Turn Of Helix Research Articles

Reconfigurable Multi-Turns Planar Plasma Helical Antenna

A reconfigurable wideband circularly polarized plasma helical antenna is designed for wireless applications in the frequency band from 6 to 12 GHz. The proposed antenna structure is suitable to be integrated with electronic circuits for different applications. An optimization for different parameters of the antenna for wideband end-fire radiation characteristics is investigated. The antenna has matching impedance bandwidth of 48% with maximum gain of 8.5 dBi and wideband circular polarization of 31%. The antenna gain and bandwidth for different numbers of helix turns are increased with varying the plasma frequency. An improvement in the antenna gain and radiation efficiency is achieved via loading the antenna with dielectric lenses of different shapes. The end-fire directional gain is improved to 11.5 dBi for hemispherical lens and 10.5 dBi for quarter spherical lens with HPBW of 40°.

Molecular modeling and computational study of the chiral-dependent structures and properties of self-assembling diphenylalanine peptide nanotubes.

The structure and properties of diphenylalanine (FF) peptide nanotubes (PNT) based on phenylalanine were investigated by various molecular modeling methods. The main approach employed semi-empirical quantum-chemical methods (PM3 and AM1). Ab initio, density functional theory methods and molecular mechanical approaches were also used. Both model structures and structures extracted from experimental crystallographic databases obtained by X-ray methods were examined. A comparison of optimized model structures and structures obtained by natural self-assembly revealed important differences depending on chirality: D and L. In both the cases, the effect of chirality on the results of self-assembly of FF PNT was established: PNT based on the D-FF has large condensation energy E0 in the transverse direction, and form thicker and shorter PNT bundles than those based on L-FF. A topological difference was established: model PNT were optimized into structures consisting of rings, while naturally self-assembled PNT consisted of helical turns. The latter nanotubes differed from the original L-FF and D-FF and formed helix structures of different chirality signs in accordance with the alternation rule of chirality due to macromolecule hierarchy. A topological transition between ring and helix turn PNT structures is discussed: self-assembled natural helix structures are favorable and their energy is lower by a value of the order of one to several eV.

Familial L723P Mutation Can Shift the Distribution between the Alternative APP Transmembrane Domain Cleavage Cascades by Local Unfolding of the Ε-Cleavage Site Suggesting a Straightforward Mechanism of Alzheimer's Disease Pathogenesis.

Alzheimer's disease is an age-related pathology associated with accumulation of amyloid-β peptides, products of enzymatic cleavage of amyloid-β precursor protein (APP) by secretases. Several familial mutations causing early onset of the disease have been identified in the APP transmembrane (TM) domain. The mutations influence production of amyloid-β, but the molecular mechanisms of this effect are unclear. The "Australian" (L723P) mutation located in the C-termini of APP TM domain is associated with autosomal-dominant, early onset Alzheimer's disease. Herein, we describe the impact of familial L723P mutation on the structural-dynamic behavior of APP TM domain studied by high-resolution NMR in membrane-mimicking micelles and augmented by molecular dynamics simulations in explicit lipid bilayer. We found L723P mutation to cause local unfolding of the C-terminal turn of the APP TM domain helix and increase its accessibility to water required for cleavage of the protein backbone by γ-secretase in the ε-site, thus switching between alternative ("pathogenic" and "non-pathogenic") cleavage cascades. These findings suggest a straightforward mechanism of the pathogenesis associated with this mutation, and are of generic import for understanding the molecular-level events associated with APP sequential proteolysis resulting in accumulation of the pathogenic forms of amyloid-β. Moreover, age-related onset of Alzheimer's disease can be explained by a similar mechanism, where the effect of mutation is emulated by the impact of local environmental factors, such as oxidative stress and/or membrane lipid composition. Knowledge of the mechanisms regulating generation of amyloidogenic peptides of different lengths is essential for development of novel treatment strategies of the Alzheimer's disease.

Functional characterization in vitro of twelve naturally occurring variants of the human pancreatic polypeptide receptor NPY4R

Obesity has become a global health problem and therefore understanding of the mechanisms regulating hunger and satiety is of utmost importance for the development of new treatment strategies. The Y4 receptor, encoded by the NPY4R gene, and its ligand pancreatic polypeptide (PP) have been reported to mediate a satiety signal. Multiple genetic studies have reported an association between NPY4R copy number and body weight. The gene also displays several SNP variants, many of which lead to amino acid differences, making it interesting to study. We have investigated the functional properties of 12 naturally occurring amino acid sequence variants of the Y4 and interpret the results in relation to sequence conservation and our structural model of the human Y4 receptor protein. Three receptor variants, Cys201ECL2Tyr, Val2716.41Leu and Asn3187.49Asp, were found to completely lose functional response, measured as inositol phosphate turnover, while retaining membrane expression. They display high sequence conservation and have important roles in the receptor structure. For two receptor variants the potency of PP was significantly decreased, Cys34NTSer (EC50 = 2.9 nM, p < .001) and Val1353.46Met (EC50 = 3.0 nM, p < .01), compared to wild-type Y4 (EC50 = 0.68 nM). Cys34 forms a disulphide bond with Cys298, linking the N-terminal part to ECL3. The Val1353.46Met variant has an amino acid replacement located in the TM3 helix, one helix turn above the highly conserved ERH motif. This position has influence on the network of residues involved in receptor activation and subsequent inactivation. Sequence conservation and the structural model are consistent with these results. The remaining seven positions had no significant effect on the receptor's functional response compared to wild-type Y4. These positions display more variation during evolution. Understanding of the interactions between the Y4 receptor and its native PP agonist and the effects of amino acid variation on its functional response will hopefully lead to future therapeutic possibilities.

Nucleosome spacing periodically modulates nucleosome chain folding and DNA topology in circular nucleosome arrays

The length of linker DNA that separates nucleosomes is highly variable, but its mechanistic role in modulating chromatin structure and functions remains unknown. Here, we established an experimental system using circular arrays of positioned nucleosomes to investigate whether variations in nucleosome linker length could affect nucleosome folding, self-association, and interactions. We conducted EM, DNA topology, native electrophoretic assays, and Mg2+-dependent self-association assays to study intrinsic folding of linear and circular nucleosome arrays with linker DNA length of 36 bp and 41 bp (3.5 turns and 4 turns of DNA double helix, respectively). These experiments revealed that potential artifacts arising from open DNA ends and full DNA relaxation in the linear arrays do not significantly affect overall chromatin compaction and self-association. We observed that the 0.5 DNA helical turn difference between the two DNA linker lengths significantly affects DNA topology and nucleosome interactions. In particular, the 41-bp linkers promoted interactions between any two nucleosome beads separated by one bead as expected for a zigzag fiber, whereas the 36-bp linkers promoted interactions between two nucleosome beads separated by two other beads and also reduced negative superhelicity. Monte Carlo simulations accurately reproduce periodic modulations of chromatin compaction, DNA topology, and internucleosomal interactions with a 10-bp periodicity. We propose that the nucleosome spacing and associated chromatin structure modulations may play an important role in formation of different chromatin epigenetic states, thus suggesting implications for how chromatin accessibility to DNA-binding factors and the RNA transcription machinery is regulated.

Functional characterization of BcrR: a one-component transmembrane signal transduction system for bacitracin resistance.

Bacitracin is a cell wall targeting antimicrobial with clinical and agricultural applications. With the growing mismatch between antimicrobial resistance and development, it is essential we understand the molecular mechanisms of resistance in order to prioritize and generate new effective antimicrobials. BcrR is a unique membrane-bound one-component system that regulates high-level bacitracin resistance in Enterococcus faecalis. In the presence of bacitracin, BcrR activates transcription of the bcrABD operon conferring resistance through a putative ATP-binding cassette (ABC) transporter (BcrAB). BcrR has three putative functional domains, an N-terminal helix-turn-helix DNA-binding domain, an intermediate oligomerization domain and a C-terminal transmembrane domain. However, the molecular mechanisms of signal transduction remain unknown. Random mutagenesis of bcrR was performed to generate loss- and gain-of-function mutants using transcriptional reporters fused to the target promoter PbcrA. Fifteen unique mutants were isolated across all three proposed functional domains, comprising 14 loss-of-function and one gain-of-function mutant. The gain-of-function variant (G64D) mapped to the putative dimerization domain of BcrR, and functional analyses indicated that the G64D mutant constitutively expresses the PbcrA-luxABCDE reporter. DNA-binding and membrane insertion were not affected in the five mutants chosen for further characterization. Homology modelling revealed putative roles for two key residues (R11 and S33) in BcrR activation. Here we present a new model of BcrR activation and signal transduction, providing valuable insight into the functional characterization of membrane-bound one-component systems and how they can coordinate critical bacterial responses, such as antimicrobial resistance.

Conformational Dynamics of Damage Processing by Human DNA Glycosylase NEIL1

Endonuclease VIII-like protein 1 (NEIL1) is a DNA repair enzyme found in higher eukaryotes, including humans. It belongs to the helix–two turn–helix (H2TH) structural superfamily together with Escherichia coli formamidopyrimidine–DNA glycosylase (Fpg) and endonuclease VIII (Nei), and removes a variety of oxidized purine and pyrimidine bases from DNA. Structural, modeling and kinetic studies have established that the bacterial H2TH superfamily enzymes proceed through several conformational intermediates while recognizing and removing their cognate lesions. Here we apply stopped-flow kinetics with detection of intrinsic Trp fluorescence and Förster resonance energy transfer fluorescence to follow the conformational dynamics of human NEIL1 and DNA when the enzyme interacts with undamaged DNA, or DNA containing cleavable or non-cleavable abasic sites, or dihydrouracil lesions. NEIL1 processed a natural abasic site and a damaged base in DNA equally well but showed an additional fluorescently discernible step when DHU was present, likely reflecting additional rearrangements during base eversion into the enzyme's active site. With undamaged DNA and DNA containing a non-cleavable abasic site analog, (3-hydroxytetrahydrofuran-2-yl)methyl phosphate, NEIL1 was diverted to a non-productive DNA conformation early in the reaction. Our results support the view of NEIL1 as an enzyme that actively destabilizes damaged DNA and uses multiple checkpoints along the reaction coordinate to drive substrate lesions into the active site while rejecting normal bases and non-substrate lesions.

Contribution of Base Damages to the Molecular Radiosensitization Mechanism of Platinum Chemotherapeutic Drugs

AbstractThe measurement of clustered damages in Pt‐chemotherapeutic‐drugs‐DNA complexes induced by low‐energy (0‐30 eV) electrons (LEEs) may provide further understanding of the synergy mechanism in cancer treatment with concomitant chemoradiation therapy (CRT). Five‐monolayer films of Pt‐DNA complexes, containing cisplatin, carboplatin and oxaliplatin with ratio 5:1 were irradiated with mono‐energetic electrons of 10 eV, the most prominent energy for bond dissociation by LEE impact. Damages to plasmid DNA including crosslinks, SSBs, DSBs and the loss of the supercoiled configuration were analyzed by the electrophoresis. Base damages (BDs) occurring within two turns of DNA helix were detected by the treatment of E. coli base excision repair endonuclease (Nth and Fpg). The total DNA damages to Pt‐DNA complexes was found to be 350 ± 42, 296 ± 45 and 434 ± 46 ×10−15 electron−1molecule−1, respectively, while the percentages of BDs in this total were 56%, 54% and 60%, respectively. Compared to unmodified DNA, binding of Pt‐drugs to DNA increased BDs by factors of 1.9, 1.6 and 2.6, respectively, which partly resulted in significant enhancements of potentially lethal lesions (i. e., crosslinks, double strand breaks (DSBs) and non‐DSB cluster damages). These results reveal the significant role that LEEs play in the formation of clustered DNA damages related to BDs, which are expected to contribute to the higher efficacy of cancer treatment by CRT with the Pt‐drugs investigated.

Study of a toroidal-helical pipe as an innovative static mixer in laminar flows

In this paper we present the design of a novel, passive mixer, to enhance mixing and residence time distribution for promoting transport and reaction mechanisms in such devices. The goal is to understand and optimize the flow patterns for enhancing mixing in laminar flows through toroidal helical pipes, inspired by the coiled flow inverter (CFI) (Saxena and Nigam, 1984). A toroidal helix is a smooth analytical curve winding around a torus. It is characterized by three parameters: the radius of the torus’ centerline, the radius of the torus’ cross-section, and the number of turns it winds around the torus. Unlike the torus or the straight helix which have constant curvatures, the toroidal helix has a spatially oscillating curvature. We found that this causes the otherwise separated pair of Dean vortices to couple together, periodically re-orient, shrink and grow within each turn of the pipe. The resultant complex streamlines span the entire cross-section and enhances mixing via advective means. By constraining the total pipe length, a meaningful comparison of mixing efficiency within a given volume of pipe can be assessed as the torus’s cross-section radius and the number of helix turns are systematically varied. Reynolds number of up to 400 is explored with the number of turns of 3, 5, 7 and 8. The optimization study shows that the best mixing performance is achieved using a moderate number of turns. Apart from flow pattern and mixing efficiency, we also studied the pressure drop to monitor increased energy consumption and residence time distribution of the flow to monitor degree of mixing.

Structural basis, stoichiometry, and thermodynamics of binding of the chemokines KC and MIP2 to the glycosaminoglycan heparin

Keratinocyte-derived chemokine (KC or mCXCL1) and macrophage inflammatory protein 2 (MIP2 or mCXCL2) play nonredundant roles in trafficking blood neutrophils to sites of infection and injury. The functional responses of KC and MIP2 are intimately coupled to their interactions with glycosaminoglycans (GAGs). GAG interactions orchestrate chemokine concentration gradients and modulate receptor activity, which together regulate neutrophil trafficking. Here, using NMR, molecular dynamics (MD) simulations, and isothermal titration calorimetry (ITC), we characterized the molecular basis of KC and MIP2 binding to the GAG heparin. Both chemokines reversibly exist as monomers and dimers, and the NMR analysis indicates that the dimer binds heparin with higher affinity. The ITC experiments indicate a stoichiometry of two GAGs per KC or MIP2 dimer and that the enthalpic and entropic contributions vary significantly between the two chemokine-heparin complexes. NMR-based structural models of heparin-KC and heparin-MIP2 complexes reveal that different combinations of residues from the N-loop, 40s turn, β3-strand, and C-terminal helix form a binding surface within a monomer and that both conserved residues and residues unique to a particular chemokine mediate the binding interactions. MD simulations indicate significant residue-specific differences in their contribution to binding and affinity for a given chemokine and between chemokines. On the basis of our observations that KC and MIP2 bind to GAG via distinct molecular interactions, we propose that the differences in these GAG interactions lead to differences in neutrophil recruitment and play nonoverlapping roles in resolution of inflammation.

Crystal structure of an Lrs14-like archaeal biofilm regulator from Sulfolobus acidocaldarius.

The small winged helix-turn-helix (wHTH) proteins of the Lrs14 family are major transcriptional regulators and act as archaeal biofilm regulators (AbfRs) in the crenarchaeote Sulfolobus acidocaldarius. Here, the first crystal structure of an AbfR ortholog, AbfR2, the deletion of which is known to impair biofilm formation, is presented. Like most other wHTH orthologs, AbfR2 is dimeric in solution as well as in its 2.45 Å resolution crystal structure. Given the presence of three independent AbfR2 dimers in the asymmetric unit, the crystal structure shows a considerable degree of conformational variation within the dimer, the antiparallel orientations of which are stabilized by coiled-coil interaction between H4 helices. Conserved anchor interactions between helices H0 and H4 of AbfR2 further contribute to dimer stabilization. The combined structural and bioinformatic analysis reveals cluster-specific structural differences between different members of the Lrs14 protein family.

Synthesis of new 1,2-dideoxy C-linked carbo-β-amino acids and α/β-peptides with 11/9-helix, helix-turn and helix-turn-helix structures

The present study describes the synthesis of new C-linked carbo-β-amino acids [β-Caa(1,2-ddx)], with a 1,2-dideoxy D-xylo furanoside side chain (a tetrahydro furan derivative). The stereochemistry at the newly created amine centers was determined by modified Mosher method. The (S)-β-Caa(1,2-ddx) prepared from d-mannose diacetonide were utilized for the synthesis of 1:1 α/β-peptides with L-Ala. The conformational analysis (NMR, MD and CD) revealed the presence of 11/9-helix, helix induced helix-turn (HT) and helix-turn-helix (HTH) in these peptides. These side chains with tetrahydrofuran ring facilitated the formation of robust helix, unlike some other side chains from earlier studies.

BIOINFORMATIC STUDY OF AN ANTITUMOR PROTEIN, AZURIN

Objective: The main objective of this study is to analyze the structure and function of an antitumor protein, azurin, thereby giving validation to the protein structure and existing physicochemical properties in the anticancer protein which are responsible for the anticancer activity.Methods: Protein sequence analysis was done using Basic Local Alignment Search Tool (BLAST) with ten different randomly selected species of Pseudomonas obtained from GenBank. The physicochemical properties, prediction of secondary structure, identification of motifs and domains, three-dimensional (3-D) structure of the antitumor protein, validation through Ramachandran plot, multiple sequence alignment (MSA), and phylogenetic analysis were studied and functional property was confirmed through in silico docking.Results: The similarity search (BLAST-P analysis) for the primary sequence from GenBank carried out showed 86% similarity to the second sequence, azurin (Pseudomonas nitroreducens). The ProtParam, ExPASy tool server indicated the presence of essential physicochemical properties in azurin. Secondary structure prediction revealed random coil, extended strand, alpha helix, and beta turn. The study on domains indicated the presence of one domain in azurin responsible for the anticancer activity. The 3-D structural analysis revealed azurin as metalloprotein, of length-128, and polymer-1 with α-helices, β-sheets, and β-barrels. The validation carried out through Ramachandran plot showed the presence of two outliers (phi and psi). The biological relationship between the input sequences was studied through MSA and phylogenetic analysis. Further, azurin docked against the target protein (p53 tumor suppressor) showed the maximum binding affinity confirming its functional property of causing apoptosis.Conclusion: All the properties analyzed in the present study revealed that the azurin protein can act as a very good anticancer agent, and through the phylogenetic analysis, it was identified that Pseudomonas nitroreducens was closely related to the test organism Pseudomonas aeruginosa.

Dynamics of pitch change in chiral azobenzene-doped liquid crystals

Dynamics of pitch change in chiral azobenzene-doped liquid crystals (CAdLCs) has been investigated. Theoretically, the pitch change in CAdLCs is discontinuous. Completed behavior of the discontinuous pitch jump in a fixed thickness cell is analyzed based on the calibration term, which is a key length parameter of the gradually increasing elastic potential energy with time, according to Hooke's law. At a specific time, the energy reaches maximum value and then releases to provide a compressed/extended force to discontinuously change pitch to minimize the energy of the whole system. At other times, the compressed/extended force disturbs the uniformity of planar texture if the surface anchoring energy is weak. Discontinuous pitch jump can be observed in CAdLCs with a few turns of helix. Thus, a novel method to evaluate the pitch of CAdLCs with only two turns of the helix after UV illumination is feasible. In contrast, discontinuous pitch jump in the previous work is hard to be noticed if CAdLCs has a large number of turns of helix. The behavior of pitch change in CAdLCs on the bases of the number of turns of helix and the cell thickness will be discussed in detail.

Axial-Mode Performance Characteristics of a Thin-Wire Square Helical Antenna

This paper, using an adaptation of a method described by Kornhauser for a circular helix antenna in a 1951 publication, rigorously develops hitherto unavailable explicit analytical expressions for the far-zone electric fields radiated in free space, by a thin-wire helical antenna, of square cross-section. It is shown in the presentation that these radiation field expressions for the square helical antenna represent a general case, from which corresponding expressions, exactly as published elsewhere for the square-loop and linear geometries, are recoverable: to support the correctness of the formulation. And subsequently using the expressions as basis, the presentation undertakes a systematic investigation of the characteristic performance features of the square helical antenna, mounted on a ground plane of infinite extent; when operated in the axial mode, and for various values of square-loop perimeter and number of helix turns. For computational data, the antenna’s current distribution is determined via the method of moments with piece-wise linear basis and testing functions, after invoking the image theory. In addition to the radiated electric field, numerical results concerning axial ratio as well as the directive gain, for the square helix antenna, and for a range of antenna physical dimensions, are presented in graphical formats. These results very clearly indicate that the axial-mode performance of the square helical antenna is comparable with that of the conventional circular helical antenna.

Mechanism of Anion Conduction in the Calcium-Activated Chloride Channel TMEM16A

The calcium-activated chloride channel TMEM16A mediates selective anion conduction upon activation by intracellular calcium. Using the cryo-EM structure of mouse TMEM16A as a template, we have investigated the mechanism of anion conduction by patch-clamp electrophysiology. In the structure, an hourglass-shaped, protein-enclosed aqueous conduit populated by basic residues is found in each subunit in a homodimer. We analysed the conduction characteristics of alanine mutants of these basic residues and found a position-dependent effect on ion conduction that is manifested in the rectification of current-voltage relationships. This underlines their importance for the electrostatics in the narrow neck region of the pore creating a favourable environment for anion conduction. The compromised conduction characteristics of the cysteine mutant of a basic residue located on α-helix 5 at the intracellular end of the narrow neck can be reverted to the wild-type phenotype upon reaction with the small, positively charged MTSEA, indicating the intracellular accessibility of the site and reinforcing the role of the positive potential for anion conduction. The equivalent mutation of a residue located one helix turn towards the extracellular side is inaccessible, consistent with its location in the constricted part of the pore. When analysed in the context of a phenomenological model of ion permeation, it appears that the positively charged residues in the aqueous pore facilitate anion conduction by lowering local energy barrier(s) according to their specific position in the pore. Because the major energy barriers are located at the inner and outer ends of the pore, it is plausible that anions dehydrate as they enter the narrow conduit for conduction, a process that might be facilitated by the resident basic residues.

Visualization of complex DNA damage along accelerated ions tracks

The most deleterious DNA lesions induced by ionizing radiation are clustered DNA double-strand breaks (DSB). Clustered or complex DNA damage is a combination of a few simple lesions (single-strand breaks, base damage etc.) within one or two DNA helix turns. It is known that yield of complex DNA lesions increases with increasing linear energy transfer (LET) of radiation. For investigation of the induction and repair of complex DNA lesions, human fibroblasts were irradiated with high-LET 15N ions (LET = 183.3 keV/μm, E = 13MeV/n) and low-LET 60Co γ-rays (LET ≈ 0.3 keV/μm) radiation. DNA DSBs (γH2AX and 53BP1) and base damage (OGG1) markers were visualized by immunofluorecence staining and high-resolution microscopy. The obtained results showed slower repair kinetics of induced DSBs in cells irradiated with accelerated ions compared to 60Co γ-rays, indicating induction of more complex DNA damage. Confirming previous assumptions, detailed 3D analysis of γH2AX/53BP1 foci in 15N ions tracks revealed more complicated structure of the foci in contrast to γ-rays. It was shown that proteins 53BP1 and OGG1 involved in repair of DNA DSBs and modified bases, respectively, were colocalized in tracks of 15N ions and thus represented clustered DNA DSBs.

Optically Controllable Linear-Polarization Rotator Using Chiral-Azobenzene-Doped Liquid Crystals.

A linear-polarization rotator based on the optically tunable pitch of chiral-azobenzene-doped liquid crystals (CAdLCs) has been investigated. It is shown that the orientation of linearly polarized (LP) light can be optically tuned using CAdLCs and that the transmitted light possesses a good degree of linear polarization (DoLP). Experimental and simulation (4 × 4 Berreman matrix) results show that the rotation angle is dependent on the pitch as well as the number of turns of the cholesteric LC helix. Some causes to affect the DoLP of the output LP lights during photoisomerization are also discussed. Moreover, a calibration term, β(t), is also introduced to elucidate the behavior of the discontinuous change of the CAdLC pitch in a fixed cell thickness.

Structural inhibition of dynamin-mediated membrane fission by endophilin.

Dynamin, which mediates membrane fission during endocytosis, binds endophilin and other members of the Bin-Amphiphysin-Rvs (BAR) protein family. How endophilin influences endocytic membrane fission is still unclear. Here, we show that dynamin-mediated membrane fission is potently inhibited in vitro when an excess of endophilin co-assembles with dynamin around membrane tubules. We further show by electron microscopy that endophilin intercalates between turns of the dynamin helix and impairs fission by preventing trans interactions between dynamin rungs that are thought to play critical roles in membrane constriction. In living cells, overexpression of endophilin delayed both fission and transferrin uptake. Together, our observations suggest that while endophilin helps shape endocytic tubules and recruit dynamin to endocytic sites, it can also block membrane fission when present in excess by inhibiting inter-dynamin interactions. The sequence of recruitment and the relative stoichiometry of the two proteins may be critical to regulated endocytic fission.

Development of Selective Peptide Catalysts with Secondary Structural Frameworks.

Enzymes are biogenic catalysts that enable the vital activity of organisms. Enzymes promote reactions in a selective manner with a high level of substrate recognition ability. The development of such a sophisticated catalyst has been one of the goals for chemists. A synthetic peptide is the prime candidate to realize an enzyme-like catalyst. Considering that the catalytic function of enzymes derives from their molecular structures, the key for the creation of a peptide catalyst might be the introduction of a specific three-dimensional structure. Our motivation was to find a peptide catalyst with a versatile secondary structural framework and apply the peptide to a variety of selective reactions. Although helical-peptide-catalyzed asymmetric epoxidation of enones is popular, no other highly enantioselective reaction with a helical peptide has been reported. It was found that resin-supported α-helical polyleucine promoted asymmetric conjugate addition of a carbon nucleophile to enones via the formation of an iminium intermediate at the N-terminal amino group. By changing the helical chain to a repetitive Leu-Leu-Aib (Aib = α-aminoisobutyric acid) sequence and introducing a few amino acids to the N-terminus, a highly enantioselective peptide catalyst was obtained. The helical peptide catalyst was applicable for a tandem enamine/iminium-mediated reaction and asymmetric epoxidation of enones. Although the extension of the helical peptide to conjugate addition of a nucleophile to an enal was not successful simply by attaching proline to the N-terminus of the helix, the incorporation of a β-turn motif was effective to improve the catalytic performance. In the sequence of such a turn-helix-type peptide, the helical part was seemingly distant from the N-terminal amino group; however, the hydrophobicity, structure, and chirality of the helix largely affected the reaction. The turn-helix-type peptide promoted a wide range of asymmetric reactions: conjugated additions of hydride and carbon nucleophiles to enals via the iminium activation and α-oxyamination of aldehydes via the enamine activation. The peptides with turn-helix and helix frameworks were also employed for several reactions that were difficult to achieve with low-molecular-weight catalysts: enzyme-cocatalyzed asymmetric oxidation in water, diastereo- and enantioselective cyclopropanation, regioselective reduction of dienals, kinetic resolution of planar-chiral compounds, and desymmetrization to induce planar chirality. To explore other types of peptide catalysts, a combinatorial library screening was performed. On the way, it was revealed that a histidyl residue assisted to accelerate a reaction via reversible addition to an iminium intermediate. Through the screening of random peptide libraries, novel peptide sequences for efficient and enantioselective conjugate addition were discovered. Although we have no information about the molecular structure of the newly found peptides, they can be an entry point for establishing a versatile framework of peptide catalysts.