Wolfgang Reischl

H2O2-dependent translocation of TCTP into the nucleus enables its interaction with VDR in human keratinocytes: TCTP as a further module in calcitriol signalling

Translationally controlled tumour protein (TCTP) is an evolutionarily highly conserved molecule implicated in many processes related to cell cycle progression, proliferation and growth, to the protection against harmful conditions including apoptosis and to the human allergic response. We are showing here that after application of mild oxidative stress, human TCTP relocates from the cytoplasm to the nuclei of HaCaT keratinocytes where it directly associates with the ligand-binding domain of endogenous vitamin D(3) receptor (VDR) through its helical domain 2 (AA 71-132). Interestingly, the latter harbours a putative nuclear hormone receptor coregulatory LxxLL-like motif which seems to be involved in the interaction. Moreover, we demonstrate that VDR transcriptionally induces the expression of TCTP by binding to a previously unknown VDR response element within the TCTP promotor. Conversely, ectopically overexpressed TCTP downregulates the amount of VDR on both mRNA as well as protein level. These data, to conclude, suggest a kind of feedback regulation between TCTP and VDR to regulate a variety of (Ca(2+) dependent) cellular effects and in this way further underscore the physiological relevance of this novel protein-protein interaction.

Solvent effect on previtamin D conformational equilibrium and photoreactions

Abstract The effect of solvent polarity on the conformational equilibrium of previtamin D has been discussed in terms of the abundance (5) of its conformers calculated by molecular mechanics in conjunction with nuclear magnetic resonance experimental data available in the literature. It has been assumed that polar reaction media shift the conformational equilibrium towards the most non-strained cZc conformations with the OH group in pseudo-equatorial orientation. 7-Dehydrocholesterol (provitamin D) photoisomerization on irradiation at λ = 254 nm has been studied in ethanol and hexane by UV spectroscopy. A consideration of the observed differences in combination with the calculations of the reaction kinetics provides an estimation of the quantum yields of previtamin D cis-trans isomerization and additional experimental evidence for the solvent-induced changes in the conformational equilibrium of previtamin D in favour of cZc forms in polar environments.

On the conformational flexibility of vitamin D

The conformational flexibility of vitamin D was investigated by a combination of force field calculations, LIS measurements and LIS simulations. Besides the two A-ring chair forms, A-ring twist forms were detected and were attributed to steric interactions arising from the substitution pattern of this class of seco-steroids.ZusammenfassungDie konformationelle Beweglichkeit von Vitamin D wurde mittels einer Kombination aus Kraftfeld Rechnungen, LIS-Messungen und LIS-Rechnungen untersucht. Neben den beiden A-Ring Sesselformen wurden auch A-Ring Twistformen aufgefunden. Die Ursache für das Vorhandensein von diesen Twistformen liegt in sterischen Wechselwirkungen, verursacht durch das Substitutionsmuster des A-Ringes in diesem seco-Steroid.

Molecular mechanics-based conformational analysis of previtamin D and its A-ring analogues

SummaryThe ground-state conformational analysis of previtamin D and analogues with different substituents at C-3, C-1, and C-10 have been performed by force-field calculations. Differences in the photochemistry of these analogues are discussed in view of the concept of ground-state conformational control in photochemical reactions. The effect of complexes of previtamin D with silanol derivatives, formedvia hydrogen bonds, on their conformational equilibrium has been calculated. An increase in the population ofcZc conformers with increasing size of the silanol molecules (as a model for a heterogeneous silica surface) was observed.ZusammenfassungEine Konformationsanalyse des Grundzustandes von Previtamin D and von an C-1, C-3 und C-10 substituierten Analogen wurde mit Hilfe von Kraftfeldrechnungen durchgeführt. Unterschiedliches Reaktionsverhalten bei den photochemischen Umsetzungen dieser Verbindungen werden unter dem Gesichtspunkt der Grundzustandskontrolle von photochemischen Reaktionen diskutiert. Der Einfluß von Komplexbildung über Wasserstoffbrücken von Previtamin D mit Silanolen wurde berechnet. Eine Zunahme der Population dercZc-Konformeren mit zunehmender Größe des Silanols (ein Modell für eine heterogene Kieselgeloberfläche) wurde dabei beobachtet.

Modeling of previtamin D conformational equilibrium: effect of intramolecular electrostatic interactions

Abstract The effect of intramolecular electrostatic interactions on previtamin D conformational equilibrium has been studied by MMX force-field calculations using charge-charge and dipole-dipole approximations in parallel with the analysis of simple model compounds. The very fine balance between steric and electrostatic factors determining the conformational preference has been demonstrated and is discussed in terms of a classical charge-charge interactions. The results of this search are discussed with respect to available experimental data and give clues to the noticeable incidence of atomic point charges in previtamin D ground-state equilibrium. Comparison of the results with those of semi-empirical AM1 calculations reveals that conformational search results on previtamin D are highly dependent on the computational model used and indicate that care is required both in the selection of the computational method and in the interpretation of the results.

Zur Epoxidation der Δ 7-Doppelbindung in Vitamin D3 Röntgenstrukturanalyse des 4-Phenyl-1,2,4-triazolin-3,5-dion-Addukts — eine Strukturrevision

Epoxidation of vitamin D3 withMCPBA yields exclusively the 7,8-monooxirane. Its 7R, 8R stereochemistry was established by X-ray analysis of thePTAD-adduct-derivative. This result corrects the stereochemical assignment in a previous publication7.

Zur gezielten Oxidation der Δ7-Doppelbindung in den 4-Phenyl-1,2,4-triazolin-3,5-dion-Addukten des Vitamin D3

The possibility of regio- and stereospecific oxidation of the Δ 7-double bond of the 4-phenyl-1,2,4-triazolin-3,5-dione adducts1 a and1 b of Vitamin D3 is reported. Oxidation of the corresponding benzoates2 a and2 b withm-Chlorperbenzoic acid yields the two oxirans3 a and3 b which in turn with NaI-CH3COOH-Zn after saponification to5 a and5 b lead to the allylic alcohols6 a and6 b.

Allylic hydroxylation of vitamin D with Mercury (II)trifluoroacetate

Abstract Treatment of vitamin D with Hg(OCOCF 3 ) 2 results in formation of the isovitamin D derivative 2 , which can be converted into C-1 hydroxylated 5E vitamin D derivatives.

Ab initio study of conformational stability in previtamin D, vitamin D and related model compounds

Ab initio (Hartree‐Fock and density functional) calculations have been performed for previtamin D (1) and vitamin D (2) molecules with the side-chain substituted by a methyl group, and compared with the results for their simple model compounds (3‐6). Both theories produce very similar optimized geometries, but differ in their estimation of the relative energies of the conformers. The density functional (B3LYP/6-31G(d)) calculations favors the axial conformations of the A-ring in 1a and 2a, whereas HF/6-31G studies lead to 50:50 axial‐equatorial equilibrium. In model compounds 3‐6, B3LYP/6-311G(d,p) calculations resulted in preference of equatorial OH-orientation, while higher level (MP4(SDQ)) leads to the opposite result. The axial‐equatorial equilibria in the larger biomolecules have been discussed in terms of the additional intramolecular CH/p and OH/p interactions caused by the presence of the CD-ring system. These results clearly demonstrate the necessity of considering the whole molecular structure surrounding the p-system when modeling such flexible compounds, as well as the orientations of polar groups which can significantly contribute to the stability. q 2000 Elsevier Science B.V. All rights reserved.

Theoretical studies of the first strongly allowed singlet states of 3-desoxy analogs of previtamin D, vitamin D, and their E-isomers

The characteristics of the first singlet excited states (oscillator strength, Franck-Condon and 0–0 transitions) of isomeric seco-steroids, 3-desoxy-analogs of vitamin D (6), previtamin D (8), and their 5E-isomers (7,9), have been calculated using the semiempirical QCFF method. The results obtained have been compared with the available experimental observations, as well as ground state ab initio calculations at the HF/6-31G level and agree well for vitamin D and its 5E-isomer. Comparison of UV absorption characteristics of previtamin D with calculations of 3-desoxy-previtamin D conformers indicates the need for detailed modeling of the bandshape to attain good correlation with experiment. The failure of the semiempirical approach in the case of pre-vitamin D is also reflected in the poor agreement with ab initio results for the relative ground state conformer energies. This problem can be attributed to the importance of CH/π interactions in the system which are followed via Mulliken population analysis. Using a Boltzmann conformational distribution based on the ab initio relative energies of 3-desoxy-previtamin D conformers in combination with QCFF/sol results on the absorption characteristics leads to good agreement with experiment.