Self-assembling of peptides is tuned via an extended amphipathic helix.

Four peptides, C1 (spanning the helical segment of human neuropeptide Y from residue 15 to residue 29), C2 (spanning the helical segment of 21 to 31), C3 (the C-terminal fragment of neuropeptide Y involving residues 20 to 36) and P34-C3 (replacement of the glutamine with proline in position 34 of C3) were synthesized to study interaction between species. The information about the intermolecular interactions was extracted from their self-assembly behaviors. The results from CD and NMR showed that the addition of 2,2,2-trifluoroethanol (TFE) induces a stable amphipathic helix in each peptides and an extended helix was formed at the N-terminal of C1 and the C-terminal of C3. Pulsed field gradient NMR data revealed that C3 may undergo an enhanced interaction with TFE and a more favorable self-assembly as temperature was increased. In contrast, other three peptides were found to form larger size of oligomers at lower temperature and continuously dissociate into the monomeric form with increased temperature. Our results demonstrate that the self-assembly behavior may be tuned by the entropy and the energetics contributed by an extended helical conformation at terminus.

Deletion of the carboxyl-terminal residue disrupts the amino-terminal folding, self-association, and thermal stability of an amphipathic antimicrobial peptide.

Understanding the complex relationship between amino acid sequence and protein behaviors, such as folding and self-association, is a major goal of protein research. In the present work, we examined the effects of deleting a C-terminal residue on the intrinsic properties of an amphapathic α-helix of mastoparan-B (MP-B), an antimicrobial peptide with the sequence LKLKSIVSWAKKVL-NH2. We used circular dichroism and nuclear magnetic resonance to demonstrate that the peptide MP-B([1-13]) displayed significant unwinding at the N-terminal helix compared with the parent peptide of MP-B, as the temperature increased when the residue at position 14 was deleted. Pulsed-field gradient nuclear magnetic resonance data revealed that MP-B forms a larger diffusion unit than MP-B([1-13]) at all experimental temperatures and continuously dissociates as the temperature increases. In contrast, the size of the diffusion unit of MP-B([1-13]) is almost independent of temperature. These findings suggest that deleting the flexible, hydrophobic amino acid from the C-terminus of MP-B is sufficient to change the intrinsic helical thermal stability and self-association. This effect is most likely because of the modulation of enthalpic interactions and conformational freedom that are specified by this residue. Our results implicate terminal residues in the biological function of an antimicrobial peptide.

Characterization the effects of structure and energetics of intermolecular interactions on the oligomerization of peptides in aqueous 2, 2, 2-trifluoroethanol via circular dichroism and nuclear magnetic resonance spectroscopy.

Intermolecular interactions are of fundamental importance to fully comprehend a wide range of protein behaviors such as oligomerization, folding and recognition. Two peptides, NPY([18-36]) and NPY([15-29]), segmented from human neuropeptide Y (hNPY), were synthesized in this work to study the interaction between species. Information about intermolecular interactions was extracted from their oligomerizing behaviors. The results from CD and NMR showed that the addition of 2, 2, 2-trifluoroethanol (TFE) induces a stable helix in each peptides and an extended helix in NPY([18-36]), formed between residues 30-36. Pulsed field gradient NMR data revealed that NPY([15-29]) forms a larger oligomer at lower temperatures and continuously dissociates into the monomeric form with increasing temperature. NPY([18-36]) was also found to undergo an enhanced interaction with TFE and a more favorable self-association at higher temperatures. We characterized the changes of oligomerized states with respect to temperature to infer the effects of entropy and interaction energy on the association-dissociation equilibrium. As shown by NPY([15-29]), deletion of helical secondary structure or residues from the C-terminal segment may disrupt the solvation by TFE and results in entropy increase as the oligomer dissociates. Unlike that in NPY([15-29]), the extended helix in NPY([18-36]) improves the binding of TFE, and as a result, entropy is gained via the transfer of the TFE cluster from the interface between monomeric peptides into the bulk solvent. This observation suggests that the oligomerized state may be modulated by the entropy and energetics contributed by helical segments in the oligomerization process.

Dependence of peptide self-association on intermolecular interaction by PFGNMR in TFE aqueous solution: C-terminal analogues of NPY as model peptides.

We have investigated the dependence of peptide oligomerization on intermolecular interaction in terms of both energetic and structural effect by PFGNMR. Three peptides, NPY[20-36], Pro34-NPY[20-36] and NPY[21-31], which are related to human NPY, were synthesized as models in this work. In contrast to NPY[20-36], both Pro34-NPY[20-36] and NPY[21-31] were found with descendent affinity with TFE cluster and continuous dissociating with increased temperature. The observed results can be accounted by the entropic change with temperature and the varied hydrophobic interactions between species due to the differed structures of peptides from each other. The removal of helical secondary structure or residues from C-terminal region may increase the energetic difference between peptide-peptide self-associating and peptidesolvent binding. This increased energetic difference leads to larger dependence of association-dissociation equilibrium on temperature and entropic increase while dissociating.

Hippocampal alterations in children with temporal lobe epilepsy with or without a history of febrile convulsions: evaluations with MR volumetry and proton MR spectroscopy.

BACKGROUND AND PURPOSE: The causal effect of early febrile convulsions (FC) on later-onset temporal lobe epilepsy (TLE) remains unclear. In this study, we sought to examine the hippocampal alterations in epileptic children with or without FC history by using MR spectroscopy and volumetry. METHODS: Fifty-five children ranging in age from 18 months to 15 years were enrolled in this study. Subjects were divided into three groups: the control group without either TLE or history of FC (n = 16), the TLE group with early history of FC (TLE + FC; n = 22), and the TLE group without FC history (n = 17). Measurement of hippocampal volume (HV) was performed on thin section T1-weighted images acquired with a 3D gradient echo MR image and normalized by the intracranial volume. Each individual subject had two measures of lateralization; one gives the smaller side of HV and the other the contralateral larger side of HV, assuming that the side with smaller HV is the possible primary site of seizure focus and the contralateral larger HV the secondary or normal site. Single-voxel proton MR spectroscopy of the hippocampi was performed, with metabolic ratio n-acetylaspartate (NAA)/choline (Cho) + creatine plus phosphocreatine (Cr) calculated and grouped separately as were with volumetry. RESULTS: The overall mean HV for the control group was 2.61 +/- 0.21 cm(3) at an average intracranial volume of 965 +/- 241 cm(3), and the asymmetry index for hippocampal volume was (2.32 +/- 1.58)%. The overall mean HV was 2.30 +/- 0.33 cm(3) for TLE + FC group and 2.34 +/- 0.33 cm(3) for TLE group. Mean HV differed significantly for the three groups (P < .01). When the small and large sides were analyzed separately, significant differences were found between control and TLE as well as between control and TLE + FC for the smaller side (P < .05), whereas for the larger side significant differences were found only between control and TLE + FC. In MR spectroscopic measurements, the mean NAA/(Cr + Cho) of bilateral hippocampi was 0.77 +/- 0.06 for control group, 0.62 +/- 0.12 for TLE + FC group, and 0.66 +/- 0.11 for TLE group. In terms of statistically significant difference between groups, spectroscopic results were similar to volumetric measurements, except that there was no significant interaction effect between groups and measures of asymmetrical indices (P = .272). CONCLUSION: Children with TLE and early history of FC tend to have lower hippocampal volumes and NAA/(Cr + Cho) ratios than do TLE children without FC history. The TLE + FC group seems to have increased vulnerability of the contralateral hippocampus as compared with TLE group. MR volumetry and spectroscopy are equally capable of showing the trends of hippocampal alternations in children with TLE with or without FC history.

Supratentorial cerebrospinal fluid production rate in healthy adults: quantification with two-dimensional cine phase-contrast MR imaging with high temporal and spatial resolution.

A method for objectively determining supratentorial cerebrospinal fluid (CSF) production rate is described. The method employs cine phase-contrast magnetic resonance imaging with high temporal and spatial resolution at the level of the aqueduct of Sylvius. Automatic encircling of the aqueduct was accomplished by using a pulsatility-based segmentation approach. Results in 23 healthy adults (18 men, five women; age range, 21-39 years) yielded an average CSF production rate of 305 microL/min +/- 145 (standard deviation); this rate is in good agreement with literature-reported values obtained with invasive ventriculolumbar perfusion measurements. Average operator imprecision was 23.1% if automatic segmentation was not used. The proposed method is potentially an effective means for measuring supratentorial CSF production rate in humans.

Vacuolating megalencephalic leukoencephalopathy with mild clinical course validated by diffusion tensor imaging and MR spectroscopy.

We report a case of presumed vacuolating megalencephalic leukoencephalopathy (VML) in a 5-year-old boy that was diagnosed when the patient was 34 months old. The patient presented clinically with megalencephaly and delayed onset of slowly progressive neurologic dysfunction. Serial MR imaging and biochemical analysis were performed to differentiate VML from other disease entities with megalencephaly and leukoencephalopathy of infantile onset. Information obtained with diffusion tensor MR imaging revealed nearly intact white matter anisotropy and vectors in parietal and posterior temporal lobes in which hyperintense abnormality was shown on conventional T2-weighted images, and proton MR spectra showed a significant decrease in n-acetylaspartate-creatine + phosphocreatine ratio.

Neuronal damage after ischemic injury in the middle cerebral arterial territory: deep watershed versus territorial infarction at MR perfusion and spectroscopic imaging.

PURPOSE: To determine the temporal patterns of neuronal injury between infarction subtypes and their possible association with changes in cerebral blood volume (CBV). MATERIALS AND METHODS: Twenty-five patients with ischemic injuries of middle cerebral arterial territories and receiving only conservative treatments were classified into territorial infarction (TI) (n = 16) and watershed infarction (WI) (n = 9) groups and were prospectively evaluated with longitudinal magnetic resonance (MR) examinations. Each patient underwent as many as five MR studies at various stroke stages following stroke symptom onset. Dynamic susceptibility-weighted contrast material-enhanced MR imaging was performed to yield the relative CBV (rCBV). Chemical shift imaging was used to measure the relative levels of N-acetylaspartate (NAA) and lactate of the ischemic brain tissue. Repeated-measures analysis of variance was used to examine the statistical significance in evolutional differences between TI and WI. RESULTS: For patients with TI, rCBV followed a progressively increasing pattern, from initial low values (0.46 +/- 0.28 [SD]) to peak high values (1.23 +/- 0.34) at early chronic stage. Relative NAA level decreased to 0.40 +/- 0.24 during acute stroke and was lost completely 4 days after ictus. Patients with WI showed consistently high rCBV throughout all stages, with residual relative NAA level (0.53 +/- 0.25) even at 1 month after symptom onset. Relative lactate level of patients with TI was significantly higher than that of patients with WI at the acute stage (P <.01). Differences in the temporal changes of both rCBV and brain metabolites between TI and WI were significant (P <.01). CONCLUSION: The different temporal patterns for stroke progression in TI and WI are associated with different evolutions of hemodynamics and neuronal injury.

A reinvestigation of maximal signal drop in dynamic susceptibility contrast magnetic resonance imaging.

BACKGROUND AND PURPOSE: The purpose of this study was to reevaluate the usefulness of relative maximum signal drop (rMSD), as compared to relative cerebral blood volume (rCBV) and cerebral blood flow (rCBF), in dynamic susceptibility contrast magnetic resonance imaging (MRI). METHODS: Twenty-five patients (11 with cerebral gliomas and 14 with infarcts of middle cerebral arterial territories) were included. The rMSD values were measured from 83 regions of interest and compared with measurements from corresponding rCBV and rCBF maps. RESULTS: In stroke patients, rMSD correlated strongly with rCBF (r = 0.96) but only fairly with rCBV (r = 0.69). The absence of an association between rMSD and rCBV was evident in regions of increased contrast bolus dispersion. In glioma patients, the correlation of rMSD with rCBF (r = 0.85) was similar to that of rMSD with rCBV (r = 0.80). The interparameter associations were well predicted by computer simulations. CONCLUSIONS: The authors conclude that rMSD is as useful as rCBF under a variety of pathophysiological conditions, whereas in conditions with normal mean transit time, such as brain tumors, rMSD provides equivalent blood volume information to rCBV. The simplicity of rMSD maps could lead to the increased use of perfusion-weighted MRI.