Short-chain Peptides Research Articles

Serpin A1 C-Terminal Peptides as Collagen Turnover Modulators.

The modulation of collagen turnover can be a relevant pharmacological target in the context of treating either pathological or pathophysiological conditions, such as collagen-related diseases and skin aging. Our recent work has focused on the search for short-chain peptides as lead compounds for further development of compounds that enhance the production of type I collagen. In this study we selected and synthesized overlapping peptides of the C-terminal portion of serpin A1 (residues 393-418), the impact of which on collagen production has been reported previously, in order to identify shorter and still active fragments and to provide insight on the mechanisms involved. The biological activity of each fragment was evaluated with cultured normal human dermal fibroblasts, and changes in the amounts of collagen were monitored in collected culture media by a sandwich ELISA technique developed in house. Interestingly, we identified a decapeptide, termed SA1-III (Ac-MGKVVNPTQK-NH2 ), as a promising candidate for our purposes; it is able to induce a significant increase in type I collagen levels in the culture medium of treated cells at micromolar concentrations.

Effects and mechanism of dual-frequency power ultrasound on the molecular weight distribution of corn gluten meal hydrolysates

The impact of dual-frequency power ultrasound (DPU) on the molecular weight distribution (MWD) of corn gluten meal (CGM) hydrolysates and its mechanism were investigated in the present study. The mechanism was studied from aspects of structural and nano-mechanical characteristics of the major protein fractions of CGM, viz. zein and glutelin. The results of molecular weight distribution indicated that DPU pretreatment of CGM was beneficial to the preparation of peptides with molecular weights of 200–1000Da. Moreover, FTIR spectral analysis and atomic force microscopy characterization showed that the DPU pretreatment changed the contents of secondary structure of proteins, decreased the particle height and surface roughness of glutelin, reduced the Young’s modulus and stiffness of zein while increased its adhesion force. In conclusion, DPU pretreatment of proteins before proteolysis is an efficient alternative method to produce short-chain peptides because of its positive effects originating from acoustic cavitation on the molecular conformation, nano-structures and nano-mechanical properties of proteins as well.

A single-point mutation enhances dual functionality of a scorpion toxin

Scorpion venom represents a tremendous, hitherto partially explored peptide library that has been proven to be useful not only for understanding ion channels but also for drug design. MeuTXKα3 is a functionally unknown scorpion toxin-like peptide. Here we describe new transcripts of this gene arising from alternative polyadenylation and its biological function as well as a mutant with a single-point substitution at site 30. Native-like MeuTXKα3 and its mutant were produced in Escherichia coli and their toxic function against Drosophila Shaker K+ channel and its mammalian counterparts (rKv1.1–rKv1.3) were assayed by two-electrode voltage clamp technique. The results show that MeuTXKα3 is a weak toxin with a wide-spectrum of activity on both Drosophila and mammalian K+ channels. The substitution of a proline at site 30 by an asparagine, an evolutionarily conserved functional residue in the scorpion α-KTx family, led to an increased activity on rKv1.2 and rKv1.3 but a decreased activity on the Shaker channel without changing the potency on rKv1.1, suggesting a key role of this site in species selectivity of scorpion toxins. MeuTXKα3 was also active on a variety of bacteria with lethal concentrations ranging from 4.66 to 52.01μM and the mutant even had stronger activity on some of these bacterial species. To the best of our knowledge, this is the first report on a bi-functional short-chain peptide in the lesser Asian scorpion venom. Further extensive mutations of MeuTXKα3 at site 30 could help improve its K+ channel-blocking and antibacterial functions.

Taste and move: glucose and peptide transporters in the gastrointestinal tract

What is the topic of this review? Nutrient absorption in the gastrointestinal tract requires membrane proteins embedded in the apical membrane of epithelial cells that allow bulk quantities of nutrients, such as monosaccharides and amino acids, to be moved into epithelial cells. Very recently, a new function of the transporters as nutrient sensors mediating peptide hormone release from enteroendocrine cells has been discovered. What advances does it highlight? The review covers recent advances in membrane transporter functions for the absorption and sensing of dietary peptides and sugars and their putative interplay. Nutrient transporters are integral membrane proteins responsible for uptake into enterocytes and release of nutrients into the circulation. Absorption of food breakdown products, such as fatty acids, monosaccharides or amino acids, requires high-capacity transporters. In the case of glucose, amino acids and peptides, the transporters are electrogenic in nature, coupling substrate flux to ion movement. While glucose absorption is mediated by the Na(+)-dependent SGLT1 protein, uptake of short-chain peptides is mediated by the H(+)-coupled PEPT1 protein. Interestingly, both transporters were recently shown to fulfil an additional role as intestinal 'sensors' in enteroendocrine cells, mediating the release of gastrointestinal peptide hormones into the circulation. Sensing of D-glucose and of di- and tripeptides is particularly relevant for the secretion of the incretins glucose-dependent insulinotrophic polypeptide and glucagon-like peptide 1 that promote insulin output from β-cells and mediate β-cell protection. In addition to these sensing pathways, a variety of G-protein-coupled receptors are involved in sensing of intestinal contents. D-Glucose is sensed not only by SGLT1 but also by the sweet taste receptor T1R2/3 expressed in enteroendocrine cells. Activation of T1R2/3 increases SGLT1 levels and intestinal glucose absorption. Although T1R2/3 ligands, such as artificial sweeteners, were shown to elicit incretin secretion from enteroendocrine cell lines or in vitro in tissue preparations, convincing data that this is also relevant in vivo are missing to date. However, there is growing interest in targeting intestinal sensory pathways, involving receptors but also the 'transceptors' PEPT1 and SGLT1, by use of drugs or food constituents to elicit the beneficial effects of incretins on the pancreas and metabolic control.

Tubular Unimolecular Transmembrane Channels: Construction Strategy and Transport Activities.

Lipid bilayer membranes separate living cells from their environment. Membrane proteins are responsible for the processing of ion and molecular inputs and exports, sensing stimuli and signals across the bilayers, which may operate in a channel or carrier mechanism. Inspired by these wide-ranging functions of membrane proteins, chemists have made great efforts in constructing synthetic mimics in order to understand the transport mechanisms, create materials for separation, and develop therapeutic agents. Since the report of an alkylated cyclodextrin for transporting Cu(2+) and Co(2+) by Tabushi and co-workers in 1982, chemists have constructed a variety of artificial transmembrane channels by making use of either the multimolecular self-assembly or unimolecular strategy. In the context of the design of unimolecular channels, important advances have been made, including, among others, the tethering of natural gramicidin A or alamethicin and the modification of various macrocycles such as crown ethers, cyclodextrins, calixarenes, and cucurbiturils. Many of these unimolecular channels exhibit high transport ability for metal ions, particularly K(+) and Na(+). Concerning the development of artificial channels based on macrocyclic frameworks, one straightforward and efficient approach is to introduce discrete chains to reinforce their capability to insert into bilayers. Currently, this approach has found the widest applications in the systems of crown ethers and calixarenes. We envisioned that for macrocycle-based unimolecular channels, control of the arrangement of the appended chains in the upward and/or downward direction would favor the insertion of the molecular systems into bilayers, while the introduction of additional interactions among the chains would further stabilize a tubular conformation. Both factors should be helpful for the formation of new efficient channels. In this Account, we discuss our efforts in designing new unimolecular artificial channels from tubular pillar[n]arenes by extending their lengths with various ester, hydrazide, and short peptide chains. We have utilized well-defined pillar[5]arene and pillar[6]arene as rigid frameworks that allow the appended chains to afford extended tubular structures. We demonstrate that the hydrazide and peptide chains form intramolecular N-H···O═C hydrogen bonds that enhance the tubular conformation of the whole molecule. The new pillar[n]arene derivatives have been successfully applied as unimolecular channels for the selective transport of protons, water, and amino acids and the voltage-gated transport of K(+). We also show that aromatic hydrazide helices and macrocycles appended with peptide chains are able to mediate the selective transport of NH4(+).

Purification and characterization of antioxidant peptides from enzymatically hydrolyzed chicken egg white

Egg white is considered as a rich source of high quality proteins with various bioactive peptide fractions. Enzymatic hydrolysis of proteins can be used to release bioactive fractions and different enzymes have different abilities in releasing such bioactive fractions depending on the enzyme’s site of activity on a protein. In this study, several proteases were examined for their ability to release antioxidant peptides from hen egg white and protease P was selected based on the antioxidant activity and the digestion yield of the crude protein hydrolysate. A combination of several purification steps including ultrafiltration with low molecular weight cut-off membranes, cation exchange chromatography and reversed phase high performance liquid chromatography was used to purify ‘protease P egg white hydrolysate’. Sixteen antioxidant peptides, which were derived from ovalbumin, ovotransferrin and cystatin were isolated from the most active fractions. Amino acid sequences of those peptides were determined using LC–MS/MS. Oxygen radical absorbance capacity (ORAC) values of selected short chain peptides were determined using synthetic peptides. Two peptides AEERYP and DEDTQAMP (Ala-Glu-Glu-Arg-Tyr-Pro and Asp-Glu-Asp-Thr-Gln-Ala-Met-Pro) showed the highest ORAC values. The results from this study indicate that egg white is rich in antioxidant peptides which can be used as a potential source for preparing bioactive ingredients using enzymatic hydrolysis followed by purification techniques.

Disulfide-Mediated β-Strand Dimers: Hyperstable β-Sheets Lacking Tertiary Interactions and Turns.

Disulfide bonds between cysteine residues are essential to the structure and folding of many proteins. Yet their role in the design of structured peptides and proteins has frequently been limited to use as intrachain covalent staples that reinforce existing structure or induce knot-like conformations. In β-hairpins, their placement at non-H-bonding positions across antiparallel strands has proven useful for achieving fully folded positive controls. Here we report a new class of designed β-sheet peptide dimers with strand-central disulfides as a key element. We have found that the mere presence of a disulfide bond near the middle of a short peptide chain is sufficient to nucleate some antiparallel β-sheet structure; addition of β-capping units and other favorable cross-strand interactions yield hyperstable sheets. Strand-central cystines were found to be superior to the best designed reversing turns in terms of nucleating β-sheet structure formation. We have explored the limitations and possibilities of this technique (the use of disulfides as sheet nucleators), and we provide a set of rules and rationales for the application and further design of disulfide-tethered "turnless" β-sheets.

Peptide-induced affinity binding of carbonic anhydrase to carbon nanotubes.

Although affinity binding between short chain peptides and carbon nanotube (CNT) has been reported, little is known for the study of proteins with CNT recognition and specific binding capabilities. Herein, carbonic anhydrase (CA) was functionalized via protein fusion with a single-walled carbon nanotube (SWNTs)-binding peptide, thereby forming a bioactive protein with high affinity binding capability. TEM and AFM analyses showed that the fusion CA could firmly coat to SWNTs with a surface coverage over 51%, while the enzyme maintained its catalytic activity. Structural analysis revealed that slight conformation changes were induced as a result of the fusion; however, the affinity binding of CA to the hydrophobic surface of SWNTs restored the native structure of the protein, with the conformation of the SWNT-bound CA largely resembling that of the native parent enzyme. Interfacial interactions between the fusion CA and SWNT were further investigated with Raman spectrometry and microscopic analysis. The results suggested that such peptide-induced CNT-protein binding allows the development of bioactive hybrid materials with the native structures of the protein moieties largely undisrupted.

A Heparan Sulfate-Binding Cell Penetrating Peptide for Tumor Targeting and Migration Inhibition.

As heparan sulfate proteoglycans (HSPGs) are known as co-receptors to interact with numerous growth factors and then modulate downstream biological activities, overexpression of HS/HSPG on cell surface acts as an increasingly reliable prognostic factor in tumor progression. Cell penetrating peptides (CPPs) are short-chain peptides developed as functionalized vectors for delivery approaches of impermeable agents. On cell surface negatively charged HS provides the initial attachment of basic CPPs by electrostatic interaction, leading to multiple cellular effects. Here a functional peptide (CPPecp) has been identified from critical HS binding region in hRNase3, a unique RNase family member with in vitro antitumor activity. In this study we analyze a set of HS-binding CPPs derived from natural proteins including CPPecp. In addition to cellular binding and internalization, CPPecp demonstrated multiple functions including strong binding activity to tumor cell surface with higher HS expression, significant inhibitory effects on cancer cell migration, and suppression of angiogenesis in vitro and in vivo. Moreover, different from conventional highly basic CPPs, CPPecp facilitated magnetic nanoparticle to selectively target tumor site in vivo. Therefore, CPPecp could engage its capacity to be developed as biomaterials for diagnostic imaging agent, therapeutic supplement, or functionalized vector for drug delivery.

Design and optimisation of bioactive cyclic peptides: generation of a down-regulator of TNF secretion.

Although strong binding interactions between protein receptor and ligand do not require the participation of a large number of amino acids in either site, short peptide chains are generally poor at recreating the types of protein-protein interactions which take place during cell recognition and signalling process, probably because their flexible backbones prevent the side chains from forming sufficiently rigid and stable epitopes, which can take part in binding with the desired strength and specificity. In a recently-reported study, it was shown that a proto-epitope containing F, R and S amino acids has the ability to down-regulate TNF secretion by macrophages. This paper extends these findings, putting those amino acids into a short cyclic peptide scaffold, and determining the optimal configuration required to overcome the problems of conformational instability, and give rise to molecules which have potential as therapeutic agents in human disease, such as rheumatoid arthritis.

Non-IgE Mediated Food Allergy Development after Liver Transplantation?

Background: The acquisition of new-onset food allergy after organ transplantation or transplant-acquired food allergy (TAFA) has been usually reported in adults and rarely in children. TAFA is described mainly after solid organ (e.g., liver, intestine, pancreas, kidney, lung and heart) or cord blood transplantations. In various reported studies, the male/female ratio seems to be equal. And literature data suggest that children with TAFA typically present within the first year after solid organ transplantation and they are typically allergic to multiple foods. Aim: TAFA is generally characterized with allergy to multiple foods and increased level of total and/or spesific IgE. Here, a patient with TAFA who had normal total and specific IgE test results plus minimal reaction to skin prick test for cow's milk is presented and his clinical presentation is discussed. Case Presentation: 15 month-old- boy came to our allergy clinic with complaints of vomiting after drinking cow's milk and skin rush on the area where contacted with chocolate. In his past medical history: Extrahepatic biliary atresia was diagnosed at 3 weeks age with conjugated hyperbilirubinemia (according to scintigraphy and biopsy results). Left lateral segment of liver (donor was his mother) was transplanted to him when he was at 5 months. The liver donor was not recorded as having a history of allergic disease. Methylprednisolone and tacrolimus immunosuppression were used after the transplantation, and tacrolimus therapy was continued for prophylaxis of chronic rejection. When he was at 7 months, family fed the patient with cow's milk but 3 hours later he began to vomit. He vomited five times in two hours. Then, he developed constipation. Rectal irrigation was used. Then oral intake stopped for two days. He was thought to be having food protein induced enterocolitis. His vomiting complaints repeated after intake of formula and baby food which includes grain. So he fed with special formula including short-chain peptides and free aminoacids and his symptoms improved. Family history: His father has penicillin allergy and his aunt has asthma. Physical examination revealed normal examination findings. Height and weight were within normal percentiles. Laboratory findings: WBC was 4.420/mm3, with 21% neutrophils, 6% eosinophils and 69% lymphocytes. His hemoglobin was 8.2 g/dl, platelet count was 280.000/mm3. Total IgE : <5 and ImmunoCAP specific IgE against milk, grain and other six classic foods was <0.35. Skin prick test results: saline: 0x0mm, histamine 4x4mm, Fresh cow's milk: 2x2mm, other food allergens (peanut, egg, fish, soybean, wheat): 0x0mm. Conclusion: Our patient seemed to have TAFA, cow's milk allergy with gastrointestinal manifestations (FPIES), after liver transplantation. Transplant-acquired new allergy needs to be considered after solid organ transplantation, especially when tacrolimus is used as immunosuppressive agent.

ChemInform Abstract: Transition Metal Complexes with Oligopeptides: Single Crystals and Crystal Structures

AbstractReview: 162 refs.

Novel strategy for the revalorization of olive (Olea europaea) residues based on the extraction of bioactive peptides

This work proposes a new strategy for the revalorization of residual materials from table-olive and olive oil production based on the extraction of bioactive peptides. Enzymatic hydrolysates of olive seed protein isolate were prepared by treatment with five different proteases: Alcalase, Thermolysin, Neutrase, Flavourzyme and PTN. Although all hydrolysates presented antioxidant properties, Alcalase was the enzyme that yielded the hydrolysate with the highest antioxidant capacity. All hydrolysates showed antihypertensive capacity, obtaining IC50 values from 29 to 350μg/ml. Thermolysin was the enzyme which yielded the hydrolysate with the highest ACE-inhibitory capacity. Hydrolysates were fractionated by ultrafiltration showing a high concentration of short chain peptides, which exhibited significantly higher antioxidant and antihypertensive capacities than fractions with higher molecular weights. Peptides in most active fractions were identified by LC–MS/MS, observing homologies with other recognized antioxidant and antihypertensive peptides. Finally, their antioxidant and antihypertensive capacities were evaluated after in vitro gastrointestinal digestion.

Extraction of ACE-inhibiting dipeptides from protein hydrolysates using porous carbon materials

This study reports on the extraction of strongly angiotensin-converting enzyme (ACE) inhibiting dipeptides from protein hydrolysates obtained by enzymatic proteolysis. Several dipeptides with different ACE inhibitory activities and hydrophobicities were investigated regarding to their adsorption affinity on commercially available activated carbon material Norit DLC Super 50. This porous carbon exhibits extremely high adsorption capacities for the strongest ACE inhibitor Ile-Trp (IC50=0.7μM) of 726mg/g as well as fast adsorption kinetics due to its micropore structure and small particle size. The filling of the pores was monitored by N2-physisorption revealing that complete pore filling occurred and Ile-Trp adsorption was only limited by the specific pore volume of Norit DLC Super 50, whereas less active peptides were adsorbed less efficient due to their higher hydrophobicity and did not impact Ile-Trp adsorption. After the adsorption, Ile-Trp was recovered by elution with ethanol. Three protein hydrolysates obtained by different enzyme combinations were mixed with activated carbon and the peptide adsorption was investigated by RP-HPLC. The amount of Trp-containing and ACE-inhibiting short chain peptides decreased selectively in contrast to more polar peptides, but the amount of adsorbed Ile-Trp is smaller than for single component adsorption.

Identification of multifunctional peptides from human milk

Pharmaceutical industries have renewed interest in screening multifunctional bioactive peptides as a marketable product in health care applications. In this context, several animal and plant peptides with potential bioactivity have been reported. Milk proteins and peptides have received much attention as a source of health-enhancing components to be incorporated into nutraceuticals and functional foods. By using this source, 24 peptides have been fractionated and purified from human milk using RP-HPLC. Multifunctional roles including antimicrobial, antioxidant and growth stimulating activity have been evaluated in all 24 fractions. Nevertheless, only four fractions show multiple combined activities among them. Using a proteomic approach, two of these four peptides have been identified as lactoferrin derived peptide and kappa casein short chain peptide. Lactoferrin derived peptide (f8) is arginine-rich and kappa casein derived (f12) peptide is proline-rich. Both peptides (f8 and f12) showed antimicrobial activities against both Gram-positive and Gram-negative bacteria. Fraction 8 (f8) exhibits growth stimulating activity in 3T3 cell line and f12 shows higher free radical scavenging activity in comparison to other fractions. Finally, both peptides were in silico evaluated and some insights into their mechanism of action were provided. Thus, results indicate that these identified peptides have multiple biological activities which are valuable for the quick development of the neonate and may be considered as potential biotechnological products for nutraceutical industry.

The study of cellular cytotoxicity of argireline - an anti-aging peptide.

Argireline is well know, innovative anti-aging product used in the cosmetic market. This short chain peptide is used as active ingredient in dermal ointment and creams. Argireline prevents formation of skin lines and wrinkles in a very similar way to the botulinum toxin (Botox), inhibiting neurotransmitter release at the neuromuscular junction. Argireline does not require under skin muscle injections and it is believed to be relatively safe. However, despite the fact that some toxicity data has been provided by the product manufacturer, there is an evident lack of reliable information about cytotoxicity of argireline in the literature. The aim of the presented study was to estimate the antiproliferation effect of argireline solution in several concentrations. The influence of argireline on cellular proliferation was examined against: human embryonic kidney HEK-293 cell line, human neuroblastoma IMR-32 cell line, and human primary skin fibroblasts. Tests were performed using formazan-based cell proliferation assay: EZ4U, which allows to measure the efficiency of mitochondrial oxidative activity in living cells. The argireline inhibitory concentration, IC50 values were calculated and the results were compared to the IC50 value of the reference compound: doxorubicin. In conclusion, the considered method resulted in dose-dependent argireline anti-proliferation effects. However, the significant cytotoxicity of argireline solution was observed under 18 to 10 000 fold higher concentrations (depending on cells that were examined) in comparison to doxorubicin.

Strategy of Fc-Recognizable Peptide Ligand Design for Oriented Immobilization of Antibody

A new strategy for designing a short-chain peptide ligand with high affinity to the Fc region of an antibody was proposed. The targeted antibody is human prostate specific antibody (PSA) derived from Mouse IgG2a. The ligand design strategy involves two major parts: binding site selection and peptide ligand design. One of the exposed hydrophobic patches near the bottom of the antibody's Fc region, identified from the molecular docking of naphthelene and end-capped tryptophan, was selected as the binding site. After examining the charge distribution around the binding site, various peptide ligands were designed according to the possible hydrophobic and electrostatic interactions. A peptide ligand, RRGW, was found to have high Fc binding affinity by the analysis of molecular dynamics (MD) simulation. The first two residues, two arginines, play an important role in electrostatic interaction between the peptide and the Fc region of the antibody. The fourth residue, the tryptophan, provides the VDW force; and the flexibility of peptide is achieved through the help of the third residue, the glycine. The binding affinity, recognition efficiency, and orientation factor were calculated from the results of surface plasmon resonance (SPR) measurements. The result shows that the dissociation constant is 5.56 × 10(-10) M(-1). We also found that the recognition efficiency and orientation factor on the ligand attached surface were much higher than those on negatively and positively charged surfaces. This approach provides a simple and fast strategy for small ligands design on oriented antibody immobilization.

Translation in the RNA World: Insight from the Proto-Ribosome Model

To quote Carl Woese “Translation not only defines gene expression, but it is the sine qua non without which modern (protein-based) cells would not have come into existence.” Yet to understand how this universal process might have developed requires an evolutionary RNA-World-centered concept of translation. A theory of the primitive RNA-based translation mechanism is developed starting from segments of the ribosome that comprise the symmetric A- and P-cores of the peptidyl-transferase center (PTC). We have computationally engineered RNA structural motifs, such as the frequently occurring tetra-loops and A-minor interactions, into the PTC to construct the model of a prebiotic proto-ribosome. The stability of the model, and thus the probability of its primordial existence, increases as we build up the complexity of the RNA molecule. We found that a minimal size of about 190 nucleotides (95 for each symmetric monomer) is required for the proto-ribosome to reach microsecond stability under physiological conditions. Moreover, this stable model is able to hold the charged tRNA CCA-end in both the A- and P-sites long enough, so that the substrates can be reoriented into a transition state favorable for peptide bond formation. To support our computational model of the proto-ribosome, native polyacrylamide gel electrophoresis was performed on separate A- and P-cores to confirm their unique native folding conformations; and isothermal titration calorimetry (ITC) was used to measure the binding rate of the two components with and without substrates. Our results demonstrate that a functional RNA molecule could have existed as the primitive translation apparatus capable of making short statistical peptide chains, and therefore, enable the transition of the ancient RNA world into the world of the modern cells.

Structural and functional characterization of hemp seed (Cannabis sativa L.) protein-derived antioxidant and antihypertensive peptides

The aim of this study was to identify and test efficacy of antioxidant and antihypertensive peptides present in hemp seed protein hydrolysate (HPH), which was produced through simulated gastrointestinal tract digestion of hemp seed proteins. Consecutive fractionation of HPH by reverse-phase HPLC followed by tandem mass spectrometry analysis of active peaks led to identification of 23 short-chain (⩽5 amino acids) peptides. At 0.5mg/mL, Trp-Val-Tyr-Tyr (WVYY) and Pro-Ser-Leu-Pro-Ala (PSLPA) were the most active antioxidant peptides with 67% and 58% DPPH scavenging and metal chelation activity of 94% and 96%, respectively. WVYY and PSLPA showed maximum systolic blood pressure (SBP) reduction in spontaneously hypertensive rats by 34 (2h) and 40mmHg (4h), respectively, after oral administration of 30mg/kg body weight dose. Trp-Tyr-Thr (WYT) at 2h, Ser-Val-Tyr-Thr (SVYT) at 6h, and Ile-Pro-Ala-Gly-Val (IPAGV) at 4h, each at 30mg/kg body weight dose had maximum SBP reductions of 13, 24, and 36mmHg, respectively.

Studies of conformational preferences of derivatives fragments of protein G (1IGD) using temperature dependent potentiometric titration methodology

The pKa values of charged amino-acid groups present in the sequences of the peptide excised from the C terminal hairpin of B3 domain of the immunoglobulin binding protein G from Streptococcus (1IGD 51-56): Ac-DDATKT-NH2 (Dag1) and its variants: Ac-DVATKT-NH2 (Dag2) and Ac-OVATKT-NH2 (Dag3), where D, A, T, K, V, and O denote aspartic acid, alanine, threonine, lysine, valine, and ornithine, respectively, were determined by potentiometric titration measurements at three different temperatures. Our previous studies have shown that the presence of charged amino acid residues at opposite ends of a short peptide chain can stabilize the structure. The values of ΔH and ΔS and the folding-unfolding transition temperatures calculated from the CD are in good agreement with those obtained from the DSC measurements, which indicates that the major conformational transition is associated with turn formation. The measured pKa values of Dag1, Dag2 and Dag3, except for pKa1 of Dag2, decrease with increasing temperature as expected, because deprotonation in water of these groups is an endothermic process. For Dag1 and Dag2, the pKa1 values are lower than that of the reference compound (acetic acid), which suggests the formation of a salt bridge in both peptides. The folding-unfolding transition enthalpy of Dag1 is remarkably greater than those of Dag2 and Dag3, which suggests that this compound has the most stable structure in water.