Amino Acids (v.46, #10)

l-Arginine and its metabolites in kidney and cardiovascular disease by Ada Popolo; Simona Adesso; Aldo Pinto; Giuseppina Autore; Stefania Marzocco (2271-2286).
l-Arginine is a semi essential amino acid synthesised from glutamine, glutamate and proline via the intestinal-renal axis in humans and most mammals. l-Arginine degradation occurs via multiple pathways initiated by arginase, nitric-oxide synthase, Arg: glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine and agmatine with each having enormous biological importance. Several disease are associated to an l-arginine impaired levels and/or to its metabolites: in particular various l-arginine metabolites may participate in pathogenesis of kidney and cardiovascular disease. l-Arginine and its metabolites may constitute both a marker of pathology progression both the rationale for manipulating l-arginine metabolism as a strategy to ameliorate these disease. A large number of studies have been performed in experimental models of kidney disease with sometimes conflicting results, which underlie the complexity of Arg metabolism and our incomplete knowledge of all the mechanisms involved. Moreover several lines of evidence demonstrate the role of l-arg metabolites in cardiovascular disease and that l-arg administration role in reversing endothelial dysfunction, which is the leading cause of cardiovascular diseases, such as hypertension and atherosclerosis. This review will discuss the implication of the mains l-arginine metabolites and l-arginine-derived guanidine compounds in kidney and cardiovascular disease considering the more recent literature in the field.
Keywords: Arginine; Arginine metabolites; Kidney disease; Cardiovascular disease

Proline-rich antimicrobial peptides: potential therapeutics against antibiotic-resistant bacteria by Wenyi Li; Julien Tailhades; Neil M. O’Brien-Simpson; Frances Separovic; Laszlo Otvos Jr.; M. Akhter Hossain; John D. Wade (2287-2294).
The increasing resistance of pathogens to antibiotics causes a huge clinical burden that places great demands on academic researchers and the pharmaceutical industry for resolution. Antimicrobial peptides, part of native host defense, have emerged as novel potential antibiotic alternatives. Among the different classes of antimicrobial peptides, proline-rich antimicrobial peptides, predominantly sourced from insects, have been extensively investigated to study their specific modes of action. In this review, we focus on recent developments in these peptides. They show a variety of modes of actions, including mechanism shift at high concentration, non-lytic mechanisms, as well as possessing different intracellular targets and lipopolysaccharide binding activity. Furthermore, proline-rich antimicrobial peptides display the ability to not only modulate the immune system via cytokine activity or angiogenesis but also possess properties of penetrating cell membranes and crossing the blood brain barrier suggesting a role as potential novel carriers. Ongoing studies of these peptides will likely lead to the development of more potent antimicrobial peptides that may serve as important additions to the armoury of agents against bacterial infection and drug delivery.
Keywords: Proline-rich antimicrobial peptides; Non-lytic mechanism; Membrane disruption; Immunostimulation; Cell penetration

Calmodulin (CaM) is a highly conserved protein and a crucial calcium sensor in eukaryotes. CaM is a regulator of hundreds of diverse target proteins. A wealth of studies has been carried out on the structure of CaM, both in the unliganded form and in complexes with target proteins and peptides. The outcome of these studies points toward a high propensity to attain various conformational states, depending on the binding partner. The purpose of this review is to provide examples of different conformations of CaM trapped in the crystal state. In addition, comparisons are made to corresponding studies in solution. The different CaM conformations in crystal structures are also compared based on the positions of the metal ions bound to their EF hands, in terms of distances, angles, and pseudo-torsion angles. Possible caveats and artifacts in CaM crystal structures are discussed, as well as the possibilities of trapping biologically relevant CaM conformations in the crystal state.
Keywords: Protein conformation; Crystal structure; Complex; Calcium; X-Ray crystallography; Calmodulin

O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) catalyze the dynamic cycling of intracellular, post-translational O-GlcNAc modification on thousands of Ser/Thr residues of cytosolic, nuclear, and mitochondrial signaling proteins. The identification of O-GlcNAc modified substrates has revealed a functionally diverse set of proteins, and the extent of O-GlcNAcylation fluctuates in response to nutrients and cellular stress. As a result, OGT and OGA are implicated in widespread, nutrient-responsive regulation of numerous signaling pathways and transcriptional programs. These enzymes are required for normal embryonic development and are dysregulated in metabolic and age-related disease states. While a recent surge of interest in the field has contributed to understanding the functional impacts of protein O-GlcNAcylation, little is known about the upstream mechanisms which modulate OGT and OGA substrate targeting. This review focuses on elements of enzyme structure among splice variants, post-translational modification, localization, and regulatory protein interactions which drive the specificity of OGT and OGA toward different subsets of the cellular proteome. Ongoing efforts in this rapidly advancing field are aimed at revealing mechanisms of OGT and OGA regulation to harness the potential therapeutic benefit of manipulating these enzymes’ activities.
Keywords: O-GlcNAc; OGA; OGT; Post-translational modification; Cross-talk; Signaling; Nutrient metabolism; Epigenetics; Development; Aging

Many interests have been focused on prolyl cistrans isomerization which is related to protein folding and isomer-specific biochemical recognition. Since polyproline can adopt either type I (PPI) helices with all cis amide bonds or type II (PPII) helices with all trans amide bonds, it has been a valuable model to study the prolyl isomerization. Recent studies have shown that stereoelectronic effects govern the stability of PPII structure and the rate of PPII → PPI conversion. To further explore the terminal stereoelectronic effects on polyproline conformation, herein we synthesized a series of host–guest peptides in which (2S,4S)-4-fluoroproline (flp) or (2S,4R)-4-fluoroproline (Flp) residues are incorporated into the C- or N-terminal end of a peptide and studied the thermodynamic and kinetic consequences on polyproline conformation. Circular dichroism measurements revealed that inserting 4-fluoroproline residues into the C terminus of a polyproline peptide induces a great stereoelectronic effect on PPII stability and PPII → PPI conversion rates. From the C terminus, a (Flp)3 triplet stabilizes PPII structure and increases the transition barrier of PPII → PPI conversion by 1.53 kJ mol−1 while a (flp)3 triplet destabilizes PPII conformation and reduce the PPII → PPI transition barrier by 4.61 kJ mol−1. In contrast, the 4-fluoroproline substitutions at the N terminus do not exhibit distinct stereoelectronic effects on PPII stability and PPII → PPI conversion rates. Our data demonstrate that the C-terminal stereoelectronic effects have a more dramatic impact on PPII stability and PPII → PPI conversion kinetics.
Keywords: Stereoelectronic effect; Polyproline; 4-fluoroproline; Prolyl isomerization; Transition state barrier

Thiophenyl-substituted triazolyl-thione l-alanine: asymmetric synthesis, aggregation and biological properties by Ashot S. Saghyan; Hayarpi M. Simonyan; Satenik G. Petrosyan; Arpine V. Geolchanyan; Giovanni N. Roviello; Domenica Musumeci; Valentina Roviello (2325-2332).
In this work, we report the asymmetric synthesis and characterization of an artificial amino acid based on triazolyl-thione l-alanine, which was modified with a thiophenyl-substituted moiety, as well as in vitro studies of its nucleic acid-binding ability. We found, by dynamic light scattering studies, that the synthetic amino acid was able to form supramolecular aggregates having a hydrodynamic diameter higher than 200 nm. Furthermore, we demonstrated, by UV and CD experiments, that the heteroaromatic amino acid, whose enzymatic stability was demonstrated by HPLC analysis also after 24 h of incubation in human serum, was able to bind a RNA complex, which is a feature of biomedical interest in view of innovative antiviral strategies based on modulation of RNA–RNA molecular recognition.
Keywords: Artificial amino acid; RNA; CD; Light scattering

Efficacy of the designer antimicrobial peptide SHAP1 in wound healing and wound infection by Da Jung Kim; Young Woong Lee; Myung Keun Park; Ju Ri Shin; Ki Jung Lim; Ju Hyun Cho; Sun Chang Kim (2333-2343).
Infected wounds cause delay in wound closure and impose significantly negative effects on patient care and recovery. Antimicrobial peptides (AMPs) with antimicrobial and wound closure activities, along with little opportunity for the development of resistance, represent one of the promising agents for new therapeutic approaches in the infected wound treatment. However, therapeutic applications of these AMPs are limited by their toxicity and low stability in vivo. Previously, we reported that the 19-amino-acid designer peptide SHAP1 possessed salt-resistant antimicrobial activities. Here, we analyzed the wound closure activities of SHAP1 both in vitro and in vivo. SHAP1 did not affect the viability of human erythrocytes and keratinocytes up to 200 μM, and was not digested by exposure to proteases in the wound fluid, such as human neutrophil elastase and Staphylococcus aureus V8 proteinase for up to 12 h. SHAP1 elicited stronger wound closure activity than human cathelicidin AMP LL-37 in vitro by inducing HaCaT cell migration, which was shown to progress via transactivation of the epidermal growth factor receptor. In vivo analysis revealed that SHAP1 treatment accelerated closure and healing of full-thickness excisional wounds in mice. Moreover, SHAP1 effectively countered S. aureus infection and enhanced wound healing in S. aureus-infected murine wounds. Overall, these results suggest that SHAP1 might be developed as a novel topical agent for the infected wound treatment.
Keywords: Antimicrobial peptides; SHAP1; Wound healing; Infected wound treatment; Protease resistance; Cytotoxicity

Erratum to: Efficacy of the designer antimicrobial peptide SHAP1 in wound healing and wound infection by Da Jung Kim; Young Woong Lee; Myung Keun Park; Ju Ri Shin; Ki Jung Lim; Ju Hyun Cho; Sun Chang Kim (2345-2345).

Aqueous microwave-assisted solid-phase peptide synthesis using Fmoc strategy. III: Racemization studies and water-based synthesis of histidine-containing peptides by Keiko Hojo; Natsuki Shinozaki; Koushi Hidaka; Yuko Tsuda; Yoshinobu Fukumori; Hideki Ichikawa; John D. Wade (2347-2354).
In this study, we describe the first aqueous microwave-assisted synthesis of histidine-containing peptides in high purity and with low racemization. We have previously shown the effectiveness of our synthesis methodology for peptides including difficult sequences using water-dispersible 9-fluorenylmethoxycarbonyl-amino acid nanoparticles. It is an organic solvent-free, environmentally friendly method for chemical peptide synthesis. Here, we studied the racemization of histidine during an aqueous-based coupling reaction with microwave irradiation. Under our microwave-assisted protocol using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, the coupling reaction can be efficiently performed with low levels of racemization of histidine. Application of this water-based microwave-assisted protocol with water-dispersible 9-fluorenylmethoxycarbonyl-amino acid nanoparticles led to the successful synthesis of the histidine-containing hexapeptide neuropeptide W-30 (10–15), Tyr-His-Thr-Val-Gly-Arg-NH2, in high yield and with greatly reduced histidine racemization.
Keywords: Histidine; Microwave-assisted synthesis; Nanoparticles; Racemization; Solid-phase peptide synthesis; Synthesis in water

A direct comparison of tumor angiogenesis with 68Ga-labeled NGR and RGD peptides in HT-1080 tumor xenografts using microPET imaging by Yahui Shao; Wansheng Liang; Fei Kang; Weidong Yang; Xiaowei Ma; Guiyu Li; Shu Zong; Kai Chen; Jing Wang (2355-2364).
Peptides containing asparagine-glycine-arginine (NGR) and arginine-glycine-aspartic acid (RGD) sequence are being developed for tumor angiogenesis-targeted imaging and therapy. The aim of this study was to compare the efficacy of NGR- and RGD-based probes for imaging tumor angiogenesis in HT-1080 tumor xenografts. Two PET probes, 68Ga-NOTA-G3-NGR2 and 68Ga-NOTA-G3-RGD2, were successfully prepared. In vitro stability, partition coefficient, tumor cell binding, as well as in vivo biodistribution properties were also analyzed for both PET probes. The results revealed that the two probes were both hydrophilic and stable in vitro and in vivo, and they were excreted predominately and rapidly through the kidneys. For both probes, the higher tumor uptake and lower accumulation in vital organs were determined. No significant difference between two probes was observed in terms of tumor uptake and the in vivo biodistribution properties. We concluded that these two probes are promising in tumor angiogenesis imaging. 68Ga-NOTA-G3-NGR2 has the potential as an alternative for PET imaging in patients with fibrosarcoma, and it may offer an opportunity to noninvasively monitor CD13-targeted therapy.
Keywords: MicroPET imaging; NGR; RGD; CD13; Integrin; Tumor angiogenesis; 68Ga labeling

Effects of dietary l-glutamine supplementation on specific and general defense responses in mice immunized with inactivated Pasteurella multocida vaccine by Shuai Chen; Shuping Liu; Fengmei Zhang; Wenkai Ren; Nengzhang Li; Jie Yin; Jielin Duan; Yuanyi Peng; Gang Liu; Yulong Yin; Guoyao Wu (2365-2375).
Little is known about effects of dietary glutamine supplementation on specific and general defense responses in a vaccine-immunized animal model. Thus, this study determined roles for dietary glutamine supplementation in specific and general defense responses in mice immunized with inactivated Pasteurella multocida vaccine. The measured variables included: (1) the production of pathogen-specific antibodies; (2) mRNA levels for pro-inflammatory cytokines, toll-like receptors and anti-oxidative factors; and (3) the distribution of P. multocida in tissues and the expression of its major virulence factors in vivo. Dietary supplementation with 0.5 % glutamine had a better protective role than 1 or 2 % glutamine against P. multocida infection in vaccine-immunized mice, at least partly resulting from its effects in modulation of general defense responses. Dietary glutamine supplementation had little effects on the production of P. multocida-specific antibodies. Compared to the non-supplemented group, dietary supplementation with 0.5 % glutamine had no effect on bacterial burden in vivo but decreased the expression of major virulence factors in the spleen. Collectively, supplementing 0.5 % glutamine to a conventional diet provides benefits in vaccine-immunized mice by enhancing general defense responses and decreasing expression of specific virulence factors.
Keywords: Glutamine; Pasteurella multocida ; Vaccine; Virulence factors; Immune response

Effects of divergent resistance exercise contraction mode and dietary supplementation type on anabolic signalling, muscle protein synthesis and muscle hypertrophy by Stine Klejs Rahbek; Jean Farup; Andreas Buch Møller; Mikkel Holm Vendelbo; Lars Holm; Niels Jessen; Kristian Vissing (2377-2392).
Greater force produced with eccentric (ECC) compared to concentric (CONC) contractions, may comprise a stronger driver of muscle growth, which may be further augmented by protein supplementation. We investigated the effect of differentiated contraction mode with either whey protein hydrolysate and carbohydrate (WPH + CHO) or isocaloric carbohydrate (CHO) supplementation on regulation of anabolic signalling, muscle protein synthesis (MPS) and muscle hypertrophy. Twenty-four human participants performed unilateral isolated maximal ECC versus CONC contractions during exercise habituation, single-bout exercise and 12 weeks of training combined with WPH + CHO or CHO supplements. In the exercise-habituated state, p-mTOR, p-p70S6K, p-rpS6 increased by approximately 42, 206 and 213 %, respectively, at 1 h post-exercise, with resistance exercise per se; whereas, the phosphorylation was exclusively maintained with ECC at 3 and 5 h post-exercise. This acute anabolic signalling response did not differ between the isocaloric supplement types, neither did protein fractional synthesis rate differ between interventions. Twelve weeks of ECC as well as CONC resistance training augmented hypertrophy with WPH + CHO group compared to the CHO group (7.3 ± 1.0 versus 3.4 ± 0.8 %), independently of exercise contraction type. Training did not produce major changes in basal levels of Akt-mTOR pathway components. In conclusion, maximal ECC contraction mode may constitute a superior driver of acute anabolic signalling that may not be mirrored in the muscle protein synthesis rate. Furthermore, with prolonged high-volume resistance training, contraction mode seems less influential on the magnitude of muscle hypertrophy, whereas protein and carbohydrate supplementation augments muscle hypertrophy as compared to isocaloric carbohydrate supplementation .
Keywords: Whey protein; Hypertrophy signalling; Eccentric/concentric exercise

Kynurenic acid inhibits colon cancer proliferation in vitro: effects on signaling pathways by Katarzyna Walczak; Waldemar A. Turski; Grażyna Rajtar (2393-2401).
Kynurenic acid (KYNA), a tryptophan metabolite, inhibits proliferation of several cancer cell lines including colon cancer, renal cancer and glioblastoma cells. Previous studies reported that inhibitory properties of KYNA may be related to interactions of KYNA with cell cycle regulators and signaling proteins. However, the exact molecular interaction of KYNA with signaling pathways in colon cancer cells has not been studied to date. The molecular mechanism of KYNA activity towards colon cancer cells may be of great importance taking into consideration that KYNA is present in several tissues and physiological fluids, including gastrointestinal tract, and it is also present in various products of human diet. In this study, the inhibitory effect of KYNA on activation of phosphoinositide 3-kinase/Akt (PI3K/Akt) and mitogen-activated protein kinase (MAPK) signaling pathways in colon adenocarcinoma HT-29 cells was revealed. KYNA decreased phosphorylation of Akt, ERK 1/2 and p38 kinases in HT-29 cells. Interestingly, the study revealed also unexpected effect of KYNA on Wnt pathway in HT-29 cells. KYNA in millimolar concentrations increased protein expression of β-catenin. However, the nuclear translocation of β-catenin in HT-29 cells exposed to KYNA was not observed. Moreover, KYNA 1 mM increased antiproliferative properties of inhibitors of signaling pathways: wortmannin, PD98059, SB202190 and IWR-1. Taking into consideration these results, KYNA may be seen as a potential chemopreventive agent in colon cancer or supportive agent in standard cancer chemotherapy. However, the interactions between KYNA, Wnt signaling pathway and β-catenin need further studies to exclude potential effect of KYNA on colon carcinogenesis.
Keywords: Kynurenic acid; Colon cancer; Signaling pathways; PI3K/Akt pathway; MAPK; Wnt pathway

Dietary l-glutamine supplementation modulates microbial community and activates innate immunity in the mouse intestine by Wenkai Ren; Jielin Duan; Jie Yin; Gang Liu; Zhong Cao; Xia Xiong; Shuai Chen; Tiejun Li; Yulong Yin; Yongqing Hou; Guoyao Wu (2403-2413).
This study was conducted to determine effects of dietary supplementation with 1 % l-glutamine for 14 days on the abundance of intestinal bacteria and the activation of intestinal innate immunity in mice. The measured variables included (1) the abundance of Bacteroidetes, Firmicutes, Lactobacillus, Streptococcus and Bifidobacterium in the lumen of the small intestine; (2) the expression of toll-like receptors (TLRs), pro-inflammatory cytokines, and antibacterial substances secreted by Paneth cells and goblet cells in the jejunum, ileum and colon; and (3) the activation of TLR4-nuclear factor kappa B (NF-κB), mitogen-activated protein kinases (MAPK), and phosphoinositide-3-kinases (PI3K)/PI3K-protein kinase B (Akt) signaling pathways in the jejunum and ileum. In the jejunum, glutamine supplementation decreased the abundance of Firmicutes, while increased mRNA levels for antibacterial substances in association with the activation of NF-κB and PI3K-Akt pathways. In the ileum, glutamine supplementation induced a shift in the Firmicutes:Bacteroidetes ratio in favor of Bacteroidetes, and enhanced mRNA levels for Tlr4, pro-inflammatory cytokines, and antibacterial substances participating in NF-κB and JNK signaling pathways. These results indicate that the effects of glutamine on the intestine vary with its segments and compartments. Collectively, dietary glutamine supplementation of mice beneficially alters intestinal bacterial community and activates the innate immunity in the small intestine through NF-κB, MAPK and PI3K-Akt signaling pathways.
Keywords: Glutamine; Paneth cell; Firmicutes; NF-κB; Innate immunity

A routine method for cloning, expressing and purifying Aβ(1–42) for structural NMR studies by Daniel K. Weber; Marc-Antoine Sani; John D. Gehman (2415-2426).
Nuclear magnetic resonance (NMR) is a key technology in the biophysicist’s toolbox for gaining atomic-level insight into structure and dynamics of biomolecules. Investigation of the amyloid-β peptide (Aβ) of Alzheimer’s disease is one area where NMR has proven useful, and holds even more potential. A barrier to realizing this potential, however, is the expense of the isotopically enriched peptide required for most NMR work. Whereas most biomolecular NMR studies employ biosynthetic methods as a very cost-effective means to obtain isotopically enriched biomolecules, this approach has proven less than straightforward for Aβ. Furthermore, the notorious propensity of Aβ to aggregate during purification and handling reduces yields and increases the already relatively high costs of solid phase synthesis methods. Here we report our biosynthetic and purification developments that yield pure, uniformly enriched 15N and 13C15N Aβ(1–42), in excess of 10 mg/L of culture media. The final HPLC-purified product was stable for long periods, which we characterize by solution-state NMR, thioflavin T assays, circular dichroism, electrospray mass spectrometry, and dynamic light scattering. These developments should facilitate further investigations into Alzheimer’s disease, and perhaps misfolding diseases in general.
Keywords: Recombinant peptide; Uniform labeling; Amyloid beta peptide; Alzheimer’s disease; Protein NMR; SUMO; Thioflavin T assay; Circular dichroism

A concise synthesis of benzimidazoles via the microwave-assisted one-pot batch reaction of amino acids up to a 10-g scale by Pai Peng; Jin-Feng Xiong; Guang-Zhen Mo; Jia-Li Zheng; Ren-Hong Chen; Xiao-Yun Chen; Zhao-Yang Wang (2427-2433).
An efficient method for the synthesis of aminomethyl benzimidazoles is developed by using a one-pot batch reaction between amino acids and o-phenylenediamines. This reaction proceeds smoothly in an unmodified household microwave oven, even though scale-up is to 10 g. A desirable method for the quick synthesis of benzimidazoles, which are used as a kind of important intermediates in drug synthesis, is provided by the scale-up utilization of amino acid resource.
Keywords: Benzimidazoles; One-pot synthesis; Amino acids; o-Phenylenediamine; Microwave irradiation

Design and synthesis of mono and bicyclic tetrapeptides thioester as potent inhibitor of histone deacetylases by Md. Ashraful Hoque; Md. Shahidul Islam; Md. Nurul Islam; Tamaki Kato; Norikazu Nishino; Akihiro Ito; Minoru Yoshida (2435-2444).
Inhibitors of histone deacetylases (HDACs) are a promising class of anticancer agents that have an effect on gene regulation. The naturally occurring cyclic depsipeptide FK228 containing disulfide and Largazole possessing thioester functionalities act as pro-drugs and share the same HDAC inhibition mechanism in cell. Inspired from these facts, we have reported bicyclic tetrapeptide disulfide HDAC inhibitors resembling FK228 with potent activity and enhanced selectivity. In the present study, we report the design and synthesis of several mono and bicyclic tetrapeptide thioester HDAC inhibitors that share the inhibition mechanism similar to Largazole. Most of the compounds showed HDAC1 and HDAC4 inhibition and p21 promoting activity in nanomolar ranges. Among these the monocyclic peptides 1, 2 and bicyclic peptide, 4 are notable demanding more advanced research to be promising anticancer drug candidates.
Keywords: Histone deacetylase inhibitors; Depsipeptide; Largazole; Bicyclic tetrapeptides

Erratum to: Radiation protection from whole-body gamma irradiation (6.7 Gy): behavioural effects and brain protein-level changes by an aminothiol compound GL2011 in the Wistar rat by Minu Karthika Ganesan; Milos Jovanovic; Bojana Secerov; Marija Ignjatovic; Martin Bilban; Pavle Andjus; Amal El Refaei; Gangsoo Jung; Lin Li; Ajinkya Sase; Weiqiang Chen; Goran Bacic; Gert Lubec (2445-2445).