An unusual C-H center dot center dot center dot O hydrogen bond mediated reversal of polypeptide chain direction in a synthetic peptide helix

An unusual C-terminal conformation has been detected in a synthetic decapeptide designed to analyze the stereochemistry of helix termination in polypeptides. The crystal structure of the decapeptide Boc-Leu-Aib-Val-Ala-Leu-Aib-Val-(D)Ala-(D)Leu-Aib-OMe reveals a helical segment spanning residues 1-7 and helix termination by formation of a Schellman motif, generated by (D)Ala(8) adopting the left-handed helical (alpha(L)) conformation. The extended conformation at (D)Leu(9) results in a compact folded structure, stabilized by a potentially strong C-H ... O hydrogen bond between Ala(4) (CH)-H-alpha and (D)Leu(9)CO. The parameters for C-H ... O interaction are Ala(4) (CH)-H-alpha .. O=C (D)Leu(9) distance 3.27 Angstrom C-alpha-H .. O angle 176 degrees, and O .. H-alpha distance 2.29 Angstrom. This structure suggests that insertion of contiguous D-residues may provide a handle for the generation of designed structures containing more than one helical segment folded in a compact manner. (C) 2000 Academic Press.

Implications of Energy Profile and Storage on Energy Harvesting Sensor Link Performance

Energy harvesting sensors (EHS), which harvest energy from the environment in order to sense and then communicate their measurements over a wireless link, provide the tantalizing possibility of perpetual lifetime operation of a sensor network. The wireless communication link design problem needs to be revisited for these sensors as the energy harvested can be random and small and not available when required. In this paper, we develop a simple model that captures the interactions between important parameters that govern the communication link performance of a EHS node, and analyze its outage probability for both slow fading and fast fading wireless channels. Our analysis brings out the critical importance of the energy profile and the energy storage capability on the EHS link performance. Our results show that properly tuning the transmission parameters of the EHS node and having even a small amount of energy storage capability improves the EHS link performance considerably.

Gene expression profile of epithelial cells and mesenchymal cells derived from limbal explant culture

Purpose: Limbal stem cell deficiency is a challenging clinical problem and the current treatment involves replenishing the depleted limbal stem cell (LSC) pool by either limbal tissue transplantation or use of cultivated limbal epithelial cells (LEC). Our experience of cultivating the LEC on denuded human amniotic membrane using a feeder cell free method, led to identification of mesenchymal cells of limbus (MC-L), which showed phenotypic resemblance to bone marrow derived mesenchymal stem cells (MSC-BM). To understand the transcriptional profile of these cells, microarray experiments were carried out.Methods: RNA was isolated from cultured LEC, MC-L and MSC-BM and microarray experiments were carried out by using Agilent chip (4x44 k). The microarray data was validated by using Realtime and semiquntitative reverse transcription polymerase chain reaction. Results: The microarray analysis revealed specific gene signature of LEC and MC-L, and also their complementary role related to cytokine and growth factor profile, thus supporting the nurturing roles of the MC-L. We have also observed similar and differential gene expression between MC-L and MSC-BM.Conclusions: This study represents the first extensive gene expression analysis of limbal explant culture derived epithelial and mesenchymal cells and as such reveals new insight into the biology, ontogeny, and in vivo function of these cells.

Linear gramicidin activates neutrophil functions and the activation is blocked by chemotactic peptide receptor antagonist

The activation of functional responses in rabbit peritoneal neutrophils by gramicidin and the chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, was studied. Gramicidin activated superoxide generation, lysosomal enzyme release and a decrease in fluorescence of chlortetracycline-loaded cells, as for the chemotactic peptide. The maximum intensities of the responses by gramicidin were lower than that by chemotactic peptide. Responses by both these peptides could be inhibited by t-butyloxycarbonyl-methionyl-leucyl-phenylalanine, a chemotactic peptide receptor antagonist. Gramicidin gave responses at low doses comparable to that of the chemotactic peptide.

Synthetic peptide models for the redox-active disulfide loop of glutaredoxin. Conformational studies

Two cyclic peptide disulfides Boc-Cys-Pro-X-Cys-NHMe (X = L-Tyr or L-Phe) have been synthesized as models for the 14-membered redox-active disulfide loop of glutaredoxin. 'H NMR studies at 270 MHz in chloroform solutions establish a type I 0-turn conformation for the Pro-X segment in both peptides, stabilized by a 4-1 hydrogen bond between the Cys(1) CO and Cys(4) NH groups. Nuclear Overhauser effects establish that the aromatic ring in the X = Phe peptide is oriented over the central peptide unit. In dimethyl sulfoxide solutions two conformational species are observed in slow exchange on the NMR time scale, for both peptides. These are assigned to type I and type I1 p-turn structures with -Pro-Tyr(Phe)-as the corner residues. The structural assignments are based on correlation of NMR parameters with model 14-membered cyclic cystine peptides with Pro-X spacers. Circular dichroism studies based on the -S-Sn- u* transition suggest a structural change in the disulfide bridge with changing solvent polarity, establishing conformational coupling between the peptide backbone and the disulfide linkage in these systems.

A Five-Level Inverter Scheme for a Four-Pole Induction Motor Drive by Feeding the Identical Voltage-Profile Windings From Both Sides

This paper presents a five-level inverter scheme with four two-level inverters for a four-pole induction motor (IM) drive. In a conventional three-phase four-pole IM, there exists two identical voltage-profile winding coil groups per phase around the armature, which are connected in series and spatially apart by two pole pitches. In this paper, these two identical voltage-profile pole-pair winding coils in each phase of the IM are disconnected and fed from four two-level inverters from four sides of the windings with one-fourth dc-link voltage as compared to a conventional five-level neutral-point-clamped inverter. The scheme presented in this paper does not require any special design modification for the induction machine. For this paper, a four-pole IM drive is used, and the scheme can be easily extended to IMs with more than four poles. The proposed scheme is experimentally verified on a four-pole 5-hp IM drive.

Mechanism of interaction of the antileukemic drug cytosine arabinoside with aromatic peptides : role of sugar conformation and peptide backbone

Interaction of the antileukemic drugs, cytosine-arabinoside (Ara-C) and adenosine-arabinoside (Ara-A) and a structural analogue, cytidine, with aromatic dipeptides has been studied by fluorescence and NMR spectroscopy. Ara-C and cytidine bind tryptophanyl and histidyl dipeptides but not tyrosyl dipeptides, while Ara-A does not bind to any of them. Both studies indicate association involving stacking of aromatic moieties. NMR spectra also indicate a protonation of the histidine moiety by Ara-C. In case of cytidine, the chemical shifts observed on binding to His-Phe imply that the backbone protons of the dipeptide participate in the binding. The conformation of the sugar and the base seem to play a very important role in the binding phenomenon as three similar molecules, Ara-C, Ara-A and cytidine bind in totally different ways.

Peptide models for b-turns.A circular dichroism study

The circular dichroism spectra of four 0-turn model peptides, Z-Aib-Pro-Aib-Pro- OMe (l), Piv-Pro-Aib-NHMe (2), Piv-Pro-D-Ala-NHMe (3) and Piv-Pro-Val-NHMe (4) have been examined under a wide range of solvent conditions, using methanol, hexafluoroisopropanol and cyclohexane. Type I and Type I1 0-turns have been observed for peptides 1 and 2 respectively, in the solid state, while the Pro-D-Ala sequence adopts a Type I1 Sturn in a related peptide crystal structure. A class C spectrum is observed for 1 in various solvents, suggesting a variant of a Type I(II1) structure. The Type I1 f3-turn is characterized by a CD spectrum having two positive CD bands at - 230 nm and - 202 nm, a feature observed in Piv-Pro- D-Ala-NHMe in cyclohexane and methanol and for Piv-Pro-Aib-NHMe in methanol. Peptide 2 exhibits solvent dependent CD spectra, which may be rationalized by considering Type 11, I11 and V reverse turn structures. Piv-Pro- Val-NHMe adopts nonaturn structures in polar solvents, but exhibits a class B spectrum in cyclohexane suggesting a population of Type I &turns.

A helical peptide containing a majority of valyl residues. The crystal structure of t-butyloxy- carbonyl-(L-valyl-_-aminoisobutyryl)3-L-valyl methyl ester onohydrate

The monohydrate of the heptapeptide t-butyloxycarbonyl-(L-valyl-α-aminoiso-butyryl)3-L-valyl methyl ester crystallizes in the orthorhombic space group P212121 with four molecules in a unit cell with the dimensions α= 9.375, b = 19.413 and c = 25.878 ÅA. The structure has been solved by direct methods and refined to an R value of 0.059 for 3633 observed reflections. The molecule in the structure exists as a slightly distorted 310-helix stabilized by five 4 -> 1 intramolecular hydrogen bonds, indicating the overwhelming influence of α-aminoisobutyryl (Aib) residues in dictating helical fold even when a majority of residues in the peptide have a low intrinsic propensity to be in helices. Contrary to what is expected in helical structures, the valyl side chains, two of which are disordered, exhibit all three possible conformations. The molecules arrange themselves in a head-to-tail fashion along the c-axis. The columns thus generated pack nearly hexagonally in the crystal.

Conformation of a 16-residue zervamicin IIA analog peptide containing three different structural features: 310-helix, alpha helix and ß-bend ribbon

Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib- Pro-Ala-Aib-Pro-Aib-Pro-Phe-OM(we here Boc is t-butoxycarbonyla nd Aib is a-aminoisobutyriac cid), a synthetica polar analog of the membrane-activefu ngal peptide antibioticz ervamtycinII A, crystallizesi n spaceg roupP 1 withZ =1 and cell parameters a = 9.086 ?0.002 A, b = 10.410 ?+ 0.002 A, c = 28.188 ? 0.004 A, a = 86.13 ? 0.01?, 13 = 87.90 ? 0.01?, and y = 89.27 ? 0.01?;o veralla greementf actorR = 7.3% for 7180 data (Fo > 3cr) and 0.91-A resolution. The peptide backbone makes a continuous spiral that begins as a 310-helix at the N-terminus, changes to an a-helix for two turns, and ends in a spiral of three fl-bends in a ribbon. Each of the fl-bends contains a proline residue at one of the corners. The torsion angles 4i range from -51? to -91? (average value -64o), and the torsion angles ai range from -1? to -46? (average value -31?). There are 10 intramolecularN H...OCh ydrogenb onds in the helix and two directh ead-to-taihl ydrogenb ondsb etween successive molecules. Two H20 and two CH30H solvent molecules fill additional space with appropriate hydrogen bonding in the head-to-tail region, and two additional H20 molecules form hydrogen bonds with carbonyl oxygens near the curve in the helix at Pro-10. Since there is only one peptide molecule per cell in space group P1, the molecules repeat only by translation, and consequently the helices pack parallel to each other.

Aqueous channels within apolar peptide aggregates. Solvated helix of Boc-Aib-Ala-Leu-Aib-Ala-Leu-Aib- -Ala-Leu-Aib-OMe. H2O.CH3OH

Although the peptide Boc-Aibl-Ala2-Leu3- Aib4-Alas Leu'-Aib7-Ala8-Leu9-Aib'0-OMe [with a t-butoxycarbonyl(Boc) blocking group at the amino terminus, a methyl ester (OMe) at the carboxyl terminus, and four a-aminoisobutyric (Aib) residues] has a 3-fold repeat of residues, the helix formed by the peptide backbone is irregular. The carboxyl-terminal half assumes an at-helical form with torsion angles ) and r of approximately -60° and -45°, respectively, whereas the amino-terminal half is distorted by an insertion of a water molecule between the amide nitrogen of Ala5 [N(5)] and the carbonyl oxygen of Ala2 [0(2)]. The water molecule W(1) acts as a bridge by forming hydrogen bonds N(5).W(1) (2.93 A) and W(1)---0(2) (2.86 A). The distortion of the helix exposes the carbonyl oxygens of Aib' and Aib4 to the outside environment, with the consequence that the helix assumes an amphiphilic character despite having all apolar residues. Neighboring helices in the crystal run in antiparallel directions. On one side of a helix there are only hydrophobic contacts with efficient interdigitation of leucine side chains with those from the neighboring helix. On the other side of the helix there are hydrogen bonds between protruding carbonyl oxygens and four water molecules that separate two neighboring helices. Along the helix axis the helices bind head-to-tail with a direct hydrogen bond N(2)-0(9) (3.00 A). Crystals grown from methanol/water solution are in space group P2, with a = 15.778 ± 0.004 A, b = 11.228 ± 0.002 A, c = 18.415 ± 0.003 A, = 102.10 ± 0.02ur and two formula units per cell for C49HON1003 2H2OCH3OH. The overall agreement factorR is 7.5% for 3394 reflections observed with intensities >3a(F), and the resolution is 0.90 A.

A possible role for a low molecular weight peptide in regulation of testosterone production by rat Leydig cells

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of Percoll purified Leydig cell proteins from 20- and 120-day-old rats revealed a significant decrease in a low molecular weight peptide in the adult rats. Administration of human chorionic gonadotropin to immature rats resulted in a decrease in the low molecular weight peptide along with increase in testosterone production. Modulation of the peptide by human chorionic gonadotropin could be confirmed by Western blotting. The presence of a similar peptide could be detected by Western blotting in testes of immature mouse, hamster, guinea pig but not in adrenal, placenta and corpus luteum. Administration of testosterone propionate which is known to inhibit the pituitary luteinizing hormone levels in adult rats resulted in an increase in the low molecular weight peptide, as checked by Western blotting. It is suggested that this peptide may have a role in regulation of acquisition of responsiveness to luteinizing hormone by immature rat Leydig cells.

PeptideMine - A webserver for the design of peptides for protein-peptide binding studies derived from protein-protein interactomes

Background: Signal transduction events often involve transient, yet specific, interactions between structurally conserved protein domains and polypeptide sequences in target proteins. The identification and validation of these associating domains is crucial to understand signal transduction pathways that modulate different cellular or developmental processes. Bioinformatics strategies to extract and integrate information from diverse sources have been shown to facilitate the experimental design to understand complex biological events. These methods, primarily based on information from high-throughput experiments, have also led to the identification of new connections thus providing hypothetical models for cellular events. Such models, in turn, provide a framework for directing experimental efforts for validating the predicted molecular rationale for complex cellular processes. In this context, it is envisaged that the rational design of peptides for protein-peptide binding studies could substantially facilitate the experimental strategies to evaluate a predicted interaction. This rational design procedure involves the integration of protein-protein interaction data, gene ontology, physico-chemical calculations, domain-domain interaction data and information on functional sites or critical residues. Results: Here we describe an integrated approach called ``PeptideMine'' for the identification of peptides based on specific functional patterns present in the sequence of an interacting protein. This approach based on sequence searches in the interacting sequence space has been developed into a webserver, which can be used for the identification and analysis of peptides, peptide homologues or functional patterns from the interacting sequence space of a protein. To further facilitate experimental validation, the PeptideMine webserver also provides a list of physico-chemical parameters corresponding to the peptide to determine the feasibility of using the peptide for in vitro biochemical or biophysical studies. Conclusions: The strategy described here involves the integration of data and tools to identify potential interacting partners for a protein and design criteria for peptides based on desired biochemical properties. Alongside the search for interacting protein sequences using three different search programs, the server also provides the biochemical characteristics of candidate peptides to prune peptide sequences based on features that are most suited for a given experiment. The PeptideMine server is available at the URL: http://caps.ncbs.res.in/peptidemine