Sensing form - finger gaiting as key to tactile object exploration - a data glove analysis of a prototypical daily task.

BACKGROUND: Motor hand skill and associated dexterity is important for meeting the challenges of daily activity and an important resource post-stroke. In this context, the present study investigated the finger movements of right-handed subjects during tactile manipulation of a cuboid, a prototypical task underlying tactile exploration. During one motor act, the thumb and fingers of one hand surround the cuboid in a continuous and regular manner. While the object is moved by the guiding thumb, the opposed supporting fingers are replaced once they reach their joint limits by free fingers, a mechanism termed finger gaiting. METHODS: For both hands of 22 subjects, we acquired the time series of consecutive manipulations of a cuboid at a frequency of 1 Hz, using a digital data glove consisting of 29 sensors. Using principle component analysis, we decomposed the short action into motor patterns related to successive manipulations of the cuboid. The components purport to represent changing grasp configurations involving the stabilizing fingers and guiding thumb. The temporal features of the components permits testing whether the distinct configurations occur at the frequency of 1 Hz, i.e. within the time window of 1 s, and, thus, taxonomic classification of the manipulation as finger gaiting. RESULTS: The fraction of variance described by the principal components indicated that three components described the salient features of the single motor acts for each hand. Striking in the finger patterns was the prominent and varying roles of the MCP and PIP joints of the fingers, and the CMC joint of the thumb. An important aspect of the three components was their representation of distinct finger configurations within the same motor act. Principal component and graph theory analysis confirmed modular, functionally synchronous action of the involved joints. The computation of finger trajectories in one subject illustrated the workspace of the task, which differed for the right and left hands. CONCLUSION: In this task one complex motor act of 1 s duration could be described by three elementary and hierarchically ordered grasp configurations occurring at the prescribed frequency of 1 Hz. Therefore, these configurations represent finger gaiting, described until now only in artificial systems, as the principal mechanism underlying this prototypical task. TRIAL REGISTRATION: clinicaltrials.gov, NCT02865642 , registered 12 August 2016.

Conformational Properties of the Chemotherapeutic Drug Analogue Epothilone A: How to Model a Flexible Protein Ligand Using Scarcely Available Experimental Data.

Epothilones are among the most potent chemotherapeutic drugs used for the treatment of cancer. Epothilone A (EpoA), a natural product, is a macrocyclic molecule containing 34 non-hydrogen atoms and a thiazole side chain. NMR studies of EpoA in aqueous solution, unbound as well as bound to αß-tubulin, and unbound in dimethyl sulfoxide (DMSO) solution have delivered sets of nuclear Overhauser effect (NOE) atom-atom distance bounds, but no structures based on NMR data are present in structural data banks. X-ray diffraction of crystals has provided structures of EpoA unbound and bound to αß-tubulin. Since both crystal structures derived from X-ray diffraction intensities do not completely satisfy the three available sets of NOE distance bounds for EpoA, molecular dynamics (MD) simulations have been employed to obtain conformational ensembles in aqueous and in DMSO solution that are compatible with the respective NOE data. It was found that EpoA displays a larger conformational variability in DMSO than in water and the two conformational ensembles show little overlap. Yet, they both provide conformational scaffolds that are energetically accessible at physiological temperature and pressure.

Automatic lung segmentation of magnetic resonance images: A new approach applied to healthy volunteers undergoing enhanced Deep-Inspiration-Breath-Hold for motion-mitigated 4D proton therapy of lung tumors.

Background and purpose: Respiratory suppression techniques represent an effective motion mitigation strategy for 4D-irradiation of lung tumors with protons. A magnetic resonance imaging (MRI)-based study applied and analyzed methods for this purpose, including enhanced Deep-Inspiration-Breath-Hold (eDIBH). Twenty-one healthy volunteers (41-58 years) underwent thoracic MR scans in four imaging sessions containing two eDIBH-guided MRIs per session to simulate motion-dependent irradiation conditions. The automated MRI segmentation algorithm presented here was critical in determining the lung volumes (LVs) achieved during eDIBH. Materials and methods: The study included 168 MRIs acquired under eDIBH conditions. The lung segmentation algorithm consisted of four analysis steps: (i) image preprocessing, (ii) MRI histogram analysis with thresholding, (iii) automatic segmentation, (iv) 3D-clustering. To validate the algorithm, 46 eDIBH-MRIs were manually contoured. Sørensen-Dice similarity coefficients (DSCs) and relative deviations of LVs were determined as similarity measures. Assessment of intrasessional and intersessional LV variations and their differences provided estimates of statistical and systematic errors. Results: Lung segmentation time for 100 2D-MRI planes was âˆ¼ 10 s. Compared to manual lung contouring, the median DSC was 0.94 with a lower 95 % confidence level (CL) of 0.92. The relative volume deviations yielded a median value of 0.059 and 95 % CLs of -0.013 and 0.13. Artifact-based volume errors, mainly of the trachea, were estimated. Estimated statistical and systematic errors ranged between 6 and 8 %. Conclusions: The presented analytical algorithm is fast, precise, and readily available. The results are comparable to time-consuming, manual segmentations and other automatic segmentation approaches. Post-processing to remove image artifacts is under development.

Influence of 63Ser phosphorylation and dephosphorylation on the structure of the stathmin helical nucleation sequence: a molecular dynamics study.

Phosphorylation is an important mechanism regulating protein-protein interactions involving intrinsically disordered protein regions. Stathmin, an archetypical example of an intrinsically disordered protein, is a key regulator of microtubule dynamics in which phosphorylation of 63Ser within the helical nucleation sequence strongly down-regulates the tubulin binding and microtubule destabilizing activities of the protein. Experimental studies on a peptide encompassing the 19-residue helical nucleation sequence of stathmin (residues 55-73) indicate that phosphorylation of 63Ser destabilizes the peptide's secondary structure by disrupting the salt bridges supporting its helical conformation. In order to investigate this hypothesis at atomic resolution, we performed molecular dynamics simulations of nonphosphorylated and phosphorylated stathmin-[55-73] at room temperature and pressure, neutral pH, and explicit solvation using the recently released GROMOS force field 54A7. In the simulations of nonphosphorylated stathmin-[55-73] emerged salt bridges associated with helical configurations. In the simulations of 63Ser phosphorylated stathmin-[55-73] these configurations dispersed and were replaced by a proliferation of salt bridges yielding disordered configurations. The transformation of the salt bridges was accompanied by emergence of numerous interactions between main and side chains, involving notably the oxygen atoms of the phosphorylated 63Ser. The loss of helical structure induced by phosphorylation is reversible, however, as a final simulation showed. The results extend the hypothesis of salt bridge derangement suggested by experimental observations of the stathmin nucleation sequence, providing new insights into regulation of intrinsically disordered protein systems mediated by phosphorylation.

Distinguishing transient from persistent tactile agnosia after partial anterior circulation infarcts - Behavioral and neuroimaging evidence for white matter disconnection.

From a cohort of 36 patients presenting apperceptive tactile agnosia after first cortical ischemic stroke, 14 showed temporary impairment at admission. A previous multi-voxel analysis of the cortical lesions, using as explanatory variable the course of tactile object recognition performance over the recovery period of 9 months, partitioned the cohort into three subgroups. Of the 14 patients constituting two of the subgroups, 7 recovered from their impairment whereas 7 did not. These two subgroups could not be distinguished at admission. The primary aim of the present study is to present two assessments that can do so. The first assessment comprises a pattern of behavioral measures, determined via principal component analysis, encoded in three tests: picking small objects, macrogeometrical discrimination and tactile object recognition. The receiver operating characteristic curve derived from permutation of the behavioral test scores yielded an 80% probability of correct identification of the patient subgroup and an 8% probability for false identification. As done with the permuted scores, the pattern could predict the persistence of affliction of new stroke patients with tactile agnosia. The second predictive assessment extends our previous evaluation of cortical MRI lesion maps to include subcortical regions. Confirming our previous study, the lesions of the persistently impaired subgroup disrupted significantly the anterior arcuatus fasciculus and associated superior longitudinal fasciculus III in the ipsilesional hemisphere, impeding reciprocal information transfer between supramarginal gyrus and both the ventral premotor cortex and Brodmann area 44. Due to the importance of interhemispheric information transfer in tactile agnosia, we performed a supplementary analysis of tactile object recognition scores. It showed that haptic information transfer from the non-affected to the affected hands in the persistent cases partly restored function during the nine months, possibly following restoration of functional interhemispheric haptic information transfer at the border of posterior corpus callosum and splenium. In conclusion, the combined findings of the cortical lesion at subarea PFt of the inferior parietal lobule and the associated subcortical tract lesions permit almost perfect prediction of persistent impairment of tactile object recognition. The study substantiates the need for combined analysis of both cortical lesions and white matter tract disconnections.

Methods of NMR structure refinement: molecular dynamics simulations improve the agreement with measured NMR data of a C-terminal peptide of GCN4-p1.

The C-terminal trigger sequence is essential in the coiled-coil formation of GCN4-p1; its conformational properties are thus of importance for understanding this process at the atomic level. A solution NMR model structure of a peptide, GCN4p16-31, encompassing the GCN4-p1 trigger sequence was proposed a few years ago. Derived using a standard single-structure refinement protocol based on 172 nuclear Overhauser effect (NOE) distance restraints, 14 hydrogen-bond and 11 phi torsional-angle restraints, the resulting set of 20 NMR model structures exhibits regular alpha-helical structure. However, the set slightly violates some measured NOE bounds and does not reproduce all 15 measured (3)J(H(N)-H(Calpha))-coupling constants, indicating that different conformers of GCN4p16-31 might be present in solution. With the aim to resolve structures compatible with all NOE upper distance bounds and (3)J-coupling constants, we executed several structure refinement protocols employing unrestrained and restrained molecular dynamics (MD) simulations with two force fields. We find that only configurational ensembles obtained by applying simultaneously time-averaged NOE distance and (3)J-coupling constant restraining with either force field reproduce all the experimental data. Additionally, analyses of the simulated ensembles show that the conformational variability of GCN4p16-31 in solution admitted by the available set of 187 measured NMR data is larger than represented by the set of the NMR model structures. The conformations of GCN4p16-31 in solution differ in the orientation not only of the side-chains but also of the backbone. The inconsistencies between the NMR model structures and the measured NMR data are due to the neglect of averaging effects and the inclusion of hydrogen-bond and torsional-angle restraints that have little basis in the primary, i.e. measured NMR data.

Data-driven analyses of an fMRI study of a subject experiencing phosphenes.

PURPOSE: To compare two data-driven methods of statistical image analysis, principal and independent component analysis (PCA, ICA), in identifying neural networks related to the transient occurrence of phosphenes experienced by a female patient subsequent to a brain infarct. MATERIALS AND METHODS: An initial functional magnetic resonance imaging (fMRI) session consisted of two acquisitions: one of the patient experiencing phosphenes and a second responding to a well-defined visual stimulation paradigm. A second fMRI session 6 months later, when the patient no longer experienced phosphenes, consisted of an acquisition in which no stimulation was presented. Analysis of correlations between the temporal expression coefficients and models of the hemodynamic response identified salient components. Spectral analysis confirmed the identification. The phosphene model was based solely on the subjective report of the patient. RESULTS: Both methods revealed occipital cortical and subcortical areas known to be sites for visual information-processing during stimulation, as did SPM. In addition, higher-order visual areas such as the precuneus and the lateral parietal cortex were implicated in the PCA of the phosphenes. CONCLUSION: The analyses suggest the capability of data-driven approaches to identify the brain structures involved in these transient, spontaneous visual events.

Neural networks engaged in tactile object manipulation: patterns of expression among healthy individuals.

BACKGROUND: Somatosensory object discrimination has been shown to involve widespread cortical and subcortical structures in both cerebral hemispheres. In this study we aimed to identify the networks involved in tactile object manipulation by principal component analysis (PCA) of individual subjects. We expected to find more than one network. METHODS: Seven healthy right-handed male volunteers (aged 22 to 44 yrs) manipulated with their right hand aluminium spheres during 5 s with a repetition frequency of 0.5-0.7 Hz. The correlation coefficients between the principal component temporal expression coefficients and the hemodynamic response modelled by SPM (ecc) determined the task-related components. To establish reproducibility within subjects and similarity of functional connectivity patterns among subjects, regional correlation coefficients (rcc) were computed between task-related component image volumes. By hierarchically categorizing, selecting and averaging the task-related component image volumes across subjects according to the rccs, mean component images (MCIs) were derived describing neural networks associated with tactile object manipulation. RESULTS: Two independent mean component images emerged. Each included the primary sensorimotor cortex contralateral to the manipulating hand. The region extended to the premotor cortex in MCI 1, whereas it was restricted to the hand area of the primary sensorimotor cortex in MCI 2. MCI 1 showed bilateral involvement of the paralimbic anterior cingulate cortex (ACC), whereas MCI 2 implicated the midline thalamic nuclei and two areas of the rostral dorsal pons. CONCLUSIONS: Two distinct networks participate in tactile object manipulation as revealed by the intra- and interindividual comparison of individual scans. Both were employed by most subjects, suggesting that both are involved in normal somatosensory object discrimination.

Early prediction of long-term tactile object recognition performance after sensorimotor stroke.

Until now tactile agnosia has been reported only in small, but detailed cross-sectional case studies. Here we show that multi-voxel pattern analysis (MVPA) of early diffusion-weighted lesion maps can be used to accurately predict long-term recovery of tactile object recognition (TOR) in 35 subjects with varying hand skill impairment and associated specific daily activity limitation after cortical sensori-motor stroke. Multiple regression analysis revealed the essentially dysfunctional subprocesses for object recognition in the specifically impaired subjects, i.e., grasping as determined by a subtest of Jebsen Taylor hand function test, and perception of macrogeometrical object properties. The Gaussian process regression of MVPA represents a function that relates a selection of lesioned voxels as input variables to TOR performance scores as target variables. On the behavioural level, patients fell into three recovery subgroups, depending on TOR performance over the observation period. Only baseline motor hand skill and shape discrimination were significantly correlated with the TOR trajectories. To define functionally meaningful voxels, we combined information from MVPA of lesion maps and a priori knowledge of regions of interest derived from a data bank for shape recognition. A high significance for the predicted TOR performances over nine months could be verified by permutation tests, leading us to expect that the model generalises to larger patient cohorts with first cortical ischemic stroke. The lesion sites of the persistently impaired subjects exhibited an overlap with critical areas related to the MVPA prediction map in the cytoarchitectonic areas PFt of inferior parietal lobule and OP1 of parietal operculum which are associated with higher order sensory processing. This ultimate check corroborated the significance of the MVPA map for the prediction of tactile object recognition. The clinical implication of our study is that neuroimaging data acquired immediately after first stroke could facilitate individual forecasting of post-stroke recovery.

Exploring the conserved water site and hydration of a coiled-coil trimerisation motif: a MD simulation study.

The solvent structure and dynamics around ccbeta-p, a 17-residue peptide that forms a parallel three-stranded alpha-helical coiled coil in solution, was analysed through 10 ns explicit solvent molecular dynamics (MD) simulations at 278 and 330 K. Comparison with two corresponding simulations of the monomeric form of ccbeta-p was used to investigate the changes of hydration upon coiled-coil formation. Pronounced peaks in the solvent density distribution between residues Arg8 and Glu13 of neighbouring helices show the presence of water bridges between the helices of the ccbeta-p trimer; this is in agreement with the water sites observed in X-ray crystallography experiments. Interestingly, this water site is structurally conserved in many three-stranded coiled coils and, together with the Arg and Glu residues, forms part of a motif that determines three-stranded coiled-coil formation. Our findings show that little direct correlation exists between the solvent density distribution and the temporal ordering of water around the trimeric coiled coil. The MD-calculated effective residence times of up to 40 ps show rapid exchange of surface water molecules with the bulk phase, and indicate that the solvent distribution around biomolecules requires interpretation in terms of continuous density distributions rather than in terms of discrete molecules of water. Together, our study contributes to understanding the principles of three-stranded coiled-coil formation.

The effect of a single dose of escitalopram on sensorimotor networks.

INTRODUCTION: Serving as a pilot study of poststroke pharmacotherapy, the present investigation was intended to establish the effect of a single dose of escitalopram on motor task performance in normal volunteers. METHODS: Ten healthy volunteers of median age 63 years including four females performed a well-studied tactile manipulation task in two fMRI sessions using a double-blind cross-over design. The sessions began approximately three hours after ingestion of 20 mg escitalopram or placebo presented in pseudorandom order. The fMRI image sequences were submitted to principal component analysis (PCA). RESULTS: Based on volume correlations of task-related principal components with the mean component images derived in our previous study, we established the reproducibility of two networks of sensorimotor activity proposed there. The network reflecting motor control (cerebral pattern I) appeared invariably in placebo and verum conditions. In contrast, the other network, attributed to diminished motor control due to distracting mental processing (cerebral pattern II), emerged less regularly and exhibited more variability. Second-level PCAs of both conditions confirmed the findings of the initial analysis. Specifically, it validated the dominant and invariable expression of cerebral pattern I after application of a single dose of escitalopram. Dynamic causal modeling confirmed enhanced motor output as a result of a significantly increased connectivity between primary motor cortex and dorsal premotor cortex. CONCLUSION: This pilot study suggests the promise of stimulation by a specific serotonin reuptake inhibitor in regard to recovery and preservation of motor control after stroke.

Configurational entropy elucidates the role of salt-bridge networks in protein thermostability.

Detailed knowledge of how networks of surface salt bridges contribute to protein thermal stability is essential not only to understand protein structure and function but also to design thermostable proteins for industrial applications. Experimental studies investigating thermodynamic stability through measurements of free energy associated with mutational alterations in proteins provide only macroscopic evidence regarding the structure of salt-bridge networks and assessment of their contribution to protein stability. Using explicit-solvent molecular dynamics simulations to provide insight on the atomic scale, we investigate here the structural stability, defined in terms of root-mean-square fluctuations, of a short polypeptide designed to fold into a stable trimeric coiled coil with a well-packed hydrophobic core and an optimal number of intra- and interhelical surface salt bridges. We find that the increase of configurational entropy of the backbone and side-chain atoms and decreased pair correlations of these with increased temperature are consistent with nearly constant atom-positional root-mean-square fluctuations, increased salt-bridge occupancies, and stronger electrostatic interactions in the coiled coil. Thus, our study of the coiled coil suggests a mechanism in which well-designed salt-bridge networks could accommodate stochastically the disorder of increased thermal motion to produce thermostability.

Molecular-dynamics simulations of C- and N-terminal peptide derivatives of GCN4-p1 in aqueous solution.

We report the investigation of two 16-residue peptides in aqueous solution by means of molecular-dynamics simulations. The peptides constitute the C- and N-terminal halves of the 33-residue monomer whose dimer constitutes the leucine zipper of the yeast transcriptional activator, denoted GCN4-p1. To examine a hypothesis about coiled-coil formation, in which the C-terminal half contains a helix-formation trigger site absent in the N-terminal half, experimental studies of the two peptides have determined their helix propensities under several conditions of temperature, pH, and salt concentration with circular dichroism. An NMR experiment provides additional evidence. At temperatures of 278 and 325 K and pH 7.5, mixtures of alpha- and pi-helical secondary structure constitute the most probable conformations in both C- and N-terminal halves. A bifurcated salt bridge between Arg25 and Glu22/20 correlates with the structural fluctuations of the C-terminal half. It also exhibits a persistent loop at the N-terminal end involving the side chains of His18 and Glu22, which is reminiscent of helix-capping boxes. Nonreversible unfolding appears to occur abruptly in the Arg25 mutant, suggesting a cooperative event. Analysis does not indicate that the N-terminal half is less stable than the C-terminal half, indicating that 100 ns is too short a period to observe complete unfolding.

A Thalamic-Fronto-Parietal Structural Covariance Network Emerging in the Course of Recovery from Hand Paresis after Ischemic Stroke.

AIM: To describe structural covariance networks of gray matter volume (GMV) change in 28 patients with first-ever stroke to the primary sensorimotor cortices, and to investigate their relationship to hand function recovery and local GMV change. METHODS: Tensor-based morphometry maps derived from high-resolution structural images were subject to principal component analyses to identify the networks. We calculated correlations between network expression and local GMV change, sensorimotor hand function and lesion volume. To verify which of the structural covariance networks of GMV change have a significant relationship to hand function, we performed an additional multivariate regression approach. RESULTS: Expression of the second network, explaining 9.1% of variance, correlated with GMV increase in the medio-dorsal (md) thalamus and hand motor skill. Patients with positive expression coefficients were distinguished by significantly higher GMV increase of this structure during stroke recovery. Significant nodes of this network were located in md thalamus, dorsolateral prefrontal cortex, and higher order sensorimotor cortices. Parameter of hand function had a unique relationship to the network and depended on an interaction between network expression and lesion volume. Inversely, network expression is limited in patients with large lesion volumes. CONCLUSION: Chronic phase of sensorimotor cortical stroke has been characterized by a large scale co-varying structural network in the ipsilesional hemisphere associated specifically with sensorimotor hand skill. Its expression is related to GMV increase of md thalamus, one constituent of the network, and correlated with the cortico-striato-thalamic loop involved in control of motor execution and higher order sensorimotor cortices. A close relation between expression of this network with degree of recovery might indicate reduced compensatory resources in the impaired subgroup.

Probing the Structure and Dynamics of Proteins by Combining Molecular Dynamics Simulations and Experimental NMR Data.

NMR experiments provide detailed structural information about biological macromolecules in solution. However, the amount of information obtained is usually much less than the number of degrees of freedom of the macromolecule. Moreover, the relationships between experimental observables and structural information, such as interatomic distances or dihedral angle values, may be multiple-valued and may rely on empirical parameters and approximations. The extraction of structural information from experimental data is further complicated by the time- and ensemble-averaged nature of NMR observables. Combining NMR data with molecular dynamics simulations can elucidate and alleviate some of these problems, as well as allow inconsistencies in the NMR data to be identified. Here, we use a number of examples from our work to highlight the power of molecular dynamics simulations in providing a structural interpretation of solution NMR data.

Insights into EB1 structure and the role of its C-terminal domain for discriminating microtubule tips from the lattice.

End-binding proteins (EBs) comprise a conserved family of microtubule plus end-tracking proteins. The concerted action of calponin homology (CH), linker, and C-terminal domains of EBs is important for their autonomous microtubule tip tracking, regulation of microtubule dynamics, and recruitment of numerous partners to microtubule ends. Here we report the detailed structural and biochemical analysis of mammalian EBs. Small-angle X-ray scattering, electron microscopy, and chemical cross-linking in combination with mass spectrometry indicate that EBs are elongated molecules with two interacting CH domains, an arrangement reminiscent of that seen in other microtubule- and actin-binding proteins. Removal of the negatively charged C-terminal tail did not affect the overall conformation of EBs; however, it increased the dwell times of EBs on the microtubule lattice in microtubule tip-tracking reconstitution experiments. An even more stable association with the microtubule lattice was observed when the entire negatively charged C-terminal domain of EBs was replaced by a neutral coiled-coil motif. In contrast, the interaction of EBs with growing microtubule tips was not significantly affected by these C-terminal domain mutations. Our data indicate that long-range electrostatic repulsive interactions between the C-terminus and the microtubule lattice drive the specificity of EBs for growing microtubule ends.

Exploring the trigger sequence of the GCN4 coiled-coil: biased molecular dynamics resolves apparent inconsistencies in NMR measurements.

Trigger sequences are indispensable elements for coiled-coil formation. The monomeric helical trigger sequence of the yeast transcriptional activator GCN4 has been investigated recently using several solution NMR observables including nuclear Overhauser enhancement (NOE) intensities and 3J(HN, HCα)-coupling constants, and a set of 20 model structures was proposed. Constrained to satisfy the NOE-derived distance bounds, the NMR model structures do not appear to reproduce all the measured 3J(HN-HCα)-coupling constant values, indicating that the α-helical propensity is not uniform along the GCN4 trigger sequence. A recent methodological study of unrestrained and restrained molecular dynamics (MD) simulations of the GCN4 trigger sequence in solution showed that only MD simulations incorporating time-averaged NOE distance restraints and instantaneous or local-elevation 3J-coupling restraints could satisfy the entire set of the experimental data. In this report, we assess by means of cluster analyses the model structures characteristic of the two simulations that are compatible with the measured data and compare them with the proposed 20 NMR model structures. Striking characteristics of the MD model structures are the variability of the simulated configurations and the indication of entropic stability mediated by the aromatic N-terminal residues 17Tyr and 18His, which are absent in the set of NMR model structures.

Functional connectivity in tactile object discrimination: a principal component analysis of an event related fMRI-Study.

BACKGROUND: Tactile object discrimination is an essential human skill that relies on functional connectivity between the neural substrates of motor, somatosensory and supramodal areas. From a theoretical point of view, such distributed networks elude categorical analysis because subtraction methods are univariate. Thus, the aim of this study was to identify the neural networks involved in somatosensory object discrimination using a voxel-based principal component analysis (PCA) of event-related functional magnetic resonance images. METHODOLOGY/PRINCIPAL FINDINGS: Seven healthy, right-handed subjects aged between 22 and 44 years were required to discriminate with their dominant hand the length differences between otherwise identical parallelepipeds in a two-alternative forced-choice paradigm. Of the 34 principal components retained for analysis according to the 'bootstrapped' Kaiser-Guttman criterion, t-tests applied to the subject-condition expression coefficients showed significant mean differences between the object presentation and inter-stimulus phases in PC 1, 3, 26 and 32. Specifically, PC 1 reflected object exploration or manipulation, PC 3 somatosensory and short-term memory processes. PC 26 evinced the perception that certain parallelepipeds could not be distinguished, while PC 32 emerged in those choices when they could be. Among the cerebral regions evident in the PCs are the left posterior parietal lobe and premotor cortex in PC 1, the left superior parietal lobule (SPL) and the right cuneus in PC 3, the medial frontal and orbitofrontal cortex bilaterally in PC 26, and the right intraparietal sulcus, anterior SPL and dorsolateral prefrontal cortex in PC 32. CONCLUSIONS/SIGNIFICANCE: The analysis provides evidence for the concerted action of large-scale cortico-subcortical networks mediating tactile object discrimination. Parallel to activity in nodes processing object-related impulses we found activity in key cerebral regions responsible for subjective assessment and validation.

Molecular basis of coiled-coil formation.

Coiled coils have attracted considerable interest as design templates in a wide range of applications. Successful coiled-coil design strategies therefore require a detailed understanding of coiled-coil folding. One common feature shared by coiled coils is the presence of a short autonomous helical folding unit, termed "trigger sequence," that is indispensable for folding. Detailed knowledge of trigger sequences at the molecular level is thus key to a general understanding of coiled-coil formation. Using a multidisciplinary approach, we identify and characterize here the molecular determinants that specify the helical conformation of the monomeric early folding intermediate of the GCN4 coiled coil. We demonstrate that a network of hydrogen-bonding and electrostatic interactions stabilize the trigger-sequence helix. This network is rearranged in the final dimeric coiled-coil structure, and its destabilization significantly slows down GCN4 leucine zipper folding. Our findings provide a general explanation for the molecular mechanism of coiled-coil formation.