Structures of designed armadillo repeat proteins binding to peptides fused to globular domains

Designed armadillo repeat proteins (dArmRP) are α‐helical solenoid repeat proteins with an extended peptide binding groove that were engineered to develop a generic modular technology for peptide recognition. In this context, the term “peptide” not only denotes a short unstructured chain of amino acids, but also an unstructured region of a protein, as they occur in termini, loops, or linkers between folded domains. Here we report two crystal structures of dArmRPs, in complex with peptides fused either to the N‐terminus of Green Fluorescent Protein or to the C‐terminus of a phage lambda protein D. These structures demonstrate that dArmRPs bind unfolded peptides in the intended conformation also when they constitute unstructured parts of folded proteins, which greatly expands possible applications of the dArmRP technology. Nonetheless, the structures do not fully reflect the binding behavior in solution, that is, some binding sites remain unoccupied in the crystal and even unexpected peptide residues appear to be bound. We show how these differences can be explained by restrictions of the crystal lattice or the composition of the crystallization solution. This illustrates that crystal structures have to be interpreted with caution when protein–peptide interactions are characterized, and should always be correlated with measurements in solution.     

Isolation and structural characterization of recombinant human neu differentiation factor expressed in Escherichia coli

Recombinant human neu differentiation factor produced in engineered E. coli was isolated and subject to structural characterization. The recombinant molecule can be prepared to apparent purity and is active in stimulating receptor tyrosine autophosphorylation in cultural cells expressing HER2 receptor. The 229 amino-acid polypeptide consists of eight cysteines, of which two cysteines near the N-terminus are disulfide-bonded to form an immunoglobulin-like domain and the remaining six cysteines at the C-terminus cross-link to form an epidermal growth factor-like structure. Detailed chemical characterization of the recombinant molecule by peptide mapping in conjunction with Edman sequencing and mass spectrometry reveals that the bacterially produced recombinant neu differentiation factor preparation is properly folded and contains the correct disulfide structure. The peptide mapping procedure is also useful in identifying abnormal peptides derived from deamidation and oxidation of Asn and Met residues, respectively.     

Robust production of a peptide library using methodological synchronization

Peptide libraries have proven to be useful in applications such as substrate profiling, drug candidate screening and identifying protein–protein interaction partners. However, issues of fidelity, peptide length, and purity have been encountered when peptide libraries are chemically synthesized. Biochemically produced libraries, on the other hand, circumvent many of these issues due to the fidelity of the protein synthesis machinery. Using thioredoxin as an expression partner, a stably folded peptide scaffold (avian pancreatic polypeptide) and a compatible cleavage site for human rhinovirus 3C protease, we report a method that allows robust expression of a genetically encoded peptide library, which yields peptides of high purity. In addition, we report the use of methodological synchronization, an experimental design created for the production of a library, from initial cloning to peptide characterization, within a 5-week period of time. Total peptide yields ranged from 0.8% to 16%, which corresponds to 2–70 mg of pure peptide. Additionally, no correlation was observed between the ability to be expressed or overall yield of peptide-fusions and the intrinsic chemical characteristics of the peptides, indicating that this system can be used for a wide variety of peptide sequences with a range of chemical characteristics.     

Peptide and glycopeptide dendrimers. Part II

Recent progress in peptide and glycopeptide chemistry make the preparation of peptide and glycopeptide dendrimers of acceptable purity, with designed structural and immunochemical properties reliable. New methodologies using unprotected peptide building blocks have been developed to further increase the possibilities of their design and improve their preparation and separation. The sophisticated design of peptide and glycopeptide dendrimers has led to their use as antigens and immunogens, for serodiagnosis and other biochemical uses including drug delivery. Dendrimers bearing peptide with predetermined secondary structures are useful tools in protein de novo design. This article covers synthesis and applications of multiple antigen peptides (MAPs), multiple antigen glycopeptides (MAGs), multiple antigen peptides based on sequential oligopeptide carriers (MAP‐SOCs), glycodendrimers and template‐assembled synthetic proteins (TASPs). In part II the preparation of MAPs, and the utility of glycodendrimers and TASPs are discussed. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Peptide and glycopeptide dendrimers. Part I

Recent progress in peptide and glycopeptide chemistry make the preparation of peptide and glycopeptide dendrimers of acceptable purity, with designed structural and immunochemical properties reliable. New methodologies using unprotected peptide building blocks have been developed to further increase possibilities of their design and improve their preparation and separation. Sophisticated design of peptide and glycopeptide dendrimers has led to their use as antigens and immunogens, for serodiagnosis and other biochemical uses including drug delivery. Dendrimers bearing peptide with predetermined secondary structures are useful tools in protein de novo design. This article covers synthesis and applications of multiple antigen peptides (MAPs), multiple antigen glycopeptides (MAGs), multiple antigen peptides based on sequential oligopeptide carriers (MAP‐SOCs), glycodendrimers and template‐assembled synthetic proteins (TASPs). Part I deals with the development of various structural forms of MAPs as well as their application as antigens, immunogens, and for immunodiagnostic and biochemical purposes. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Chemical ligation and cleavage on solid support facilitate recombinant peptide purification

Recombinant peptide technology offers a promising means alternative to chemical synthesis and natural extraction of peptides. The bottleneck in the process of recombinant peptide production is the paucity of efficient purification protocols to eliminate heterogeneity of the desired preparation. Here, we introduce a combination strategy to facilitate purification of recombinant therapeutic peptide via native chemical ligation and chemical cleavage on a solid support. In this study, one promising therapeutic peptide called for type-2 diabetes, GLP-1(7-37), was prepared with high yield and purity without an expensive HPLC purification. Furthermore, this method is also useful for the preparation of isotopically labeled NMR peptide samples. Hopefully, this strategy combining chemical ligation with chemical cleavage on a solid support will ameliorate the production of important recombinant pharmaceutical peptides.     

Oxidative folding and preparation of α‐conotoxins for use in high‐throughput structure–activity relationship studies

α‐Conotoxins are peptide neurotoxins that selectively inhibit various subtypes of nicotinic acetylcholine receptors. They are important research tools for studying numerous pharmacological disorders, with profound potential for developing drug leads for treating pain, tobacco addiction, and other conditions. They are characterized by the presence of two disulfide bonds connected in a globular arrangement, which stabilizes a bioactive helical conformation. Despite extensive structure–activity relationship studies that have produced α‐conotoxin analogs with increased potency and selectivity towards specific nicotinic acetylcholine receptor subtypes, the efficient production of diversity‐oriented α‐conotoxin combinatorial libraries has been limited by inefficient folding and purification procedures. We have investigated the optimized conditions for the reliable folding of α‐conotoxins using simplified oxidation procedures for use in the accelerated production of synthetic combinatorial libraries of α‐conotoxins. To this end, the effect of co‐solvent, redox reagents, pH, and temperature on the proportion of disulfide bond isomers was determined for α‐conotoxins exhibiting commonly known Cys loop spacing frameworks. In addition, we have developed high‐throughput ‘semi‐purification’ methods for the quick and efficient parallel preparation of α‐conotoxin libraries for use in accelerated structure–activity relationship studies. Our simplified procedures represent an effective strategy for the preparation of large arrays of correctly folded α‐conotoxin analogs and permit the rapid identification of active hits directly from high‐throughput pharmacological screening assays. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

幽门螺杆菌Lpp20蛋白的生物信息学分析

目的：分析幽门螺杆菌Lpp20蛋白的主要化学和免疫学分子特征,为基因工程疫苗和诊断抗原的研究奠定基础。方法：根据Lpp20蛋白的氨基酸序列,应用生物信息学工具分析其蛋白序列,预测其信号肽、跨膜区、疏水性、二级结构、三级结构等性质。结果：Lpp20蛋白具有一段信号肽、脂蛋白信号肽酶切位点及脂盒模体,没有跨膜区,可能是一个外周膜蛋白;Lpp20蛋白的二级结构以α螺旋为主,其三级结构为一个致密的球状。结论：为基于幽门螺杆菌Lpp20蛋白的疫苗开发打下了基础。     

Lipid-destabilising properties of a peptide with structural plasticity

The Chameleon peptide (Cham) is a peptide designed from two regions of the GB1 protein, one folded as an alpha-helix and the other as a beta structure. Depending on the environment, the Cham peptide adopts an alpha or a beta conformation when inserted in different locations of GB1. This environment dependence is also observed for tilted peptides. These short protein fragments, able to destabilise organised system, are mainly folded in beta structure in water and in alpha helix in a hydrophobic environment, like the lipid bilayer. In this paper, we tested whether the Cham peptide can be qualified as a tilted peptide. For this, we have compared the properties of Cham peptide (hydrophobicity, destabilising properties, conformation) to those of tilted peptides. The results suggest that Cham is a tilted peptide. Our study, together the presence of tilted fragments in transconformational proteins, suggests a relationship between tilted peptides and structural lability.     

Structure‐antigenicity of the V3 region of SIVmac envelope glycoprotein

The objective of this study was to analyze the immunogenicity and antigenicity of the V3 domain (Cys313–Cys346) of the external envelope glycoprotein gp125 of SIVmac251. The corresponding peptide was synthesized and characterized as linear and cyclic peptides. Our results showed that this region, as for HIV‐1, contained an immunodominant epitope. The antigenicity was similar for the linear and cyclic peptides when tested against a panel of 15 sera from SIV infected macaques. Similarly, both peptide structures presented similar immunogenicity as shown by the characterization of the anti‐peptide antibodies produced in rabbits against the cyclic and linear forms. But, unexpectedly, the antibodies produced against linear peptides recognized with a relatively higher intensity the native envelope gp140 than those produced against the cyclic structure. Furthermore, we showed that these antibodies recognized better the deglycosylated form of the glycoprotein. But, in contrast to the neutralizing activity obtained with anti‐V3 peptides from HIV‐1, no antiviral activity was obtained with antibodies generated against linear or cyclic SIVmac V3 peptides. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

DNA display of biologically active proteins for in vitro protein selection

In vitro display technologies are powerful tools for screening peptides with desired functions. We previously proposed a DNA display system in which streptavidin-fused peptides are linked with their encoding DNAs via biotin labels in emulsion compartments and successfully applied it to the screening of random peptide libraries. Here we describe its application to functional and folded proteins. By introducing peptide linkers between streptavidin and fused proteins, we achieved highly efficient (>95%) formation of DNA-protein conjugates. Furthermore, we successfully enriched a glutathione-S-transferase gene by a factor of 20-30-fold per round on glutathione-coupled beads. Thus, DNA display should be useful for rapidly screening or evolving proteins based on affinity selection.     

Basis of substrate binding by the chaperonin GroEL.

The molecular chaperonins are essential proteins involved in protein folding, complex assembly, and polypeptide translocation. While there is abundant structural information about the machinery and the mechanistic details of its action are well studied, it is yet unresolved how chaperonins recognize a large number of structurally unrelated polypeptides in their unfolded or partially folded forms. To determine the nature of chaperonin-substrate recognition, we have characterized by NMR methods the interactions of GroEL with synthetic peptides that mimic segments of unfolded proteins. In previous work, we found using transferred nuclear Overhauser effect (trNOE) analysis that two 13 amino acid peptides bound GroEL in an amphipathic alpha-helical conformation. By extending the study to a variety of peptides with differing sequence motifs, we have observed that peptides can adopt conformations other than alpha-helix when bound to GroEL. Furthermore, peptides of the same composition exhibited significantly different affinities for GroEL as manifested by the magnitude of trNOEs. Binding to GroEL correlates well with the ability of the peptide to cluster hydrophobic residues on one face of the peptide, as determined by the retention time on reversed-phase (RP) HPLC. We conclude that the molecular basis of GroEL-substrate recognition is the presentation of a hydrophobic surface by an incompletely folded polypeptide and that many backbone conformations can be accommodated.     

Analysis of Hormone–Receptor Interaction Sites Using Synthetic Peptides: Receptor Binding Regions of the α-Subunit of Human Choriogonadotropin

Synthetic peptides are valuable tools for determining sites of interaction between hormones and their receptors. We have learned much about linear receptor binding regions of the glycoprotein hormone human choriogonadotropin (hCG) using synthetic peptides corresponding to its primary sequence. Of paramount importance in any study using synthetic peptides as a tool to investigate protein structure are an efficient means of peptide purification and a definitive measure of peptide purity and composition. Purification is easily achieved for all but the most hydrophobic peptides using preparative reverse-phase HPLC. Of the methods available for analysis of peptide purity, mass spectrometry is perhaps the most useful and often most rapid approach. Other essential components of studies involving synthetic peptides and hormone binding are reproducible hormone labeling, receptor preparations, and bioassays. The ability of peptides to compete with hCG for binding to specific receptors is tested in radioreceptor binding assays and bioassays with transformed Leydig cell lines. These cells express the lutropin receptor that is coupled to a measurable endpoint such as cAMP or steroid production. The conditions for these assays are optimized for rapid and accurate measurement of peptide activity. Since the three-dimensional structure of hCG is not known, a systematic approach to the identification of potential receptor binding sites is advocated. First, a comprehensive analysis using synthetic overlapping peptides of uniform length that span the entire sequence of the α-subunit is employed. This approach is an effective means for surveying the entire subunit for receptor binding sites. Next, the boundaries of the active regions are delimited by a series of nested peptides sequentially shortened in length. The importance of each residue within the delimited binding regions is then studied using a series of peptides containing single alanine substitutions. Finally, modifications to enhance activity of the synthetic peptides are further made on the basis of data from alanine substitution studies, circular dichroic analysis, and molecular modeling. These studies provide valuable information to aid in the design of synthetic hormone analogs and for further analysis of the structure–function of hCG via site-directed mutagenesis.     

Metal ion complexation and folding of linear peptides

A Linear peptide, GASYQDLG was synthesised and used as a model to evaluate the effects of nickel additions to increase the conformational stability. The NMR data obtained for the peptide and its histidyl derivative (H)(3)GASYQDLG(H)(3) suggest that in solution folded structures are present only for the H-tagged peptide-Ni(II) ion system. These results suggest that metal ions and additions of a double histidine tags of suitable length can be used as efficient tools to reduce peptide flexibility without other internal modifications. Synthesis of H-tagged analogs could offer a promising strategy for large-scale preparation of diagnostic tools and, in general, whenever more rigid molecular structures should be advisable.     

Synthesis,biological activity and conformational analysis of head‐to‐tail cyclic analogues of LL37 and histatin 5

LL37 and histatin 5 are antimicrobial peptides. LL37 exhibits killing activity against a broad spectrum of pathogens, whereas histatin 5 is primarily an antifungal agent. Head‐to‐tail cyclization of histatin 5 did not affect its antimicrobial and haemolytic activity. The cyclic LL37 exhibits identical antifungal and haemolytic activity as does LL37. Its antimicrobial activity varied in one dilution depending on the kind of bacteria. The structure of cyclic peptides was studied by circular dichroism spectroscopy. Both peptides undergo a conformational change leading to stabilisation of their α‐helical structure in the presence of negatively charged sodium dodecyl sulfate micelles. However, with cyclic histatin 5, the presence of Zn²⁺ ions is also necessary to fuse the peptide to the micelle. The specific action of the Zn²⁺ ions is attributed to the presence of a zinc‐binding motif, His‐Glu‐X‐X‐His. It has been speculated that this zinc complexing may be related to the well‐established anticandidal activity. In the case of cyclic LL37, also the presence of a zwitterionic dodecylphosphocholine micelle induces formation of the helical structure. A microwave‐assisted procedure for the cleavage of a peptide from the 2‐chlorotrityl chloride resin was, for the first time, successfully used to obtain protected peptide fragments that can be applied to the preparation of head‐to‐tail cyclopeptides or to condensation of peptidic fragments. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Synthetic peptides derived from the sequence of a lasso peptide microcin J25 show antibacterial activity

Microcin J25 (MccJ25) is a plasmid-encoded, ribosomally synthesized antibacterial peptide with a unique lasso structure. The lasso structure, produced with the aid of two processing enzymes, provides exceptional stability to MccJ25. We report the synthesis of six peptides (1-6), derived from the MccJ25 sequence, that are designed to form folded conformation by disulfide bond formation and electrostatic or hydrophobic interactions. Two peptides (1 and 6) display good activity against Salmonella newport, and are the first synthetic derivatives of MccJ25 that are bactericidal. Peptide 1 displays potent activity against several Salmonella strains including two MccJ25 resistant strains. The solution conformation and the stability studies of the active peptides suggest that they do not fold into a lasso conformation and peptide 1 displays antimicrobial activity by inhibition of target cell respiration. Like MccJ25, the synthetic MccJ25 derivatives display minimal toxicity to mammalian cells suggesting that these peptides act specifically on bacterial cells.     

C-terminal truncation of Vascular Endothelial Growth Factor mimetic helical peptide preserves structural and receptor binding properties

Vascular Endothelial Growth Factor mimetic peptides have interesting applications in therapeutic angiogenesis. Recently, we described the proangiogenic properties of a 15 mer peptide designed on the N-terminal helix 17-25 of VEGF. The peptide was stabilized introducing well known peptide chemical tools among which N- and C-terminal capping sequence. Here, we show that the C-terminal sequence does not affect the structural and biological properties of the full-length peptide. In fact, a C-terminal truncated analog peptide resulted in a well folded and stable helix retaining the ability to bind to VEGF receptors. This study will allow to develop smaller peptidomimetic analogs able to modulate the VEGF-dependent angiogenesis.     

Conformational exchange on the microsecond time scale in alpha-helix and beta-hairpin peptides measured by 13C NMR transverse relaxation

13C-NMR relaxation experiments (T(1), T(2), T(1)(rho), and NOE) were performed on selectively enriched residues in two peptides, one hydrophobic staple alpha-helix-forming peptide GFSKAELAKARAAKRGGY and one beta-hairpin-forming peptide RGITVNGKTYGR, in water and in water/trifluoroethanol (TFE). Exchange contributions, R(ex), to spin-spin relaxation rates for (13)C(alpha) and (13)C(beta) groups were derived and were ascribed to be mainly due to peptide folding-unfolding. To evaluate the exchange time, tau(ex), from R(ex), the chemical shift difference between folded and unfolded states, Deltadelta, and the populations of these states, p(i), were determined from the temperature dependence of (13)C chemical shifts. For both peptides, values for tau(ex) fell in the 1 micros to 10 micros range. Under conditions where the peptides are most folded (water/TFE, 5 degrees C), tau(ex) values for all residues in each respective peptide were essentially the same, supporting the presence of a global folding-unfolding exchange process. Rounded-up average tau(ex) values were 4 micros for the helix peptide and 9 micros for the hairpin peptide. This 2-3-fold difference in exchange times between helix and hairpin peptides is consistent with that observed for folding-unfolding of other small peptides.