Biphasic tissue Doppler waveforms during isovolumic phases are associated with asynchronous deformation of subendocardial and subepicardial layers.

Subendocardial and subepicardial layers of the left ventricle (LV) are characterized with right- and left-handed helical orientations of myocardial fibers. We investigated the origin of biphasic deformations of the LV wall during isovolumic contraction (IVC) and relaxation (IVR). In eight open-chest adult pigs, strain rates were measured along the right- and left-handed helical directions in the LV anterior wall by implanting 16 sonomicrometry crystals. Sonomicrometry strain rates were compared with the longitudinal subendocardial strain rates obtained by tissue Doppler imaging. During ejection and diastolic filling, shortening and lengthening occurred synchronously along the right- and left-handed helical directions. However, during IVC and IVR, the deformations were dissimilar in the two directions. Transmural shortening during IVC occurred along the right-handed helical direction and was accompanied with transient lengthening in the left-handed helical direction. Conversely, during IVR, the LV lengthened along the left-handed helical direction and shortened in the right-handed helical direction. Peak subendocardial strain rates obtained by tissue Doppler imaging during IVC and IVR correlated with corresponding sonomicrometry strain rate values obtained along the right- and left-handed helical directions (r = 0.81, P < 0.001 and r = 0.70, P = 0.001, respectively). Our data suggest that brief counterdirectional movements occur within the LV wall during IVC and IVR. Shortening along the right-handed helical direction is accompanied with reciprocal lengthening in the left-handed helical direction during IVC and vice versa during IVR. The results support an association between asynchronous deformation of subendocardial and subepicardial muscle fibers and the biphasic isovolumic movements observed with high-resolution tissue Doppler imaging.     

The influence of a chiral amino acid on the helical handedness of PNA in solution and in crystals

The X-ray structure of a self-complementary PNA hexamer (H-CGTACG-L-Lys-NH(2)) has been determined to 2.35 A resolution. The introduction of an L-lysine moiety has previously been shown to induce a preferred left-handedness of the PNA double helices in aqueous solution. However, in the crystal structure an equal amount of interchanging right- and left-handed helices is observed. The lysine moieties are pointing into large solvent channels and no significant interactions between this moiety and the remaining PNA molecule are observed. In contrast, molecular mechanics calculations show a preference for the left-handed helix of this hexameric PNA in aqueous solution as expected. The calculations indicate that the difference in the free energy of solvation between the left-handed and the right-handed helix is the determining factor for the preference of the left-handed helix in aqueous solution.     

Statistical mechanical studies of polypeptides. 1. Theory of the helix-coil transition including right- and left-handed helical states

The Lifson-Roig and Zimm-Bragg theories of the helix–coil transition in polypeptides are generalized to include both right- and left-handed α-helical states. The partition functions for these more general theories are formulated in terms of the parameters u, v_R, V_L, W_R, and w_L for the generalized Lifson-Roig theory and σ_R, σ_L, s_R, and s_L for the generalized Zimm-Bragg theory. Matrix equations are derived for calculating such average molecular properties as the fraction of the amino acid residues hydrogen bonded into right- and left-handed α-helices, the average number of right- and left-handed helical sequences per molecule, the number-average length (in residues) of the right- and left-handed helical sequences, and the degree of solvent binding to the peptide NH and CO groups. These equations are shown to be conveniently adaptable to machine methods of calculation, thus avoiding the difficulty of solving an eigenvalue problem where the secular equation is of a high order. A discussion is given of the various energetic and entropic effects which determine the screw sense and stability of helices and of the extent to which it is valid to interpret experimental data by adjustment of the parameters of these statistical mechanical theories which include in their formulation only near-neighbor interactions between residues.     

Intervening sequences in human fetal globin genes adopt left-handed Z helices

The large intervening sequences ( IVS2 ) of three human fetal globin genes contain tracts of alternating purine-pyrimidine sequences approximately 40-60 base pairs in length which adopt left-handed Z DNA helices under the influence of negative supercoiling. The amount of negative supercoiling (approximately 0.045) required for the right- to left-handed transitions is within the physiological range. The structural aberrations between the right- and left-handed helices were mapped by sequencing the S1 nuclease cleavage sites. Two-dimensional gel electrophoretic analyses of the supercoil-induced relaxation served to characterize the type and length of left-handed structure. Furthermore, binding studies with several types of antibodies confirmed the presence of left-handed helices. Since these simple sequences appear to be hotspots for recombination and gene conversion, unusual DNA conformations may participate in genetic expression.     

Conformational studies of polymers and copolymers of L-aspartate esters. I. Preparation and solution studies

An alcoholysis method is described for the modification of high molecular weight poly(β-benzyl L -asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n-propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L -aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β-methyl L -aspartate) has the left-handed helix sense, the others are right-handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right-handed form of the copolymers of benzyl L -aspartate and ethyl L -aspartate results in a transition to the left-handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β-n-propyl L -aspartate) undergoes a transition from the right- to the left-handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right- or left-handed helical form.     

Features of the Brain Functional Organization in Right- and Left-handed 6- to 7-Year-Old Children during Visuospatial Performance of Different Complexity: I. Comparative Analysis of EEG Parameters during Simple Visuospatial Performance

The spectral power density and coherence of the rhythmic EEG components of the and ranges were analyzed in 6- to 7-year-old right- and left-handed children during simple visuospatial performance. Both similar and distinct features in the time course of EEG parameters were revealed in right- and left-handed children. No asymmetry in the right- and left-hemispheric involvement in correlation with the type of manual asymmetry was observed.     

Role of Motor Asymmetry and of Sex in Lateralization of Autonomic Effects

The paper presents data on the populational laterality proportions among men and women. Analysis of cardiac rhythm variations in right- and left-handed men and women in rest and during mental loading has shown a more pronounced sympathetic domination in left-handed examinees unlike right-handers. The most significant differences in the autonomic balance during mental loading were revealed between the left-handed and right-handed men. An earlier physiological maturation was established to be more characteristic of left-handed women as compared with right-handers. On the background of low and high levels of estrogens a correlation was revealed between the level of hormones and parameters of autonomic balance of the autonomic nervous system both in right-handed and left-handed women.     

On the helix sense of gramicidin A single channels.

In order to resolve whether gramicidin A channels are formed by right- or left-handed beta-helices, we synthesized an optically reversed (or mirror image) analogue of gramicidin A, called gramicidin A-, to test whether it forms channels that have the same handedness as channels formed by gramicidin M- (F. Heitz et al., Biophys. J. 40:87-89, 1982). In gramicidin M- the four tryptophan residues have been replaced with phenylalanine, and the circular dichroism (CD) spectrum therefore reflects almost exclusively contributions from the polypeptide backbone. The CD spectrum of gramicidin M- in dimyristoylphosphatidylcholine vesicles is consistent with a left-handed helical backbone folding motif (F. Heitz et al., Biophys. Chem. 24:149-160, 1986), and the CD spectra of gramicidins A and A- are essentially mirror images of each other. Based on hybrid channel experiments, gramicidin A- and M- channels are structurally equivalent, while gramicidin A and A- channels are nonequivalent, being of opposite helix sense. Gramicidin A- channels are therefore left-handed, and natural gramicidin A channels in phospholipid bilayers are right-handed beta 6.3-helical dimers.     

Features of the Brain Functional Organization in Right- and Left-Handed 6- to 7-Year-Old Children during Visuospatial Performance of Different Complexity: II. Analysis of EEG Parameters during Complex Visuospatial Performance

The features of brain functional organization during complex visuospatial performance were studied in 6- to 7-year-old right- and left-handed children. Differences in the brain functional organization were revealed between children with different profiles of manual asymmetry. Presentation of complex experimental tasks to right-handed children resulted in the formation of selective functional connections between centers, which is indicative of the use of economical and efficient mechanisms of the organization of activity. Generalized functional integration was observed in left-handed children, which reflected an immature type of regulation of cortical activity.     

The sound of one-hand clapping: handedness and perisylvian neural correlates of a communicative gesture in chimpanzees

Whether lateralization of communicative signalling in non-human primates might constitute prerequisites of hemispheric specialization for language is unclear. In the present study, we examined (i) hand preference for a communicative gesture (clapping in 94 captive chimpanzees from two research facilities) and (ii) the in vivo magnetic resonance imaging brain scans of 40 of these individuals. The preferred hand for clapping was defined as the one in the upper position when the two hands came together. Using computer manual tracing of regions of interest, we measured the neuroanatomical asymmetries for the homologues of key language areas, including the inferior frontal gyrus (IFG) and planum temporale (PT). When considering the entire sample, there was a predominance of right-handedness for clapping and the distribution of right- and left-handed individuals did not differ between the two facilities. The direction of hand preference (right- versus left-handed subjects) for clapping explained a significant portion of variability in asymmetries of the PT and IFG. The results are consistent with the view that gestural communication in the common ancestor may have been a precursor of language and its cerebral substrates in modern humans.     

Nectar discovery speeds and multimodal displays: assessing nectar search times in bees with radiating and non-radiating guides

Floral displays are often composed of areas of contrasting stimuli which flower visitors use as guides, increasing both foraging efficiency and the likelihood of pollen transfer. Many aspects of how these displays benefit foraging efficiency are still unexplored, particularly those surrounding multimodal signals and the spatial arrangement of the display components. We compare the nectar discovery times of forager bumblebees (Bombus terrestris) when presented with artificial flowers with unimodal or compound displays of visual and/or olfactory stimuli, positioned in either radiating or non-radiating arrangements. We found that the addition of individual display components from either modality reduces nectar discovery time but there was no time benefit to bimodal displays over unimodal displays or any benefit to radiating stimuli arrangements over non-radiating arrangements. However, preference tests revealed a time advantage to radiating unimodal visual patterns over non-radiating unimodal visual patterns when both types were displayed simultaneously. These results suggest that the benefits of multimodal stimuli arrangements to pollinators are unrelated to benefits in nectar discovery time. Our results also suggest that spatial patterns of scent can be used as nectar guides and can reduce nectar discovery times without the aid of visual stimuli.     

Does the handedness of the pebble crab Eriphia smithii influence its attack success on two dextral snail species?

The predaceous crab Eriphia smithii (Xanthidae) has one larger claw with molar teeth on either the right or the left cheliped, which it uses to crush the shell of prey. Whether the handedness of crabs affected successful predation on two snail species, Nerita albicilla (Neritidae) and Planaxis sulcatus (Planaxidae) was experimentally investigated. The fate of snails of each species was analysed by multiple logistic regression with three explanatory variables: handedness, shell-size index and individuality of crabs. No effect of handedness was detected in attacks on N. albicilla , probably as a result of the spherical and more symmetrical shell morphology of this species. In contrast, right-handedness contributed to greater attack success on P. sulcatus , which has more conical shells. Further investigation of how snail shells were broken revealed that left-handed crabs had more difficulty breaking the aperture of larger P. sulcatus , which was thought to cause the difference in attack success between right- and left-handed crabs. The advantages conferred by handedness are discussed.     

Thermodynamics of left-handed helix formation

The thermodynamics of right- and left-handed helix formation by poly[d(G-C)] X poly[d(G-C)] and by poly-(dG-m5dC) X poly(dG-m5dC) were measured spectrophotometrically and calorimetrically. From the spectrophotometric measurements the thermal stabilities of the alternative helical conformations were evaluated as a function of counterion concentration. From the calorimetric measurements the enthalpies of either right-handed or left-handed helix formation were determined. The corresponding experimental delta H values are -8.6 and -11.2 kcal/mol base pairs for the two conformations in poly[dG-C)] X poly[d(G-C)], and -9.0 and -12.7 kcal/mol base pairs, respectively, for poly(dG-m5dC) X poly(dG-m5dC).     

Crystallization and solid-state reaction as a route to asymmetric synthesis from achiral starting materials

Many molecules which are achiral can crystallize in chiral (enantiomorphic) crystals and, under suitable conditions, crystals of only one chirality may be obtained. The formation of right- or left-handed crystals in excess is equally probable. Lattice-controlled (topochemical) photochemical or thermal solid-state reactions may then afford stable, optically active products. In the presence of the chiral products, achiral reactants may preferentially produce crystals of one chirality, leading to a feedback mechanism for the generation and amplification of optical activity. Amplification of optical activity can also be achieved by solid-state reactions. The optical synthesis of biologically relevant compounds by such routes may be envisaged.     

Electron diffraction studies of poly(α-aminoisobutyric acid)

Electron diffraction photographs of poly (α-aminoisobutyric acid) treated with dichloracetic acid are shown to be consistent with space group R3c. This is strong evidence for a hexagonal cell in which right- and left-handed 3₁₀-helices form a honeycomb structure. It appears that the dichloracetic acid molecules are located in the centers of the holes.     

Molecular genetic analysis of left-right handedness in plants

Handedness in plant growth may be most familiar to us when we think of tendrils or twining plants, which generally form consistent right- or left-handed helices as they climb. The petals of several species are sometimes arranged like fan blades that twist in the same direction. Another less conspicuous example is 'circumnutation', the oscillating growth of axial organs, which alternates between a clockwise and an anti-clockwise direction. To unravel molecular components and cellular determinants of handedness, we screened Arabidopsis thaliana seedlings for helical growth mutants with fixed handedness. Recessive spiral1 and spiral2 mutants show right-handed helical growth in roots, hypocotyls, petioles and petals; semi-dominant lefty1 and lefty2 mutants show opposite left-handed growth in these organs. lefty mutations are epistatic to spiral mutations. Arabidopsis helical growth mutants with fixed handedness may be impaired in certain aspects of cortical microtubule functions, and characterization of the mutated genes should lead us to a better understanding of how microtubules function in left-right handedness in plants.     

Temperature-dependent CD and NMR studies on a synthetic oligonucleotide containing a B-Z junction at high salt

It is now accepted that two or more conformations may exist within the same DNA molecule, thereby generating conformational junctions. The presence of B-Z junctions between right- and left-handed DNA conformations has been detected in plasmids by a number of techniques. Preliminary characterization of the first example of a B-Z junction is a short DNA oligonucleotide has recently been reported [Sheardy, R. D. (1988) Nucleic Acids Res. 16, 1153-1167]. We report additional CD and NMR data that support the existence of the junction in this model oligomer. These studies indicate that only three base pairs are involved in the junction and only one of these is dramatically distorted. Furthermore, the NMR saturation-transfer experiments suggest the junction's internal motion is temperature dependent.     

Crab scars reveal survival advantage of left-handed snails

Biological asymmetries are important elements of the structure and function of many living organisms. Using the Plio-Pleistocene fossil record of crab predation on morphologically similar pairs of right- and left-handed snail species, we show here for the first time, contrary to traditional wisdom, that rare left-handed coiling promotes survival from attacks by right-handed crabs. This frequency-dependent result influences the balance of selection processes that maintain left-handedness at the species level and parallels some social interactions in human cultures, such as sports that involve dual contests between opponents of opposite handedness.     

Machine learning shows torsion angle preferences in left-handed and right-handed quadruplex DNAs

Left-handed G quadruplexes (LHG4) have been recently discovered as a new class of G quadruplexes. The biological functions of LHG4s are still unknown, but they share a striking resemblance to Z-DNA in their helicity and jagged phosphate backbone. To further understand structural features of the LHG4s that define their left handedness, we have employed human-interpretable machine-learning methods to classify right- and left-handed G4s purely based on torsional angle analysis. Our results reveal the importance of the α, β, δ, and χ angles in left-handed structuring across both Z-DNAs and LHG4s. Our analysis may serve as the first step to understanding the conditions of formation for LHG4s and their potential biological relevance.     

Effect of side chains on the conformational energy and rotational strength of the n-pi transition for some alpha-helical poly-alpha-amino acids

Calculations of the dependence of the conformational energy and the rotational strength of the amide n–π* electronic transition (in a series of α-helical polyhel-α- amino acids with different side chains) on conformation have been carried out. The conformational energies were computed by procedures developed in this laboratory; the computation of rotational strengths was carried out by the method of Schellman and Oriel, with a slight modification. Polyamino acids with both nonpolar and polar side chains were considered; in the latter case, it was assumed that the only influence of the polar side chain was on the backbone conformation and on the electrostatic field which perturbs the amide chromophore of the backbone. Only conformations in the range of backbone dihedral angles of the right- and left-handed a-helices were considered, and the assumption of regularity (i.e., uniformity of dihedral angles in every residue) was made. The rotational strength per residue was found to vary markedly with chain length (in oligomers of up to 40 residues long); both the conformational energy per residue and the rotational strength per residue were found to vary significantly with the backbone conformation, which in turn depends on the nature of the side chain. The geometry of the hydrogen bond in the α-helical backbone is the most important factor which influences the dependence of the rotational strength on conformation. The implications of these results, for the interpretation of experimental circular dichroism and optical rotatory dispersion data, are discussed.