cascade of inflammatory and immune processes that lead to the destruction of gingival tissues and ultimately alveolar bone loss and tooth loss. Treatment of periodontal disease with conventional antibiotics does not appear to be effective in the absence of mechanical debridement. An alternative treatment may be found in antimicrobial peptides and proteins, which can be bactericidal and anti-inflammatory and block the inflammatory effects of bacterial toxins. The peptides have co-evolved with oral bacteria, which have not developed significant peptide resistance. Over 45 antibacterial proteins are found in human saliva and gingival crevicular fluid. The proteins and peptides belong to several different functional families and offer broad protection from invading microbes. Several antimicrobial peptides and proteins (AMPs) serve as templates for the development of therapeutic peptides and peptide mimetics, although to date none have demonstrated efficacy in human trials. CONCLUSIONS: Existing and newly identified AMPs may be developed for therapeutic use in periodontal disease or can serve as templates for peptide and peptide mimetics with improved therapeutic indices.

In vivo activity and low toxicity of the second-generation antimicrobial peptide DGL13K.

Antimicrobial peptides have been evaluated as possible alternatives to traditional antibiotics. The translational potential of the antimicrobial peptide DGL13K was tested with focus on peptide toxicity and in vivo activity in two animal models. DGL13K was effective against Pseudomonas aeruginosa, Staphylococcus aureus and methicillin-resistant S. aureus with minimal bactericidal concentrations similar to the minimal inhibitory concentration. The peptide showed low toxicity to human red blood cells and HEK cells with median lethal dose around 1 mg/ml. The median lethal dose in greater wax moth larvae (Galleria mellonella) was about 125mg/kg while the peptide caused no skin toxicity in a mouse model. A novel high-throughput luminescence assay was used to test peptide activity in infected G. mellonella, thus reducing vertebrate animal use. DGL13K killed P. aeruginosa in both the G. mellonella model and a mouse burn wound infection model, with bacterial viability 3-10-fold lower than in untreated controls. Future experiments will focus on optimizing peptide delivery, dose and frequency to further improve the antibacterial effect.

P. gingivalis interactions with epithelial cells.

Dental plaque, a microbial biofilm that accumulates on teeth and initiates periodontal disease, is composed of hundreds of different bacterial species within an organized structure. The biofilm bacteria and their byproducts irritate the gingival epithelium and induce an "inflammatory response". The perturbation of epithelial cells by bacteria is the first stage in the initiation of inflammatory and immune processes which eventually cause destruction of the tissues surrounding and supporting the teeth, and ultimately result in tooth loss. This review addresses the early bacterial-epithelial cell interactions and the subsequent responses of the epithelial cell. It includes discussion of how epithelial Toll-like receptors (TLRs) respond to different bacterial challenges, the variable antimicrobial peptides released and the host signaling responses which trigger release of these molecules and the overall fate of these cells in terms of survival, apoptosis, or cell lysis.

Design of bacteria-agglutinating peptides derived from parotid secretory protein, a member of the bactericidal/permeability increasing-like protein family.

Parotid secretory protein (PSP) (SPLUNC2), a potential host-defense protein related to bactericidal/permeability-increasing protein (BPI), was used as a template to design antibacterial peptides. Based on the structure of BPI, new PSP peptides were designed and tested for antibacterial activity. The peptides did not exhibit significant bactericidal activity or inhibit growth but the peptide GL-13 induced bacterial matting, suggesting passive agglutination of bacteria. GL-13 was shown to agglutinate the Gram negative bacteria Pseudomonas aeruginosa and Aggregatibacter (Actinobacillus) actinomycetemcomitans, Gram positive Streptococcus gordonii and uncoated sheep erythrocytes. Bacterial agglutination was time and dose-dependent and involved hydrophobic interactions. Variant forms of GL-13 revealed that agglutination also depended on the number of amine groups on the peptide. GL-13 inhibited the adhesion of bacteria to plastic surfaces and the peptide prevented the spread of P. aeruginosa infection in a lettuce leaf model, suggesting that GL-13 is active in vivo. Moreover, GL-13-induced agglutination enhanced the phagocytosis of P. aeruginosa by RAW 264.7 macrophage cells. These results suggest that GL-13 represents a class of antimicrobial peptides, which do not directly kill bacteria but instead reduce bacterial adhesion and promote agglutination, leading to increased clearance by host phagocytic cells. Such peptides may cause less bacterial resistance than traditional antibiotic peptides.

A D-enantiomer of the antimicrobial peptide GL13K evades antimicrobial resistance in the Gram positive bacteria Enterococcus faecalis and Streptococcus gordonii.

Antimicrobial peptides represent an alternative to traditional antibiotics that may be less susceptible to bacterial resistance mechanisms by directly attacking the bacterial cell membrane. However, bacteria have a variety of defense mechanisms that can prevent cationic antimicrobial peptides from reaching the cell membrane. The L- and D-enantiomers of the antimicrobial peptide GL13K were tested against the Gram-positive bacteria Enterococcus faecalis and Streptococcus gordonii to understand the role of bacterial proteases and cell wall modifications in bacterial resistance. GL13K was derived from the human salivary protein BPIFA2. Minimal inhibitory concentrations were determined by broth dilution and a serial assay used to determine bacterial resistance. Peptide degradation was determined in a bioassay utilizing a luminescent strain of Pseudomonas aeruginosa to detect peptide activity. Autolysis and D-alanylation-deficient strains of E. faecalis and S. gordonii were tested in autolysis assays and peptide activity assays. E. faecalis protease inactivated L-GL13K but not D-GL13K, whereas autolysis did not affect peptide activity. Indeed, the D-enantiomer appeared to kill the bacteria prior to initiation of autolysis. D-alanylation mutants were killed by L-GL13K whereas this modification did not affect killing by D-GL13K. The mutants regained resistance to L-GL13K whereas bacteria did not gain resistance to D-GL13K after repeated treatment with the peptides. D-alanylation affected the hydrophobicity of bacterial cells but hydrophobicity alone did not affect GL13K activity. D-GL13K evades two resistance mechanisms in Gram-positive bacteria without giving rise to substantial new resistance. D-GL13K exhibits attractive properties for further antibiotic development.

Secretory granule biogenesis and chromogranin A: master gene, on/off switch or assembly factor?

Secretory granules are found in specialized cell types, including endocrine cells, suggesting that a coordinated programme of gene expression is involved in their biogenesis. Indeed, it has been proposed that chromogranin A (CgA) acts as an on/off switch for secretory granule biogenesis. However, this proposed function is difficult to reconcile with the large body of evidence suggesting that secretory granules exist in the absence of CgA and that cells can synthesize CgA in the absence of secretory granules. Indeed, recent evidence suggests that, rather than a master gene or universal on/off switch, a series of on/off switches combines to induce expression of subsets of secretory granule-associated genes. The assembly of newly synthesized proteins and the inclusion of existing granule proteins would produce functional secretory granules. CgA and related proteins might act as assembly factors in this process.

N-terminal proteolytic processing of porcine chromogranin A in parathyroid tissue.

Chromogranin A (CgA) is a glycoprotein stored in secretory granules of many endocrine and neuroendocrine cells. CgA undergoes tissue specific processing to release regulatory peptides. In the parathyroid, although processing is limited and variable, several CgA-derived peptides have been characterized including parastatin and betagranin. An early stage of CgA processing is the generation of a 64-kDa fragment (CgA64). In this study, we have purified CgA64 from porcine parathyroid glands by chromatographic separations. Edman degradation of this CgA64 yielded the N-terminal sequence NDQAELKEGTEEASSKEAAEKRGDXAVEKND corresponding to pCgA(94-125). Amino acid composition suggests that CgA64 corresponds to CgA(94-430) (i.e. the entire CgA molecule, less the N-terminal residues 1-93). To determine the origin of CgA64, we fractionated parathyroid membrane vesicles by sucrose gradient centrifugation. Intact CgA is predominantly located in dense sucrose fractions (secretory granules), whereas CgA64 is located near the top of the gradient (soluble protein fraction). In vitro incubation of these fractions revealed that the conversion of CgA did not occur in intact granules. These results indicate that CgA64 is not present in intact granules suggesting that it is not a naturally occurring secretory product in parathyroid cells.

Antimicrobial GL13K peptide coatings killed and ruptured the wall of Streptococcus gordonii and prevented formation and growth of biofilms.

Infection is one of the most prevalent causes for dental implant failure. We have developed a novel antimicrobial peptide coating on titanium by immobilizing the antimicrobial peptide GL13K. GL13K was developed from the human salivary protein BPIFA2. The peptide exhibited MIC of 8 µg/ml against planktonic Pseudonomas aeruginosa and their biofilms were reduced by three orders of magnitude with 100 µg/ml GL13K. This peptide concentration also killed 100% of Streptococcus gordonii. At 1 mg/ml, GL13K caused less than 10% lysis of human red blood cells, suggesting low toxicity to mammalian cells. Our GL13K coating has also previously showed bactericidal effect and inhibition of biofilm growth against peri-implantitis related pathogens, such as Porphyromonas gingivalis. The GL13K coating was cytocompatible with human fibroblasts and osteoblasts. However, the bioactivity of antimicrobial coatings has been commonly tested under (quasi)static culture conditions that are far from simulating conditions for biofilm formation and growth in the oral cavity. Oral salivary flow over a coating is persistent, applies continuous shear forces, and supplies sustained nutrition to bacteria. This accelerates bacteria metabolism and biofilm growth. In this work, the antimicrobial effect of the coating was tested against Streptococcus gordonii, a primary colonizer that provides attachment for the biofilm accretion by P. gingivalis, using a drip-flow biofilm bioreactor with media flow rates simulating salivary flow. The GL13K peptide coatings killed bacteria and prevented formation and growth of S. gordonii biofilms in the drip-flow bioreactor and under regular mild-agitation conditions. Surprisingly the interaction of the bacteria with the GL13K peptide coatings ruptured the cell wall at their septum or polar areas leaving empty shell-like structures or exposed protoplasts. The cell wall rupture was not detected under regular culture conditions, suggesting that cell wall rupture induced by GL13K peptides also requires media flow and possible attendant biological sequelae of the conditions in the bioreactor.

Bio-inspired stable antimicrobial peptide coatings for dental applications.

We developed a novel titanium coating that has applications for preventing infection-related implant failures in dentistry and orthopedics. The coating incorporates an antimicrobial peptide, GL13K, derived from parotid secretory protein, which has been previously shown to be bactericidal and bacteriostatic in solution. We characterized the resulting physicochemical properties, resistance to degradation, activity against Porphyromonas gingivalis and in vitro cytocompatibility. Porphyromonas gingivalis is a pathogen associated with dental peri-implantitis, an inflammatory response to bacteria resulting in bone loss and implant failure. Our surface modifications obtained a homogeneous, highly hydrophobic and strongly anchored GL13K coating that was resistant to mechanical, thermochemical and enzymatic degradation. The GL13K coatings had a bactericidal effect and thus significantly reduced the number of viable bacteria compared to control surfaces. Finally, adequate proliferation of osteoblasts and human gingival fibroblasts demonstrated the GL13K coating's cytocompatibility. The robustness, antimicrobial activity and cytocompatibility of GL13K-biofunctionalized titanium make it a promising candidate for sustained inhibition of bacterial biofilm growth. This surface chemistry provides a basis for development of multifunctional bioactive surfaces to reduce patient morbidities and improve long-term clinical efficacy of metallic dental and orthopedic implants.

Antimicrobial peptides in periodontal innate defense.

The development of oral biofilms and the host response to biofilm bacteria and their toxins are important factors in the development of periodontal disease. An early component of the host response is the secretion of antimicrobial proteins and peptides (AMPs) by salivary glands, oral epithelial cells and neutrophils. Over 45 AMPs have been identified in the oral cavity. All are found in saliva and several are also present in gingival crevicular fluid. Of these, 13 are up regulated in periodontal disease while 11 are downregulated. However, the concentrations of most AMPs found in oral fluids are below the effective in vitro concentrations, suggesting that local concentrations must be higher for effect or that additional biological functions are important in the oral cavity. Thus, in addition to direct antibacterial activity (e.g. bactericidal activity, bacterial agglutination), AMPs may affect the course of periodontal disease by inactivating bacterial or host proteases (e.g. secretory leukoprotease inhibitor) or bind bacterial toxins, including lipopolysaccharides (e.g. LL-37). Several AMPs (e.g. defensins) also act as immune system alarmins, i.e. endogenous mediators that recruit and activate antigen-presenting cells to enhance innate and adaptive immune responses. The differential regulation of AMP expression in periodontal disease suggests that AMP panels, including up- and downregulated proteins, can be used in oral fluid diagnosis of periodontal disease and to monitor treatment outcome.

Lysine substitutions convert a bacterial-agglutinating peptide into a bactericidal peptide that retains anti-lipopolysaccharide activity and low hemolytic activity.

GL13NH2 is a bacteria-agglutinating peptide derived from the sequence of the salivary protein parotid secretory protein (PSP, BPIFA2, SPLUNC2, C20orf70). The peptide agglutinates both Gram negative and Gram positive bacteria, and shows anti-lipopolysaccharide activity in vitro and in vivo. However, GL13NH2 does not exhibit bactericidal activity. To generate a more cationic peptide with potential bactericidal activity, three amino acid residues were replaced with lysine residues to generate the peptide GL13K. In this report, the antibacterial and anti-inflammatory activities of GL13K were characterized. GL13K had lost the ability to agglutinate bacteria but gained bactericidal activity. Substitution of individual amino acids in GL13K with alanine did not restore bacterial agglutination. GL13K was bactericidal against Pseudomonas aeruginosa, Streptococcus gordonii and Escherichia coli but not Porphyromonas gingivalis. Unlike the agglutinating activity of GL13NH2, the bactericidal activity of GL13K against P. aeruginosa was retained in the presence of saliva. Both GL13NH2 and GL13K exhibited anti-lipopolysaccharide activity. In GL13K, this activity appeared to depend on a serine hydroxyl group. GL13K protected mice from lipopolysaccharide-induced sepsis and the peptide exhibited a low level of hemolysis, suggesting that it may be suitable for in vivo application.