1.
Cell-penetrating properties of the transactivator of transcription and polyarginine (R9) peptides, their conjugative effect on nanoparticles and the prospect of conjugation with arsenic trioxide.
Source
aNanomedicine-Laboratory of Immunology and Molecular Biomedical Research (LIMBR), Centre for Biotechnology and Interdisciplinary Biosciences (BioDeakin), Institute for Technology and Research Innovation (ITRI), Geelong Technology Precinct (GTP), Deakin University, Geelong, Vic., Australia bNano-biotech Lab, Department of Zoology, K.M. College, University of Delhi, Delhi, India.
Abstract
Cell-penetrating peptides (CPPs) are short chains of amino acids with the distinct ability to cross cell plasma membranes. They are usually between seven and 30 residues in length. The mechanism of action is still a highly debated subject among researchers; it seems that a commonality between all CPPs is the presence of positively charged residues within the amino acid chain. Polyarginine and the transactivator of transcription peptide are two widely used CPPs. One distinct application of these CPPs is the ability to further enhance the therapeutic properties of a range of different agents. One group of agents of particular importance are nanoparticles (NPs). Most NPs have no mechanism for cellular uptake. Hence, by conjugating CPPs to NPs, the amount of NPs taken up by cells can be increased, and therefore, the therapeutic benefits can be maximized. Some examples of this will be explored further in this review. In addition to CPPs, the concept of conjugation with the anticancer drug arsenic trioxide is reviewed and the prospect of transactivator of transcription-conjugated arsenic trioxide albumin microspheres is also discussed. Recent locked nucleic acid technology to stabilize nucleotides (RNA or DNA) aptamer complexes able to target cancer cells more specifically and selectively to kill tumour cells and spare normal body cells. NPs tagged with modified locked nucleic acid-aptamers have the potential to kill cancer cells more specifically and effectively while sparing normal cells.
A fluorescent amino acid probe to monitor efficiency of peptide conjugation to glass surfaces for high density microarrays.
Source
Department of Bioengineering and Center for Bioengineering Research, Bourns College of Engineering, University of California at Riverside, 900 University Avenue, Riverside, CA 92521, USA. jiayu.liao@ucr.edu.
Abstract
Using a fluorescent NBD amino acid, new protease substrates were developed that are attractive because of the excellent chemical stability and long wavelength of excitation (480 nm) of the NBD fluorophore. The fluorescent peptidesare synthesized by Fmoc solid-phase peptide synthesis. An example peptide was efficiently immobilized onto a microarray surface using click chemistry, and its proteolysis was monitored by fluorescence imaging. Excellent site specificity was achieved for the protease. Fluorescent peptides are also used to monitor the conjugation efficiency onto a surface using a standard microarray scanner.
Rational Design of Single-Composition ABC Collagen Heterotrimers.
Source
Departments of †Chemistry and ‡Bioengineering, Rice University , Houston, Texas 77005, United States.
Abstract
Design of heterotrimeric ABC collagen triple helices is challenging due to the large number of competing species that may be formed. Given the required one amino acid stagger between adjacent peptide strands in this fold, a ternary mixture of peptides can form as many as 27 triple helices with unique composition or register. Previously we have demonstrated that electrostatic interactions can be used to bias the helix population toward a desired target. However, homotrimeric assemblies have always remained the most thermally stable species in solution and therefore comprised a significant component of the peptide mixture. In this work we incorporate complementary modifications to this triple-helical design strategy to destabilize an undesirable competing state while compensating for this destabilization in the desired ABC composition. The result of these modifications is a new ABC triple-helical system with high thermal stability and control over composition, as observed by NMR. An additional set of modifications, which exchanges aspartate for glutamate, results in an overall lowering of stability of the ABC triple helix yet shows further improvement in the system's specificity. This rationally designed system helps to elucidate the rules governing the self-assembly of synthetic collagen triple helices and sheds light on the biological mechanisms of collagen assembly.
Minimal essential length of Clostridium botulinum C3 peptides to enhance neuronal regenerative growth and connectivity in a non-enzymatic mode.
Source
Center for Anatomy, Functional Cell Biology, Charité-Universitätsmedizin Berlin, Germany Department of Morphology & BIOMED Institute, Hasselt University, Belgium Université Pierre et Marie Curie, Institut de la Vision, Paris, France) Institute of Toxicology, Hannover Medical School (MHH), Germany.
Abstract
C3 ADP-ribosyltransferase is a valuable tool to study Rho-dependent cellular processes. In the current study we investigated the impact of enzyme-deficient peptides derived from Clostridium botulinum C3 transferase in the context of neuronal process elongation and branching, synaptic connectivity, and putative beneficial effects on functional outcome following traumatic injury to the CNS. By screening a range of peptidic fragments we identified three short peptides from C3bot that promoted axon and dendrite outgrowth in cultivated hippocampal neurons. Furthermore, one of these fragments, a 26-amino acid peptide covering the residues 156-181 enhanced synaptic connectivity in primary hippocampal culture. This peptide was also effective to foster axon outgrowth and re-innervation in organotypical brain slice culture. To evaluate the potential of the 26mer to foster repair mechanisms after CNS injury we applied this peptide to mice subjected to spinal cord injury by either compression impact or hemisection. A single local administration at the site of the lesion improved locomotor recovery. In addition, histological analysis revealed an increased serotonergic input to lumbar motoneurons in treated compared to control mice. Pull-down assays showed that lesion-induced up-regulation of RhoA activity within the spinal cord was largely blocked by C3bot peptides despite the lack of enzymatic activity. © 2012 The Authors Journal of Neurochemistry© 2012 International Society for Neurochemistry.
© 2012 The Authors. Journal of Neurochemistry © 2012 International Society for Neurochemistry.
Structural and Energetic Effects in the Molecular Recognition of Protonated Peptidomimetic Bases by 18-Crown-6.
Abstract
Absolute 18-crown-6 (18C6) affinities of nine protonated peptidomimetic bases are determined using guided ion beam tandem mass spectrometry techniques. The bases (B) included in this work are mimics for the n-terminal amino group and the side chains of the basic amino acids, i.e., the favorable sites for binding of 18C6 to peptides and proteins. Isopropylamine is chosen as a mimic for the n-terminal amino group, imidazole and 4-methylimidazole are chosen as mimics for the side chain of histidine (His), 1-methylguanidine is chosen as a mimic of the side chain of arginine (Arg), and several primary amines including: methylamine, ethylamine, n-propylamine, n-butylamine, and 1,5-diamino pentane as mimics for the side chain of lysine (Lys). Theoretical electronic structure calculations are performed to determine stable geometries and energetics for neutral and protonated 18C6 and the peptidomimetic bases, as well as the proton bound complexes comprised of these species, (B)H+(18C6). The measured 18C6 binding affinities of the Lys side chain mimics are larger than the measured binding affinities of the mimics for Arg and His. These results suggest that the Lys side chains should be the preferred binding sites for 18C6 complexation to peptides and proteins. Present results also suggest that competition between Arg or His and Lys for 18C6 is not significant. The mimic for the n-terminal aminogroup, exhibits a measured binding affinity for 18C6 that is similar to or greater than that of the Lys side chain mimics. However, theory suggests that binding to n-terminal amino group mimic is weaker than to all of the Lys mimics. These results suggest that the n-terminal amino group may compete with the Lys side chains for 18C6 complexation.
Towards a stable α-cycloalkyl amino acid with a photo-switchable cationic side-chain.
Abstract
The N-alkylated indanyliden-pyrroline (NAIP) Schiff base 3 is an unnatural α-amino acid precursor potentially useful for the preparation of semi-synthetic peptides and proteins incorporating charged side-chains whose structure can be modulated via Z/E photoisomerization. Here we report that the heteroallylic protons of 3 lead to partial loss of ethanol accompanied by formation of the novel heterocyclic system 4 during attempted de-protection. We also show that the same protons catalyze the thermal isomerization of 3 making the light-driven conformational control concept ineffective for times longer than a few hours. These problems are not present in the previously unreported compound 5 where the acidic methyl group is replaced by a H atom. Therefore 5, rather than 3, constitutes a promising prototype for the design of building-blocks capable to modulate the electrostatic potential of a protein in specific locations via light irradiation.
Neutralizing Epitopes in the MPER of HIV-1 gp41 Are Influenced by the Transmembrane Domain and the Plasma Membrane.
Source
Dept. of Molecular Biology and Biochemistry.
Abstract
Failure to elicit broadly (b) neutralizing (Nt) antibodies (Abs) against the membrane proximal external region of HIV-1 gp41 (MPER), reflects the difficulty of mimicking its neutralization-competent structure (NCS). Here, we analyzed MPER antigenicity in the context of the plasma membrane, and identified a role for the gp41 transmembrane domain (TM) in exposing the epitopes of three bNt monoclonal (M)Abs (2F5, 4E10, Z13e1). We transiently expressed DNA constructs encoding gp41 ectodomain fragments fused to either the TM of the platelet-derived growth factor receptor (PDGFR), or the gp41 TM and cytoplasmic tail domain (CT). Constructs encoding the MPER tethered to the gp41 TM followed by a 27-residue CT fragment (MPER-TM1) produced optimal MAb binding. Critical binding residues for the three Nt MAbs were identified using a panel of 24 MPER-TM1 mutants bearing single amino-acid substitutions in the MPER; many were previously shown to affect MAb-mediated viral neutralization. Moreover, non-Nt mutants of MAbs 2F5 and 4E10 exhibited a reduction in binding to MPER-TM1, yet maintained binding to synthetic MPER peptides, indicating that MPER-TM1 better approximates the MPER NCS than peptides. Substitution of the gp41 TM and CT of MPER-TM1 with the PDGFR TM reduced binding by MAb 4E10, but not 2F5, indicating the gp41 TM plays a pivotal role in orienting the 4E10 epitope, and more globally, in affecting MPER exposure.
Exploiting the mutanome for tumor vaccination.
Source
TRON - Translational Oncology at the University Medical Center, University Medical Center of the Johannes Gutenberg-University Mainz.
Abstract
Multiple genetic events and subsequent clonal evolution drive carcinogenesis, making disease elimination with single targeted drugs difficult. The multiplicity of gene mutations derived from clonal heterogeneity therefore represents an ideal setting for multi-epitope tumor vaccination. Here we used NGS exome resequencing to identify 941 non-synonymous somatic point mutations in B16F10 murine melanoma cells, with 589 of those mutations in expressed genes. Potential driver mutations occurred in classical tumor suppressor genes and genes involved in proto-oncogenic signaling pathways that control cell proliferation, adhesion, migration and apoptosis. Aim1 and Trrap mutations known to be altered in human melanoma were included among those found. The immunogenicity and specificity of 50 validated mutations was determined by immunizing mice with long peptides encoding the mutated epitopes. One-third of thesepeptides were found to be immunogenic, with 60% in this group eliciting immune responses directed preferentially against the mutated sequence as compared to the wild type sequence. In tumor transplant models, peptide immunization conferred in vivo tumor control in protective and therapeutic settings, thereby qualifying mutated epitopes that include single amino acid substitutions as effective vaccines. Together, our findings provide a comprehensive picture of the mutanome of B16F10 melanoma which is used widely in immunotherapy studies. Additionally, they offer insight into the extent of the immunogenicity of non-synonymous base substitution mutations. Lastly, they argue that the use of deep sequencing to systematically analyze immunogenicity mutations may pave the way for individualized immunotherapy of cancer patients.
Constrained α/γ-peptides: a new stable extended structure in solution without any hydrogen bond and characterized by a four-fold symmetry.
Source
Univ Paris-Sud, Laboratoire de Chimie des Procédés et Substances Naturelles, ICMMO, UMR 8182, CNRS, Bât 410, Orsay, F-91405, France. valerie.alezra@u-psud.fr.
Abstract
Small α/γ-peptides alternating α-aminoisobutyric acid and cyclic γ-amino acid residues are described. NMR studies together with restrained simulated annealing revealed that an extended backbone conformation largely dominates in solution for as short as 4-residues long oligomers. This new fold type is devoid of any hydrogen bond and characterized by a four-fold symmetry.
Controlling Self-Assembly of Engineered Peptides on Graphite by Rational Mutation.
Abstract
Self-assembly of proteins on surfaces is utilized in many fields to integrate intricate biological structures and diverse functions with engineered materials. Controlling proteins at bio-solid interfaces relies on establishing key correlations between their primary sequences and resulting spatial organizations on substrates. Protein self-assembly, however, remains an engineering challenge. As a novel approach, we demonstrate here that short dodecapeptides selected by phage display are capable of self-assembly on graphite and form long-range ordered biomolecular nanostructures. Using atomic force microscopy and contact angle studies, we identify three amino-acid domains along the primary sequence that steer peptide ordering and lead to nanostructures with uniformly displayed residues. The peptides are further engineered via simple mutations to control fundamental interfacial processes, including initial binding, surface aggregation and growth kinetics, and intermolecular interactions. Tailoring short peptides via their primary sequence offers versatile control over molecular self-assembly, resulting in well-defined surface properties essential in building engineered, chemically rich, bio-solid interfaces.
Proteomic changes in cerebrospinal fluid of presymptomatic and affected persons carrying familial Alzheimer disease mutations.
Source
Mary S. Easton Center for Alzheimer's Disease Research, 10911 Weyburn Ave, Ste 200, Los Angeles, CA 90095. jringman@mednet.ucla.edu.
Abstract
OBJECTIVE:
To identify cerebrospinal fluid (CSF) protein changes in persons who will develop familial Alzheimer disease (FAD) due to PSEN1 and APP mutations, using unbiased proteomics.
DESIGN:
We compared proteomic profiles of CSF from individuals with FAD who were mutation carriers (MCs) and related noncarriers (NCs). Abundant proteins were depleted and samples were analyzed using liquid chromatography-electrospray ionization-mass spectrometry on a high-resolution time-of-flight instrument. Tryptic peptides were identified by tandem mass spectrometry. Proteins differing in concentration between the MCs and NCs were identified.
SETTING:
A tertiary dementia referral center and a proteomic biomarker discovery laboratory.
PARTICIPANTS:
Fourteen FAD MCs (mean age, 34.2 years; 10 are asymptomatic, 12 have presenilin-1 [PSEN1 ] gene mutations, and 2 have amyloid precursor protein [APP ] gene mutations) and 5 related NCs (mean age, 37.6 years).
RESULTS:
Fifty-six proteins were identified, represented by multiple tryptic peptides showing significant differences between MCs and NCs (46 upregulated and 10 downregulated); 40 of these proteins differed when the analysis was restricted to asymptomatic individuals. Fourteen proteins have been reported in prior proteomic studies in late-onset AD, including amyloid precursor protein, transferrin, α(1)β-glycoprotein, complement components, afamin precursor, spondin 1, plasminogen, hemopexin, and neuronal pentraxin receptor. Many other proteins were unique to our study, including calsyntenin 3, AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) 4 glutamate receptor, CD99 antigen, di- N-acetyl-chitobiase, and secreted phosphoprotein 1.
CONCLUSIONS:
We found much overlap in CSF protein changes between individuals with presymptomatic and symptomatic FAD and those with late-onset AD. Our results are consistent with inflammation and synaptic loss early in FAD and suggest new presymptomatic biomarkers of potential usefulness in drug development.
Identification of Interaction Site of Propeptide toward Mature Carboxypeptidase Y (mCPY) Based on the Similarity between Propeptide and CPY Inhibitor (I(C)).
Source
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University.
Abstract
Both the propeptide in the precursor carboxypeptidase Y (proCPY) and the mature CPY (mCPY)-specific endogenous inhibitor (I(C)) inhibit CPY activity. The N-terminal inhibitory reactive site of I(C) (the N-terminal seven amino acids of I(C)) binds to the substrate-binding site of mCPY and is essential for mCPY inhibition, but the mechanism of mCPY inhibition by the propeptide is poorly understood. In this study, sequence alignment between I(C) and proCPY indicated that a sequence similar to the N-terminal region of I(C) was present in proCPY. In particular, a region including the C-terminus of the propeptide was similar to the N-terminal seven amino acids of I(C). In the presence of peptides identical to the N-terminus of I(C) and the C-terminus of the propeptide, CPY activity was competitively inhibited. The C-terminal region of the propeptide might bind to the substrate-binding site of mCPY.
Ordered and disordered proteins as nanomaterial building blocks.
Source
Department of Bioengineering, University of California, Berkeley, CA, USA.
Abstract
Proteins possess a number of attractive properties that have contributed to their recent emergence as nanoscale building blocks for biomaterials and bioinspired materials. For instance, the amino acid sequence of a protein can be precisely controlled and manipulated via recombinant DNA technology, and proteins can be biosynthesized with very high purity and virtually perfect monodispersity. Most importantly, protein-based biomaterials offer the possibility of technologically harnessing the vast array of functions that these biopolymers serve in nature. In this review, we discuss recent progress in the field of protein-based biomaterials, with an overall theme of relating protein structure to material properties. We begin by discussing materials based on proteins that have well-defined three-dimensional structures, focusing specifically on elastin- and silk-like peptides. We then explore the newer field of materials based on intrinsically disordered proteins, using nucleoporin and neurofilament proteins as case studies. A key theme throughout the review is that specific environmental stimuli can trigger protein conformational changes, which in turn can alter macroscopic material properties and function. WIREs Nanomed Nanobiotechnol 2012 doi: 10.1002/wnan.1160 For further resources related to this article, please visit the WIREs website.
Copyright © 2012 Wiley Periodicals, Inc.
Evidence for Two Putative Holin-Like Peptides Encoding Genes of Bacillus pumilus Strain WAPB4.
Source
Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Rangsit Campus, Klonglaung, Pathumthai, 12121, Thailand, Aunpad@yahoo.com.
Abstract
An open reading frame encoding a 71-amino acid BhlA bacteriocin-related holin-like peptide was present upstream of 86-amino acid holin-like peptide, xhlB, encoding gene in the genome of Bacillus pumilus strain WAPB4. Analysis of BhlA using TMHMM server suggested one putative transmembrane domain at the N-terminal part and a number of highly charged amino acid residues at the C-terminal part. XhlB of B. pumilus strain WAPB4 composed of two putative transmembrane domains separated by a β-turn, and numerous charged residues in the C-terminus. The dual start motifs were found in both BhlA and XhlB. Structural analysis of their sequence revealed features characteristic for holin. To analyze the effect of BhlA on bacteria cell, its ORF was cloned and expressed in Escherichia coli BL21(DE3). Expression of holin-like peptide, BhlA, was found to be toxic to the host cell. The site of action of BhlA is on the cell membrane and caused bacterial death by cell membrane disruption as clearly demonstrated by transmission electron microscopy or TEM.
S4(13)-PV cell-penetrating peptide induces physical and morphological changes in membrane-mimetic lipid systems and cell membranes: Implications for cell internalization.
Source
Centre for Neurosciences and Cell Biology, University of Coimbra, Portugal.
Abstract
The present work aims to gain insights into the role of peptide-lipid interactions in the mechanisms of cellular internalization and endosomal escape of the S4(13)-PV cell-penetrating peptide, which has been successfully used in our laboratory as a nucleic acid delivery system. A S4(13)-PV analogue, S4(13)-PVscr, displaying a scrambled aminoacid sequence, deficient cell internalization and drug delivery inability, was used in this study for comparative purposes. DSC, fluorescence polarization and SAXS/WAXS techniques showed that both peptides interacted with anionic membranes composed of phosphatidylglycerol or a mixture of this lipid with phosphatidylethanolamine, increasing the lipid order, shifting the phase transition to higher temperatures and raising the correlation length between the bilayers. However, S4(13)-PVscr, in contrast to the wild-type peptide, did not promote lipid domain segregation and induced the formation of an inverted hexagonal lipid phase instead of a cubic phase in the lipid systems assayed. Electron microscopy showed that, as opposed to S4(13)-PVscr, the wild-type peptide induced the formation of a non-lamellar organization in membranes of HeLa cells. We concluded that lateral phase separation and destabilization of membrane lamellar structure without compromising membrane integrity are on the basis of the lipid-driven and receptor-independent mechanism of cell entry of S4(13)-PV peptide. Overall, our results can contribute to a better understanding of the role of peptide-lipid interactions in the mechanisms of CPP membrane translocation, helping in the future design of more efficient CPP-based drug delivery systems.
Copyright © 2011. Published by Elsevier B.V.
Comparison of the Effects of Human β-defensin 3, Vancomycin, and Clindamycin on Staphylococcus aureus Biofilm Formation.
Abstract
Despite improvements in surgical techniques and implant design in orthopedic surgery, implantation-associated infections are still a challenging problem for surgeons. In 2006, trace quantities of human β-defensin 3 (hBD-3) were found in human bone tissue and bone cells. Human β-defensin 3 is a 45-amino-acid peptide that is considered the most promising class of defensin antimicrobial peptides and may help in the prevention and treatment of implantation-associated infections. Studies of the effectiveness of hBD-3 against Staphylococcus aureus showed that hBD-3 was more potent at low concentrations than other antibiotics. The effect of hBD-3 on S aureus biofilms has not been reported. We studied the effect of hBD-3, vancomycin, and clindamycin on S aureus biofilms and on the survival of the bacteria in the biofilms.Staphylococcus aureus biofilms were examined with confocal scanning laser microscopy. Staining with LIVE/DEAD BacLight viability stain (Molecular Probes Europe BV, Leiden, The Netherlands) differentiated between live and dead bacteria within the biofilms, and extracellular polymeric substances (slime) from the biofilms was evaluated after staining with calcofluor white (Sigma Chemical Company, Rocky Hill, New Jersey). Human β-defensin 3 and clindamycin reduced the S aureus biofilm area. Human β-defensin 3 was significantly more effective against bacteria from the S aureus biofilms than was clindamycin. Vancomycin did not reduce the S aureus biofilm area.
Copyright 2012, SLACK Incorporated.
- PMID:
- 22229614
- [PubMed - in process]
Cis-trans peptide variations in structurally similar proteins.
Source
INSERM UMR-S 665, Dynamique des Structures et Interactions des Macromolécules Biologiques (DSIMB), Université Denis Diderot-Paris 7, INTS, 6, rue Alexandre Cabanel, 75739, Paris Cedex 15, France.
Abstract
The presence of energetically less favourable cis peptides in protein structures has been observed to be strongly associated with its structural integrity and function. Inter-conversion between the cis and trans conformations also has an important role in the folding process. In this study, we analyse the extent of conservation of cis peptides among similar folds. We look at both the amino acid preferences and local structural changes associated with such variations. Nearly 34% of the Xaa-Proline cis bonds are not conserved in structural relatives; Proline also has a high tendency to get replaced by another amino acid in the trans conformer. At both positions bounding the peptide bond, Glycine has a higher tendency to lose the cis conformation. The cis conformation of more than 30% of β turns of type VIb and IV are not found to be conserved in similar structures. A different view using Protein Block-based description of backbone conformation, suggests that many of the local conformational changes are highly different from the general local structural variations observed among structurally similar proteins. Changes between cis and trans conformations are found to be associated with the evolution of new functions facilitated by local structural changes. This is most frequent in enzymes where new catalytic activity emerges with local changes in the active site. Cis-trans changes are also seen to facilitate inter-domain and inter-protein interactions. As in the case of folding, cis-trans conversions have been used as an important driving factor in evolution.
Structure and function of OprD protein in Pseudomonas aeruginosa: From antibiotic resistance to novel therapies.
Source
Division of Respiratory Medicine, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong 510080, China.
Abstract
Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen isolated from patients with nosocomial infections. Due to its intrinsic and acquired antimicrobial resistance, limited classes of antibiotics can be used for the treatment of infection with P. aeruginosa. Of these, the carbapenems are very important; however, the occurrence of carbapenem-resistant strains is gradually increasing over time. Deficiency of the outer membrane protein OprD confers P. aeruginosa a basal level of resistance to carbapenems, especially to imipenem. Functional studies have revealed that loops 2 and 3 in the OprD protein contain the entrance and/or binding sites for imipenem. Therefore, any mutation in loop 2 and/or loop 3 that causes conformational changes could result in carbapenem resistance. OprD is also a common channel for someamino acids and peptides, and competition with carbapenems through the channel may also occur. Furthermore, OprD is a highly regulated protein at transcriptional and post-transcriptional levels by some metals, small bioactive molecules,amino acids, and efflux pump regulators. Because of its hypermutability and highly regulated properties, OprD is thought to be the most prevalent mechanism for carbapenem resistance in P. aeruginosa. Developing new strategies to combat infection with carbapenem-resistant P. aeruginosa lacking OprD is an ongoing challenge.
Copyright © 2011 Elsevier GmbH. All rights reserved.
Copper(II)-Binding Ability of Stereoisomeric cis- and trans-2-Aminocyclohexanecarboxylic Acid-l-Phenylalanine Dipeptides. A Combined CW/Pulsed EPR and DFT Study.
Source
Institute of Structural Chemistry, Chemical Research Center of the Hungarian Academy of Sciences , Pusztaszeri út 59-67, H-1025 Budapest, Hungary.
Abstract
With the aim of an improved understanding of the metal-complexation properties of alicyclic β-amino acid stereoisomers, and their peptides, the complex equilibria and modes of coordination with copper(II) of l-phenylalanine (F) derivatives of cis/trans-2-aminocyclohexanecarboxylic acid (c/tACHC), i.e. the dipeptides F-c/tACHC and c/tACHC-F, were investigated by a combination of CW and pulsed EPR methods. For the interpretation of the experimental data, DFT quantum-chemical calculations were carried out. Simulation of a pH-dependent series of room-temperature CW-EPR spectra revealed the presence of EPR-active complexes ([Cu(aqua)](2+), [CuL](+), [CuLH(-1)], [CuLH(-2)](-), and [CuL(2)H(-1)](-)), and an EPR-inactive species ([Cu(2)L(2)H(-3)](-)) in aqueous solutions for all studied cases. [CuLH](2+) was included in the equilibrium model for the c/tACHC-F-copper(II) systems, and [CuL(2)], together with two coordination isomers of [CuL(2)H(-1)](-), were also identified in the F-tACHC-copper(II) system. Comparison of the complexation properties of the diastereomeric ligand pair F-(1S,2R)-ACHC and F-(1R,2S)-ACHC did not reveal significant differences. Considerably lower formation constants were obtained for the trans than for the cis isomers for both the F-c/tACHC and the c/tACHC-F pairs in the case of [CuLH(-1)] involving tridentate coordination by the amino, the deprotonated peptide, and the carboxylate groups. A detailed structural analysis by pulsed EPR methods and DFT calculations indicated that there was no significant destabilization for the complexes of the trans isomers. The lower stability of their complexes was explained by the limitation that only the conformer with donor groups in equatorial-equatorial ring positions can bind to copper(II), whereas both equatorial-axial conformers of the cis isomers are capable of binding. From a consideration of the proton couplings obtained with X-band (1)H HYSCORE, (2)H exchange experiments, and DFT, the thermodynamically most stable cyclohexane ring conformer was assigned for all four [CuLH(-1)] complexes. For the F-cACHC case, the conformer did not match the most stable conformer of the free ligand.
Fine-tuning the π-π Aromatic Interactions in Peptides: Somatostatin Analogues Containing Mesityl Alanine.
Source
Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac, 10, 08028 Barcelona (Spain).
Abstract
The π-π aromatic interactions between amino acids 6, 7, and 11 in the natural hormone somatostatin are crucial for conformational stability. In their Communication (DOI: 10.1002/anie.201106406), M. J. Macias, A. Riera, and co-workers describe that peptidic analogues obtained by replacing each phenylalanine with mesitylalanine are conformationally more rigid than the parent hormone. This strategy has yielded the first 3D structures of 14-amino-acid somatostatin analogues.
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