Β-turn Type Research Articles

RETRACTED: Analysis and prediction of β-turn types using multinomial logistic regression and artificial neural network

So far various statistical and machine learning techniques applied for prediction of β-turns. The majority of these techniques have been only focused on the prediction of β-turn location in proteins. We developed a hybrid approach for analysis and prediction of different types of β-turn. A two-stage hybrid model developed to predict the β-turn types I, II, IV and VIII. Multinomial logistic regression was initially used for the first time to select significant parameters in prediction of β-turn types using a self-consistency test procedure. The extracted parameters were consisted of 80 amino acid positional occurrences and 20 amino acid percentages in β-turn sequence. The most significant parameters were then selected using multinomial logistic regression model. Among these, the occurrences of glutamine, histidine, glutamic acid and arginine, respectively, in positions i, i+1, i+2 and i+3 of β-turn sequence had an overall relationship with 5 β-turn types. A neural network model was then constructed and fed by the parameters selected by multinomial logistic regression to build a hybrid predictor. The networks have been trained and tested on a non-homologous dataset of 565 protein chains by nine fold cross-validation. It has been observed that the hybrid model gives a Matthews correlation coefficient (MCC) of 0.473 and 0.124, respectively, for β-turn types II and VIII which are best among previously reported results. Our model also distinguished the different types of β-turn in the embedded binary logit comparisons which have not carried out so far. Available on request from the authors.

Alzheimer’s-disease-associated conformation of intrinsically disordered tau protein studied by intrinsically disordered protein liquid-phase competitive enzyme-linked immunosorbent assay

Tau protein, the major constituent of paired helical filaments in Alzheimer’s disease, belongs to the intrinsically disordered proteins (IDPs). IDPs are an emerging group in the protein kingdom characterized by the absence of a rigid three-dimensional structure. Disordered proteins usually acquire a “functional fold” upon binding to their interaction partner(s). This property of IDPs implies the need for innovative approaches to measure their binding affinity. We have mapped and measured the Alzheimer’s-disease-associated epitope on intrinsically disordered tau protein with a novel two-step sandwich competitive enzyme-linked immunosorbent assay (ELISA). This approach allowed us to determine the binding affinity of disordered tau protein in liquid phase without any disturbance to the competitive equilibrium and without any need for covalent or noncovalent modification of tau protein. Furthermore, the global fitting method, used for the reconstruction of tau binding curves, significantly improved the assay readout. The proposed novel competitive ELISA allowed us to determine the changes in the standard Gibbs energy of binding, thus enabling measurement of tau protein conformation in the core of paired helical filaments. IDP competitive ELISA results showed, for the first time, that the tau protein C terminus of the Alzheimer’s-disease-derived paired helical filaments core subunit adopts β-turn type I′ fold and is accessible from solution.

Kinetics and Thermodynamics of Type VIII β-Turn Formation: A CD, NMR, and Microsecond Explicit Molecular Dynamics Study of the GDNP Tetrapeptide

We report an experimental and theoretical study on type VIII β-turn using a designed peptide of sequence GDNP. CD and NMR studies reveal that this peptide exists in equilibrium between type VIII β-turn and extended conformations. Extensive MD simulations give a description of the free energy landscape of the peptide in which we retrieve the same two main conformations suggested by the experiments. The free energy difference between the two conformational states is very small and the transition between them occurs within a few kT at 300 K on a nanosecond timescale. The equilibrium is mainly driven by entropic contribution, which favors extended conformations over β-turns. This confirms other theoretical studies showing that β-turns are marginally stable in water solution because of the larger entropy of the extended state unless some stabilizing interactions exist. Our observations may be extended to any type of β-turn and have important consequences for protein folding. A comparison of our MD and CD results also suggests a possible type VIII β-turn CD signature indicated by one main band at 200 nm, close to that of random coil, and a fairly large shoulder at 220 nm. Last, our results clearly show that the XXXP motif can only fold into a type VIII β-turn, which is consistent with its fairly strong propensity for this type of turn. This important finding may help for peptide design and is in line with recent studies on bioactive elastin peptides.

Model Dipeptides Incorporating the trans Cyclohexane Analogues of Phenylalanine: Further Evidence of the Relationship Between Side‐Chain Orientation and β‐Turn Type.

ChemInformVolume 37, Issue 5 Natural Products Model Dipeptides Incorporating the trans Cyclohexane Analogues of Phenylalanine: Further Evidence of the Relationship Between Side-Chain Orientation and β-Turn Type. Marta Lasa, Marta Lasa Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorAna I. Jimenez, Ana I. Jimenez Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorMaria M. Zurbano, Maria M. Zurbano Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorCarlos Cativiela, Carlos Cativiela Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this author Marta Lasa, Marta Lasa Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorAna I. Jimenez, Ana I. Jimenez Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorMaria M. Zurbano, Maria M. Zurbano Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this authorCarlos Cativiela, Carlos Cativiela Dep. Quim. Org., Inst. Cienc. Mater. Aragon, CSIC-Univ. Zaragoza, E-50009 Zaragoza, SpainSearch for more papers by this author First published: 09 January 2006 https://doi.org/10.1002/chin.200605197AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume37, Issue5January 31, 2006 RelatedInformation

Model dipeptides incorporating the trans cyclohexane analogues of phenylalanine: further evidence of the relationship between side-chain orientation and β-turn type

In order to study the influence of the side-chain orientation on the peptide backbone conformation we have synthesised the model dipeptides t-BuCO- l-Pro-(1 S,2 R)-c 6Phe-NHMe and t-BuCO- l-Pro-(1 R,2 S)-c 6Phe-NHMe, incorporating each enantiomer of the trans cyclohexane analogue of phenylalanine ( trans-1-amino-2-phenylcyclohexanecarboxylic acid). The orientation of the aromatic side-chain determines the β-turn type accommodated by these peptides to the point that the (1 S,2 R)-c 6Phe derivative retains the type I β-turn in the crystalline state, in contrast to the behaviour exhibited by the natural counterpart t-BuCO- l-Pro- l-Phe-NHMe.

M-Aminobenzoic acid inserted β-turn in acyclic tripeptides: a peptidomimetic design

X-ray diffraction studies show that peptides Boc-Leu-Aib- m-ABA-OMe ( I ) (Aib, α-aminoisobutyric acid; m-ABA, meta-aminobenzoic acid) and Boc-Phe-Aib- m-ABA-OMe ( II ) adopt a type-II β-turn conformation, solely stabilized by co-operative steric interactions amongst the amino acid residues. This type of β-turn without any intramolecular hydrogen bonding is generally referred to as an open turn. Although there are some examples of constrained cyclic peptides in which o-substituted benzenes have been inserted to mimic the turn region of the neurotrophin, a nerve growth factor, peptides I and II present novel two examples where m-aminobenzoic acid has been incorporated in the β-turn of acyclic tripeptides. The result also demonstrates the first crystallographic evidence of a β-turn structure containing an inserted m-aminobenzoic acid, which can be considered as a rigid γ-aminobutyric acid with an all-trans extended configuration.

Refinement of Repeated β-turn Structure for Silk I Conformation of Bombyx mori Silk Fibroin Using 13C Solid-State NMR and X-ray Diffraction Methods

Refinement of the structural model of silk I (the structure of Bombyx mori silk fibroin before spinning in the solid state) proposed previously was performed on the basis of a detailed analysis of the 13C solid-state NMR data using two-dimensional (2D) spin-diffusion NMR and REDOR of stable isotope-labeled (AG)15, coupled with the X-ray diffraction analysis of the crystalline fraction of B. mori silk fibroin. The repeated β-turn type II structure was proposed, with the torsion angles (φ, ψ) = (−62°, 125°) for Ala residue and (φ, ψ) = (77°, 10°) for Gly residue of poly(Ala-Gly) chain, which satisfies both solid-state NMR and X-ray diffraction data quantitatively. The torsion angles determined in this work were slightly different from the previous angles, (φ, ψ) = (−60°, 130°) for Ala residue and (φ, ψ) = (70°, 30°) for Gly residue. The intra- and intermolecular hydrogen bonding was formed alternatively along the chain. The solid-state NMR is sensitive to the local conformation of a chain, but X-ray diffrac...

Aromatic–aromatic and proline–aromatic interactions in endomorphin-1 and endomorphin-2

We investigated the aromatic–aromatic and proline–aromatic interactions in endomorphin-1 and endomorphin-2, and different types of these interactions were observed. For all the interacting pairs, the preferred geometric orientations were identified. We examined these interactions in the preferred secondary structures, which are different types of β-turns and γ-turns. These results revealed that the majority of the turn structures contained one of the interacting aromatic–aromatic or proline–aromatic pairs. On the basis of our results, it can be assumed that these interactions may be important in the determination and stabilization of the structures of endomorphins. Furthermore, our observations suggest that a conformation stabilized by an aromatic–aromatic or proline–aromatic interaction can play an important role in the association with the receptor.

Evidence for Domain-specific Recognition of SK and Kv Channels by MTX and HsTx1 Scorpion Toxins

Maurotoxin (MTX) and HsTx1 are two scorpion toxins belonging to the alpha-KTx6 structural family. These 34-residue toxins, cross-linked by four disulfide bridges, share 59% sequence identity and fold along the classical alpha/beta scaffold. Despite these structural similarities, they fully differ in their pharmacological profiles. MTX is highly active on small (SK) and intermediate (IK) conductance Ca(2+)-activated (K(+)) channels and on voltage-gated Kv1.2 channel, whereas HsTx1 potently blocks voltage-gated Kv1.1 and Kv1.3 channels only. Here, we designed and chemically produced MTX-HsTx1, a chimera of both toxins that contains the N-terminal helical region of MTX (sequence 1-16) and the C-terminal beta-sheet region of HsTx1 (sequence 17-34). The three-dimensional structure of the peptide in solution was solved by (1)H NMR. MTX-HsTx1 displays the activity of MTX on SK channel, whereas it exhibits the pharmacological profile of HsTx1 on Kv1.1, Kv1.2, Kv1.3, and IK channels. These data demonstrate that the helical region of MTX exerts a key role in SK channel recognition, whereas the beta-sheet region of HsTx1 is crucial for activity on all other channel types tested.

Recurring main-chain anion-binding motifs in short polypeptides: nests

A novel tripeptide motif called a nest has recently been described in proteins with the function of binding anionic, or partially anionic, atoms such as carbonyl O atoms. In the present work, a search for nests in small polypeptides stored in the Cambridge Structural Database is reported. 37 unique examples were found: over half form part of hydrogen-bond arrangements resembling those in proteins, such as Schellman/paperclip loop motifs, various types of beta-turn and Asx-turns or Ser/Thr-turns, while a third are in novel situations, some involving binding to anionic groups from other molecules within the crystal complex. An example is the antibiotic vancomycin, which incorporates a prominent nest forming part of a peptide-binding site. This nest binds the carboxylate of the C-terminal D-alanine of the bacterial cell-wall precursor peptide, thereby inhibiting the final step of bacterial cell-wall synthesis. As in proteins, a number of nests occur in short peptides with an alternating glycine/L-amino-acid sequence but, uniquely to non-ribosomally synthesized short peptides, several nests within them are constructed from alternating D- and L-amino acids, and such sequences seem to specially favour nests.

Structure-activity relationships of endomorphin-1, endomorphin-2 and morphiceptin by molecular dynamics methods

A conformational analysis of endomorphin-1 (Tyr-Pro-Trp-Phe-NH 2, EM1), endomorphin-2 (Tyr-Pro-Phe-Phe-NH 2, EM2) and morphiceptin (Tyr-Pro-Phe-Pro-NH 2, MC), as μ-opioid receptor ligands was performed by the simulated annealing (SA) method and solvated molecular dynamics (MD) calculations. In SA experiments, 1000 conformers were generated for each peptide with both cis and trans Tyr–Pro peptide bond isomers. The populations of the conformers in the different regions of the Ramachandran plots and the numbers of the various types of turns and the distribution of distances of the main pharmacophore elements (i.e. phenolic OH of Tyr 1, tyramine N and the aromatic side-chain of Phe 3) for the three peptides were compared. EM1 and EM2 seemed to be almost identical in their conformational features, ca. 30% of their conformers possessed turns with a significant ratio of β-turn type III, while in MC a drastic decrease in the number of turns and an increase of the number of extended structures were observed. According to the differences in the Φ 3– Ψ 3 Ramachandran plots, the Phe 3 pharmacophore was affected in MC. Also, a pairwise comparison of the interaction energies between all fragments of the peptides (i.e. between backbone and side-chain fragments of each amino acid residue) showed that the presence of Pro 4 in MC initiated increased repulsive interactions toward the Pro 2–Phe 3 fragment relative to Phe 4 toward the Pro 2–Phe 3 and Pro 2–Trp 3 fragments in EM2 and EM1, respectively, accounting for its decreased opioid activity. The conformational analysis was repeated by isotherm molecular dynamics calculations in a periodic box with a modified GROMOS96 force field. The results support our previous experience.

Molecular Dynamics Simulation of Conformational Change of Poly(Ala-Gly) from Silk I to Silk ΙΙ in Relation to Fiber Formation Mechanism of Bombyx mori Silk Fibroin

The fiber formation mechanism of Bombyx mori silk fibroin by silkworm is essentially the structural change from silk I (the silk fibroin structure before spinning in the solid state) to silk II (the silk fibroin structure after spinning) under external forces in both silk gland and spinneret of B. mori silkworm. Recently, we proposed structural models for silk I and silk II forms of the model peptide (Ala-Gly)15 of B. mori silk fibroin using mainly solid-state NMR methods. In this paper, molecular dynamics (MD) calculation was performed to simulate the structural change of poly(Ala-Gly) from silk I to silk II and to clarify the detailed mechanism of the silk fiber formation. The silk I structure (repeated β-turn type II) changes to silk II structure (heterogeneous structure, but mainly antiparallel β-sheet) by stretching of the chain with MD simulation, but the change occurs only under very high temperature such as 1000 K and large tensile stress (1.0 GPa). However, the structural change during the MD simulation occurs more easily by taking into account several external forces (the presence of water molecules around the silk chains, and application of both shear and tensile stresses to the silk fibroin) applied to the silk fibroin simultaneously. The heterogeneous structure of the silk fiber determined previously with solid-state NMR could be reproduced well with the MD calculation and then molecular mechanics calculation after removal of water molecules.

Cyclotetrapeptides with alternating d-Ala residues: synthesis and spectroscopic studies

Three cyclotetrapeptides, c[Leu- d-Ala-Xaa- d-Ala], where Xaa is Leu ( P1), Lys ( P2) and Glu ( P3) were synthesized and studied by 1H and 13C NMR and CD spectroscopy. These cyclotetrapeptides exhibit similar coupling constants, 3 J HNHα, in the range of 8.56–9.93 Hz, commonly observed for β-turn structures. All amide proton chemical shifts for P1, P2 and P3 exhibited linear dependence on temperature with moderate temperature coefficients ranging from −3.1 to −9.8 ppb/K. Amide proton signal broadening was observed for all residues in P1, P2 and P3, indicating that they are solvent accessible. The number of resonance observed for P1 was half of the total counts, indicating a C2 symmetric conformation. P2 and P3 exhibit similar CD in solvents of varying dielectric constants and dilutions, with characteristic positive CD bands at ca. 210 and 222 nm, which correspond to a β-turn type structure. Small CD/temperature effect was also observed with isodichroic points, consistent with conformational stability and a well-populated cyclotetrapeptide energy state. These heterochiral cyclotetrapeptides consisting of alternating d-Ala residues adopt stabilized open β-turn conformations and may be useful as a ligand template for further functionalization.

Structure of Silks Determined with Solid-State NMR and Development of New Silk-like Materials

The solid-state structures of Bombyx mori silk fibroin before and after spinning were determined with several solid-state NMR. A repeated β-turn type II structure was proposed for the former model and a heterogeneous structure which consists of two kinds of β-sheet structure with different inter-chain arrangement and distorted β-turn for the latter. New silk-like materials with several repeated sequences selected from B. mori and Samia cynthia ricini silk fibroins, and spider dragline silk were designed and produced using genetic engineering methods. The silk-like materials containing the cell-adhesive sequence, Arg-Gly-Asp, from fibronectin were produced similarly and their high cell-adhesive abilities were observed.

Determination of the Torsion Angles of Alanine and Glycine Residues of Bombyx Mori Silk Fibroin and the Model Peptides in the Silk I and Silk II Forms Using 2D Spin Diffusion Solid-State NMR under Off Magic Angle Spinning

The structures of two crystalline forms of Bombyx mori silk fibroin, before and after the spinning process from silkworm, have been known as silk I and silk II, respectively. Most recently, we proposed a silk I structure of alternating copolypeptide (Ala-Gly)15 as a “repeated β-turn type II structure”. In this paper, two-dimensional spin diffusion solid-state NMR under off magic angle spinning was applied to determine the torsion angles of the alanine and glycine residues of the same peptide with silk II structure. The angles were determined to be φ, ψ = −150°, 150° within experimental error of ±10° for both residues, which supports an antiparallel β-sheet structure of silk II. Next, [1,2-13C]glycine was incorporated into B. mori silk fibroin by feeding [1,2-13C]glycine to silkworms to evaluate the torsion angle ψ of glycine residues in the silk fibroin directly. The angles were evaluated as ψ = 30° and ψ = 150° for silk I and silk II forms, respectively. The evaluation was also performed for the torsion ...

The Structural Basis of Compstatin Activity Examined by Structure-Function-based Design of Peptide Analogs and NMR

We have previously identified compstatin, a 13-residue cyclic peptide, that inhibits complement activation by binding to C3 and preventing C3 cleavage to C3a and C3b. The structure of compstatin consists of a disulfide bridge and a type I beta-turn located at opposite sides to each other. The disulfide bridge is part of a hydrophobic cluster, and the beta-turn is part of a polar surface. We present the design of compstatin analogs in which we have introduced a series of perturbations in key structural elements of their parent peptide, compstatin. We have examined the consistency of the structures of the designed analogs compared with compstatin using NMR, and we have used the resulting structural information to make structure-complement inhibitory activity correlations. We propose the following. 1) Even in the absence of the disulfide bridge, a linear analog has a propensity for structure formation consistent with a turn of a 3(10)-helix or a beta-turn. 2) The type I beta-turn is a necessary but not a sufficient condition for activity. 3) Our substitutions outside the type I beta-turn of compstatin have altered the turn population but not the turn structure. 4) Flexibility of the beta-turn is essential for activity. 5) The type I beta-turn introduces reversibility and sufficiently separates the two sides of the peptide, whereas the disulfide bridge prevents the termini from drifting apart, thus aiding in the formation of the hydrophobic cluster. 6) The hydrophobic cluster at the linked termini is involved in binding to C3 and activity but alone is not sufficient for activity. 7) beta-Turn residues Gln(5) (Asn(5))-Asp(6)-Trp(7)(Phe(7))-Gly(8) are specific for the turn formation, but only Gln(5)(Asn(5))-Asp(6)-Trp(7)-Gly(8) residues are specific for activity. 8) Trp(7) is likely to be involved in direct interaction with C3, possibly through the formation of a hydrogen bond. Finally we propose a binding model for the C3-compstatin complex.

BetaTPred: prediction of beta-TURNS in a protein using statistical algorithms.

beta-turns play an important role from a structural and functional point of view. beta-turns are the most common type of non-repetitive structures in proteins and comprise on average, 25% of the residues. In the past numerous methods have been developed to predict beta-turns in a protein. Most of these prediction methods are based on statistical approaches. In order to utilize the full potential of these methods, there is a need to develop a web server. This paper describes a web server called BetaTPred, developed for predicting beta-TURNS in a protein from its amino acid sequence. BetaTPred allows the user to predict turns in a protein using existing statistical algorithms. It also allows to predict different types of beta-TURNS e.g. type I, I', II, II', VI, VIII and non-specific. This server assists the users in predicting the consensus beta-TURNS in a protein. The server is accessible from http://imtech.res.in/raghava/betatpred/

Raman Spectrum of Model Peptide (Ala-Gly)15 for Bombyx mori Silk Fibroin with Silk I Form and Theoretical Calculation According to Repeated .BETA.-Turn Type II Structural Model.

We observed Raman spectra of Silk I and Silk II powders of (Ala-Gly)15, which is a model peptide of crystalline region of Bombyx mori silk fibroin. Additionally Raman spectra of Ac-(Gly-Ala)4-NHMe and Ac-(Gly-Ala)3-NHMe with Silk I and Silk II forms were calculated according to the repeated β-turn type II structural model and β-sheet model, respectively. The ab initio molecular orbital calculation was used for the theoretical calculation. The calculated results could reproduce the spectra. Especially, in silk I form, observation of splitting of amide I and III bands was in agreement with the predicted bands according to the repeated β-turn type II structural model.

A repeated β-turn structure in Poly(Ala-Gly) as a model for silk I of Bombyx mori silk fibroin studied with two-dimensional spin-diffusion NMR under off magic angle spinning and rotational echo double resonance

The structure of a crystalline form of Bombyx mori silk fibroin, commonly found before the spinning process (known as silk I), was proposed by combining data obtained from two-dimensional spin-diffusion nuclear magnetic resonance under off magic angle spinning, rotational-echo double-resonance (REDOR), previously reported X-ray diffraction analyses and 13C NMR chemical shifts. Instead of B. mori silk fibroin with silk I structure, we used the sequential model peptide (Ala-Gly)15. The structure of the sequential model peptide is characterized as silk I after dissolving the peptide in 9 M LiBr and then dialyzing against water. Moreover, 13C or 15N-labeled sites may be introduced easily at any position in (Ala-Gly)15 by the solid phase synthesis method for these NMR experiments. The torsional angles of (Ala-Gly)15 with silk I structure were determined as (−60(±5)°, 130(±5)°) and (70(±5)°, 30(±5)°) for Ala and Gly residues, respectively. The formation of the intra-molecular hydrogen bonding along the chain was confirmed from REDOR NMR by determination of the inter-atomic distance between the nitrogen and carbon atoms comprising the intra-molecular hydrogen bonding. The structure is named a repeated β-turn type II-like structure.

Analysis of gammabeta, betagamma, gammagamma, betabeta multiple turns in proteins.

The number of gamma-turns in a representative protein dataset selected from the current Protein Data Bank has increased almost seven times during the past decade. Eighty percent classic gamma-turns and 57% inverse gamma-turns are associated as multiple turns with either another y-turn or a beta-turn. We refer to these as multiple turns of the (gammabeta)1,2,3 or (betagamma)1,2,3 type, depending upon whether the gamma-turn is before or after the beta-turn along the protein chain, respectively. However, for multiple turns involving only gamma-turns, we follow the nomenclature analogous to that proposed earlier for the multiple (or double) beta-turns. Fifty-eight per cent beta-turns are associated as multiple turns with another beta-turn. We extracted multiple turns from the protein dataset and classified them on the basis of individual gamma- or beta-turn types and the number of overlapping residues. Furthermore, we evaluated the amino acid positional potentials and determined the statistically significant amino acid preferences, hydrogen bond/side-chain interaction preferences in the multiple turns and secondary structure preferences for residues immediately flanking these turns. The results of our analysis would be useful in the modeling, prediction or design of multiple turns in proteins. The amino acid sequence corresponding to the multiple turn, position in the protein chain, PDB Code/chain in which multiple turn is present and the individual turn types constituting the multiple turns are available from our website and this information would also be integrated in our Database of Structural Motifs in Proteins (http://www.cdfd.org.in/dsmp.html).