Library-derived Peptide Research Articles

A library-derived peptide inhibitor of the BZLF1 transcription factor.

Transcription factor dysregulation is associated with many diseases, including cancer. Peptide-based molecules are increasingly recognised as important modulators of difficult intracellular protein-protein interaction targets, with peptide library screening consequently proven to be a viable strategy in developing inhibitors against a wide range of transcription factors (TFs). However, current strategies simply select the highest affinity of binding to a target TF rather than the ability to inhibit TF function. Here, we utilise our Transcription Block Survival (TBS) screening platform to enable high-throughput identification of peptides that inhibit TFs from binding to cognate DNA sites, hence inhibiting functionality. In this study, we explore whether the TBS can be expanded to derive a potent and functional peptide inhibitor of the BZLF1 transcription factor. The library-derived peptide, AcidicW, is shown to form a more stable dimer with BZLF1 than the BZLF1 homodimer, with a thermal denaturation temperature exceeding 80°C. AcidicW can also functionally inhibit the BZLF1:TRE DNA interaction with high potency and an IC50 of 612 nM.

Library-Derived Peptide Aggregation Modulators of Parkinson's Disease Early-Onset α-Synuclein Variants.

Parkinson’s Disease (PD) is characterized by the accumulation of Lewy bodies in dopaminergic neurons. The main protein component of Lewy bodies, α-synuclein (αS), is also firmly linked to PD through the identification of a number of single point mutations that are autosomal dominant for early-onset disease. Consequently, the misfolding and subsequent aggregation of αS is thought to be a key stage in the development and progression of PD. Therefore, modulating the aggregation pathway of αS is an attractive therapeutic target. Owing to the fact that all but one of the familial mutations is located in the preNAC 45–54 region of αS, we previously designed a semi-rational library using this sequence as a design scaffold. The 45–54 peptide library was screened using a protein-fragment complementation assay approach, leading to the identification of the 4554W peptide. The peptide was subsequently found to be effective in inhibiting primary nucleation of αS, the earliest stage of the aggregation pathway. Here, we build upon this previous work by screening the same 45–54 library against five of the known αS single-point mutants that are associated with early-onset PD (A30P, E46K, H50Q, G51D, and A53T). These point mutations lead to a rapid acceleration of PD pathology by altering either the rate or type of aggregates formed. All ultimately lead to earlier disease onset and were therefore used to enforce increased assay stringency during the library screening process. The ultimate aim was to identify a peptide that is effective against not only the familial αS variant from which it has been selected but that is also effective against WT αS. Screening resulted in five peptides that shared common residues at some positions, while deviating at others. All reduced aggregation of the respective target, with several also identified to be effective at reducing aggregation when incubated with other variants. In addition, our results demonstrate that a previously optimized peptide, 4554W(N6A), is highly effective against not only WT αS but also several of the single-point mutant forms and hence is a suitable baseline for further work toward a PD therapeutic.

A Downsized and Optimised Intracellular Library-Derived Peptide Prevents Alpha-Synuclein Primary Nucleation and Toxicity Without Impacting Upon Lipid Binding

Misfolding and aggregation of alpha-synuclein (αS) within dopaminergic neurons is a key factor in the development and progression of a group of age-related neurodegenerative diseases, termed synucleinopathies, that include Parkinson’s disease (PD). We previously derived a peptide inhibitor from a 209,952-member intracellular library screen by employing the preNAC region (45–54) as a design template. At least six single-point mutations firmly linked to early-onset Parkinson’s disease (E46K, H50Q, G51D, A53T/E/V) are located within this region, strongly implicating a pathogenic role within αS that leads to increased cytotoxicity. A library-derived ten residue peptide, 4554W, was consequently shown to block αS aggregation at the point of primary nucleation via lipid induction, inhibiting its conversion into downstream cytotoxic species. Here we couple truncation with a full alanine scan analysis, to establish the effect upon the αS aggregation pathway relative to 4554W. This revealed the precise residues responsible for eliciting inhibitory interaction and function, as well as those potentially amenable to modification or functionalisation. We find that modification N6A combined with N-terminal truncation results in a peptide of significantly increased efficacy. Importantly, our data demonstrate that the peptide does not directly disrupt αS lipid-binding, a desirable trait since antagonists of αS aggregation and toxicity should not impede association with small synaptic neurotransmitter vesicles, and thus not disrupt dopaminergic vesicle fusion and recycling. This work paves the way toward the major aim of deriving a highly potent peptide antagonist of αS pathogenicity without impacting on native αS function.

Distinctive Conformation of Minor Site‐Specific Nuclear Localization Signals Bound to Importin‐α

Nuclear localization signals (NLSs) contain one or two clusters of basic residues and are recognized by the import receptor importin-α. There are two NLS-binding sites (major and minor) on importin-α and the major NLS-binding site is considered to be the primary binding site. Here, we used crystallographic and biochemical methods to investigate the binding between importin-α and predicted 'minor site-specific' NLSs: four peptide library-derived peptides, and the NLS from mouse RNA helicase II/Guα. The crystal structures reveal that these atypical NLSs indeed preferentially bind to the minor NLS-binding site. Unlike previously characterized NLSs, the C-terminal residues of these NLSs form an α-helical turn, stabilized by internal H-bond and cation-π interactions between the aromatic residues from the NLSs and the positively charged residues from importin-α. This helical turn sterically hinders binding at the major NLS-binding site, explaining the minor-site preference. Our data suggest the sequence RXXKR[K/X][F/Y/W]XXAF as the optimal minor NLS-binding site-specific motif, which may help identify novel proteins with atypical NLSs.

Isothermal Titration Calorimetry Reveals Differential Binding Thermodynamics of Variable Region-identical Antibodies Differing in Constant Region for a Univalent Ligand

The classical view of immunoglobulin molecules posits two functional domains defined by the variable (V) and constant (C) regions, which are responsible for antigen binding and antibody effector functions, respectively. These two domains are thought to function independently. However, several lines of evidence strongly suggest that C region domains can affect the specificity and affinity of an antibody for its antigen (Ag), independent of avidity-type effects. In this study, we used isothermal titration calorimetry to investigate the thermodynamic properties of the interactions of four V region-identical monoclonal antibodies with a univalent peptide antigen. Comparison of the binding of IgG1, IgG2a, IgG2b, and IgG3 with a 12-mer peptide mimetic of Cryptococcus neoformans polysaccharide revealed a stoichiometry of 1.9-2.0 with significant differences in thermodynamic binding parameters. Binding of this peptide to the antibodies was dominated by favorable entropy. The interaction of these antibodies with biotinylated peptides manifested greater enthalpy than for native peptides indicating that biotin labeling affected the types of Ag-Ab complexes formed. Our results provide unambiguous thermodynamic evidence for the notion that the C region can affect the interaction of the V region with an Ag.

Structural Analysis of Immunotherapeutic Peptides for Autoimmune Myasthenia Gravis,

Myasthenia gravis (MG) and its animal model, experimental MG (EAMG), are autoimmune disorders in which major pathogenic antibodies are directed against the main immunogenic region (MIR) of the nicotinic acetylcholine receptor (nAChR). In an earlier attempt to develop peptide mimotopes capable of preventing the anti-MIR-mediated pathogenicity, the peptide Pep.1 was initially identified from phage display, and subsequently, Cyclic extended Pep.1 (Cyc.ext.Pep.1), which incorporates eight additional residues into the Pep.1 sequence and has an affinity for the anti-MIR antibody mAb198 3 orders of magnitude greater than that of Pep.1, was developed. In an animal model, Pep.1 shows no ability to inhibit mAb198-induced EAMG, whereas Cyc.ext.Pep.1 successfully blocks anti-MIR antibody 198 (mAb198)-induced EAMG. Our aim in this study was to identify the structural characteristics related to the different affinities for mAb198 of Pep.1 and Cyc.ext.Pep.1 using NMR spectroscopy and alanine scanning analysis. The NMR structural analysis revealed that Pep.1 is very flexible in solution, whereas Cyc.ext.Pep.1 is highly rigid within a region containing several turn structures. Interestingly, TRNOE experiments revealed that mAb198-bound Pep.1, particularly in the region between Asn7 and Glu11, shows significant structural similarity to the region between Asn10 and Glu14 of Cyc.ext.Pep.1, which is critical for interaction with mAb198. We therefore conclude the higher affinity of Cyc.ext.Pep.1 for mAb198 reflects the fact that incorporation of additional residues producing a single disulfide bond endows Pep.1 with a conformational rigidity that mimics the structure of mAb198-bound Pep.1. Furthermore, our results suggest that cyclic extended peptides could be utilized generally as useful tools to optimize the affinity of phage library-derived peptide antigens.

Cyclic peptide interleukin 5 antagonists mimic CD turn recognition epitope for receptor alpha.

The cyclic peptide AF17121 (Ac-VDECWRIIASHTWFCAEE) that inhibits interleukin 5 (IL-5) function and IL-5 receptor alpha-chain (IL-5Ralpha) binding has been derived from recombinant random peptide library screening and follow-up synthetic variation. To better understand the structural basis of its antagonist activity, AF17121 and a series of analogs of the parent peptide were prepared by solid phase peptide synthesis. Sequence variation was focused on the charged residues Asp(2), Glu(3), Arg(6), Glu(17), and Glu(18). Two of those residues, Glu(3) and Arg(6), form an EXXR motif that was found to be common among library-derived IL-5 antagonists. The E and R in the EXXR motif have a proximity similar to charged residues in a previously identified receptor alpha binding region, the beta-strand between the C- and D-helices of human IL-5. Optical biosensor interaction kinetics and cell proliferation assays were used to evaluate the antagonist activities of the purified synthetic peptides, by measuring competition with the highly active single chain IL-5. Analogs in which acidic residues (Asp(2), Glu(3), Glu(17), and Glu(18)) were replaced individually by Ala retained substantial competition activity, with multiple replacements in these residues leading to fractional loss of potency at most. In contrast, R6A analogs had strongly reduced competition activity. The results reveal that the arginine residue is crucial for the IL-5Ralpha binding of AF17121, while the acidic residues are not essential though likely complex-stabilizing particularly in the Asp(2)-Glu(3) region. By CD, AF17121 exhibited mostly disordered structure with evidence for a small beta-sheet content, and replacement of the arginine had no influence on the observed secondary structure of the peptides. The dominance of Arg(6) in AF17121 activity corresponds to previous findings of dominance of the positive charge balance in the antiparallel beta-sheet of IL-5 composed of (88)EERRR(92) in one strand of the CD turn region of IL-5 and with Arg(32) in the neighboring beta-strand. These results argue that AF17121 and related library-derived peptides function by mimicking the CD turn receptor alpha recognition epitope in IL-5 and open the way to small molecule antagonist design.

Potent Grb2-SH2 domain antagonists not relying on phosphotyrosine mimics.

Development of Grb2-SH2 domain antagonists is an effective approach to inhibit the growth of malignant cells by modulating Grb2-related Ras signaling. We report here potent Grb2-SH2 domain antagonists that do not rely on phosphotyrosine or its mimics. These non-phosphorylated antagonists were developed and further modified by constraining the backbone conformation and optimizing amino acid side chains of a phage library-derived peptide, G1TE. After extensive SAR studies and structural optimization, non-phosphorylated peptide 12 was discovered with an IC(50) of 75 nM. This potent peptidomimetic provides a novel template for the development of non-pTyr containing Grb2-SH2 domain antagonists and acts as a chemotherapeutic lead for the treatment of erbB2-related cancer.

Rapid sequencing of library-derived peptides by partial edman degradation and mass spectrometry.

ADVERTISEMENT RETURN TO ISSUEPREVReportNEXTRapid Sequencing of Library-Derived Peptides by Partial Edman Degradation and Mass SpectrometryPeng Wang, Gulnur Arabaci, and Dehua PeiView Author Information Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210 Cite this: J. Comb. Chem. 2001, 3, 3, 251–254Publication Date (Web):March 30, 2001Publication History Received28 November 2000Published online30 March 2001Published inissue 1 May 2001https://doi.org/10.1021/cc000102lCopyright © 2001 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views457Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (44 KB) Supporting Info (1)»Supporting Information Supporting Information SUBJECTS:Crystal cleavage,Degradation,Mass spectrometry,Monomers,Peptides and proteins Get e-Alerts

Solution NMR Structure of the Complex of Alpha-Bungarotoxin with a Library-Derived Peptide (NMR, Average Structure)

Solution NMR Structure of the Complex of Alpha-Bungarotoxin with a Library-Derived Peptide (NMR, Average Structure)

Three-dimensional solution structure of the complex of alpha-bungarotoxin with a library-derived peptide.

The solution structure of the complex between alpha-bungarotoxin (alpha-BTX) and a 13-residue library-derived peptide (MRYYESSLKSYPD) has been solved using two-dimensional proton-NMR spectroscopy. The bound peptide adopts an almost-globular conformation resulting from three turns that surround a hydrophobic core formed by Tyr-11 of the peptide. The peptide fills an alpha-BTX pocket made of residues located at fingers I and II, as well as at the C-terminal region. Of the peptide residues, the largest contact area is formed by Tyr-3 and Tyr-4. These findings are in accord with the previous data in which it had been shown that substitution of these aromatic residues by aliphatic amino acids leads to loss of binding of the modified peptide with alpha-BTX. Glu-5 and Leu-8, which also remarkably contribute to the contact area with the toxin, are present in all the library-derived peptides that bind strongly to alpha-BTX. The structure of the complex may explain the fact that the library-derived peptide binds alpha-BTX with a 15-fold higher affinity than that shown by the acetylcholine receptor peptide (alpha185-196). Although both peptides bind to similar sites on alpha-BTX, the latter adopts an extended conformation when bound to the toxin [Basus, V., Song, G. & Hawrot, E. (1993) Biochemistry 32, 12290-12298], whereas the library peptide is nearly globular and occupies a larger surface area of alpha-BTX binding site.

The alpha-bungarotoxin binding site on the nicotinic acetylcholine receptor: analysis using a phage-epitope library.

The nicotinic acetylcholine receptor (AcChoR) is a ligand-gated ion channel that is activated upon binding of acetylcholine. alpha-Neurotoxins, in particular alpha-bungarotoxin (alpha-BTX), bind specifically and with high affinity to the AcChoR and compete with binding of the natural ligand. We employed a 15-mer phage-display peptide library to select epitopes reacting with alpha-BTX. Phages bearing the motif YYXSSL as a consensus sequence were found to bind with high affinity to alpha-BTX. The library-derived peptide (MRYYESSLKSYPD) bears amino acid sequence similarities to a region of the alpha-subunit of the Torpedo muscle AcChoR, as well as of other muscle and neuronal AcChoRs that bind alpha-BTX. The library-derived peptide and the corresponding peptides containing residues 187-199 of the Torpedo AcChoR alpha-subunit (WVYYTCCPDTPYL), as well as peptides analogous to the above region in the neuronal AcChoR (e.g., human alpha7; ERFYECCKEPYPD) that binds alpha-BTX, inhibit the binding of alpha-BTX to the intact Torpedo AcChoR with IC50 values of 10(-6) M. A synthetic peptide from a neuronal AcChoR that does not bind alpha-BTX (e.g., human alpha2; ERKYECCKEPYPD) which differs by just one amino acid from the homologous peptide from the alpha-BTX-binding protein (alpha7)-i.e., Lys in alpha2 and Tyr in alpha7-does not inhibit the binding of alpha-BTX to Torpedo AcChoR. These results indicate the requirement for two adjacent aromatic amino acid residues for binding to alpha-BTX.