Structural analysis of lipid complexes of GM2-activator protein

The GM2-activator protein (GM2-AP) is a small lysosomal lipid transfer protein essential for the hydrolytic conversion of ganglioside GM2 to GM3 by beta-hexosaminidase A. The crystal structure of human apo-GM2-AP is known to consist of a novel beta-cup fold with a spacious hydrophobic interior. Here, we present two new structures of GM2-AP with bound lipids, showing two different lipid-binding modes within the apolar pocket. The 1.9A structure with GM2 bound shows the position of the ceramide tail and significant conformational differences among the three molecular copies in the asymmetric unit. The tetrasaccharide head group is not visible and is presumed to be disordered. However, its general position could be established through modeling. The structure of a low-pH crystal, determined at 2.5A resolution, has a significantly enlarged hydrophobic channel that merges with the apolar pocket. Electron density inside the pocket and channel suggests the presence of a trapped phospholipid molecule. Structure alignments among the four crystallographically unique monomers provide information on the potential role for lipid binding of flexible chain segments at the rim of the cavity opening. Two discrete orientations of the S130-T133 loop define an open and a closed configuration of the hydrophobic channel that merges with the apolar pocket. We propose: (i) that the low-pH structure represents an active membrane-binding conformation; (ii) that the mobile S130-T133 loop serves as a gate for passage of ligand into the apolar pocket; and (iii) that this loop and the adjacent apolar V59-W63 loop form a surface patch with two exposed tryptophan residues that could interface with lipid bilayers.     

Ecdysone metabolism in adult crickets,Gryllus bimaculatus

The fate of injected [³H]ecdysone has been investigated in female and male adults of the Mediterranean field cricket, Gryllus binaculatus (de Geer). The metabolism is similar in both sexes and at various stages of adult life. Several classes of apolar metabolites (A1–A5) represent the major compounds. The amount of polar conjugates is low in all tissues, as are the concentrations of 20-hydroxyecdysone. Ovaries are the only organs capable of storing considerable amounts of ecdysteroids. The amount of radiolabelled ecdysteroid activity (mostly [³H]ecdysone) excreted during the first 24 hr after injection is high.The chemical identity of the apolar metabolites is not yet known. A2, which is the major apolar compound, has recently been identified as a complex of ecdysone conjugates with abundant long-chain fatty acids (Hoffman et al., 1985 Life Sci.37, 185–192). Incubations with tissue homogenates in vitro have shown that several organs are capable of converting ecdysone into apolar compounds. Apolar ecdysteroid acyl esters represent a newly identified class of ecdysone conjugates from insects. Their role in regulation of free ecdysteroid titres during the reproductive period in female crickets is discussed.     

Cell type–specific expression of SEPT3-homology subgroup members controls the subunit number of heteromeric septin complexes

Septins are filament-forming proteins important for organizing the cortex of animal and fungal cells. In mammals, 13 septin paralogues were recently shown to assemble into core heterohexamer and heterooctamer complexes, which serve as building blocks for apolar filamentous structures that differ among cell types. To determine how tissue-specific septin paralogue expression may shape core heteromer repertoires and thereby modulate properties of septin filaments, we devised protocols to analyze native septin heteromers with distinct numbers of subunits. Our evidence based on genetically manipulated human cells supports and extends recent concepts of homology subgroup–restricted assembly into distinct categories of apolar heterohexamers and heterooctamers. We also identify a category of tetramers that have a subunit composition equivalent to an octameric building block. These atypical tetramers are prevalent in lymphocytes and neural tissues, in which octamers are abundant but hexamers are rare. Our results can be explained by tissue-specific expression of SEPT3 subgroup members: SEPT3, SEPT9, and SEPT12. These serve as cognate subunits in either heterooctamers or atypical tetramers but exhibit different preferences in various tissues. The identified tissue-specific repertoires of septin heteromers provide insights into how higher-order septin structures with differential properties and stabilities may form in diverse animal cell types.     

Topogenic signals in integral membrane proteins

Integral membrane proteins are characterized by long apolar segments that cross the lipid bilayer. Polar domains flanking these apolar segments have a more balanced amino acid composition, typical for soluble proteins. We show that the apolar segments from three different kinds of membrane-assembly signals do not differ significantly in amino acid content, but that the inside/outside location of the polar domains correlates strongly with their content of arginyl and lysyl residues, not only for bacterial inner-membrane proteins, but also for eukaryotic.proteins from the endoplasmic reticulum, the plasma membrane, the inner mitochondrial membrane, and the chloroplast thylakoid membrane. A positive-inside rule thus seems to apply universally to all integral membrane proteins, with apolar regions targeting for membrane integration and charged residues providing the topological information.     

The Shape of an Auxin Pulse,and What It Tells Us about the Transport Mechanism

Auxin underlies many processes in plant development and physiology, and this makes it of prime importance to understand its movements through plant tissues. In stems and coleoptiles, classic experiments showed that the peak region of a pulse of radio-labelled auxin moves at a roughly constant velocity down a stem or coleoptile segment. As the pulse moves it becomes broader, at a roughly constant rate. It is shown here that this ‘spreading rate’ is larger than can be accounted for by a single channel model, but can be explained by coupling of channels with differing polar transport rates. An extreme case is where strongly polar channels are coupled to completely apolar channels, in which case auxin in the apolar part is ‘dragged along’ by the polar part in a somewhat diffuse distribution. The behaviour of this model is explored, together with others that can account for the experimentally observed spreading rates. It is also shown that saturation of carriers involved in lateral transport can explain the characteristic shape of pulses that result from uptake of large amounts of auxin.     

Specific assay for radiolabelled digoxin and its known apolar metabolites in biological fluids. I.

A specific assay method for radiolabelled digoxin and its known apolar metabolites in plasma, urine and saliva was developed. The assay permits the delineation of the pharmacokinetics of digoxin and its metabolites after single-dose administration of the drug to humans. Column chromatographic and solvent extraction procedures were used for the separation of apolar and polar compounds. Thin-layer chromatography was applied for the individual and specific assessment of digoxin and its apolar metabolites. Apolar and polar standards were used for quantitative assessments of all the procedures used. Accuracy and precision of the assay developed were evaluated in plasma, urine and saliva using biological samples spiked with known amounts of standards and by measuring replicates of biological samples obtained from pharmacokinetic studies with digoxin administration to humans.     

Induction of cytoplasmic polarity in heterokaryons of mouse 4-cell-stage blastomeres fused with 8-cell- and 16-cell-stage blastomeres

Cell surface and cytoplasmic polarity is exhibited by the blastomeres of mouse preimplantation embryos following compaction at the 8-cell stage of cleavage. It has been hypothesized that cytoplasmic polarity is initiated by plasma membrane functions of polar blastomeres that are absent from apolar blastomeres. To test this hypothesis the plasma membranes of "test" polar and apolar 8-cell- and 16-cell-stage blastomeres were inserted into the plasma membrane of "carrier" 4-cell-stage blastomeres by polyethylene glycol-mediated fusion of carrier-test blastomere pairs. After a 4-hr culture period each heterokaryon was scored for the distribution of two marker organelles--lipid droplets and nuclei--with respect to their proximity to the plasma membrane insert from the test blastomere. Plasma membrane inserts from polar test blastomeres were identified by labeling their apical domains with fluorescently tagged (succinylated) concanavalin A. The incidence of polar heterokaryons (those exhibiting a discrete fluorescently labeled area of plasma membrane corresponding to the apical domain inherited from the test blastomere) was 55/85 (69%) and 48/79 (61%) for 8-cell-stage and 16-cell-stage test blastomeres, respectively. In all polar heterokaryons, both nuclei were subjacent to the fluorescent label (apical domain of a polar plasma membrane insert), while the majority of lipid droplets resided in the hemisphere opposite the fluorescent label. In all 61 apolar heterokaryons examined (those lacking a discrete fluorescently labeled plasma membrane area) both nuclei were centrally located and lipid droplets were randomly distributed. These observations are consistent with the hypothesis that cytoplasmic polarity can be initiated by properties that distinguish the plasma membranes of polar blastomeres from those of apolar blastomeres.     

Ecdysteroid titre and metabolism to novel apolar derivatives in adult female Boophilus microplus (Ixodidae)

The free ecdysteroid titre determined by radioimmunoassay in adult female Boophilus microplus showed a peak just prior to full engorgement and detachment of the ticks and decreased subsequently to a very low value. In contrast, the titre of polar ecdysteroid conjugates was very low. Ecdysone was the major ecdysteroid at peak titre and was accompanied by much lower levels of 20-hydroxyecdysone. In newly detached ticks, injected [³H]ecdysone was metabolized primarily (80%) into much less polar compounds, which could be resolved into at least three groups by reversed-phase h.p.l.c. These [³H] “apolar” metabolites were transferred to the newly laid eggs, where they accounted for the vast preponderance of ecdysteroids, the level of free hormone being low. Hydrolysis of the three groups of compounds with an esterase preparation from porcine liver yielding [³H]ecdysone, together with the release of [³H] ecdysteroid and fatty acids upon alkaline saponification of the compounds, suggests that they are of a fatty acyl ester nature. The chemical transformation of these “esters” into the corresponding acetonide derivatives indicates that the 2- and 3-hydroxyls of ecdysone remain unsubstituted in these compounds. Several tick tissues, including Malpighian tubules, ovaries, gut, and fat body, metabolized [³H]ecdysone in vitro forming the “apolar esters” as major products. The maternal ecdysteroid “esters” may function as storage forms of hormone (presumably hormonally inactive), which could be hydrolysed enzymically during embryogenesis releasing free ecdysteroids. Such enzymic hydrolysis of [³H]ecdysone “esters” by homogenates from developing eggs of B. microplus has been demonstrated.     

Ontogenetic and seasonal development of wax composition and cuticular transpiration of ivy (Hedera helix L.) sun and shade leaves

The ontogenetic and seasonal development of wax composition and cuticular transpiration of sun and shade leaves of ivy (Hedera helix L.) was analysed by investigating leaves varying in age between 4 and 202 d. It was discovered that the total amount of solvent-extractable wax was composed of two distinct fractions, separable by column chromatography: (i) a less polar or apolar monomeric wax fraction consisting of the typical linear, long-chain aliphatics usually described as cuticular wax components and (ii) a polar, oligomeric wax fraction consisting of primary alcohols and acids mostly esterified to C₁₂-, C₁₄- and C₁₆-ω-hydroxyfatty acids. The apolar wax fraction, which could be analysed directly by gas chromatography coupled with mass spectrometry (GC-MS), exhibited pronounced seasonal changes in composition. Wax amounts in the apolar fraction reached a maximum after about 30 d and gradually decreased again during the remaining period of the season investigated. In contrast, the polar wax fraction, which was analysable by GC-MS only after transesterification, rapidly increased early in the season, reaching a plateau after 40 d, and then remained constant during the rest of the season. Thus, total amounts of solvent-extractable cuticular waxes, which can be determined gravimetrically, will only be detected by GC-MS after fractionation and transesterification, a methodological approach rarely applied in the past in cuticular wax analysis. Additionally, investigation of the cutin polymer matrix after depolymerisation through transesterification, revealed that only those primary alcohols and acids forming an essential part of the apolar and the polar wax fractions were esterified during the investigated season and incorporated in increasing amounts into the cutin polymer matrix (matrix-bound wax fraction). Thus, it can be concluded that a complete analysis of cuticular wax of ivy and its seasonal development can only be achieved if all the relevant fractions (i) the less polar or apolar, (ii) the polar and (iii) the wax fraction bound to the cutin polymer matrix are investigated. Cuticular transpiration rapidly decreased within the first 30 d and essentially remained constant during the rest of the season. Thus, changes in cuticular water permeability were closely correlated with the most prominent changes in wax amounts and composition occurring during the first 30 d of ontogenetic leaf development. However, during the remainder of the year, up to 202 d, cuticular transport properties remained constant, although significant quantitative and qualitative changes in cuticular wax composition continued to occur. Thus, our study clearly demonstrated that there will be no simple relationship between chemical composition of cuticular waxes and transport properties of isolated ivy leaf cuticles. Received: 2 March 1998 / Accepted: 26 June 1998     

Lignin-polymer blends: evaluation of compatibility by image analysis

This paper opens onto a general discussion on the development of new polymeric materials obtained from lignin blends. The aim is (i) to look for good polymer candidates to obtain a good compatibility with lignins (that is among semi polar polymers), and (ii) to look for good lignin candidates to obtain a good compatibility with polymers showing extreme behaviours (very polar, e.g. starch, or apolar, e.g. polypropylene). The compatibility is simply assessed through the blend morphology, as studied by visible microscopy. The morphology of the blends obtained from semi polar polymers is very sensitive to the variation of the solubility parameters. In a low range of polymer solubility parameters (delta delta = 1 cal cm(-3)), both heterogeneous and homogeneous systems are obtained. These blends could be easily improved by a careful choice in the polymer structure (particularly in the family of biodegradable polyesters); it could be possible also to take advantage of lignin variability to improve the compatibility. Only low molecular weight lignins are compatible with apolar and very polar matrixes. These compounds induce interesting specific properties, and original methods have to be looked for in order to improve their production.     

Probable occurrence of ecdysteroid fatty acid esters in different classes of arthropods

We investigated the fate of injected [³H]ecdysone or [³H]20-hydroxyecdysone in various species of ticks, spiders, scorpions, myriapods, crustaceans and insects. Most of these arthropods were able to convert the ecdysteroids to esterase-labile metabolites with a very apolar behaviour in reverse-phase HPLC. Some of them have retention times similar to the apolar conjugates AP2 of the tick, Ornithodoros moubata, which have been identified recently as ecdysteroids esterified as C₂₂ with palmitic, stearic, oleic or linoleic acid [Diehl et al. (1985a) Int. J. invert. Reprod. Devl.8, 1–13]. Others are less apolar and could correspond to the AP1 from O. moubata. The possible function of these metabolites remains to be established. They could represent inactivation products and/or a hormone storage-form for embryos.     

Medium chain length alkane solvent-cell transfer rates in two-liquid phase, pseudomonas oleovorans cultures

The oxidation of medium chain length alkanes and alkenes (C6 to C12) by Pseudomonas oleovorans and related, biocatalytically active recombinant organisms, in two-liquid phase cultures can be used for the biochemical production of several interesting fine chemicals. The volumetric productivities that can be attained in two-liquid phase systems can be, in contrast to aqueous fermentations, limited by the transport of substrates from an apolar phase to the cells residing in the aqueous phase and by toxic effects of apolar solvents on microbial cells. We have assessed the impact of these possible limitations on attainable productivities in two-liquid phase fermentations operated with mcl-alkanes. Pseudomonas oleovorans grows well in two-liquid phase media containing a bulk n-octane phase as the sole carbon source. However, cells are also damaged, typically resulting in a cell lysis rate of about 0.08 to 0. 10 h-1. These rates could be lowered by 50 to 70% to 0.03 h-1 and substrate yields increased from 0.55 to 0.85 g g-1 by diluting octane in non-metabolizable long-chain hydrocarbon solvents. Transfer rates of medium chain length (mcl) alkanes from the apolar phase to the cells were determined by following growth and the rate at which carbon-containing metabolites accumulated in the different phases of the cultures. mcl-Alkane solvent-cell transfer rates of at least 79, 64, and 18 mmol per liter of aqueous medium per hour were determined for n-heptane, n-octane, and n-decane, respectively. Rates of up to 30 mmol L-1 h-1 were observed under octane-limiting conditions in systems where the apolar substrate was dissolved to concentrations below 3% (v/v) in hexadecene. Based on low power input experiments, we estimated the maximum obtainable mass transfer rates in large scale processes to be in the range of 13 mmol L-1 h-1 for decane and higher than 45 mmol L-1 h-1 for octane and heptane. The results indicate that high solvent to cell mass transfer rates and minimized cell damage will enable high production rates in two-liquid phase bioprocesses, justifying ongoing efforts to attain high densities of catalytically, highly active cells in such systems. Copyright 1998 John Wiley & Sons, Inc.     

A review about nothing: Are apolar cavities in proteins really empty?

Cavities within proteins that are strictly apolar typically appear to be empty. It has been suggested, however, that water molecules may be present within such cavities but are too disordered to be seen in conventional crystallographic analyses. In contrast, it is argued here that solvent mobility will be limited by the size of the cavity and for this reason high‐occupancy solvent in cavities of typical volume should be readily detectable using X‐ray crystallography. Recent experimental studies of cavity hydration are reviewed. Such studies are consistent with theoretical predictions that it is energetically unfavorable to have a single water molecule in an apolar cavity. As apolar cavities become larger, a point is reached where it is favorable to have the cavity occupied by a cluster of mutually H‐bonded water molecules. The exact size of such a cavity in a protein is yet to be verified.     

Solid model compounds and the thermodynamics of protein unfolding.

Analysis of thermodynamic data on the dissolution of solid cyclic dipeptides into water in terms of group additivity provides a rationale for the enthalpy and entropy convergence temperatures observed for small globular protein denaturation and the dissolution of model compounds into water. Convergence temperatures are temperatures at which the extrapolated enthalpy or entropy changes for a series of related compounds take on a common value. At these temperatures (TH* and TS*) the apolar contributions to the corresponding thermodynamic values (delta H degrees and delta S degrees) are shown to be zero. Other contributions such as hydrogen bonding and configurational effects can then be evaluated and their quantitative effects on the stability of globular proteins assessed. It is shown that the denaturational heat capacity is composed of a large positive contribution from the exposure of apolar groups and a significant negative contribution from the exposure of polar groups in agreement with previous results. The large apolar contribution suggests that a liquid hydrocarbon model of the hydrophobic effect does not accurately represent the apolar contribution to delta H degrees of denaturation. Rather, significant enthalpic stabilizing contributions are found to arise from peptide groups (hydrogen bonding). Combining the average structural features of globular proteins (i.e. number of residues, fraction of buried apolar groups and fraction of hydrogen bonds) with their specific group contributions permits a first-order prediction of the thermodynamic properties of proteins. The predicted values compare well with literature values for cytochrome c, myoglobin, ribonuclease A and lysozyme. The major thermodynamic features are described by the number of peptide and apolar groups in a given protein.     

Cell interactions influence the fate of mouse blastomeres undergoing the transition from the 16- to the 32-cell stage

Newly formed polar and apolar 1/16 blastomeres were isolated and cultured singly, or in various combinations, through division to form 32-cell blastomeres. The morphology of the resulting cell cluster appeared to depend upon the nature and composition of the cell combination used. In most polar + apolar couplets, the polar cell enveloped the apolar cell, and following division, a 4/32 cluster was thereby generated containing two trophectoderm-like external cells derived from the polar cell and two ICM-like internal cells derived from the apolar cells. A polar cell cultured in isolation divided to give either two trophectoderm-like external cells or a trophectoderm-like cell and an ICM-like cell. Two polar cells cultured together generated clusters in which the ratio of trophectoderm-like:ICM-like cells was 4:0 or 3:1. Most apolar cells cultured together in couplets polarized, and generated 4/32 clusters containing either purely trophectoderm-like or a mixture of trophectoderm- and ICM-like cells. The results are consistent with the notion that continuing interactions between polar and apolar cells are necessary to maintain their respective fates as trophectoderm and ICM, and that in the absence of these interactions polar cells can generate ICM cells by a differentiative division and apolar cells can generate trophectoderm cells by polarizing in response to asymmetric cell contacts.     

Quaternary structure of intestinal maltase-glucoamylase in pancreatectomized rats

Detergent-solubilized intestinal maltase-glucoamylase was isolated 1 week postpancreatectomy (dMpanc) and purified in the presence of detergent and protease inhibitors. Upon sodium dodecyl sulfate - polyacrylamide gel electrophoresis under nondissociating conditions, the major band had a molecular weight of 280,000, slightly smaller than similar bands from detergent (dM) and papain (pM) solubilized maltase from nonpancreatectomized rats. Upon octyl-Sepharose CL-4B chromatography, 57% of the enzyme was eluted by aqueous buffer, unlike pM which was almost completely eluted or dM, 95% of which bound to the column. All fractions of dMpanic from octyl-Sepharose 4B were reduced, by boiling +/- beta-mercaptoethanol, to monomeric subunits, indicating that processing by pancreatic enzymes at the level of the brush border is not a requirement for the appearance of subunits in the rat. As well, under these dissociating conditions, the 145,000 subunit previously identified with the apolar terminus was present in all fractions of dMpanc, including the aqueous fraction, whereas pM contained only the 130,000 subunit. The presence of dMpanc in the aqueous fraction cannot be explained, therefore, by proteolytic cleavage of an apolar anchor segment from the 145,000 subunit. Pancreatic enzymes may affect the enzyme in a minor fashion, however, since aqueous solubility was enhanced and the apparent molecular weight was reduced by pancreatectomy, suggesting a more compact conformation with shielding of apolar segments.     

Growth of nutrient-replete Microcystis PCC 7806 cultures is inhibited by an extracellular signal produced by chlorotic cultures

The frequency of cyanobacterial blooms has been increasing all over the world. These blooms are often toxic and have become a serious health problem. The aim of this work was to search for population density control mechanisms that could inhibit the proliferation of the toxic bloom-forming genus Microcystis. Microcystis PCC 7806 cultured for long periods in liquid ASM-1 medium loses its characteristic green colour. When a medium of chlorotic cultures is added to a nutrient-replete culture, cell density increase is drastically reduced when compared with controls. Inhibition of cell proliferation occurs in Microcystis cultures from any growth stage and was not strain-specific, but other genera tested showed no response. Investigations on the mechanism of growth inhibition showed that cultures treated with the conditioned medium acquired a pale colour, with pigment concentration similar to that found in chlorotic cultures. Ultrastructural examination showed that the conditioned medium induced thylakoid membrane disorganization, typical of chlorotic cells, in nutrient-replete cultures. An active extract was obtained and investigations showed that activity was retained after heating and after addition of an apolar solvent. This indicates that activity of the conditioned medium from chlorotic cells results from non-protein, apolar compound(s).     

Preparation and utilization of a reagent for the isolation and purification of low-molecular-mass thiols

Problems inherent in the isolation of thiols from natural sources, such as oxidation, undesirable addition reactions, and low concentration of thiol species in cell-free extracts, can be circumvented by reversible derivatization to a less labile form which can be concentrated selectively. These objectives are realized by converting thiols to heterodisulfides in which the thiol partner is an apolar thiol with strong affinity for hydrophobic stationary phases. When reacted with 2-S-(2(')-thiopyridyl)-6-hydroxynaphthyldisulfide at pH<5, where most thiol species are relatively stable to atmospheric oxidation, mixed disulfides with 2-mercapto-6-hydroxynaphthalene as the apolar partner are obtained in good yield and can be concentrated onto a hydrophobic stationary phase. Such heterodisulfides exhibit excellent chromatographic properties when separated on reversed-phase media and the derivatization reaction can, therefore, be conveniently monitored. Following their isolation as the heterodisulfides the thiol species of interest are recovered by reduction and facile separation from the apolar 2-mercapto-6-hydroxynaphthalene partner.     

A structural model of the acetylcholine receptor channel based on partition energy and helix packing calculations.

A structural model of the transmembrane portion of the acetylcholine receptor was developed from sequences of all its subunits by using transfer energy calculations to locate transmembrane alpha-helices and to calculate which helical side chains should be in contact with water inside the channel, with portions of other transmembrane helices, or with lipid hydrocarbon chains. "Knobs-into-holes" side chain packing calculations were used with other factors to stack the transmembrane alpha-helices together. In the model each subunit has the following structures in order along the sequence from the NH2 terminus: a large extracellular domain of undetermined structure, a short apolar alpha-helix that lies on the extracellular lipid surface of the membrane; three apolar transmembrane alpha-helices (I, II, and III), a cytoplasmic domain of undetermined structure, an amphipathic transmembrane alpha-helix (L) that forms the channel lining, a short extracellular alpha-helix, another apolar transmembrane alpha-helix (IV), and a small cytoplasmic domain formed by the COOH-terminal end of the chain. Three concentric layers form the pore. A bundle of five amphipathic L helices forms the channel lining. This bundle is surrounded by a bundle of 10 alternating II and III helices. Helices I and IV cover portions of the outer surface of the bundle formed by helices II and III. Positions of disulfide bridges are predicted and a mechanism for opening and closing conformational changes is proposed that requires tilting transmembrane helices and possibly a thiol-disulfide interchange reaction.     

Theoretical prediction of the basic helix types in alpha,beta-hybrid peptides

This study provides a complete overview on all possible helical- folding patterns, their stabilities, and their detailed molecular structure in the novel foldamer class of alpha,beta-hybrid peptides on the basis of ab initio molecular orbital (MO) theory. The results indicate a considerable intrinsic potential of backbone folding. As found for other peptide foldamers, representatives of mixed or beta-helices are most stable in more apolar media, whereas polar environments favor the helices with the hydrogen bonds pointing in only one direction. The theoretical results confirm the hydrogen-bonding patterns found in the first experimental studies on these hybrid peptides. Selecting special backbone substitution patterns, the secondary structure potential of the alpha,beta-hybrid peptides could be of great importance for a rational peptide and protein design.