ABSTRACT
Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++G*, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and related to the physical structure of the compounds. The absolute configuration could be established directly in each case by comparing experimental and theoretical spectra. In addition, we have been able to document the changes that occur both in structures and in the VA and VCD spectra due to substituent effects on the oxirane ring.
Subject(s)
Epoxy Compounds/chemistry , Isomerism , Methylation , Models, Molecular , Molecular Structure , Spectrum AnalysisABSTRACT
Density-functional theory (DFT) calculations utilizing the Becke 3LYP hybrid functional have been carried out for N-acetyl L-alanine N'-methylamide and examined with respect to the effect of water on the structure, the vibrational frequencies, vibrational absorption (VA), vibrational circular dichroism (VCD), Raman spectra, and Raman optical activity (ROA) intensities. The large changes due to hydration in the structures, and the relative stability of the conformer, reflected in the VA, VCD, Raman spectra, and ROA spectra observed experimentally, are reproduced by the DFT calculations. A neural network has been constructed for reproducing the inverse scattering data (we infer the structural coordinates from spectroscopic data) that the DFT method could produce. The purpose of the network has also been to generate the large set of conformational states associated with each set of spectroscopic data for a given conformer of the molecule by interpolation. Finally the neural network performances are used to monitor a sensitivity analysis of the importance of secondary structures and the influence of the solvent. The neural network is shown to be good in distinguishing the different conformers of the small alanine peptide, especially in the gas phase.
Subject(s)
Alanine/analogs & derivatives , Alanine/chemistry , Algorithms , Dipeptides/chemistry , Models, Molecular , Nerve Net , Proteins/chemistry , Spectrum Analysis/methods , Water/chemistry , Binding Sites , Circular Dichroism/methods , Computer Simulation , Molecular Conformation , Protein Binding , Protein Conformation , Solutions , Solvents/chemistry , Spectrum Analysis, Raman/methods , VibrationABSTRACT
Electronic structures of small peptides were calculated 'ab initio' with the help of Density Functional Theory (DFT) and molecular dynamics that rendered a set of conformational states of the peptides. For the structures of these states it was possible to derive atomic polar tensors that allowed us to construct vibrational spectra for each of the conformational states with low energy. From the spectra, neural networks could be trained to distinguish between the various states and thus be able to generate a larger set of relevant structures and their relation to secondary structures of the peptides. The calculations were done both with solvent atoms (up to ten water molecules) and without, and hence the neural networks could be used to monitor the influence of the solvent on hydrogen bond formation. The calculations at this stage only involved very short peptide fragments of a few alanine amino acids but already at this stage they could be compared with reasonable agreements to experiments. The neural networks are shown to be good in distinguishing the different conformers of the small alanine peptides, especially when in the gas phase. Also the task of predicting protein fold-classes, defined from line-geometry, seems promising.
Subject(s)
Neural Networks, Computer , Peptides/chemistry , Protein Conformation , Algorithms , Amino Acids/chemistry , Models, Molecular , SolventsABSTRACT
The pim-1 oncogene is regulated by hematopoietic cytokine receptors, encodes a serine/threonine protein kinase, and cooperates with c-myc in lymphoid cell transformation. Using a yeast two-hybrid screen, we found that Pim-1 protein binds to p100, a transcriptional coactivator that interacts with the c-Myb transcription factor. Pim-1 phosphorylated p100 in vitro, formed a stable complex with p100 in animal cells, and functioned downstream of Ras to stimulate c-Myb transcriptional activity in a p100-dependent manner. Thus, Pim-1 and p100 appear to be components of a novel signal transduction pathway affecting c-Myb activity, linking all three to the cytokine-regulated control of hematopoietic cell growth, differentiation, and apoptosis.
